<?php
/** @license MIT
 * Copyright 2017 J. King, Dustin Wilson et al.
 * See LICENSE and AUTHORS files for details */

declare(strict_types=1);
namespace JKingWeb\Arsse;

use PasswordGenerator\Generator as PassGen;
use JKingWeb\DrUUID\UUID;
use JKingWeb\Arsse\Misc\Query;
use JKingWeb\Arsse\Misc\Context;
use JKingWeb\Arsse\Misc\Date;
use JKingWeb\Arsse\Misc\ValueInfo;

class Database {
    const SCHEMA_VERSION = 3;
    const LIMIT_ARTICLES = 50;
    // articleList verbosity levels
    const LIST_MINIMAL      = 0; // only that metadata which is required for context matching
    const LIST_CONSERVATIVE = 1; // base metadata plus anything that is not potentially large text
    const LIST_TYPICAL      = 2; // conservative, with the addition of content
    const LIST_FULL         = 3; // all possible fields

    /** @var Db\Driver */
    public $db;

    public function __construct($initialize = true) {
        $driver = Arsse::$conf->dbDriver;
        $this->db = $driver::create();
        $ver = $this->db->schemaVersion();
        if ($initialize && $ver < self::SCHEMA_VERSION) {
            $this->db->schemaUpdate(self::SCHEMA_VERSION);
        }
    }

    protected function caller(): string {
        return debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 3)[2]['function'];
    }

    public static function driverList(): array {
        $sep = \DIRECTORY_SEPARATOR;
        $path = __DIR__.$sep."Db".$sep;
        $classes = [];
        foreach (glob($path."*".$sep."Driver.php") as $file) {
            $name = basename(dirname($file));
            $class = NS_BASE."Db\\$name\\Driver";
            $classes[$class] = $class::driverName();
        }
        return $classes;
    }

    public function driverSchemaVersion(): int {
        return $this->db->schemaVersion();
    }

    public function driverSchemaUpdate(): bool {
        if ($this->db->schemaVersion() < self::SCHEMA_VERSION) {
            return $this->db->schemaUpdate(self::SCHEMA_VERSION);
        }
        return false;
    }

    public function driverCharsetAcceptable(): bool {
        return $this->db->charsetAcceptable();
    }

    protected function generateSet(array $props, array $valid): array {
        $out = [
            [], // query clause
            [], // binding types
            [], // binding values
        ];
        foreach ($valid as $prop => $type) {
            if (!array_key_exists($prop, $props)) {
                continue;
            }
            $out[0][] = "$prop = ?";
            $out[1][] = $type;
            $out[2][] = $props[$prop];
        }
        $out[0] = implode(", ", $out[0]);
        return $out;
    }

    protected function generateIn(array $values, string $type) {
        $out = [
            [], // query clause
            [], // binding types
        ];
        // the query clause is just a series of question marks separated by commas
        $out[0] = implode(",", array_fill(0, sizeof($values), "?"));
        // the binding types are just a repetition of the supplied type
        $out[1] = array_fill(0, sizeof($values), $type);
        return $out;
    }

    public function begin(): Db\Transaction {
        return $this->db->begin();
    }

    public function metaGet(string $key) {
        return $this->db->prepare("SELECT value from arsse_meta where key = ?", "str")->run($key)->getValue();
    }

    public function metaSet(string $key, $value, string $type = "str"): bool {
        $out = $this->db->prepare("UPDATE arsse_meta set value = ? where key = ?", $type, "str")->run($value, $key)->changes();
        if (!$out) {
            $out = $this->db->prepare("INSERT INTO arsse_meta(key,value) values(?,?)", "str", $type)->run($key, $value)->changes();
        }
        return (bool) $out;
    }

    public function metaRemove(string $key): bool {
        return (bool) $this->db->prepare("DELETE from arsse_meta where key = ?", "str")->run($key)->changes();
    }

    public function userExists(string $user): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        return (bool) $this->db->prepare("SELECT count(*) from arsse_users where id = ?", "str")->run($user)->getValue();
    }

    public function userAdd(string $user, string $password = null): string {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        } elseif ($this->userExists($user)) {
            throw new User\Exception("alreadyExists", ["action" => __FUNCTION__, "user" => $user]);
        }
        if ($password===null) {
            $password = (new PassGen)->length(Arsse::$conf->userTempPasswordLength)->get();
        }
        $hash = "";
        if (strlen($password) > 0) {
            $hash = password_hash($password, \PASSWORD_DEFAULT);
        }
        $this->db->prepare("INSERT INTO arsse_users(id,password) values(?,?)", "str", "str")->runArray([$user,$hash]);
        return $password;
    }

    public function userRemove(string $user): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        if ($this->db->prepare("DELETE from arsse_users where id = ?", "str")->run($user)->changes() < 1) {
            throw new User\Exception("doesNotExist", ["action" => __FUNCTION__, "user" => $user]);
        }
        return true;
    }

    public function userList(string $domain = null): array {
        $out = [];
        if ($domain !== null) {
            if (!Arsse::$user->authorize("@".$domain, __FUNCTION__)) {
                throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $domain]);
            }
            $domain = str_replace(["\\","%","_"], ["\\\\", "\\%", "\\_"], $domain);
            $domain = "%@".$domain;
            foreach ($this->db->prepare("SELECT id from arsse_users where id like ?", "str")->run($domain) as $user) {
                $out[] = $user['id'];
            }
        } else {
            if (!Arsse::$user->authorize("", __FUNCTION__)) {
                throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => "global"]);
            }
            foreach ($this->db->query("SELECT id from arsse_users") as $user) {
                $out[] = $user['id'];
            }
        }
        return $out;
    }

    public function userPasswordGet(string $user): string {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        } elseif (!$this->userExists($user)) {
            throw new User\Exception("doesNotExist", ["action" => __FUNCTION__, "user" => $user]);
        }
        return (string) $this->db->prepare("SELECT password from arsse_users where id = ?", "str")->run($user)->getValue();
    }

    public function userPasswordSet(string $user, string $password = null): string {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        } elseif (!$this->userExists($user)) {
            throw new User\Exception("doesNotExist", ["action" => __FUNCTION__, "user" => $user]);
        }
        if ($password===null) {
            $password = (new PassGen)->length(Arsse::$conf->userTempPasswordLength)->get();
        }
        $hash = "";
        if (strlen($password) > 0) {
            $hash = password_hash($password, \PASSWORD_DEFAULT);
        }
        $this->db->prepare("UPDATE arsse_users set password = ? where id = ?", "str", "str")->run($hash, $user);
        return $password;
    }

    public function userPropertiesGet(string $user): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $prop = $this->db->prepare("SELECT name,rights from arsse_users where id = ?", "str")->run($user)->getRow();
        if (!$prop) {
            throw new User\Exception("doesNotExist", ["action" => __FUNCTION__, "user" => $user]);
        }
        return $prop;
    }

    public function userPropertiesSet(string $user, array $properties): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        } elseif (!$this->userExists($user)) {
            throw new User\Exception("doesNotExist", ["action" => __FUNCTION__, "user" => $user]);
        }
        $valid = [ // FIXME: add future properties
            "name" => "str",
        ];
        list($setClause, $setTypes, $setValues) = $this->generateSet($properties, $valid);
        if (!$setClause) {
            // if no changes would actually be applied, just return
            return $this->userPropertiesGet($user);
        }
        $this->db->prepare("UPDATE arsse_users set $setClause where id = ?", $setTypes, "str")->run($setValues, $user);
        return $this->userPropertiesGet($user);
    }

    public function userRightsGet(string $user): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        return (int) $this->db->prepare("SELECT rights from arsse_users where id = ?", "str")->run($user)->getValue();
    }

    public function userRightsSet(string $user, int $rights): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__, $rights)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        } elseif (!$this->userExists($user)) {
            throw new User\Exception("doesNotExist", ["action" => __FUNCTION__, "user" => $user]);
        }
        $this->db->prepare("UPDATE arsse_users set rights = ? where id = ?", "int", "str")->run($rights, $user);
        return true;
    }

