<?php

const PARSER_DEBUG = 0;
const XPATH_DEBUG = 0;

/**
 * Trait DomQuery
 *
 * requires:
 *
	$this->dom = $dom;
	$this->contextnode = null;
 */
trait DomQuery {
	public function find(string $pat) : Node
	{
		$els = $this->findAll($pat);
		if (!count($els)) {
			if (PARSER_DEBUG) {
				echo "---- match failed; context: ---\n";
				echo $this->toXml() ."\n";
			}

			throw new \Exception("No match: $pat");
		}
		if (count($els) > 1) {
			if (PARSER_DEBUG) {
				echo "Query results:\n";
				foreach ($els as $el) {
					echo $el->toXml()."\n";
				}
			}
			throw new \Exception("Multiple match (".count($els)."x): $pat");
		}
		return $els[0];
	}

	/**
	 * @param $pat
	 * @return array|Node[]
	 * @throws Exception
	 */
	public function findAll(string $pat) : array
	{
		# node
		if (preg_match('/^([a-z0-9_-]+)$/i', $pat, $matches)) {
			return $this->x("//$matches[1]");
		}

		# .class, node.class
		if (preg_match('/^(?P<elem>[a-z0-9_-]*)\.(?P<cls>[a-z0-9_-]+)$/i', $pat, $matches)) {
			$elem = $matches['elem'] ?: '*';
			return $this->x("//{$elem}[contains(concat(' ',normalize-space(@class),' '),' $matches[cls] ')]");
		}

		// #id
		if (preg_match('/^#(\w+)$/', $pat, $matches)) {
			return $this->x("//*[id='$matches[1]']");
		}

		# [attr=value], node[attr=value] (allows quotes)
		if (preg_match('/^(?P<elem>[a-z0-9_-]*)\[(?P<attr>[a-z0-9_-]+)(?P<op>[$*~^]|)=[\'"]?(?P<val>[^\'"\]]+)[\'"]?\]$/', $pat, $matches)) {
			$elem = $matches['elem'] ?: '*';
			$op = $matches['op'];

			switch ($op) {
				case '':
					return $this->x("//{$elem}[@$matches[attr]='$matches[val]']");
				case '^':
					return $this->x("//{$elem}[starts-with(@$matches[attr], '$matches[val]')]");
				// this doesnt work..
//				case '$':
//					$vlen = strlen($matches['val']);
//					return $this->x("//{$elem}['$matches[val]' = substring(@$matches[attr], string-length(@$matches[attr]) - $vlen)]");
				case '*':
				case '~':
					return $this->x("//{$elem}[contains(@$matches[attr], '$matches[val]')]");
			}
		}

		# [attr^=value], node[attr^=value] (allows quotes)
		if (preg_match('/^(?P<elem>[a-z0-9_-]*)\[(?P<attr>[a-z0-9_-]+)^=[\'"]?(?P<val>[^\'"\]]+)[\'"]?\]$/', $pat, $matches)) {
			$elem = $matches['elem'] ?: '*';
			return $this->x("//{$elem}[@$matches[attr]='$matches[val]']");
		}

		# [attr], node[attr]
		if (preg_match('/^(?P<elem>[a-z0-9_-]*)\[(?P<attr>[a-z0-9_-]+)\]$/', $pat, $matches)) {
			$elem = $matches['elem'] ?: '*';
			return $this->x("//{$elem}[@$matches[attr]]");
		}

		throw new \Exception("Unknown pattern: $pat");
	}

	public function x(string $x) : array
	{
		$xpath = new DOMXpath($this->dom);
		if (strpos($x, '//') === 0 && $this->contextnode) {
			$x = '.' . $x;
		}

		if (XPATH_DEBUG) echo "\nxpath is: $x\n";

		$elements = $xpath->query($x, $this->contextnode) ?? [];
		$elems = [];
		foreach($elements as $e) {
			$elems[] = new Node($this->dom, $e);
		}
		return $elems;
	}
}


class Html
{
	use DomQuery;

	public function __construct(string $html)
	{
		$dom = new DomDocument();

		if (PARSER_DEBUG) echo "Creating HTML parser from:\n" . $html . "\n\n";

		@$dom->loadHTML($html); // suppress spammy warnings
		$this->dom = $dom;
		$this->contextnode = null;
	}

	public function toXml() : string
	{
		return $this->dom->saveXml();
	}
}


class Node
{
	use DomQuery;

	public function __construct(DOMDocument $dom, DOMNode $element)
	{
		$this->dom = $dom;
		$this->element = $element;
		$this->contextnode = $element;
	}

	public function __get($name)
	{
		return $this->element->getAttribute($name);
	}

	public function text() : string
	{
		return $this->element->nodeValue ?? '';
	}

	/**
	 * @return array|Node[]
	 */
	public function childNodes() : array
	{
		$elems = [];
		foreach($this->element->childNodes as $e) {
			$elems[] = new Node($this->dom, $e);
		}
		return $elems;
	}

	/**
	 * @return Node
	 */
	public function childNode() : Node
	{
		$cn = $this->childNodes();
		if (count($cn) > 1) {
			throw new \Exception("More than one childnode.");
		}
		return $cn[0];
	}

	public function toXml() : string
	{
		return $this->element->ownerDocument->saveXml($this->element);
	}
}