<?php

/**
 * This file is part of RSS-Bridge, a PHP project capable of generating RSS and
 * Atom feeds for websites that don't have one.
 *
 * For the full license information, please view the UNLICENSE file distributed
 * with this source code.
 *
 * @package Core
 * @license http://unlicense.org/ UNLICENSE
 * @link    https://github.com/rss-bridge/rss-bridge
 */

/**
 * An abstract class for bridges that need to transform existing RSS or Atom
 * feeds.
 *
 * This class extends {@see BridgeAbstract} with functions to extract contents
 * from existing RSS or Atom feeds. Bridges that need to transform existing feeds
 * should inherit from this class instead of {@see BridgeAbstract}.
 *
 * Bridges that extend this class don't need to concern themselves with getting
 * contents from existing feeds, but can focus on adding additional contents
 * (i.e. by downloading additional data), filtering or just transforming a feed
 * into another format.
 *
 * @link http://www.rssboard.org/rss-0-9-1 RSS 0.91 Specification
 * @link http://web.resource.org/rss/1.0/spec RDF Site Summary (RSS) 1.0
 * @link http://www.rssboard.org/rss-specification RSS 2.0 Specification
 * @link https://tools.ietf.org/html/rfc4287 The Atom Syndication Format
 *
 * @todo The parsing functions should all be private. This class is complicated
 * enough without having to consider children overriding functions.
 */
abstract class FeedExpander extends BridgeAbstract
{
    /** Indicates an RSS 1.0 feed */
    const FEED_TYPE_RSS_1_0 = 'RSS_1_0';

    /** Indicates an RSS 2.0 feed */
    const FEED_TYPE_RSS_2_0 = 'RSS_2_0';

    /** Indicates an Atom 1.0 feed */
    const FEED_TYPE_ATOM_1_0 = 'ATOM_1_0';

    /**
     * Holds the title of the current feed
     *
     * @var string
     */
    private $title;

    /**
     * Holds the URI of the feed
     *
     * @var string
     */
    private $uri;

    /**
     * Holds the icon of the feed
     *
     */
    private $icon;

    /**
     * Holds the feed type during internal operations.
     *
     * @var string
     */
    private $feedType;

    /**
     * Collects data from an existing feed.
     *
     * Children should call this function in {@see BridgeInterface::collectData()}
     * to extract a feed.
     *
     * @param string $url URL to the feed.
     * @param int $maxItems Maximum number of items to collect from the feed
     * (`-1`: no limit).
     * @return self
     */
    public function collectExpandableDatas($url, $maxItems = -1)
    {
        if (empty($url)) {
            throw new \Exception('There is no $url for this RSS expander');
        }

        Debug::log(sprintf('Loading from %s', $url));

        /* Notice we do not use cache here on purpose:
         * we want a fresh view of the RSS stream each time
         */

        $mimeTypes = [
            MrssFormat::MIME_TYPE,
            AtomFormat::MIME_TYPE,
            '*/*',
        ];
        $httpHeaders = ['Accept: ' . implode(', ', $mimeTypes)];
        $content = getContents($url, $httpHeaders);
        if ($content === '') {
            throw new \Exception(sprintf('Unable to parse xml from `%s` because we got the empty string', $url));
        }
        // Maybe move this call earlier up the stack frames
        // Disable triggering of the php error-handler and handle errors manually instead
        libxml_use_internal_errors(true);
        // Consider replacing libxml with https://www.php.net/domdocument
        // Intentionally not using the silencing operator (@) because it has no effect here
        $rssContent = simplexml_load_string(trim($content));
        if ($rssContent === false) {
            $xmlErrors = libxml_get_errors();
            foreach ($xmlErrors as $xmlError) {
                if (Debug::isEnabled()) {
                    Debug::log(trim($xmlError->message));
                }
            }
            if ($xmlErrors) {
                // Render only the first error into exception message
                $firstXmlErrorMessage = $xmlErrors[0]->message;
            }
            throw new \Exception(sprintf('Unable to parse xml from `%s` %s', $url, $firstXmlErrorMessage ?? ''));
        }
        // Restore previous behaviour in case other code relies on it being off
        libxml_use_internal_errors(false);

        // Commented out because it's spammy
        // Debug::log(sprintf("RSS content is ===========\n%s===========", var_export($rssContent, true)));

        switch (true) {
            case isset($rssContent->item[0]):
                Debug::log('Detected RSS 1.0 format');
                $this->feedType = self::FEED_TYPE_RSS_1_0;
                $this->collectRss1($rssContent, $maxItems);
                break;
            case isset($rssContent->channel[0]):
                Debug::log('Detected RSS 0.9x or 2.0 format');
                $this->feedType = self::FEED_TYPE_RSS_2_0;
                $this->collectRss2($rssContent, $maxItems);
                break;
            case isset($rssContent->entry[0]):
                Debug::log('Detected ATOM format');
                $this->feedType = self::FEED_TYPE_ATOM_1_0;
                $this->collectAtom1($rssContent, $maxItems);
                break;
            default:
                Debug::log(sprintf('Unable to detect feed format from `%s`', $url));
                throw new \Exception(sprintf('Unable to detect feed format from `%s`', $url));
        }