    public function sessionCreate(string $user): string {
        // If the user isn't authorized to perform this action then throw an exception.
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // generate a new session ID and expiry date
        $id = UUID::mint()->hex;
        $expires = Date::add(Arsse::$conf->userSessionTimeout);
        // save the session to the database
        $this->db->prepare("INSERT INTO arsse_sessions(id,expires,user) values(?,?,?)", "str", "datetime", "str")->run($id, $expires, $user);
        // return the ID
        return $id;
    }

    public function sessionDestroy(string $user, string $id): bool {
        // If the user isn't authorized to perform this action then throw an exception.
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // delete the session and report success.
        return (bool) $this->db->prepare("DELETE FROM arsse_sessions where id = ? and user = ?", "str", "str")->run($id, $user)->changes();
    }

    public function sessionResume(string $id): array {
        $maxAge = Date::sub(Arsse::$conf->userSessionLifetime);
        $out = $this->db->prepare("SELECT id,created,expires,user from arsse_sessions where id = ? and expires > CURRENT_TIMESTAMP and created > ?", "str", "datetime")->run($id, $maxAge)->getRow();
        // if the session does not exist or is expired, throw an exception
        if (!$out) {
            throw new User\ExceptionSession("invalid", $id);
        }
        // if we're more than half-way from the session expiring, renew it
        if ($this->sessionExpiringSoon(Date::normalize($out['expires'], "sql"))) {
            $expires = Date::add(Arsse::$conf->userSessionTimeout);
            $this->db->prepare("UPDATE arsse_sessions set expires = ? where id = ?", "datetime", "str")->run($expires, $id);
        }
        return $out;
    }

    public function sessionCleanup(): int {
        $maxAge = Date::sub(Arsse::$conf->userSessionLifetime);
        return $this->db->prepare("DELETE FROM arsse_sessions where expires < CURRENT_TIMESTAMP or created < ?", "datetime")->run($maxAge)->changes();
    }

    protected function sessionExpiringSoon(\DateTimeInterface $expiry): bool {
        // calculate half the session timeout as a number of seconds
        $now = time();
        $max = Date::add(Arsse::$conf->userSessionTimeout, $now)->getTimestamp();
        $diff = intdiv($max - $now, 2);
        // determine if the expiry time is less than half the session timeout into the future
        return (($now + $diff) >= $expiry->getTimestamp());
    }

    public function folderAdd(string $user, array $data): int {
        // If the user isn't authorized to perform this action then throw an exception.
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // normalize folder's parent, if there is one
        $parent = array_key_exists("parent", $data) ? $this->folderValidateId($user, $data['parent'])['id'] : null;
        // validate the folder name and parent (if specified); this also checks for duplicates
        $name = array_key_exists("name", $data) ? $data['name'] : "";
        $this->folderValidateName($name, true, $parent);
        // actually perform the insert
        return $this->db->prepare("INSERT INTO arsse_folders(owner,parent,name) values(?,?,?)", "str", "int", "str")->run($user, $parent, $name)->lastId();
    }

    public function folderList(string $user, $parent = null, bool $recursive = true): Db\Result {
        // if the user isn't authorized to perform this action then throw an exception.
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // check to make sure the parent exists, if one is specified
        $parent = $this->folderValidateId($user, $parent)['id'];
        $q = new Query(
            "SELECT
                id,name,parent,
                (select count(*) from arsse_folders as parents where coalesce(parents.parent,0) = coalesce(arsse_folders.id,0)) as children,
                (select count(*) from arsse_subscriptions where coalesce(folder,0) = coalesce(arsse_folders.id,0)) as feeds
            FROM arsse_folders"
        );
        if (!$recursive) {
            $q->setWhere("owner = ?", "str", $user);
            $q->setWhere("coalesce(parent,0) = ?", "strict int", $parent);
        } else {
            $q->setCTE("folders", "SELECT id from arsse_folders where owner = ? and coalesce(parent,0) = ? union select arsse_folders.id from arsse_folders join folders on arsse_folders.parent=folders.id", ["str", "strict int"], [$user, $parent]);
            $q->setWhere("id in (SELECT id from folders)");
        }
        $q->setOrder("name");
        return $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues());
    }

    public function folderRemove(string $user, $id): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => __FUNCTION__, "field" => "folder", 'type' => "int > 0"]);
        }
        $changes = $this->db->prepare("DELETE FROM arsse_folders where owner = ? and id = ?", "str", "int")->run($user, $id)->changes();
        if (!$changes) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "folder", 'id' => $id]);
        }
        return true;
    }

    public function folderPropertiesGet(string $user, $id): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => __FUNCTION__, "field" => "folder", 'type' => "int > 0"]);
        }
        $props = $this->db->prepare("SELECT id,name,parent from arsse_folders where owner = ? and id = ?", "str", "int")->run($user, $id)->getRow();
        if (!$props) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "folder", 'id' => $id]);
        }
        return $props;
    }

    public function folderPropertiesSet(string $user, $id, array $data): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // verify the folder belongs to the user
        $in = $this->folderValidateId($user, $id, true);
        $name = array_key_exists("name", $data);
        $parent = array_key_exists("parent", $data);
        if ($name && $parent) {
            // if a new name and parent are specified, validate both together
            $this->folderValidateName($data['name']);
            $in['name'] = $data['name'];
            $in['parent'] = $this->folderValidateMove($user, (int) $id, $data['parent'], $data['name']);
        } elseif ($name) {
            // if we're trying to rename the root folder, this simply fails
            if (!$id) {
                return false;
            }
            // if a new name is specified, validate it
            $this->folderValidateName($data['name'], true, $in['parent']);
            $in['name'] = $data['name'];
        } elseif ($parent) {
            // if a new parent is specified, validate it
            $in['parent'] = $this->folderValidateMove($user, (int) $id, $data['parent']);
        } else {
            // if no changes would actually be applied, just return
            return false;
        }
        $valid = [
            'name' => "str",
            'parent' => "int",
        ];
        list($setClause, $setTypes, $setValues) = $this->generateSet($in, $valid);
        return (bool) $this->db->prepare("UPDATE arsse_folders set $setClause, modified = CURRENT_TIMESTAMP where owner = ? and id = ?", $setTypes, "str", "int")->run($setValues, $user, $id)->changes();
    }

    protected function folderValidateId(string $user, $id = null, bool $subject = false): array {
        // if the specified ID is not a non-negative integer (or null), this will always fail
        if (!ValueInfo::id($id, true)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "folder", 'type' => "int >= 0"]);
        }
        // if a null or zero ID is specified this is a no-op
        if (!$id) {
            return ['id' => null, 'name' => null, 'parent' => null];
        }
        // check whether the folder exists and is owned by the user
        $f = $this->db->prepare("SELECT id,name,parent from arsse_folders where owner = ? and id = ?", "str", "int")->run($user, $id)->getRow();
        if (!$f) {
            throw new Db\ExceptionInput($subject ? "subjectMissing" : "idMissing", ["action" => $this->caller(), "field" => "folder", 'id' => $id]);
        }
        return $f;
    }

