<?php
declare(strict_types=1);
namespace JKingWeb\Arsse;
use PasswordGenerator\Generator as PassGen;
use JKingWeb\Arsse\Database\Query;

class Database {

    const SCHEMA_VERSION = 1;
    const FORMAT_TS      = "Y-m-d h:i:s";
    const FORMAT_DATE    = "Y-m-d";
    const FORMAT_TIME    = "h:i:s";

    public    $db;
    protected $dateFormatDefault = "sql";

    public function __construct() {
        $driver = Data::$conf->dbDriver;
        $this->db = new $driver(INSTALL);
        $ver = $this->db->schemaVersion();
        if(!INSTALL && $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 function dateFormatDefault(string $set = null): string {
        if(is_null($set)) return $this->dateFormatDefault;
        $set = strtolower($set);
        if(in_array($set, ["sql", "iso8601", "unix", "http"])) {
            $this->dateFormatDefault = $set;
        }
        return $this->dateFormatDefault;
    }
    
    static public function listDrivers(): 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 schemaVersion(): int {
        return $this->db->schemaVersion();
    }

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

    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 settingGet(string $key) {
        $row = $this->db->prepare("SELECT value, type from arsse_settings where key = ?", "str")->run($key)->getRow();
        if(!$row) return null;
        switch($row['type']) {
            case "int":       return (int) $row['value'];
            case "numeric":   return (float) $row['value'];
            case "text":      return $row['value'];
            case "json":      return json_decode($row['value']);
            case "timestamp": return date_create_from_format("!".self::FORMAT_TS, $row['value'], new DateTimeZone("UTC"));
            case "date":      return date_create_from_format("!".self::FORMAT_DATE, $row['value'], new DateTimeZone("UTC"));
            case "time":      return date_create_from_format("!".self::FORMAT_TIME, $row['value'], new DateTimeZone("UTC"));
            case "bool":      return (bool) $row['value'];
            case "null":      return null;
            default:          return $row['value'];
        }
    }

    public function begin(): Db\Transaction {
        return $this->db->begin();
    }
    
    public function settingSet(string $key, string $value): bool {
        $out = !$this->db->prepare("UPDATE arsse_settings set value = ? where key is ?", "str", "str")->run($value, $key)->changes();
        if(!$out) {
            $out = $this->db->prepare("INSERT INTO arsse_settings(key,value)", "str", "str")->run($key, $value)->changes();
        }
        return (bool) $out;
    }

    public function settingRemove(string $key): bool {
        $this->db->prepare("DELETE from arsse_settings where key is ?", "str")->run($key);
        return true;
    }

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

    public function userAdd(string $user, string $password = null): string {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        if($this->userExists($user)) throw new User\Exception("alreadyExists", ["action" => __FUNCTION__, "user" => $user]);
        if($password===null) $password = (new PassGen)->length(Data::$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 $user): bool {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        if($this->db->prepare("DELETE from arsse_users where id is ?", "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(!Data::$user->authorize("@".$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[] = $user['id'];
            }
        } else {
            if(!Data::$user->authorize("", __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => "global"]);
            foreach($this->db->prepare("SELECT id from arsse_users")->run() as $user) {
                $out[] = $user['id'];
            }
        }
        return $out;
    }

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

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

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

    public function userPropertiesSet(string $user, array $properties): array {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        if(!$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);
        $this->db->prepare("UPDATE arsse_users set $setClause where id is ?", $setTypes, "str")->run($setValues, $user);
        return $this->userPropertiesGet($user);
    }

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

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

    public function folderAdd(string $user, array $data): int {
        // If the user isn't authorized to perform this action then throw an exception.
        if(!Data::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // if the desired folder name is missing or invalid, throw an exception
        if(!array_key_exists("name", $data) || $data['name']=="") {
            throw new Db\ExceptionInput("missing", ["action" => __FUNCTION__, "field" => "name"]);
        } else if(!strlen(trim($data['name']))) {
            throw new Db\ExceptionInput("whitespace", ["action" => __FUNCTION__, "field" => "name"]);
        }
        // normalize folder's parent, if there is one
        $parent = array_key_exists("parent", $data) ? (int) $data['parent'] : 0;
        if($parent===0) {
            // if no parent is specified, do nothing
            $parent = null;
        } else {
            // if a parent is specified, make sure it exists and belongs to the user; get its root (first-level) folder if it's a nested folder
            $p = $this->db->prepare("SELECT id from arsse_folders where owner is ? and id is ?", "str", "int")->run($user, $parent)->getValue();
            if(!$p) throw new Db\ExceptionInput("idMissing", ["action" => __FUNCTION__, "field" => "parent", 'id' => $parent]);
        }
        // check if a folder by the same name already exists, because nulls are wonky in SQL
        // FIXME: How should folder name be compared? Should a Unicode normalization be applied before comparison and insertion?
        if($this->db->prepare("SELECT count(*) from arsse_folders where owner is ? and parent is ? and name is ?", "str", "int", "str")->run($user, $parent, $data['name'])->getValue() > 0) {
            throw new Db\ExceptionInput("constraintViolation"); // FIXME: There needs to be a practical message here
        }
        // actually perform the insert (!)
        return $this->db->prepare("INSERT INTO arsse_folders(owner,parent,name) values(?,?,?)", "str", "int", "str")->run($user, $parent, $data['name'])->lastId();
    }

