<?php


namespace App\Classes;


class Meta
{
    private static $STATUS = array(
        "initialized"=>0,
        "success"=>1,
        "fail"=>2
    );
    private $metaData;
    private $url;
    private $html;
    private $status;
    private $meta;

    /**
     * __construct
     *
     * Require the url of the webpage for meta data extraction
     *
     * @access public
     * @param  string $url
     */
    public function __construct($url) {
        $this->url = $url;
        $this->metaData = new \StdClass;
        $this->metaData->title = "";
        $this->metaData->description = "";
        $this->metaData->keywords = "";
        $this->metaData->image = "";
        $this->initialized();
    }

    /**
     * parse
     *
     * Parse the meta data from the given url and populate data member $metaData
     *
     * @access public
     * @return integer
     */
    public function parse() {
        // load HTML as DOMDocument object for parsing
        $this->html = new \DOMDocument;
        libxml_use_internal_errors(true);
        $this->html->loadHTML(file_get_contents($this->url));

        // php built-in get_meta_tags() only read those with name "title", "description" and so on
        // so I wrote my own version supporting twitter:title, og:title, etc.
        $this->meta = $this->my_get_meta_tags($this->url);

        $this->success(); // assume successful

        // possible to add more method such as getAuthor()
        $this->getTitle();
        $this->getDescription();
        $this->getKeywords();
        $this->getImage();

        return $this->status;
    }


    /**
     * finalize
     *
     * Export the meta data parsed
     *
     * @access public
     * @return StdClass
     */
    public function finalize() {
        $tmp = new \StdClass;
        $tmp->url = $this->url;
        $tmp->title = $this->metaData->title;
        $tmp->description = $this->metaData->description;
        $tmp->image = $this->metaData->image;
        $tmp->status = $this->status;
        $tmp->keywords = $this->metaData->keywords;
        return $tmp;
    }

    /**
     * my_get_meta_tags
     *
     * Require the url to be parsed, read every meta tags found
     *
     * @access private
     * @param  string $url
     * @return array
     */
    private function my_get_meta_tags($url) {
        $metatags = $this->html->getElementsByTagName("meta");
        $tmeta = array();
        for ($i=0; $i<$metatags->length; ++$i) {
            $item = $metatags->item($i);
            $name = $item->getAttribute('name');

            if (empty($name)) {
                // og meta tags, or twitter meta tags
                $tmeta[$item->getAttribute('property')] = $item->getAttribute('content');
            }
            else {
                // conventional meta tags
                $tmeta[$name] = $item->getAttribute('content');
            }
        }
        return $tmeta;
    }

    /**
     * initizlized
     *
     * Set the state of the object to be initizlied
     *
     * @access private
     */
    private function initialized() {
        $this->status = self::$STATUS["initialized"];
    }

    /**
     * success
     *
     * Set the state of the object to be successful
     *
     * @access private
     */
    private function success() {
        $this->status = self::$STATUS["success"];
    }

    /**
     * fail
     *
     * Set the state of the object to be failed
     *
     * @access private
     */
    private function fail() {
        $this->status = self::$STATUS["fail"];
    }

    /**
     * getTitle
     *
     * Read meta title based on priorities of the tag name/property,
     * fallback to reading <title> and <h1> if meta title not present
     *
     * @access private
     */
    private function getTitle() {
        if (isset($this->meta["og:title"])) {
            $this->metaData->title = $this->meta["og:title"];
            return;
        }

        if (isset($this->meta["twitter:title"])) {
            $this->metaData->title = $this->meta["twitter:title"];
            return;
        }

        if (isset($this->meta["title"])) {
            $this->metaData->title = $this->meta["title"];
            return;
        }

        $title = $this->html->getElementsByTagName("title") or $title = $this->html->getElementsByTagName("h1");
        // taking either the title or h1 tag
        if (!$title->length) {
            // if no h1 tag, nothing good enough to be the site title
            $this->fail();
            return;
        }
        else {
            $this->metaData->title = ($title->length) ? $title->item(0)->nodeValue : "";
        }
    }

    /**
     * getDescription
     *
     * Read meta description based on priorities of the tag name/property.
     * No fallback, it doesn't read anything except for the meta tag
     *
     * @access private
     */
    private function getDescription() {
        if (isset($this->meta["og:description"])) {
            $this->metaData->description = $this->meta["og:description"];
            return;
        }

        if (isset($this->meta["twitter:description"])) {
            $this->metaData->description = $this->meta["twitter:description"];
            return;
        }

        if (isset($this->meta["description"])) {
            $this->metaData->description = $this->meta["description"];
            return;
        }

        $this->fail();
        return;
    }


    private function getKeywords() {
        if (isset($this->meta["og:keywords"])) {
            $this->metaData->keywords = $this->meta["og:keywords"];
            return;
        }

        if (isset($this->meta["twitter:keywords"])) {
            $this->metaData->keywords = $this->meta["twitter:description"];
            return;
        }

        if (isset($this->meta["keywords"])) {
            $this->metaData->keywords = $this->meta["keywords"];
            return;
        }

        $this->fail();
        return;
    }


    /**
     * getImage
     *
     * Read meta image url based on priorities of the tag name/property.
     * No fallback, it doesn't read anything except for the meta tag
     *
     * @access private
     */
    private function getImage() {
        if (isset($this->meta["og:image"])) {
            $this->metaData->image = $this->meta["og:image"];
            return;
        }

        if (isset($this->meta["twitter:image"])) {
            $this->metaData->image = $this->meta["twitter:image"];
            return;
        }

        if (isset($this->meta["image"])) {
            $this->metaData->image = $this->meta["image"];
            return;
        }

        $this->fail();
    }
}