    protected function folderValidateMove(string $user, $id = null, $parent = null, string $name = null) {
        $errData = ["action" => $this->caller(), "field" => "parent", 'id' => $parent];
        if (!$id) {
            // the root cannot be moved
            throw new Db\ExceptionInput("circularDependence", $errData);
        }
        $info = ValueInfo::int($parent);
        // the root is always a valid parent
        if ($info & (ValueInfo::NULL | ValueInfo::ZERO)) {
            $parent = null;
        } else {
            // if a negative integer or non-integer is specified this will always fail
            if (!($info & ValueInfo::VALID) || (($info & ValueInfo::NEG))) {
                throw new Db\ExceptionInput("idMissing", $errData);
            }
            $parent = (int) $parent;
        }
        // if the target parent is the folder itself, this is a circular dependence
        if ($id==$parent) {
            throw new Db\ExceptionInput("circularDependence", $errData);
        }
        // make sure both that the prospective parent exists, and that the it is not one of its children (a circular dependence);
        // also make sure that a folder with the same prospective name and parent does not already exist: if the parent is null,
        // SQL will happily accept duplicates (null is not unique), so we must do this check ourselves
        $p = $this->db->prepare(
            "WITH RECURSIVE
                target as (select ? as user, ? as source, ? as dest, ? as rename),
                folders as (SELECT id from arsse_folders join target on owner = user and coalesce(parent,0) = source union select arsse_folders.id as id from arsse_folders join folders on arsse_folders.parent=folders.id)
            ".
            "SELECT
                ((select dest from target) is null or exists(select id from arsse_folders join target on owner = user and coalesce(id,0) = coalesce(dest,0))) as extant,
                not exists(select id from folders where id = coalesce((select dest from target),0)) as valid,
                not exists(select id from arsse_folders join target on coalesce(parent,0) = coalesce(dest,0) and name = coalesce((select rename from target),(select name from arsse_folders join target on id = source))) as available
            ",
            "str",
            "strict int",
            "int",
            "str"
        )->run($user, $id, $parent, $name)->getRow();
        if (!$p['extant']) {
            // if the parent doesn't exist or doesn't below to the user, throw an exception
            throw new Db\ExceptionInput("idMissing", $errData);
        } elseif (!$p['valid']) {
            // if using the desired parent would create a circular dependence, throw a different exception
            throw new Db\ExceptionInput("circularDependence", $errData);
        } elseif (!$p['available']) {
            // if a folder with the same parent and name already exists, throw another different exception
            throw new Db\ExceptionInput("constraintViolation", ["action" => $this->caller(), "field" => (is_null($name) ? "parent" : "name")]);
        }
        return $parent;
    }

    protected function folderValidateName($name, bool $checkDuplicates = false, $parent = null): bool {
        $info = ValueInfo::str($name);
        if ($info & (ValueInfo::NULL | ValueInfo::EMPTY)) {
            throw new Db\ExceptionInput("missing", ["action" => $this->caller(), "field" => "name"]);
        } elseif ($info & ValueInfo::WHITE) {
            throw new Db\ExceptionInput("whitespace", ["action" => $this->caller(), "field" => "name"]);
        } elseif (!($info & ValueInfo::VALID)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "name", 'type' => "string"]);
        } elseif ($checkDuplicates) {
            // make sure that a folder with the same prospective name and parent does not already exist: if the parent is null,
            // SQL will happily accept duplicates (null is not unique), so we must do this check ourselves
            $parent = $parent ? $parent : null;
            if ($this->db->prepare("SELECT exists(select id from arsse_folders where coalesce(parent,0) = ? and name = ?)", "strict int", "str")->run($parent, $name)->getValue()) {
                throw new Db\ExceptionInput("constraintViolation", ["action" => $this->caller(), "field" => "name"]);
            }
            return true;
        } else {
            return true;
        }
    }

    public function subscriptionAdd(string $user, string $url, string $fetchUser = "", string $fetchPassword = "", bool $discover = true): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // check to see if the feed exists
        $check = $this->db->prepare("SELECT id from arsse_feeds where url = ? and username = ? and password = ?", "str", "str", "str");
        $feedID = $check->run($url, $fetchUser, $fetchPassword)->getValue();
        if ($discover && is_null($feedID)) {
            // if the feed doesn't exist, first perform discovery if requested and check for the existence of that URL
            $url = Feed::discover($url, $fetchUser, $fetchPassword);
            $feedID = $check->run($url, $fetchUser, $fetchPassword)->getValue();
        }
        if (is_null($feedID)) {
            // if the feed still doesn't exist in the database, add it to the database; we do this unconditionally so as to lock SQLite databases for as little time as possible
            $feedID = $this->db->prepare('INSERT INTO arsse_feeds(url,username,password) values(?,?,?)', 'str', 'str', 'str')->run($url, $fetchUser, $fetchPassword)->lastId();
            try {
                // perform an initial update on the newly added feed
                $this->feedUpdate($feedID, true);
            } catch (\Throwable $e) {
                // if the update fails, delete the feed we just added
                $this->db->prepare('DELETE from arsse_feeds where id = ?', 'int')->run($feedID);
                throw $e;
            }
        }
        // Add the feed to the user's subscriptions and return the new subscription's ID.
        return $this->db->prepare('INSERT INTO arsse_subscriptions(owner,feed) values(?,?)', 'str', 'int')->run($user, $feedID)->lastId();
    }

    public function subscriptionList(string $user, $folder = null, bool $recursive = true, int $id = null): Db\Result {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // validate inputs
        $folder = $this->folderValidateId($user, $folder)['id'];
        // create a complex query
        $q = new Query(
            "SELECT
                arsse_subscriptions.id as id,
                feed,url,favicon,source,folder,pinned,err_count,err_msg,order_type,added,
                arsse_feeds.updated as updated,
                topmost.top as top_folder,
                coalesce(arsse_subscriptions.title, arsse_feeds.title) as title,
                (SELECT count(*) from arsse_articles where feed = arsse_subscriptions.feed) - (SELECT count(*) from arsse_marks where subscription = arsse_subscriptions.id and read = 1) as unread
             from arsse_subscriptions
                join user on user = owner
                join arsse_feeds on feed = arsse_feeds.id
                left join topmost on folder=f_id"
        );
        $q->setOrder("pinned desc, title collate nocase");
        // define common table expressions
        $q->setCTE("user(user)", "SELECT ?", "str", $user);  // the subject user; this way we only have to pass it to prepare() once
        // topmost folders belonging to the user
        $q->setCTE("topmost(f_id,top)", "SELECT id,id from arsse_folders join user on owner = user where parent is null union select id,top from arsse_folders join topmost on parent=f_id");
        if ($id) {
            // this condition facilitates the implementation of subscriptionPropertiesGet, which would otherwise have to duplicate the complex query; it takes precedence over a specified folder
            // if an ID is specified, add a suitable WHERE condition and bindings
            $q->setWhere("arsse_subscriptions.id = ?", "int", $id);
        } elseif ($folder && $recursive) {
            // if a folder is specified and we're listing recursively, add a common table expression to list it and its children so that we select from the entire subtree
            $q->setCTE("folders(folder)", "SELECT ? union select id from arsse_folders join folders on parent = folder", "int", $folder);
            // add a suitable WHERE condition
            $q->setWhere("folder in (select folder from folders)");
        } elseif (!$recursive) {
            // if we're not listing recursively, match against only the specified folder (even if it is null)
            $q->setWhere("coalesce(folder,0) = ?", "strict int", $folder);
        }
        return $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues());
    }

    public function subscriptionCount(string $user, $folder = null): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // validate inputs
        $folder = $this->folderValidateId($user, $folder)['id'];
        // create a complex query
        $q = new Query("SELECT count(*) from arsse_subscriptions");
        $q->setWhere("owner = ?", "str", $user);
        if ($folder) {
            // if the specified folder exists, add a common table expression to list it and its children so that we select from the entire subtree
            $q->setCTE("folders(folder)", "SELECT ? union select id from arsse_folders join folders on parent = folder", "int", $folder);
            // add a suitable WHERE condition
            $q->setWhere("folder in (select folder from folders)");
        }
        return (int) $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->getValue();
    }

    public function subscriptionRemove(string $user, $id): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => __FUNCTION__, "field" => "feed", 'type' => "int > 0"]);
        }
        $changes = $this->db->prepare("DELETE from arsse_subscriptions where owner = ? and id = ?", "str", "int")->run($user, $id)->changes();
        if (!$changes) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "feed", 'id' => $id]);
        }
        return true;
    }

    public function subscriptionPropertiesGet(string $user, $id): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => __FUNCTION__, "field" => "feed", 'type' => "int > 0"]);
        }
        // disable authorization checks for the list call
        Arsse::$user->authorizationEnabled(false);
        $sub = $this->subscriptionList($user, null, true, (int) $id)->getRow();
        Arsse::$user->authorizationEnabled(true);
        if (!$sub) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "feed", 'id' => $id]);
        }
        return $sub;
    }