    public function folderList(string $user, int $parent = null, bool $recursive = true): Db\Result {
        // if the user isn't authorized to perform this action then throw an exception.
        if(!Data::$user->authorize($user, __FUNCTION__)) {
            throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        }
        // check to make sure the parent exists, if one is specified
        if(!is_null($parent)) {
            if(!$this->db->prepare("SELECT count(*) from arsse_folders where owner is ? and id is ?", "str", "int")->run($user, $parent)->getValue()) {
                throw new Db\ExceptionInput("idMissing", ["action" => __FUNCTION__, "field" => "parent", 'id' => $parent]);
            }
        }
        // if we're not returning a recursive list we can use a simpler query
        if(!$recursive) {
            return $this->db->prepare("SELECT id,name,parent from arsse_folders where owner is ? and parent is ?", "str", "int")->run($user, $parent);
        } else {
            return $this->db->prepare(
                "WITH RECURSIVE folders(id) as (SELECT id from arsse_folders where owner is ? and parent is ? union select arsse_folders.id from arsse_folders join folders on arsse_folders.parent=folders.id) ".
                "SELECT id,name,parent from arsse_folders where id in(SELECT id from folders) order by name",
            "str", "int")->run($user, $parent);
        }
    }

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

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

    public function folderPropertiesSet(string $user, int $id, array $data): bool {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        // validate the folder ID and, if specified, the parent to move it to
        $parent = null;
        if(array_key_exists("parent", $data)) $parent = $data['parent'];
        $f = $this->folderValidateId($user, $id, $parent, true);
        // if a new name is specified, validate it
        if(array_key_exists("name", $data)) {
            $this->folderValidateName($data['name']);
        }
        $data = array_merge($f, $data);
        // check to make sure the target folder name/location would not create a duplicate (we must do this check because null is not distinct in SQL)
        $existing = $this->db->prepare("SELECT id from arsse_folders where owner is ? and parent is ? and name is ?", "str", "int", "str")->run($user, $data['parent'], $data['name'])->getValue();
        if(!is_null($existing) && $existing != $id) {
            throw new Db\ExceptionInput("constraintViolation"); // FIXME: There needs to be a practical message here
        }
        $valid = [
            'name' => "str",
            'parent' => "int",
        ];
        list($setClause, $setTypes, $setValues) = $this->generateSet($data, $valid);
        return (bool) $this->db->prepare("UPDATE arsse_folders set $setClause where owner is ? and id is ?", $setTypes, "str", "int")->run($setValues, $user, $id)->changes();
    }

    protected function folderValidateId(string $user, int $id = null, int $parent = null, bool $subject = false): array {
        if(is_null($id)) {
            // if no ID is specified this is a no-op, unless a parent is specified, which is always a circular dependence
            if(!is_null($parent)) {
                throw new Db\ExceptionInput("circularDependence", ["action" => $this->caller(), "field" => "parent", 'id' => $parent]);
            }
            return [name => null, parent => null];
        }
        // check whether the folder exists and is owned by the user
        $f = $this->db->prepare("SELECT name,parent from arsse_folders where owner is ? and id is ?", "str", "int")->run($user, $id)->getRow();
        if(!$f) throw new Db\ExceptionInput($subject ? "subjectMissing" : "idMissing", ["action" => $this->caller(), "field" => "folder", 'id' => $parent]);
        // if we're moving a folder to a new parent, check that the parent is valid
        if(!is_null($parent)) {
            // make sure both that the parent exists, and that the parent is not either the folder itself or one of its children (a circular dependence)
            $p = $this->db->prepare(
                "WITH RECURSIVE folders(id) as (SELECT id from arsse_folders where owner is ? and id is ? union select arsse_folders.id from arsse_folders join folders on arsse_folders.parent=folders.id) ".
                "SELECT id,(id not in (select id from folders)) as valid from arsse_folders where owner is ? and id is ?",
                "str", "int", "str", "int"
            )->run($user, $id, $user, $parent)->getRow();
            if(!$p) {
                // if the parent doesn't exist or doesn't below to the user, throw an exception
                throw new Db\ExceptionInput("idMissing", ["action" => $this->caller(), "field" => "parent", 'id' => $parent]);
            } else {
                // if using the desired parent would create a circular dependence, throw a different exception
                if(!$p['valid']) throw new Db\ExceptionInput("circularDependence", ["action" => $this->caller(), "field" => "parent", 'id' => $parent]);
            }
        }
        return $f;
    }

