<?php
class FeedParser {

	/** @var DOMDocument */
	private $doc;

	/** @var string|null */
	private $error = null;

	/** @var array<string> */
	private $libxml_errors = [];

	/** @var array<FeedItem> */
	private $items = [];

	/** @var string|null */
	private $link;

	/** @var string|null */
	private $title;

	/** @var FeedParser::FEED_*|null */
	private $type;

	/** @var DOMXPath|null */
	private $xpath;

	const FEED_RDF = 0;
	const FEED_RSS = 1;
	const FEED_ATOM = 2;

	function __construct(string $data) {
		libxml_use_internal_errors(true);
		libxml_clear_errors();
		$this->doc = new DOMDocument();
		$this->doc->loadXML($data);

		mb_substitute_character("none");

		$error = libxml_get_last_error();

		if ($error) {
			foreach (libxml_get_errors() as $error) {
				if ($error->level == LIBXML_ERR_FATAL) {
					// currently only the first error is reported
					$this->error ??= Errors::format_libxml_error($error);
					$this->libxml_errors[] = Errors::format_libxml_error($error);
				}
			}
		}
		libxml_clear_errors();
	}

	function init() : void {
		$root = $this->doc->firstChild;
		$xpath = new DOMXPath($this->doc);
		$xpath->registerNamespace('atom', 'http://www.w3.org/2005/Atom');
		$xpath->registerNamespace('atom03', 'http://purl.org/atom/ns#');
		$xpath->registerNamespace('media', 'http://search.yahoo.com/mrss/');
		$xpath->registerNamespace('rdf', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#');
		$xpath->registerNamespace('slash', 'http://purl.org/rss/1.0/modules/slash/');
		$xpath->registerNamespace('dc', 'http://purl.org/dc/elements/1.1/');
		$xpath->registerNamespace('content', 'http://purl.org/rss/1.0/modules/content/');
		$xpath->registerNamespace('thread', 'http://purl.org/syndication/thread/1.0');

		$this->xpath = $xpath;

		$root_list = $xpath->query("(//atom03:feed|//atom:feed|//channel|//rdf:rdf|//rdf:RDF)");

		if (!empty($root_list) && $root_list->length > 0) {

			/** @var DOMElement|null $root */
			$root = $root_list->item(0);

			if ($root) {
				switch (mb_strtolower($root->tagName)) {
				case "rdf:rdf":
					$this->type = $this::FEED_RDF;
					break;
				case "channel":
					$this->type = $this::FEED_RSS;
					break;
				case "feed":
				case "atom:feed":
					$this->type = $this::FEED_ATOM;
					break;
				default:
					$this->error ??= "Unknown/unsupported feed type";
					return;
				}
			}

			switch ($this->type) {
			case $this::FEED_ATOM:

				$title = $xpath->query("//atom:feed/atom:title")->item(0);

				if (!$title)
					$title = $xpath->query("//atom03:feed/atom03:title")->item(0);


				if ($title) {
					$this->title = $title->nodeValue;
				}

				$link = $xpath->query("//atom:feed/atom:link[not(@rel)]")->item(0);

				if (!$link)
					$link = $xpath->query("//atom:feed/atom:link[@rel='alternate']")->item(0);

				if (!$link)
					$link = $xpath->query("//atom03:feed/atom03:link[not(@rel)]")->item(0);

				if (!$link)
					$link = $xpath->query("//atom03:feed/atom03:link[@rel='alternate']")->item(0);

				/** @var DOMElement|null $link */
				if ($link && $link->hasAttributes()) {
					$this->link = $link->getAttribute("href");
				}

				$articles = $xpath->query("//atom:entry");

				if (empty($articles) || $articles->length == 0)
					$articles = $xpath->query("//atom03:entry");

				foreach ($articles as $article) {
					array_push($this->items, new FeedItem_Atom($article, $this->doc, $this->xpath));
				}

				break;
			case $this::FEED_RSS:
				$title = $xpath->query("//channel/title")->item(0);

				if ($title) {
					$this->title = $title->nodeValue;
				}

				/** @var DOMElement|null $link */
				$link = $xpath->query("//channel/link")->item(0);

				if ($link) {
					if ($link->getAttribute("href"))
						$this->link = $link->getAttribute("href");
					else if ($link->nodeValue)
						$this->link = $link->nodeValue;
				}

				$articles = $xpath->query("//channel/item");

				foreach ($articles as $article) {
					array_push($this->items, new FeedItem_RSS($article, $this->doc, $this->xpath));
				}

				break;
			case $this::FEED_RDF:
				$xpath->registerNamespace('rssfake', 'http://purl.org/rss/1.0/');

				$title = $xpath->query("//rssfake:channel/rssfake:title")->item(0);

				if ($title) {
					$this->title = $title->nodeValue;
				}

				$link = $xpath->query("//rssfake:channel/rssfake:link")->item(0);

				if ($link) {
					$this->link = $link->nodeValue;
				}

				$articles = $xpath->query("//rssfake:item");

				foreach ($articles as $article) {
					array_push($this->items, new FeedItem_RSS($article, $this->doc, $this->xpath));
				}

				break;

			}

			if ($this->title) $this->title = trim($this->title);
			if ($this->link) $this->link = trim($this->link);

		} else {
			$this->error ??= "Unknown/unsupported feed type";
			return;
		}
	}

	/** @deprecated use Errors::format_libxml_error() instead */
	function format_error(LibXMLError $error) : string {
		return Errors::format_libxml_error($error);
	}

	// libxml may have invalid unicode data in error messages
	function error() : string {
		return UConverter::transcode($this->error ?? '', 'UTF-8', 'UTF-8');
	}

	/** @return array<string> - WARNING: may return invalid unicode data */
	function errors() : array {
		return $this->libxml_errors;
	}

	function get_link() : string {
		return clean($this->link ?? '');
	}

	function get_title() : string {
		return clean($this->title ?? '');
	}

	/** @return array<FeedItem> */
	function get_items() : array {
		return $this->items;
	}

	/** @return array<string> */
	function get_links(string $rel) : array {
		$rv = array();

		switch ($this->type) {
		case $this::FEED_ATOM:
			$links = $this->xpath->query("//atom:feed/atom:link");

			foreach ($links as $link) {
				if (!$rel || $link->hasAttribute('rel') && $link->getAttribute('rel') == $rel) {
					array_push($rv, clean(trim($link->getAttribute('href'))));
				}
			}
			break;
		case $this::FEED_RSS:
			$links = $this->xpath->query("//atom:link");

			foreach ($links as $link) {
				if (!$rel || $link->hasAttribute('rel') && $link->getAttribute('rel') == $rel) {
					array_push($rv, clean(trim($link->getAttribute('href'))));
				}
			}
			break;
		}

		return $rv;
	}
}