    public function subscriptionPropertiesSet(string $user, $id, array $data): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $tr = $this->db->begin();
        // validate the ID
        $id = $this->subscriptionValidateId($user, $id, true)['id'];
        if (array_key_exists("folder", $data)) {
            // ensure the target folder exists and belong to the user
            $data['folder'] = $this->folderValidateId($user, $data['folder'])['id'];
        }
        if (array_key_exists("title", $data)) {
            // if the title is null, this signals intended use of the default title; otherwise make sure it's not effectively an empty string
            if (!is_null($data['title'])) {
                $info = ValueInfo::str($data['title']);
                if ($info & ValueInfo::EMPTY) {
                    throw new Db\ExceptionInput("missing", ["action" => __FUNCTION__, "field" => "title"]);
                } elseif ($info & ValueInfo::WHITE) {
                    throw new Db\ExceptionInput("whitespace", ["action" => __FUNCTION__, "field" => "title"]);
                } elseif (!($info & ValueInfo::VALID)) {
                    throw new Db\ExceptionInput("typeViolation", ["action" => __FUNCTION__, "field" => "title", 'type' => "string"]);
                }
            }
        }
        $valid = [
            'title'      => "str",
            'folder'     => "int",
            'order_type' => "strict int",
            'pinned'     => "strict bool",
        ];
        list($setClause, $setTypes, $setValues) = $this->generateSet($data, $valid);
        if (!$setClause) {
            // if no changes would actually be applied, just return
            return false;
        }
        $out = (bool) $this->db->prepare("UPDATE arsse_subscriptions set $setClause, modified = CURRENT_TIMESTAMP where owner = ? and id = ?", $setTypes, "str", "int")->run($setValues, $user, $id)->changes();
        $tr->commit();
        return $out;
    }

    public function subscriptionFavicon(int $id, string $user = null): string {
        $q = new Query("SELECT favicon from arsse_feeds join arsse_subscriptions on feed = arsse_feeds.id");
        $q->setWhere("arsse_subscriptions.id = ?", "int", $id);
        if (isset($user)) {
            if (!Arsse::$user->authorize($user, __FUNCTION__)) {
                throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
            }
            $q->setWhere("arsse_subscriptions.owner = ?", "str", $user);
        }
        return (string) $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->getValue();
    }

    protected function subscriptionValidateId(string $user, $id, bool $subject = false): array {
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "feed", 'type' => "int > 0"]);
        }
        $out = $this->db->prepare("SELECT id,feed from arsse_subscriptions where id = ? and owner = ?", "int", "str")->run($id, $user)->getRow();
        if (!$out) {
            throw new Db\ExceptionInput($subject ? "subjectMissing" : "idMissing", ["action" => $this->caller(), "field" => "subscription", 'id' => $id]);
        }
        return $out;
    }

    public function feedListStale(): array {
        $feeds = $this->db->query("SELECT id from arsse_feeds where next_fetch <= CURRENT_TIMESTAMP")->getAll();
        return array_column($feeds, 'id');
    }

    public function feedUpdate($feedID, bool $throwError = false): bool {
        // check to make sure the feed exists
        if (!ValueInfo::id($feedID)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => __FUNCTION__, "field" => "feed", 'id' => $feedID, 'type' => "int > 0"]);
        }
        $f = $this->db->prepare("SELECT url, username, password, modified, etag, err_count, scrape FROM arsse_feeds where id = ?", "int")->run($feedID)->getRow();
        if (!$f) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "feed", 'id' => $feedID]);
        }
        // determine whether the feed's items should be scraped for full content from the source Web site
        $scrape = (Arsse::$conf->fetchEnableScraping && $f['scrape']);
        // the Feed object throws an exception when there are problems, but that isn't ideal
        // here. When an exception is thrown it should update the database with the
        // error instead of failing; if other exceptions are thrown, we should simply roll back
        try {
            $feed = new Feed((int) $feedID, $f['url'], (string) Date::transform($f['modified'], "http", "sql"), $f['etag'], $f['username'], $f['password'], $scrape);
            if (!$feed->modified) {
                // if the feed hasn't changed, just compute the next fetch time and record it
                $this->db->prepare("UPDATE arsse_feeds SET updated = CURRENT_TIMESTAMP, next_fetch = ? WHERE id = ?", 'datetime', 'int')->run($feed->nextFetch, $feedID);
                return false;
            }
        } catch (Feed\Exception $e) {
            // update the database with the resultant error and the next fetch time, incrementing the error count
            $this->db->prepare(
                "UPDATE arsse_feeds SET updated = CURRENT_TIMESTAMP, next_fetch = ?, err_count = err_count + 1, err_msg = ? WHERE id = ?",
                'datetime',
                'str',
                'int'
            )->run(Feed::nextFetchOnError($f['err_count']), $e->getMessage(), $feedID);
            if ($throwError) {
                throw $e;
            }
            return false;
        }
        //prepare the necessary statements to perform the update
        if (sizeof($feed->newItems) || sizeof($feed->changedItems)) {
            $qInsertEnclosure = $this->db->prepare("INSERT INTO arsse_enclosures(article,url,type) values(?,?,?)", 'int', 'str', 'str');
            $qInsertCategory = $this->db->prepare("INSERT INTO arsse_categories(article,name) values(?,?)", 'int', 'str');
            $qInsertEdition = $this->db->prepare("INSERT INTO arsse_editions(article) values(?)", 'int');
        }
        if (sizeof($feed->newItems)) {
            $qInsertArticle = $this->db->prepare(
                "INSERT INTO arsse_articles(url,title,author,published,edited,guid,content,url_title_hash,url_content_hash,title_content_hash,feed) values(?,?,?,?,?,?,?,?,?,?,?)",
                'str',
                'str',
                'str',
                'datetime',
                'datetime',
                'str',
                'str',
                'str',
                'str',
                'str',
                'int'
            );
        }
        if (sizeof($feed->changedItems)) {
            $qDeleteEnclosures = $this->db->prepare("DELETE FROM arsse_enclosures WHERE article = ?", 'int');
            $qDeleteCategories = $this->db->prepare("DELETE FROM arsse_categories WHERE article = ?", 'int');
            $qClearReadMarks = $this->db->prepare("UPDATE arsse_marks SET read = 0, modified = CURRENT_TIMESTAMP WHERE article = ? and read = 1", 'int');
            $qUpdateArticle = $this->db->prepare(
                "UPDATE arsse_articles SET url = ?, title = ?, author = ?, published = ?, edited = ?, modified = CURRENT_TIMESTAMP, guid = ?, content = ?, url_title_hash = ?, url_content_hash = ?, title_content_hash = ? WHERE id = ?",
                'str',
                'str',
                'str',
                'datetime',
                'datetime',
                'str',
                'str',
                'str',
                'str',
                'str',
                'int'
            );
        }
        // actually perform updates
        $tr = $this->db->begin();
        foreach ($feed->newItems as $article) {
            $articleID = $qInsertArticle->run(
                $article->url,
                $article->title,
                $article->author,
                $article->publishedDate,
                $article->updatedDate,
                $article->id,
                $article->content,
                $article->urlTitleHash,
                $article->urlContentHash,
                $article->titleContentHash,
                $feedID
            )->lastId();
            if ($article->enclosureUrl) {
                $qInsertEnclosure->run($articleID, $article->enclosureUrl, $article->enclosureType);
            }
            foreach ($article->categories as $c) {
                $qInsertCategory->run($articleID, $c);
            }
            $qInsertEdition->run($articleID);
        }
        foreach ($feed->changedItems as $articleID => $article) {
            $qUpdateArticle->run(
                $article->url,
                $article->title,
                $article->author,
                $article->publishedDate,
                $article->updatedDate,
                $article->id,
                $article->content,
                $article->urlTitleHash,
                $article->urlContentHash,
                $article->titleContentHash,
                $articleID
            );
            $qDeleteEnclosures->run($articleID);
            $qDeleteCategories->run($articleID);
            if ($article->enclosureUrl) {
                $qInsertEnclosure->run($articleID, $article->enclosureUrl, $article->enclosureType);
            }
            foreach ($article->categories as $c) {
                $qInsertCategory->run($articleID, $c);
            }
            $qInsertEdition->run($articleID);
            $qClearReadMarks->run($articleID);
        }
        // lastly update the feed database itself with updated information.
        $this->db->prepare(
            "UPDATE arsse_feeds SET url = ?, title = ?, favicon = ?, source = ?, updated = CURRENT_TIMESTAMP, modified = ?, etag = ?, err_count = 0, err_msg = '', next_fetch = ?, size = ? WHERE id = ?",
            'str',
            'str',
            'str',
            'str',
            'datetime',
            'str',
            'datetime',
            'int',
            'int'
        )->run(
            $feed->data->feedUrl,
            $feed->data->title,
            $feed->favicon,
            $feed->data->siteUrl,
            $feed->lastModified,
            $feed->resource->getEtag(),
            $feed->nextFetch,
            sizeof($feed->data->items),
            $feedID
        );
        $tr->commit();
        return true;
    }