    protected function folderValidateName($name): bool {
        $name = (string) $name;
        if(!strlen($name)) {
            throw new Db\ExceptionInput("missing", ["action" => $this->caller(), "field" => "name"]);
        } else if(!strlen(trim($name))) {
            throw new Db\ExceptionInput("whitespace", ["action" => $this->caller(), "field" => "name"]);
        } else {
            return true;
        }
    }

    public function subscriptionAdd(string $user, string $url, string $fetchUser = "", string $fetchPassword = ""): int {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        // check to see if the feed exists
        $feedID = $this->db->prepare("SELECT id from arsse_feeds where url is ? and username is ? and password is ?", "str", "str", "str")->run($url, $fetchUser, $fetchPassword)->getValue();
        if(is_null($feedID)) {
            // if the feed doesn't exist 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
                $this->db->prepare('DELETE from arsse_feeds where id is ?', 'int')->run($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, int $folder = null, int $id = null): Db\Result {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        // create a complex query
        $q = new Query(
            "SELECT 
                arsse_subscriptions.id,
                url,favicon,source,folder,pinned,err_count,err_msg,order_type,
                DATEFORMAT(?, added) as added,
                topmost.top as top_folder,
                CASE WHEN arsse_subscriptions.title is not null THEN arsse_subscriptions.title ELSE arsse_feeds.title END as title,
                (SELECT count(*) from arsse_articles where feed is arsse_subscriptions.feed) - (SELECT count(*) from arsse_marks join user on user is owner join arsse_articles on article = arsse_articles.id where feed is arsse_feeds.id and read is 1) as unread
             from arsse_subscriptions join user on user is owner join arsse_feeds on feed = arsse_feeds.id left join topmost on folder=f_id",
             "", // where terms
             "pinned desc, title" // order by terms
        );
        // define common table expressions
        $q->setCTE("user(user) as (SELECT ?)", "str", $user);  // the subject user; this way we only have to pass it to prepare() once
        // topmost folders belonging to the user
        $q->setCTE("topmost(f_id,top) as (select id,id from arsse_folders join user on owner is user where parent is null union select id,top from arsse_folders join topmost on parent=f_id)");
        if(!is_null($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 is ?", "int", $id);
        } else if(!is_null($folder)) {
            // if a folder is specified, make sure it exists
            $this->folderValidateId($user, $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) as (SELECT ? union select id from arsse_folders join folders on parent is folder)", "int", $folder);
            // add a suitable WHERE condition
            $q->setWhere("folder in (select folder from folders)");
        }
        return $this->db->prepare($q, "str")->run($this->dateFormatDefault);
    }

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

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

    public function subscriptionPropertiesSet(string $user, int $id, array $data): bool {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        $tr = $this->db->begin();
        if(!$this->db->prepare("SELECT count(*) from arsse_subscriptions where owner is ? and id is ?", "str", "int")->run($user, $id)->getValue()) {
            // if the ID doesn't exist or doesn't belong to the user, throw an exception
            throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "feed", 'id' => $id]);
        }
        if(array_key_exists("folder", $data)) {
            // ensure the target folder exists and belong to the user
            $this->folderValidateId($user, $data['folder']);
        }
        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'])) {
                $title = (string) $data['title'];
                if(!strlen($title)) throw new Db\ExceptionInput("missing", ["action" => __FUNCTION__, "field" => "title"]);
                if(!strlen(trim($title))) throw new Db\ExceptionInput("whitespace", ["action" => __FUNCTION__, "field" => "title"]);
                $data['title'] = $title;
            }
        }
        $valid = [
            'title'      => "str",
            'folder'     => "int",
            'order_type' => "strict int",
            'pinned'     => "strict bool",
        ];
        list($setClause, $setTypes, $setValues) = $this->generateSet($data, $valid);
        $out = (bool) $this->db->prepare("UPDATE arsse_subscriptions set $setClause where owner is ? and id is ?", $setTypes, "str", "int")->run($setValues, $user, $id)->changes();
        $tr->commit();
        return $out;
    }

