<?php declare(strict_types=1);

namespace FeedReaderCentral;

use BitBadger\PDODocument\{
    Configuration, Custom, Document, DocumentException, DocumentList, Exists, Field, Find, Parameters, Patch, Query
};
use DateTimeInterface;

/**
 * An RSS or Atom feed
 */
class Feed
{
    // ***** CONSTANTS *****

    /** @var int Do not purge items */
    public const int PURGE_NONE = 0;

    /** @var int Purge all read items (will not purge unread items) */
    public const int PURGE_READ = 1;

    /** @var int Purge items older than the specified number of days */
    public const int PURGE_BY_DAYS = 2;

    /** @var int Purge items in number greater than the specified number of items to keep */
    public const int PURGE_BY_COUNT = 3;

    /**
     * Constructor
     *
     * @param int $id The ID of the feed
     * @param int $user_id The ID of the user to whom this subscription belongs
     * @param string $url The URL of the feed
     * @param string|null $title The title of this feed
     * @param string|null $updated_on The date/time items in this feed were last updated
     * @param string|null $checked_on The date/time this feed was last checked
     */
    public function __construct(public int $id = 0, public int $user_id = 0, public string $url = '',
                                public ?string $title = null, public ?string $updated_on = null,
                                public ?string $checked_on = null) { }

    // ***** STATIC FUNCTIONS *****

    /**
     * Create a document from the parsed feed
     *
     * @param ParsedFeed $parsed The parsed feed
     * @return static The document constructed from the parsed feed
     */
    public static function fromParsed(ParsedFeed $parsed): static
    {
        $it             = new static();
        $it->user_id    = $_SESSION[Key::USER_ID];
        $it->url        = $parsed->url;
        $it->title      = $parsed->title;
        $it->updated_on = $parsed->updatedOn;
        $it->checked_on = Data::formatDate('now');

        return $it;
    }

    /**
     * Update a feed's items
     *
     * @param int $feedId The ID of the feed to which these items belong
     * @param ParsedFeed $parsed The extracted Atom or RSS feed items
     * @param DateTimeInterface $lastChecked When this feed was last checked (only new items will be added)
     * @return array ['ok' => true] if successful, ['error' => message] if not
     */
    public static function updateItems(int $feedId, ParsedFeed $parsed, DateTimeInterface $lastChecked): array
    {
        $results =
            array_map(function ($item) use ($feedId) {
                try {
                    $existing = Find::firstByFields(Table::ITEM,
                        [Field::EQ('feed_id', $feedId), Field::EQ('item_guid', $item->guid)], Item::class);
                    if ($existing) {
                        if ($existing->published_on != $item->publishedOn
                            || ($existing->updated_on != ($item->updatedOn ?? ''))) {
                            Patch::byId(Table::ITEM, $existing->id, $item->patchFields());
                        }
                    } else {
                        Document::insert(Table::ITEM, Item::fromFeedItem($feedId, $item));
                    }
                    return ['ok' => true];
                } catch (DocumentException $ex) {
                    return ['error' => "$ex"];
                }
            }, array_filter($parsed->items,
                fn($it) => date_create_immutable($it->updatedOn ?? $it->publishedOn) >= $lastChecked));
        $errors = array_map(fn($it) => $it['error'], array_filter($results, fn($it) => array_key_exists('error', $it)));
        return sizeof($errors) > 0 ? ['error' => implode("\n", $errors)] : ['ok' => true];
    }

    /**
     * Purge items for a feed
     *
     * @param int $feedId The ID of the feed to be purged
     * @return array|string[]|true[] ['ok' => true] if purging was successful, ['error' => message] if not
     */
    private static function purgeItems(int $feedId): array
    {
        if (!array_search(PURGE_TYPE, [self::PURGE_READ, self::PURGE_BY_DAYS, self::PURGE_BY_COUNT])) {
            return ['error' => 'Unrecognized purge type ' . PURGE_TYPE];
        }

        $fields = [Field::EQ('feed_id', $feedId, ':feed'), Data::bookmarkField(false)];
        $sql    = Query\Delete::byFields(Table::ITEM, $fields);
        if (PURGE_TYPE == self::PURGE_READ) {
            $readField = Field::EQ('is_read', 1, ':read');
            $fields[]  = $readField;
            $sql      .= ' AND ' . Query::whereByFields([$readField]);
        } elseif (PURGE_TYPE == self::PURGE_BY_DAYS) {
            $fields[] = Field::EQ('', Data::formatDate('-' . PURGE_NUMBER . ' day'), ':oldest');
            $sql     .= " AND date(coalesce(data->>'updated_on', data->>'published_on)) < date(:oldest)";
        } elseif (PURGE_TYPE == self::PURGE_BY_COUNT) {
            $fields[] = Field::EQ('', PURGE_NUMBER, ':keep');
            $id       = Configuration::$idField;
            $table    = Table::ITEM;
            $sql     .= ' ' . <<<SQL
                AND data->>'$id' IN (
                    SELECT data->>'$id' FROM $table
                     WHERE data->>'feed_id' = :feed
                     ORDER BY date(coalesce(data->>'updated_on', data->>'published_on')) DESC
                     LIMIT -1 OFFSET :keep
                )
                SQL;
        }
        try {
            Custom::nonQuery($sql, Parameters::addFields($fields, []));
            return ['ok' => true];
        } catch (DocumentException $ex) {
            return ['error' => "$ex"];
        }
    }