    public function feedCleanup(): bool {
        $tr = $this->begin();
        // first unmark any feeds which are no longer orphaned
        $this->db->query("UPDATE arsse_feeds set orphaned = null where exists(SELECT id from arsse_subscriptions where feed = arsse_feeds.id)");
        // next mark any newly orphaned feeds with the current date and time
        $this->db->query("UPDATE arsse_feeds set orphaned = CURRENT_TIMESTAMP where orphaned is null and not exists(SELECT id from arsse_subscriptions where feed = arsse_feeds.id)");
        // finally delete feeds that have been orphaned longer than the retention period
        $limit = Date::normalize("now");
        if (Arsse::$conf->purgeFeeds) {
            // if there is a retention period specified, compute it; otherwise feed are deleted immediatelty
            $limit = Date::sub(Arsse::$conf->purgeFeeds, $limit);
        }
        $out = (bool) $this->db->prepare("DELETE from arsse_feeds where orphaned <= ?", "datetime")->run($limit);
        // commit changes and return
        $tr->commit();
        return $out;
    }

    public function feedMatchLatest(int $feedID, int $count): Db\Result {
        return $this->db->prepare(
            "SELECT id, edited, guid, url_title_hash, url_content_hash, title_content_hash FROM arsse_articles WHERE feed = ? ORDER BY modified desc, id desc limit ?",
            'int',
            'int'
        )->run($feedID, $count);
    }

    public function feedMatchIds(int $feedID, array $ids = [], array $hashesUT = [], array $hashesUC = [], array $hashesTC = []): Db\Result {
        // compile SQL IN() clauses and necessary type bindings for the four identifier lists
        list($cId, $tId)     = $this->generateIn($ids, "str");
        list($cHashUT, $tHashUT) = $this->generateIn($hashesUT, "str");
        list($cHashUC, $tHashUC) = $this->generateIn($hashesUC, "str");
        list($cHashTC, $tHashTC) = $this->generateIn($hashesTC, "str");
        // perform the query
        return $articles = $this->db->prepare(
            "SELECT id, edited, guid, url_title_hash, url_content_hash, title_content_hash FROM arsse_articles WHERE feed = ? and (guid in($cId) or url_title_hash in($cHashUT) or url_content_hash in($cHashUC) or title_content_hash in($cHashTC))",
            'int',
            $tId,
            $tHashUT,
            $tHashUC,
            $tHashTC
        )->run($feedID, $ids, $hashesUT, $hashesUC, $hashesTC);
    }

    protected function articleQuery(string $user, Context $context, array $extraColumns = []): Query {
        $extraColumns = implode(",", $extraColumns);
        if (strlen($extraColumns)) {
            $extraColumns .= ",";
        }
        $q = new Query(
            "SELECT
                $extraColumns
                arsse_articles.id as id,
                arsse_articles.feed as feed,
                arsse_articles.modified as modified_date,
                max(
                    arsse_articles.modified,
                    coalesce((select modified from arsse_marks where article = arsse_articles.id and subscription in (select sub from subscribed_feeds)),''),
                    coalesce((select modified from arsse_label_members where article = arsse_articles.id and subscription in (select sub from subscribed_feeds)),'')
                ) as marked_date,
                NOT (select count(*) from arsse_marks where article = arsse_articles.id and read = 1 and subscription in (select sub from subscribed_feeds)) as unread,
                (select count(*) from arsse_marks where article = arsse_articles.id and starred = 1 and subscription in (select sub from subscribed_feeds)) as starred,
                (select max(id) from arsse_editions where article = arsse_articles.id) as edition,
                subscribed_feeds.sub as subscription
            FROM arsse_articles"
        );
        $q->setLimit($context->limit, $context->offset);
        $q->setCTE("user(user)", "SELECT ?", "str", $user);
        if ($context->subscription()) {
            // if a subscription is specified, make sure it exists
            $id = $this->subscriptionValidateId($user, $context->subscription)['feed'];
            // add a basic CTE that will join in only the requested subscription
            $q->setCTE("subscribed_feeds(id,sub)", "SELECT ?,?", ["int","int"], [$id,$context->subscription], "join subscribed_feeds on feed = subscribed_feeds.id");
        } elseif ($context->folder()) {
            // if a folder is specified, make sure it exists
            $this->folderValidateId($user, $context->folder);
            // if it does exist, add a common table expression to list it and its children so that we select from the entire subtree
            $q->setCTE("folders(folder)", "SELECT ? union select id from arsse_folders join folders on parent = folder", "int", $context->folder);
            // add another CTE for the subscriptions within the folder
            $q->setCTE("subscribed_feeds(id,sub)", "SELECT feed,id from arsse_subscriptions join user on user = owner join folders on arsse_subscriptions.folder = folders.folder", [], [], "join subscribed_feeds on feed = subscribed_feeds.id");
        } elseif ($context->folderShallow()) {
            // if a shallow folder is specified, make sure it exists
            $this->folderValidateId($user, $context->folderShallow);
            // if it does exist, add a CTE with only its subscriptions (and not those of its descendents)
            $q->setCTE("subscribed_feeds(id,sub)", "SELECT feed,id from arsse_subscriptions join user on user = owner and coalesce(folder,0) = ?", "strict int", $context->folderShallow, "join subscribed_feeds on feed = subscribed_feeds.id");
        } else {
            // otherwise add a CTE for all the user's subscriptions
            $q->setCTE("subscribed_feeds(id,sub)", "SELECT feed,id from arsse_subscriptions join user on user = owner", [], [], "join subscribed_feeds on feed = subscribed_feeds.id");
        }
        if ($context->edition()) {
            // if an edition is specified, filter for its previously identified article
            $q->setWhere("arsse_articles.id = (select article from arsse_editions where id = ?)", "int", $context->edition);
        } elseif ($context->article()) {
            // if an article is specified, filter for it (it has already been validated above)
            $q->setWhere("arsse_articles.id = ?", "int", $context->article);
        }
        if ($context->editions()) {
            // if multiple specific editions have been requested, prepare a CTE to list them and their articles
            if (!$context->editions) {
                throw new Db\ExceptionInput("tooShort", ['field' => "editions", 'action' => __FUNCTION__, 'min' => 1]); // must have at least one array element
            } elseif (sizeof($context->editions) > self::LIMIT_ARTICLES) {
                throw new Db\ExceptionInput("tooLong", ['field' => "editions", 'action' => __FUNCTION__, 'max' => self::LIMIT_ARTICLES]); // @codeCoverageIgnore
            }
            list($inParams, $inTypes) = $this->generateIn($context->editions, "int");
            $q->setCTE(
                "requested_articles(id,edition)",
                "SELECT article,id as edition from arsse_editions where edition in ($inParams)",
                $inTypes,
                $context->editions
            );
            $q->setWhere("arsse_articles.id in (select id from requested_articles)");
        } elseif ($context->articles()) {
            // if multiple specific articles have been requested, prepare a CTE to list them and their articles
            if (!$context->articles) {
                throw new Db\ExceptionInput("tooShort", ['field' => "articles", 'action' => __FUNCTION__, 'min' => 1]); // must have at least one array element
            } elseif (sizeof($context->articles) > self::LIMIT_ARTICLES) {
                throw new Db\ExceptionInput("tooLong", ['field' => "articles", 'action' => __FUNCTION__, 'max' => self::LIMIT_ARTICLES]); // @codeCoverageIgnore
            }
            list($inParams, $inTypes) = $this->generateIn($context->articles, "int");
            $q->setCTE(
                "requested_articles(id,edition)",
                "SELECT id,(select max(id) from arsse_editions where article = arsse_articles.id) as edition from arsse_articles where arsse_articles.id in ($inParams)",
                $inTypes,
                $context->articles
            );
            $q->setWhere("arsse_articles.id in (select id from requested_articles)");
        } else {
            // if neither list is specified, mock an empty table
            $q->setCTE("requested_articles(id,edition)", "SELECT 'empty','table' where 1 = 0");
        }
        // filter based on label by ID or name
        if ($context->labelled()) {
            // any label (true) or no label (false)
            $q->setWhere((!$context->labelled ? "not " : "")."exists(select article from arsse_label_members where assigned = 1 and article = arsse_articles.id and subscription in (select sub from subscribed_feeds))");
        } elseif ($context->label() || $context->labelName()) {
            // specific label ID or name
            if ($context->label()) {
                $id = $this->labelValidateId($user, $context->label, false)['id'];
            } else {
                $id = $this->labelValidateId($user, $context->labelName, true)['id'];
            }
            $q->setWhere("exists(select article from arsse_label_members where assigned = 1 and article = arsse_articles.id and label = ?)", "int", $id);
        }
        // filter based on article or edition offset
        if ($context->oldestArticle()) {
            $q->setWhere("arsse_articles.id >= ?", "int", $context->oldestArticle);
        }
        if ($context->latestArticle()) {
            $q->setWhere("arsse_articles.id <= ?", "int", $context->latestArticle);
        }
        if ($context->oldestEdition()) {
            $q->setWhere("edition >= ?", "int", $context->oldestEdition);
        }
        if ($context->latestEdition()) {
            $q->setWhere("edition <= ?", "int", $context->latestEdition);
        }
        // filter based on time at which an article was changed by feed updates (modified), or by user action (marked)
        if ($context->modifiedSince()) {
            $q->setWhere("modified_date >= ?", "datetime", $context->modifiedSince);
        }
        if ($context->notModifiedSince()) {
            $q->setWhere("modified_date <= ?", "datetime", $context->notModifiedSince);
        }
        if ($context->markedSince()) {
            $q->setWhere("marked_date >= ?", "datetime", $context->markedSince);
        }
        if ($context->notMarkedSince()) {
            $q->setWhere("marked_date <= ?", "datetime", $context->notMarkedSince);
        }
        // filter for un/read and un/starred status if specified
        if ($context->unread()) {
            $q->setWhere("unread = ?", "bool", $context->unread);
        }
        if ($context->starred()) {
            $q->setWhere("starred = ?", "bool", $context->starred);
        }
        // filter based on whether the article has a note
        if ($context->annotated()) {
            $q->setWhere((!$context->annotated ? "not " : "")."exists(select modified from arsse_marks where article = arsse_articles.id and note <> '' and subscription in (select sub from subscribed_feeds))");
        }
        // return the query
        return $q;
    }