        return $this;
    }

    /**
     * Collect data from an RSS 1.0 compatible feed
     *
     * @link http://web.resource.org/rss/1.0/spec RDF Site Summary (RSS) 1.0
     *
     * @param string $rssContent The RSS content
     * @param int $maxItems Maximum number of items to collect from the feed
     * (`-1`: no limit).
     * @return void
     *
     * @todo Instead of passing $maxItems to all functions, just add all items
     * and remove excessive items later.
     */
    protected function collectRss1($rssContent, $maxItems)
    {
        $this->loadRss2Data($rssContent->channel[0]);
        foreach ($rssContent->item as $item) {
            $tmp_item = $this->parseItem($item);
            if (!empty($tmp_item)) {
                $this->items[] = $tmp_item;
            }
            if ($maxItems !== -1 && count($this->items) >= $maxItems) {
                break;
            }
        }
    }

    /**
     * Collect data from a RSS 2.0 compatible feed
     *
     * @link http://www.rssboard.org/rss-specification RSS 2.0 Specification
     *
     * @param int $maxItems Maximum number of items to collect from the feed (`-1`: no limit).
     * @return void
     *
     * @todo Instead of passing $maxItems to all functions, just add all items and remove excessive items later.
     */
    protected function collectRss2(\SimpleXMLElement $rssContent, $maxItems)
    {
        $rssContent = $rssContent->channel[0];
        $this->loadRss2Data($rssContent);
        foreach ($rssContent->item as $item) {
            $tmp_item = $this->parseItem($item);
            if (!empty($tmp_item)) {
                $this->items[] = $tmp_item;
            }
            if ($maxItems !== -1 && count($this->items) >= $maxItems) {
                break;
            }
        }
    }

    /**
     * Collect data from a Atom 1.0 compatible feed
     *
     * @link https://tools.ietf.org/html/rfc4287  The Atom Syndication Format
     *
     * @param object $content The Atom content
     * @param int $maxItems Maximum number of items to collect from the feed
     * (`-1`: no limit).
     * @return void
     *
     * @todo Instead of passing $maxItems to all functions, just add all items
     * and remove excessive items later.
     */
    protected function collectAtom1($content, $maxItems)
    {
        $this->loadAtomData($content);
        foreach ($content->entry as $item) {
            $tmp_item = $this->parseItem($item);
            if (!empty($tmp_item)) {
                $this->items[] = $tmp_item;
            }
            if ($maxItems !== -1 && count($this->items) >= $maxItems) {
                break;
            }
        }
    }

    /**
     * Load RSS 2.0 feed data into RSS-Bridge
     *
     * @param object $rssContent The RSS content
     * @return void
     *
     * @todo set title, link, description, language, and so on
     */
    protected function loadRss2Data($rssContent)
    {
        $this->title = trim((string)$rssContent->title);
        $this->uri = trim((string)$rssContent->link);

        if (!empty($rssContent->image)) {
            $this->icon = trim((string)$rssContent->image->url);
        }
    }

    /**
     * Load Atom feed data into RSS-Bridge
     *
     * @param object $content The Atom content
     * @return void
     */
    protected function loadAtomData($content)
    {
        $this->title = (string)$content->title;

        // Find best link (only one, or first of 'alternate')
        if (!isset($content->link)) {
            $this->uri = '';
        } elseif (count($content->link) === 1) {
            $this->uri = (string)$content->link[0]['href'];
        } else {
            $this->uri = '';
            foreach ($content->link as $link) {
                if (strtolower($link['rel']) === 'alternate') {
                    $this->uri = (string)$link['href'];
                    break;
                }
            }
        }

        if (!empty($content->icon)) {
            $this->icon = (string)$content->icon;
        } elseif (!empty($content->logo)) {
            $this->icon = (string)$content->logo;
        }
    }

    /**
     * Parse the contents of a single Atom feed item into a RSS-Bridge item for
     * further transformation.
     *
     * @param object $feedItem A single feed item
     * @return object The RSS-Bridge item
     *
     * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
     * of its own?
     */
    protected function parseATOMItem($feedItem)
    {
        // Some ATOM entries also contain RSS 2.0 fields
        $item = $this->parseRss2Item($feedItem);

        if (isset($feedItem->id)) {
            $item['uri'] = (string)$feedItem->id;
        }
        if (isset($feedItem->title)) {
            $item['title'] = html_entity_decode((string)$feedItem->title);
        }
        if (isset($feedItem->updated)) {
            $item['timestamp'] = strtotime((string)$feedItem->updated);
        }
        if (isset($feedItem->author)) {
            $item['author'] = (string)$feedItem->author->name;
        }
        if (isset($feedItem->content)) {
            $item['content'] = (string)$feedItem->content;
        }