    /**
     * Refresh a feed
     *
     * @param int $feedId The ID of the feed to be refreshed
     * @param string $url The URL of the feed to be refreshed
     * @return array|string[]|true[] ['ok' => true] if successful, ['error' => message] if not
     */
    public static function refreshFeed(int $feedId, string $url): array
    {
        $feedRetrieval = ParsedFeed::retrieve($url);
        if (key_exists('error', $feedRetrieval)) return $feedRetrieval;
        $feed = $feedRetrieval['ok'];

        try {
            $feedDoc = Find::byId(Table::FEED, $feedId, self::class);
            if (!$feedDoc) return ['error' => 'Could not derive date last checked for feed'];
            $lastChecked = date_create_immutable($feedDoc->checked_on ?? WWW_EPOCH);

            $itemUpdate = self::updateItems($feedId, $feed, $lastChecked);
            if (key_exists('error', $itemUpdate)) return $itemUpdate;

            $patch = [
                'title'      => $feed->title,
                'updated_on' => $feed->updatedOn,
                'checked_on' => Data::formatDate('now')
            ];
            if ($url == $feed->url) $patch['url'] = $feed->url;
            Patch::byId(Table::FEED, $feedId, $patch);
        } catch (DocumentException $ex) {
            return ['error' => "$ex"];
        }

        return PURGE_TYPE == self::PURGE_NONE ? ['ok' => true] : self::purgeItems($feedId);
    }

    /**
     * Add an RSS feed
     *
     * @param string $url The URL of the RSS feed to add
     * @return array ['ok' => feedId] if successful, ['error' => message] if not
     */
    public static function add(string $url): array
    {
        $feedExtract = ParsedFeed::retrieve($url);
        if (key_exists('error', $feedExtract)) return $feedExtract;

        $feed = $feedExtract['ok'];

        try {
            $fields = [Field::EQ('user_id', $_SESSION[Key::USER_ID]), Field::EQ('url', $feed->url)];
            if (Exists::byFields(Table::FEED, $fields)) {
                return ['error' => "Already subscribed to feed $feed->url"];
            }

            Document::insert(Table::FEED, self::fromParsed($feed));

            $doc = Find::firstByFields(Table::FEED, $fields, static::class);
            if (!$doc) return ['error' => 'Could not retrieve inserted feed'];

            $result = self::updateItems($doc->id, $feed, date_create_immutable(WWW_EPOCH));
            if (key_exists('error', $result)) return $result;

            return ['ok' => $doc->id];
        } catch (DocumentException $ex) {
            return ['error' => "$ex"];
        }
    }

    /**
     * Update an RSS feed
     *
     * @param Feed $existing The existing feed
     * @param string $url The URL with which the existing feed should be modified
     * @return bool[]|string[] [ 'ok' => true ] if successful, [ 'error' => message ] if not
     */
    public static function update(Feed $existing, string $url): array
    {
        try {
            Patch::byFields(Table::FEED,
                [Field::EQ(Configuration::$idField, $existing->id), Field::EQ('user_id', $_SESSION[Key::USER_ID])],
                ['url' => $url]);

            return self::refreshFeed($existing->id, $url);
        } catch (DocumentException $ex) {
            return ['error' => "$ex"];
        }
    }

    /**
     * Retrieve all feeds, optionally for a specific user
     *
     * @param int $user The ID of the user whose feeds should be retrieved (optional, defaults to all feeds)
     * @return DocumentList<Feed> A list of feeds
     * @throws DocumentException If any is encountered
     */
    public static function retrieveAll(int $user = 0): DocumentList
    {
        return $user == 0
            ? Find::all(Table::FEED, self::class)
            : Find::byFields(Table::FEED, [Field::EQ('user_id', $user)], self::class);
    }

    /**
     * Refresh all feeds
     *
     * @return array|true[]|string[] ['ok' => true] if successful,
     *      ['error' => message] if not (may have multiple error lines)
     */
    public static function refreshAll(): array
    {
        try {
            $feeds = self::retrieveAll($_SESSION[Key::USER_ID]);

            $errors = [];
            foreach ($feeds->items() as $feed) {
                $result = self::refreshFeed($feed->id, $feed->url);
                if (key_exists('error', $result)) $errors[] = $result['error'];
            }
        } catch (DocumentException $ex) {
            return ['error' => "$ex"];
        }

        return sizeof($errors) == 0 ? ['ok' => true] : ['error' => implode("\n", $errors)];
    }

    /**
     * Retrieve a feed by its ID for the current user
     *
     * @param int $feedId The ID of the feed to retrieve
     * @return static|false The data for the feed if found, false if not found
     * @throws DocumentException If any is encountered
     */
    public static function retrieveById(int $feedId): static|false
    {
        $doc = Find::byId(Table::FEED, $feedId, static::class);
        return $doc && $doc->user_id == $_SESSION[Key::USER_ID] ? $doc : false;
    }
}