    protected function articleChunk(Context $context): array {
        $exception = "";
        if ($context->editions()) {
            // editions take precedence over articles
            if (sizeof($context->editions) > self::LIMIT_ARTICLES) {
                $exception = "editions";
            }
        } elseif ($context->articles()) {
            if (sizeof($context->articles) > self::LIMIT_ARTICLES) {
                $exception = "articles";
            }
        }
        if ($exception) {
            $out = [];
            $list = array_chunk($context->$exception, self::LIMIT_ARTICLES);
            foreach ($list as $chunk) {
                $out[] = (clone $context)->$exception($chunk);
            }
            return $out;
        } else {
            return [];
        }
    }

    public function articleList(string $user, Context $context = null, int $fields = self::LIST_FULL): Db\Result {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $context = $context ?? new Context;
        // if the context has more articles or editions than we can process in one query, perform a series of queries and return an aggregate result
        if ($contexts = $this->articleChunk($context)) {
            $out = [];
            $tr = $this->begin();
            foreach ($contexts as $context) {
                $out[] = $this->articleList($user, $context, $fields);
            }
            $tr->commit();
            return new Db\ResultAggregate(...$out);
        } else {
            $columns = [];
            switch ($fields) {
                // NOTE: the cases all cascade into each other: a given verbosity level is always a superset of the previous one
                case self::LIST_FULL: // everything
                    $columns = array_merge($columns, [
                        "(select note from arsse_marks where article = arsse_articles.id and subscription in (select sub from subscribed_feeds)) as note",
                    ]);
                    // no break
                case self::LIST_TYPICAL: // conservative, plus content
                    $columns = array_merge($columns, [
                        "content",
                        "arsse_enclosures.url as media_url", // enclosures are potentially large due to data: URLs
                        "arsse_enclosures.type as media_type", // FIXME: enclosures should eventually have their own fetch method
                    ]);
                    // no break
                case self::LIST_CONSERVATIVE: // base metadata, plus anything that is not likely to be large text
                    $columns = array_merge($columns, [
                        "arsse_articles.url as url",
                        "arsse_articles.title as title",
                        "(select coalesce(arsse_subscriptions.title,arsse_feeds.title) from arsse_feeds join arsse_subscriptions on arsse_subscriptions.feed = arsse_feeds.id where arsse_feeds.id = arsse_articles.feed) as subscription_title",
                        "author",
                        "guid",
                        "published as published_date",
                        "edited as edited_date",
                        "url_title_hash||':'||url_content_hash||':'||title_content_hash as fingerprint",
                    ]);
                    // no break
                case self::LIST_MINIMAL: // base metadata (always included: required for context matching)
                    $columns = array_merge($columns, [
                        // id, subscription, feed, modified_date, marked_date, unread, starred, edition
                        "edited as edited_date",
                    ]);
                    break;
                default:
                    throw new Exception("constantUnknown", $fields);
            }
            $q = $this->articleQuery($user, $context, $columns);
            $q->setOrder("edited_date".($context->reverse ? " desc" : ""));
            $q->setOrder("edition".($context->reverse ? " desc" : ""));
            $q->setJoin("left join arsse_enclosures on arsse_enclosures.article = arsse_articles.id");
            // perform the query and return results
            return $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues());
        }
    }

    public function articleCount(string $user, Context $context = null): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $context = $context ?? new Context;
        // if the context has more articles or editions than we can process in one query, perform a series of queries and return an aggregate result
        if ($contexts = $this->articleChunk($context)) {
            $out = 0;
            $tr = $this->begin();
            foreach ($contexts as $context) {
                $out += $this->articleCount($user, $context);
            }
            $tr->commit();
            return $out;
        } else {
            $q = $this->articleQuery($user, $context);
            $q->pushCTE("selected_articles");
            $q->setBody("SELECT count(*) from selected_articles");
            return (int) $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->getValue();
        }
    }

