<?php

declare(strict_types=1);

/**
 * Very basic and naive feed parser that srapes out rss 0.91, 1.0, 2.0 and atom 1.0.
 *
 * Emit arrays meant to be used inside rss-bridge.
 *
 * The feed item structure is identical to that of FeedItem
 */
final class FeedParser
{
    public function parseFeed(string $xmlString): array
    {
        libxml_use_internal_errors(true);
        $xml = simplexml_load_string(trim($xmlString));
        $xmlErrors = libxml_get_errors();
        libxml_use_internal_errors(false);
        if ($xml === false) {
            if ($xmlErrors) {
                $firstXmlErrorMessage = $xmlErrors[0]->message;
            }
            throw new \Exception(sprintf('Unable to parse xml: %s', $firstXmlErrorMessage ?? ''));
        }
        $feed = [
            'title'     => null,
            'uri'       => null,
            'icon'      => null,
            'items'     => [],
        ];
        if (isset($xml->item[0])) {
            // rss 1.0
            $channel = $xml->channel[0];
            $feed['title'] = trim((string)$channel->title);
            $feed['uri'] = trim((string)$channel->link);
            if (!empty($channel->image)) {
                $feed['icon'] = trim((string)$channel->image->url);
            }
            foreach ($xml->item as $item) {
                $feed['items'][] = $this->parseRss1Item($item);
            }
        } elseif (isset($xml->channel[0])) {
            // rss 2.0
            $channel = $xml->channel[0];
            $feed['title'] = trim((string)$channel->title);
            $feed['uri'] = trim((string)$channel->link);
            if (!empty($channel->image)) {
                $feed['icon'] = trim((string)$channel->image->url);
            }
            foreach ($channel->item as $item) {
                $feed['items'][] = $this->parseRss2Item($item);
            }
        } elseif (isset($xml->entry[0])) {
            // atom 1.0
            $feed['title'] = (string)$xml->title;
            // Find best link (only one, or first of 'alternate')
            if (!isset($xml->link)) {
                $feed['uri'] = '';
            } elseif (count($xml->link) === 1) {
                $feed['uri'] = (string)$xml->link[0]['href'];
            } else {
                $feed['uri'] = '';
                foreach ($xml->link as $link) {
                    if (strtolower((string) $link['rel']) === 'alternate') {
                        $feed['uri'] = (string)$link['href'];
                        break;
                    }
                }
            }
            if (!empty($xml->icon)) {
                $feed['icon'] = (string)$xml->icon;
            } elseif (!empty($xml->logo)) {
                $feed['icon'] = (string)$xml->logo;
            }
            foreach ($xml->entry as $item) {
                $feed['items'][] = $this->parseAtomItem($item);
            }
        } else {
            throw new \Exception('Unable to detect feed format');
        }

        return $feed;
    }

    public function parseAtomItem(\SimpleXMLElement $feedItem): array
    {
        // 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)) {
            $contentChildren = $feedItem->content->children();
            if (count($contentChildren) > 0) {
                $content = '';
                foreach ($contentChildren as $contentChild) {
                    $content .= $contentChild->asXML();
                }
                $item['content'] = $content;
            } else {
                $item['content'] = (string)$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((string) $link['rel']) === 'alternate') {
                    $item['uri'] = (string)$link['href'];
                }
                if (strtolower((string) $link['rel']) === 'enclosure') {
                    $item['enclosures'][] = (string)$link['href'];
                }
            }
        }
        return $item;
    }

    public function parseRss2Item(\SimpleXMLElement $feedItem): array
    {
        // 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;
    }

    public function parseRss1Item(\SimpleXMLElement $feedItem): array
    {
        // 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;
    }

    public function parseRss091Item(\SimpleXMLElement $feedItem): array
    {
        $item = [
            'uri'           => null,
            'title'         => null,
            'content'       => null,
            'timestamp'     => null,
            'author'        => null,
            'uid'           => null,
            'categories'    => [],
            'enclosures'    => [],
        ];
        if (isset($feedItem->link)) {
            // todo: trim uri
            $item['uri'] = (string)$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;
    }
}