<?php
declare(strict_types=1);
namespace JKingWeb\Arsse;
use PicoFeed\Reader\Reader;
use PicoFeed\PicoFeedException;
use PicoFeed\Reader\Favicon;
use PicoFeed\Config\Config;

class Feed {
    public $data = null;
    public $favicon;
    public $parser;
    public $reader;
    public $resource;
    public $newItems = [];
    public $changedItems = [];

    public function __construct(string $url, string $lastModified = '', string $etag = '', string $username = '', string $password = '') {
        try {
            $config = new Config;
            $config->setClientUserAgent(Data::$conf->userAgentString);
            $config->setGrabberUserAgent(Data::$conf->userAgentString);

            $this->reader = new Reader($config);
            $this->resource = $this->reader->download($url, $lastModified, $etag, $username, $password);
        } catch (PicoFeedException $e) {
            throw new Feed\Exception($url, $e);
        }
    }

    public function parse(int $feedID = null): bool {
        try {
            $this->parser = $this->reader->getParser(
                $this->resource->getUrl(),
                $this->resource->getContent(),
                $this->resource->getEncoding()
            );
            $feed = $this->parser->execute();

            // Grab the favicon for the feed; returns an empty string if it cannot find one.
            // Some feeds might use a different domain (eg: feedburner), so the site url is
            // used instead of the feed's url.
            $this->favicon = (new Favicon)->find($feed->siteUrl);
        } catch (PicoFeedException $e) {
            throw new Feed\Exception($url, $e);
        }

        // PicoFeed does not provide valid ids when there is no id element. Its solution
        // of hashing the url, title, and content together for the id if there is no id
        // element is stupid. Many feeds are frankenstein mixtures of Atom and RSS, but
        // some are pure RSS with guid elements while others use the Dublin Core spec for
        // identification. These feeds shouldn't be duplicated when updated. That should
        // only be reserved for severely broken feeds.

        foreach ($feed->items as $f) {
            // Hashes used for comparison to check for updates and also to identify when an
            // id doesn't exist.
            $f->urlTitleHash = hash('sha256', $f->url.$f->title);
            $f->urlContentHash = hash('sha256', $f->url.$f->content.$f->enclosureUrl.$f->enclosureType);
            $f->titleContentHash = hash('sha256', $f->title.$f->content.$f->enclosureUrl.$f->enclosureType);

            // If there is an id element then continue. The id is used already.
            $id = (string)$f->xml->id;
            if ($id !== '') {
                continue;
            }

            // If there is a guid element use it as the id.
            $id = (string)$f->xml->guid;
            if ($id !== '') {
                $f->id = hash('sha256', $id);
                continue;
            }

            // If there is a Dublin Core identifier use it.
            $id = (string)$f->xml->children('http://purl.org/dc/elements/1.1/')->identifier;
            if ($id !== '') {
                $f->id = hash('sha256', $id);
                continue;
            }

            // If there aren't any of those there is no id.
            $f->id = '';
        }
        $this->data = $feed;
        // if a feedID is supplied, determine which items are already in the database, which are not, and which might have been edited
        if(!is_null($feedID)) {
            $this->matchToDatabase($feedID);
        }
        return true;
    }

    protected function deduplicateItems(array $items): array {
        /* Rationale:
            Some newsfeeds (notably Planet) include multiple versions of an 
            item if it is updated. As we only care about the latest, we
            try to remove any "old" versions of an item that might also be 
            present within the feed.
        */
        $out = [];
        foreach($items as $item) {
            foreach($out as $index => $check) {
                // if the two items have the same ID or any one hash matches, they are two versions of the same item
                if(
                    ($item->id && $check->id && $item->id == $check->id) ||
                    $item->urlTitleHash     == $check->urlTitleHash      ||
                    $item->urlContentHash   == $check->urlContentHash    ||
                    $item->titleContentHash == $check->titleContentHash
                ) {
                    if(// because newsfeeds are usually order newest-first, the later item should only be used if...
                        // the later item has an update date and the existing item does not
                        ($item->updatedDate && !$check->updatedDate) ||
                        // the later item has an update date newer than the existing item's
                        ($item->updatedDate && $check->updatedDate && $item->updatedDate->getTimestamp() > $check->updatedDate->getTimestamp()) ||
                        // neither item has update dates, both have publish dates, and the later item has a newer publish date
                        (!$item->updatedDate && !$check->updatedDate && $item->publishedDate && $check->publishedDate && $item->publishedDate->getTimestamp() > $check->publishedDate->getTimestamp())
                    ) {
                        // if the later item should be used, replace the existing one
                        $out[$index] = $item;
                        continue 2;
                    } else {
                        // otherwise skip the item
                        continue 2;
                    }
                }
            }
            // if there was no match, add the item
            $out[] = $item;
        }
        return $out;
    }