    public function articleMark(string $user, array $data, Context $context = null): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $context = $context ?? new Context;
        // if the context has more articles or editions than we can process in one query, perform a series of queries and return an aggregate result
        if ($contexts = $this->articleChunk($context)) {
            $out = 0;
            $tr = $this->begin();
            foreach ($contexts as $context) {
                $out += $this->articleMark($user, $data, $context);
            }
            $tr->commit();
            return $out;
        } else {
            // sanitize input
            $values = [
                isset($data['read']) ? $data['read'] : null,
                isset($data['starred']) ? $data['starred'] : null,
                isset($data['note']) ? $data['note'] : null,
            ];
            // the two queries we want to execute to make the requested changes
            $queries = [
                "UPDATE arsse_marks
                    set
                        read = case when (select honour_read from target_articles where target_articles.id = article) = 1 then (select read from target_values) else read end,
                        starred = coalesce((select starred from target_values),starred),
                        note = coalesce((select note from target_values),note),
                        modified = CURRENT_TIMESTAMP
                    WHERE
                        subscription in (select sub from subscribed_feeds)
                        and article in (select id from target_articles where to_insert = 0 and (honour_read = 1 or honour_star = 1 or (select note from target_values) is not null))",
                "INSERT INTO arsse_marks(subscription,article,read,starred,note)
                    select
                        (select id from arsse_subscriptions join user on user = owner where arsse_subscriptions.feed = target_articles.feed),
                        id,
                        coalesce((select read from target_values) * honour_read,0),
                        coalesce((select starred from target_values),0),
                        coalesce((select note from target_values),'')
                    from target_articles where to_insert = 1 and (honour_read = 1 or honour_star = 1 or coalesce((select note from target_values),'') <> '')"
            ];
            $out = 0;
            // wrap this UPDATE and INSERT together into a transaction
            $tr = $this->begin();
            // if an edition context is specified, make sure it's valid
            if ($context->edition()) {
                // make sure the edition exists
                $edition = $this->articleValidateEdition($user, $context->edition);
                // if the edition is not the latest, do not mark the read flag
                if (!$edition['current']) {
                    $values[0] = null;
                }
            } elseif ($context->article()) {
                // otherwise if an article context is specified, make sure it's valid
                $this->articleValidateId($user, $context->article);
            }
            // execute each query in sequence
            foreach ($queries as $query) {
                // first build the query which will select the target articles; we will later turn this into a CTE for the actual query that manipulates the articles
                $q = $this->articleQuery($user, $context, [
                    "(not exists(select article from arsse_marks where article = arsse_articles.id and subscription in (select sub from subscribed_feeds))) as to_insert",
                    "((select read from target_values) is not null and (select read from target_values) <> (coalesce((select read from arsse_marks where article = arsse_articles.id and subscription in (select sub from subscribed_feeds)),0)) and (not exists(select * from requested_articles) or (select max(id) from arsse_editions where article = arsse_articles.id) in (select edition from requested_articles))) as honour_read",
                    "((select starred from target_values) is not null and (select starred from target_values) <> (coalesce((select starred from arsse_marks where article = arsse_articles.id and subscription in (select sub from subscribed_feeds)),0))) as honour_star",
                ]);
                // common table expression with the values to set
                $q->setCTE("target_values(read,starred,note)", "SELECT ?,?,?", ["bool","bool","str"], $values);
                // push the current query onto the CTE stack and execute the query we're actually interested in
                $q->pushCTE("target_articles");
                $q->setBody($query);
                $out += $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->changes();
            }
            // commit the transaction
            $tr->commit();
            return $out;
        }
    }

    public function articleStarred(string $user): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        return $this->db->prepare(
            "SELECT
                count(*) as total,
                coalesce(sum(not read),0) as unread,
                coalesce(sum(read),0) as read
            FROM (
                select read from arsse_marks where starred = 1 and subscription in (select id from arsse_subscriptions where owner = ?)
            )",
            "str"
        )->run($user)->getRow();
    }

    public function articleLabelsGet(string $user, $id, bool $byName = false): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $id = $this->articleValidateId($user, $id)['article'];
        $out = $this->db->prepare("SELECT id,name from arsse_labels where owner = ? and exists(select id from arsse_label_members where article = ? and label = arsse_labels.id and assigned = 1)", "str", "int")->run($user, $id)->getAll();
        if (!$out) {
            return $out;
        } else {
            // flatten the result to return just the label ID or name
            return array_column($out, !$byName ? "id" : "name");
        }
    }

    public function articleCategoriesGet(string $user, $id): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $id = $this->articleValidateId($user, $id)['article'];
        $out = $this->db->prepare("SELECT name from arsse_categories where article = ? order by name", "int")->run($id)->getAll();
        if (!$out) {
            return $out;
        } else {
            // flatten the result
            return array_column($out, "name");
        }
    }

    public function articleCleanup(): bool {
        $query = $this->db->prepare(
            "WITH target_feed(id,subs) as (".
                "SELECT
                    id, (select count(*) from arsse_subscriptions where feed = arsse_feeds.id) as subs
                from arsse_feeds where id = ?".
            "), excepted_articles(id,edition) as (".
                "SELECT
                    arsse_articles.id, (select max(id) from arsse_editions where article = arsse_articles.id) as edition
                from arsse_articles
                    join target_feed on arsse_articles.feed = target_feed.id
                order by edition desc limit ?".
            ") ".
            "DELETE from arsse_articles where
                feed = (select max(id) from target_feed)
                and id not in (select id from excepted_articles)
                and (select count(*) from arsse_marks where article = arsse_articles.id and starred = 1) = 0
                and (
                    coalesce((select max(modified) from arsse_marks where article = arsse_articles.id),modified) <= ?
                    or ((select max(subs) from target_feed) = (select count(*) from arsse_marks where article = arsse_articles.id and read = 1) and coalesce((select max(modified) from arsse_marks where article = arsse_articles.id),modified) <= ?)
                )
            ",
            "int",
            "int",
            "datetime",
            "datetime"
        );
        $limitRead = null;
        $limitUnread = null;
        if (Arsse::$conf->purgeArticlesRead) {
            $limitRead = Date::sub(Arsse::$conf->purgeArticlesRead);
        }
        if (Arsse::$conf->purgeArticlesUnread) {
            $limitUnread = Date::sub(Arsse::$conf->purgeArticlesUnread);
        }
        $feeds = $this->db->query("SELECT id, size from arsse_feeds")->getAll();
        foreach ($feeds as $feed) {
            $query->run($feed['id'], $feed['size'], $limitUnread, $limitRead);
        }
        return true;
    }

    protected function articleValidateId(string $user, $id): array {
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "article", 'type' => "int > 0"]); // @codeCoverageIgnore
        }
        $out = $this->db->prepare(
            "SELECT
                arsse_articles.id as article,
                (select max(id) from arsse_editions where article = arsse_articles.id) as edition
            FROM arsse_articles
                join arsse_feeds on arsse_feeds.id = arsse_articles.feed
                join arsse_subscriptions on arsse_subscriptions.feed = arsse_feeds.id
            WHERE
                arsse_articles.id = ? and arsse_subscriptions.owner = ?",
            "int",
            "str"
        )->run($id, $user)->getRow();
        if (!$out) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => $this->caller(), "field" => "article", 'id' => $id]);
        }
        return $out;
    }

    protected function articleValidateEdition(string $user, int $id): array {
        if (!ValueInfo::id($id)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "edition", 'type' => "int > 0"]); // @codeCoverageIgnore
        }
        $out = $this->db->prepare(
            "SELECT
                arsse_editions.id as edition,
                arsse_editions.article as article,
                (arsse_editions.id = (select max(id) from arsse_editions where article = arsse_editions.article)) as current
            FROM arsse_editions
                join arsse_articles on arsse_editions.article = arsse_articles.id
                join arsse_feeds on arsse_feeds.id = arsse_articles.feed
                join arsse_subscriptions on arsse_subscriptions.feed = arsse_feeds.id
            WHERE
                edition = ? and arsse_subscriptions.owner = ?",
            "int",
            "str"
        )->run($id, $user)->getRow();
        if (!$out) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => $this->caller(), "field" => "edition", 'id' => $id]);
        }
        return $out;
    }