        //When "link" field is present, URL is more reliable than "id" field
        if (count($feedItem->link) === 1) {
            $item['uri'] = (string)$feedItem->link[0]['href'];
        } else {
            foreach ($feedItem->link as $link) {
                if (strtolower($link['rel']) === 'alternate') {
                    $item['uri'] = (string)$link['href'];
                }
                if (strtolower($link['rel']) === 'enclosure') {
                    $item['enclosures'][] = (string)$link['href'];
                }
            }
        }

        return $item;
    }

    /**
     * Parse the contents of a single RSS 0.91 feed item into a RSS-Bridge item
     * for further transformation.
     *
     * @param object $feedItem A single feed item
     * @return object The RSS-Bridge item
     *
     * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
     * of its own?
     */
    protected function parseRss091Item($feedItem)
    {
        $item = [];
        if (isset($feedItem->link)) {
            $item['uri'] = (string)$feedItem->link;
        }
        if (isset($feedItem->title)) {
            $item['title'] = html_entity_decode((string)$feedItem->title);
        }
        // rss 0.91 doesn't support timestamps
        // rss 0.91 doesn't support authors
        // rss 0.91 doesn't support enclosures
        if (isset($feedItem->description)) {
            $item['content'] = (string)$feedItem->description;
        }
        return $item;
    }

    /**
     * Parse the contents of a single RSS 1.0 feed item into a RSS-Bridge item
     * for further transformation.
     *
     * @param object $feedItem A single feed item
     * @return object The RSS-Bridge item
     *
     * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
     * of its own?
     */
    protected function parseRss1Item($feedItem)
    {
        // 1.0 adds optional elements around the 0.91 standard
        $item = $this->parseRss091Item($feedItem);

        $namespaces = $feedItem->getNamespaces(true);
        if (isset($namespaces['dc'])) {
            $dc = $feedItem->children($namespaces['dc']);
            if (isset($dc->date)) {
                $item['timestamp'] = strtotime((string)$dc->date);
            }
            if (isset($dc->creator)) {
                $item['author'] = (string)$dc->creator;
            }
        }

        return $item;
    }

    /**
     * Parse the contents of a single RSS 2.0 feed item into a RSS-Bridge item
     * for further transformation.
     *
     * @param object $feedItem A single feed item
     * @return object The RSS-Bridge item
     *
     * @todo To reduce confusion, the RSS-Bridge item should maybe have a class
     * of its own?
     */
    protected function parseRss2Item($feedItem)
    {
        // Primary data is compatible to 0.91 with some additional data
        $item = $this->parseRss091Item($feedItem);

        $namespaces = $feedItem->getNamespaces(true);
        if (isset($namespaces['dc'])) {
            $dc = $feedItem->children($namespaces['dc']);
        }
        if (isset($namespaces['media'])) {
            $media = $feedItem->children($namespaces['media']);
        }

        if (isset($feedItem->guid)) {
            foreach ($feedItem->guid->attributes() as $attribute => $value) {
                if (
                    $attribute === 'isPermaLink'
                    && (
                        $value === 'true' || (
                            filter_var($feedItem->guid, FILTER_VALIDATE_URL)
                            && (empty($item['uri']) || !filter_var($item['uri'], FILTER_VALIDATE_URL))
                        )
                    )
                ) {
                    $item['uri'] = (string)$feedItem->guid;
                    break;
                }
            }
        }

        if (isset($feedItem->pubDate)) {
            $item['timestamp'] = strtotime((string)$feedItem->pubDate);
        } elseif (isset($dc->date)) {
            $item['timestamp'] = strtotime((string)$dc->date);
        }

        if (isset($feedItem->author)) {
            $item['author'] = (string)$feedItem->author;
        } elseif (isset($feedItem->creator)) {
            $item['author'] = (string)$feedItem->creator;
        } elseif (isset($dc->creator)) {
            $item['author'] = (string)$dc->creator;
        } elseif (isset($media->credit)) {
            $item['author'] = (string)$media->credit;
        }

        if (isset($feedItem->enclosure) && !empty($feedItem->enclosure['url'])) {
            $item['enclosures'] = [(string)$feedItem->enclosure['url']];
        }

        return $item;
    }

    /**
     * Parse the contents of a single feed item, depending on the current feed
     * type, into a RSS-Bridge item.
     *
     * @param object $item The current feed item
     * @return object A RSS-Bridge item, with (hopefully) the whole content
     */
    protected function parseItem($item)
    {
        switch ($this->feedType) {
            case self::FEED_TYPE_RSS_1_0:
                return $this->parseRss1Item($item);
            case self::FEED_TYPE_RSS_2_0:
                return $this->parseRss2Item($item);
            case self::FEED_TYPE_ATOM_1_0:
                return $this->parseATOMItem($item);
            default:
                throw new \Exception(sprintf('Unknown version %s!', $this->getInput('version')));
        }
    }

    /** {@inheritdoc} */
    public function getURI()
    {
        if (!empty($this->uri)) {
            return $this->uri;
        }
        return parent::getURI();
    }

    /** {@inheritdoc} */
    public function getName()
    {
        if (!empty($this->title)) {
            return $this->title;
        }
        return parent::getName();
    }

    /** {@inheritdoc} */
    public function getIcon()
    {
        if (!empty($this->icon)) {
            return $this->icon;
        }
        return parent::getIcon();
    }
}