    protected function matchToDatabase(int $feedID): bool {
        // first perform deduplication on items
        $items = $this->deduplicateItems($this->data->items);
        // get as many of the latest articles in the database as there are in the feed
        $articles = Data::$db->articleMatchLatest($feedID, sizeof($items));
        // arrays holding new, edited, and tentatively new items; items may be tentatively new because we perform two passes
        $new = $tentative = $edited = [];
        // iterate through the articles and for each determine whether it is existing, edited, or entirely new
        foreach($items as $index => $i) {
            foreach($articles as $a) {
                if(
                    // the item matches if the GUID matches...
                    ($i->id && $i->id === $a['guid']) ||
                    // ... or if any one of the hashes match
                    $i->urlTitleHash     === $a['url_title_hash']     ||
                    $i->urlContentHash   === $a['url_content_hash']   ||
                    $i->titleContentHash === $a['title_content_hash']
                ) {
                    if($i->updatedDate && $i->updatedDate->getTimestamp() !== $match['edited_date']) {
                        // if the item has an edit timestamp and it doesn't match that of the article in the database, the the article has been edited
                        // we store the item index and database record ID as a key/value pair
                        $edited[$index] = $a['id'];
                        break;
                    } else if($i->urlTitleHash !== $a['url_title_hash'] || $i->urlContentHash !== $a['url_content_hash'] || $i->titleContentHash !== $a['title_content_hash']) {
                        // if any of the hashes do not match, then the article has been edited
                        $edited[$index] = $a['id'];
                        break;
                    } else {
                        // otherwise the item is unchanged and we can ignore it
                        break;
                    }
                } else {
                    // if we don't have a match, add the item to the tentatively new list
                    $tentative[] = $index;
                }
            }
        }
        if(sizeof($tentative)) {
            // if we need to, perform a second pass on the database looking specifically for IDs and hashes of the new items
            $ids = $hashesUT = $hashesUC = $hashesTC = [];
            foreach($tentative as $index) {
                $i = $items[$index];
                if($i->id) $ids[] = $id->id;
                $hashesUT[] = $i->urlTitleHash;
                $hashesUC[] = $i->urlContentHash;
                $hashesTC[] = $i->titleContentHash;
            }
            $articles = Data::$db->articleMatchIds($feedID, $ids, $hashesUT, $hashesUC, $hashesTC);
            foreach($tentative as $index) {
                $i = $items[$index];
                foreach($articles as $a) {
                    if(
                        // the item matches if the GUID matches...
                        ($i->id && $i->id === $a['guid']) ||
                        // ... or if any one of the hashes match
                        $i->urlTitleHash     === $a['url_title_hash']     ||
                        $i->urlContentHash   === $a['url_content_hash']   ||
                        $i->titleContentHash === $a['title_content_hash']
                    ) {
                        if($i->updatedDate && $i->updatedDate->getTimestamp() !== $match['edited_date']) {
                            // if the item has an edit timestamp and it doesn't match that of the article in the database, the the article has been edited
                            // we store the item index and database record ID as a key/value pair
                            $edited[$index] = $a['id'];
                            break;
                        } else if($i->urlTitleHash !== $a['url_title_hash'] || $i->urlContentHash !== $a['url_content_hash'] || $i->titleContentHash !== $a['title_content_hash']) {
                            // if any of the hashes do not match, then the article has been edited
                            $edited[$index] = $a['id'];
                            break;
                        } else {
                            // otherwise the item is unchanged and we can ignore it
                            break;
                        }
                    } else {
                        // if we don't have a match, add the item to the definite new list
                        $new[] = $index;
                    }
                }
            }
        }
        // FIXME: fetch full content when appropriate
        foreach($new as $index) {
            $this->newItems[] = $items[$index];
        }
        foreach($edited as $index => $id) {
            $this->changedItems[$id] = $items[$index];
        }
        return true;
    }
}