    public function editionLatest(string $user, Context $context = null): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $context = $context ?? new Context;
        $q = new Query("SELECT max(arsse_editions.id) from arsse_editions left join arsse_articles on article = arsse_articles.id left join arsse_feeds on arsse_articles.feed = arsse_feeds.id");
        if ($context->subscription()) {
            // if a subscription is specified, make sure it exists
            $id = $this->subscriptionValidateId($user, $context->subscription)['feed'];
            // a simple WHERE clause is required here
            $q->setWhere("arsse_feeds.id = ?", "int", $id);
        } else {
            $q->setCTE("user(user)", "SELECT ?", "str", $user);
            $q->setCTE("feeds(feed)", "SELECT feed from arsse_subscriptions join user on user = owner", [], [], "join feeds on arsse_articles.feed = feeds.feed");
        }
        return (int) $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->getValue();
    }

    public function labelAdd(string $user, array $data): int {
        // if the user isn't authorized to perform this action then throw an exception.
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // validate the label name
        $name = array_key_exists("name", $data) ? $data['name'] : "";
        $this->labelValidateName($name, true);
        // perform the insert
        return $this->db->prepare("INSERT INTO arsse_labels(owner,name) values(?,?)", "str", "str")->run($user, $name)->lastId();
    }

    public function labelList(string $user, bool $includeEmpty = true): Db\Result {
        // if the user isn't authorized to perform this action then throw an exception.
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        return $this->db->prepare(
            "SELECT
                id,name,
                (select count(*) from arsse_label_members where label = id and assigned = 1) as articles,
                (select count(*) from arsse_label_members
                    join arsse_marks on arsse_label_members.article = arsse_marks.article and arsse_label_members.subscription = arsse_marks.subscription
                 where label = id and assigned = 1 and read = 1
                ) as read
            FROM arsse_labels where owner = ? and articles >= ? order by name
            ",
            "str",
            "int"
        )->run($user, !$includeEmpty);
    }

    public function labelRemove(string $user, $id, bool $byName = false): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $this->labelValidateId($user, $id, $byName, false);
        $field = $byName ? "name" : "id";
        $type = $byName ? "str" : "int";
        $changes = $this->db->prepare("DELETE FROM arsse_labels where owner = ? and $field = ?", "str", $type)->run($user, $id)->changes();
        if (!$changes) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "label", 'id' => $id]);
        }
        return true;
    }

    public function labelPropertiesGet(string $user, $id, bool $byName = false): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $this->labelValidateId($user, $id, $byName, false);
        $field = $byName ? "name" : "id";
        $type = $byName ? "str" : "int";
        $out = $this->db->prepare(
            "SELECT
                id,name,
                (select count(*) from arsse_label_members where label = id and assigned = 1) as articles,
                (select count(*) from arsse_label_members
                    join arsse_marks on arsse_label_members.article = arsse_marks.article and arsse_label_members.subscription = arsse_marks.subscription
                 where label = id and assigned = 1 and read = 1
                ) as read
            FROM arsse_labels where $field = ? and owner = ?
            ",
            $type,
            "str"
        )->run($id, $user)->getRow();
        if (!$out) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "label", 'id' => $id]);
        }
        return $out;
    }

    public function labelPropertiesSet(string $user, $id, array $data, bool $byName = false): bool {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        $this->labelValidateId($user, $id, $byName, false);
        if (isset($data['name'])) {
            $this->labelValidateName($data['name']);
        }
        $field = $byName ? "name" : "id";
        $type = $byName ? "str" : "int";
        $valid = [
            'name'      => "str",
        ];
        list($setClause, $setTypes, $setValues) = $this->generateSet($data, $valid);
        if (!$setClause) {
            // if no changes would actually be applied, just return
            return false;
        }
        $out = (bool) $this->db->prepare("UPDATE arsse_labels set $setClause, modified = CURRENT_TIMESTAMP where owner = ? and $field = ?", $setTypes, "str", $type)->run($setValues, $user, $id)->changes();
        if (!$out) {
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "label", 'id' => $id]);
        }
        return $out;
    }

    public function labelArticlesGet(string $user, $id, bool $byName = false): array {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // just do a syntactic check on the label ID
        $this->labelValidateId($user, $id, $byName, false);
        $field = !$byName ? "id" : "name";
        $type = !$byName ? "int" : "str";
        $out = $this->db->prepare("SELECT article from arsse_label_members join arsse_labels on label = id where assigned = 1 and $field = ? and owner = ?", $type, "str")->run($id, $user)->getAll();
        if (!$out) {
            // if no results were returned, do a full validation on the label ID
            $this->labelValidateId($user, $id, $byName, true, true);
            // if the validation passes, return the empty result
            return $out;
        } else {
            // flatten the result to return just the article IDs in a simple array
            return array_column($out, "article");
        }
    }

    public function labelArticlesSet(string $user, $id, Context $context = null, bool $remove = false, bool $byName = false): int {
        if (!Arsse::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // validate the label ID, and get the numeric ID if matching by name
        $id = $this->labelValidateId($user, $id, $byName, true)['id'];
        $context = $context ?? new Context;
        $out = 0;
        // wrap this UPDATE and INSERT together into a transaction
        $tr = $this->begin();
        // first update any existing entries with the removal or re-addition of their association
        $q = $this->articleQuery($user, $context);
        $q->setWhere("exists(select article from arsse_label_members where label = ? and article = arsse_articles.id)", "int", $id);
        $q->pushCTE("target_articles");
        $q->setBody(
            "UPDATE arsse_label_members set assigned = ?, modified = CURRENT_TIMESTAMP where label = ? and assigned = not ? and article in (select id from target_articles)",
            ["bool","int","bool"],
            [!$remove, $id, !$remove]
        );
        $out += $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->changes();
        // next, if we're not removing, add any new entries that need to be added
        if (!$remove) {
            $q = $this->articleQuery($user, $context);
            $q->setWhere("not exists(select article from arsse_label_members where label = ? and article = arsse_articles.id)", "int", $id);
            $q->pushCTE("target_articles");
            $q->setBody(
                "INSERT INTO
                    arsse_label_members(label,article,subscription)
                SELECT
                    ?,id,
                    (select id from arsse_subscriptions join user on user = owner where arsse_subscriptions.feed = target_articles.feed)
                FROM target_articles",
                "int",
                $id
            );
            $out += $this->db->prepare($q->getQuery(), $q->getTypes())->run($q->getValues())->changes();
        }
        // commit the transaction
        $tr->commit();
        return $out;
    }

    protected function labelValidateId(string $user, $id, bool $byName, bool $checkDb = true, bool $subject = false): array {
        if (!$byName && !ValueInfo::id($id)) {
            // if we're not referring to a label by name and the ID is invalid, throw an exception
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "label", 'type' => "int > 0"]);
        } elseif ($byName && !(ValueInfo::str($id) & ValueInfo::VALID)) {
            // otherwise if we are referring to a label by name but the ID is not a string, also throw an exception
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "label", 'type' => "string"]);
        } elseif ($checkDb) {
            $field = !$byName ? "id" : "name";
            $type = !$byName ? "int" : "str";
            $l = $this->db->prepare("SELECT id,name from arsse_labels where $field = ? and owner = ?", $type, "str")->run($id, $user)->getRow();
            if (!$l) {
                throw new Db\ExceptionInput($subject ? "subjectMissing" : "idMissing", ["action" => $this->caller(), "field" => "label", 'id' => $id]);
            } else {
                return $l;
            }
        }
        return [
            'id'   => !$byName ? $id : null,
            'name' => $byName ? $id : null,
        ];
    }

    protected function labelValidateName($name): bool {
        $info = ValueInfo::str($name);
        if ($info & (ValueInfo::NULL | ValueInfo::EMPTY)) {
            throw new Db\ExceptionInput("missing", ["action" => $this->caller(), "field" => "name"]);
        } elseif ($info & ValueInfo::WHITE) {
            throw new Db\ExceptionInput("whitespace", ["action" => $this->caller(), "field" => "name"]);
        } elseif (!($info & ValueInfo::VALID)) {
            throw new Db\ExceptionInput("typeViolation", ["action" => $this->caller(), "field" => "name", 'type' => "string"]);
        } else {
            return true;
        }
    }
}