<?php

namespace League\HTMLToMarkdown;

/**
 * Class HtmlConverter
 *
 * A helper class to convert HTML to Markdown.
 *
 * @author Colin O'Dell <colinodell@gmail.com>
 * @author Nick Cernis <nick@cern.is>
 *
 * @link https://github.com/thephpleague/html-to-markdown/ Latest version on GitHub.
 *
 * @license http://www.opensource.org/licenses/mit-license.php MIT
 */
class HtmlConverter
{
    /**
     * @var Environment
     */
    protected $environment;

    /**
     * Constructor
     *
     * @param Environment|array $options Environment object or configuration options
     */
    public function __construct($options = array())
    {
        if ($options instanceof Environment) {
            $this->environment = $options;
        } elseif (is_array($options)) {
            $defaults = array(
                'header_style' => 'setext', // Set to 'atx' to output H1 and H2 headers as # Header1 and ## Header2
                'suppress_errors' => true, // Set to false to show warnings when loading malformed HTML
                'strip_tags' => false, // Set to true to strip tags that don't have markdown equivalents. N.B. Strips tags, not their content. Useful to clean MS Word HTML output.
                'bold_style' => '**', // Set to '__' if you prefer the underlined style
                'italic_style' => '_', // Set to '*' if you prefer the asterisk style
                'remove_nodes' => '', // space-separated list of dom nodes that should be removed. example: 'meta style script'
                'hard_break' => false, // Set to true to turn <br> into `\n` instead of `  \n`
                'list_item_style' => '-', // Set the default character for each <li> in a <ul>. Can be '-', '*', or '+'
            );

            $this->environment = Environment::createDefaultEnvironment($defaults);

            $this->environment->getConfig()->merge($options);
        }
    }

    /**
     * @return Environment
     */
    public function getEnvironment()
    {
        return $this->environment;
    }

    /**
     * @return Configuration
     */
    public function getConfig()
    {
        return $this->environment->getConfig();
    }

    /**
     * Convert
     *
     * @see HtmlConverter::convert
     *
     * @param string $html
     *
     * @return string The Markdown version of the html
     */
    public function __invoke($html)
    {
        return $this->convert($html);
    }

    /**
     * Convert
     *
     * Loads HTML and passes to getMarkdown()
     *
     * @param string $html
     *
     * @throws \InvalidArgumentException
     *
     * @return string The Markdown version of the html
     */
    public function convert($html)
    {
        if (trim($html) === '') {
            return '';
        }

        $document = $this->createDOMDocument($html);

        // Work on the entire DOM tree (including head and body)
        if (!($root = $document->getElementsByTagName('html')->item(0))) {
            throw new \InvalidArgumentException('Invalid HTML was provided');
        }

        $rootElement = new Element($root);
        $this->convertChildren($rootElement);

        // Store the now-modified DOMDocument as a string
        $markdown = $document->saveHTML();

        return $this->sanitize($markdown);
    }

    /**
     * @param string $html
     *
     * @return \DOMDocument
     */
    private function createDOMDocument($html)
    {
        $document = new \DOMDocument();

        if ($this->getConfig()->getOption('suppress_errors')) {
            // Suppress conversion errors (from http://bit.ly/pCCRSX)
            libxml_use_internal_errors(true);
        }

        // Hack to load utf-8 HTML (from http://bit.ly/pVDyCt)
        $document->loadHTML('<?xml encoding="UTF-8">' . $html);
        $document->encoding = 'UTF-8';

        if ($this->getConfig()->getOption('suppress_errors')) {
            libxml_clear_errors();
        }

        return $document;
    }

    /**
     * Convert Children
     *
     * Recursive function to drill into the DOM and convert each node into Markdown from the inside out.
     *
     * Finds children of each node and convert those to #text nodes containing their Markdown equivalent,
     * starting with the innermost element and working up to the outermost element.
     *
     * @param ElementInterface $element
     */
    private function convertChildren(ElementInterface $element)
    {
        // Don't convert HTML code inside <code> and <pre> blocks to Markdown - that should stay as HTML
        // except if the current node is a code tag, which needs to be converted by the CodeConverter.
        if ($element->isDescendantOf(array('pre', 'code')) && $element->getTagName() !== 'code') {
            return;
        }

        // If the node has children, convert those to Markdown first
        if ($element->hasChildren()) {
            foreach ($element->getChildren() as $child) {
                $this->convertChildren($child);
            }
        }

        // Now that child nodes have been converted, convert the original node
        $markdown = $this->convertToMarkdown($element);

        // Create a DOM text node containing the Markdown equivalent of the original node

        // Replace the old $node e.g. '<h3>Title</h3>' with the new $markdown_node e.g. '### Title'
        $element->setFinalMarkdown($markdown);
    }

    /**
     * Convert to Markdown
     *
     * Converts an individual node into a #text node containing a string of its Markdown equivalent.
     *
     * Example: An <h3> node with text content of 'Title' becomes a text node with content of '### Title'
     *
     * @param ElementInterface $element
     *
     * @return string The converted HTML as Markdown
     */
    protected function convertToMarkdown(ElementInterface $element)
    {
        $tag = $element->getTagName();

        // Strip nodes named in remove_nodes
        $tags_to_remove = explode(' ', $this->getConfig()->getOption('remove_nodes'));
        if (in_array($tag, $tags_to_remove)) {
            return false;
        }

        $converter = $this->environment->getConverterByTag($tag);

        return $converter->convert($element);
    }

    /**
     * @param string $markdown
     *
     * @return string
     */
    protected function sanitize($markdown)
    {
        $markdown = html_entity_decode($markdown, ENT_QUOTES, 'UTF-8');
        $markdown = preg_replace('/<!DOCTYPE [^>]+>/', '', $markdown); // Strip doctype declaration
        $markdown = trim($markdown); // Remove blank spaces at the beggining of the html

        /*
         * Removing unwanted tags. Tags should be added to the array in the order they are expected.
         * XML, html and body opening tags should be in that order. Same case with closing tags
         */
        $unwanted = array('<?xml encoding="UTF-8">', '<html>', '</html>', '<body>', '</body>', '<head>', '</head>', '&#xD;');

        foreach ($unwanted as $tag) {
            if (strpos($tag, '/') === false) {
                // Opening tags
                if (strpos($markdown, $tag) === 0) {
                    $markdown = substr($markdown, strlen($tag));
                }
            } else {
                // Closing tags
                if (strpos($markdown, $tag) === strlen($markdown) - strlen($tag)) {
                    $markdown = substr($markdown, 0, -strlen($tag));
                }
            }
        }

        return trim($markdown, "\n\r\0\x0B");
    }
    
    /**
     * Pass a series of key-value pairs in an array; these will be passed
     * through the config and set.
     * The advantage of this is that it can allow for static use (IE in Laravel).
     * An example being:
     * 
     * HtmlConverter::setOptions(['strip_tags' => true])->convert('<h1>test</h1>');
     */
    public function setOptions(array $options)
    {
        $config = $this->getConfig();

        foreach ($options as $key => $option) {
            $config->setOption($key, $option);
        }

        return $this;
    }
}