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

    public function feedListStale(): array {
        $feeds = $this->db->prepare("SELECT id from arsse_feeds where next_fetch <= CURRENT_TIMESTAMP")->run()->getAll();
        return array_column($feeds,'id');
    }
    
    public function feedUpdate(int $feedID, bool $throwError = false): bool {
        $tr = $this->db->begin();
        // check to make sure the feed exists
        $f = $this->db->prepare("SELECT url, username, password, DATEFORMAT('http', modified) AS lastmodified, etag, err_count FROM arsse_feeds where id is ?", "int")->run($feedID)->getRow();
        if(!$f) throw new Db\ExceptionInput("subjectMissing", ["action" => __FUNCTION__, "field" => "feed", 'id' => $feedID]);
        // 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 {
            $feed = new Feed($feedID, $f['url'], (string)$f['lastmodified'], $f['etag'], $f['username'], $f['password']);
            if(!$feed->modified) {
                // if the feed hasn't changed, just compute the next fetch time and record it
                $this->db->prepare("UPDATE arsse_feeds SET updated = CURRENT_TIMESTAMP, next_fetch = ? WHERE id is ?", 'datetime', 'int')->run($feed->nextFetch, $feedID);
                $tr->commit();
                return false;
            }
        } catch (Feed\Exception $e) {
            // update the database with the resultant error and the next fetch time, incrementing the error count
            $this->db->prepare(
                "UPDATE arsse_feeds SET updated = CURRENT_TIMESTAMP, next_fetch = ?, err_count = err_count + 1, err_msg = ? WHERE id is ?", 
                'datetime', 'str', 'int'
            )->run(Feed::nextFetchOnError($f['err_count']), $e->getMessage(),$feedID);
            $tr->commit();
            if($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 is ?", 'int');
            $qDeleteCategories = $this->db->prepare("DELETE FROM arsse_categories WHERE article is ?", 'int');
            $qClearReadMarks = $this->db->prepare("UPDATE arsse_marks SET read = 0, modified = CURRENT_TIMESTAMP WHERE article is ? and read is 1", 'int');
            $qUpdateArticle = $this->db->prepare(
                "UPDATE arsse_articles SET url = ?, title = ?, author = ?, published = ?, edited = ?, modified = CURRENT_TIMESTAMP, guid = ?, content = ?, url_title_hash = ?, url_content_hash = ?, title_content_hash = ? WHERE id is ?", 
                'str', 'str', 'str', 'datetime', 'datetime', 'str', 'str', 'str', 'str', 'str', 'int'
            );
        }
        // actually perform updates
        foreach($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 = ? WHERE id is ?", 
            'str', 'str', 'str', 'str', 'datetime', 'str', 'datetime', 'int'
        )->run(
            $feed->data->feedUrl,
            $feed->data->title,
            $feed->favicon,
            $feed->data->siteUrl,
            $feed->lastModified,
            $feed->resource->getEtag(),
            $feed->nextFetch,
            $feedID
        );
        $tr->commit();
        return true;
    }

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

    public function articleStarredCount(string $user, array $context = []): int {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        return $this->db->prepare("SELECT count(*) from arsse_marks where owner is ? and starred is 1", "str")->run($user)->getValue();
    }

    public function editionLatest(string $user, array $context = []): int {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        if(array_key_exists("subscription", $context)) {
            $id = $context['subscription'];
            $sub = $this->subscriptionValidateId($user, $id);
            return (int) $this->db->prepare(
                "SELECT max(arsse_editions.id) 
                    from arsse_editions 
                    left join arsse_articles on article is arsse_articles.id 
                    left join arsse_feeds on arsse_articles.feed is arsse_feeds.id
                 where arsse_feeds.id is ?",
                "int"
            )->run($sub['feed'])->getValue();
        }
        return (int) $this->db->prepare("SELECT max(id) from arsse_editions")->run()->getValue();
    }

    public function articleList(string $user): Db\Result {
        if(!Data::$user->authorize($user, __FUNCTION__)) throw new User\ExceptionAuthz("notAuthorized", ["action" => __FUNCTION__, "user" => $user]);
        return $this->db->prepare(
            "WITH
                user(user) as (SELECT ?), 
                subscribed_feeds(id) as (SELECT feed from arsse_subscriptions join user on user is owner) 
            ".
            "SELECT 
                arsse_articles.id,
                arsse_articles.url,
                title,author,content,feed,guid,
                DATEFORMAT(?, edited) as edited,
                DATEFORMAT(?, modified) as modified,
                CASE (SELECT count(*) from arsse_marks join user on user is owner where article is arsse_articles.id and read is 1) when 1 then 0 else 1 end as unread,
                (SELECT count(*) from arsse_marks join user on user is owner where article is arsse_articles.id and starred is 1) as starred,
                (SELECT max(id) from arsse_editions where article is arsse_articles.id) as latestEdition,
                url_title_hash||':'||url_content_hash||':'||title_content_hash as fingerprint,
                arsse_enclosures.url as media_url,
                arsse_enclosures.type as media_type
            FROM arsse_articles 
                join subscribed_feeds on arsse_articles.feed is subscribed_feeds.id
                left join arsse_enclosures on arsse_enclosures.article is arsse_articles.id
            ",
            "str","str","str"
        )-run($user, $this->dateFormatDefault, $this->dateFormatDefault);
    }
}