<?php
//Source: https://github.com/jenstornell/tiny-html-minifier

class TinyHtmlMinifier
{
    private $options;
    private $output;
    private $build;
    private $skip;
    private $skipName;
    private $head;
    private $elements;

    public function __construct(array $options)
    {
        $this->options = $options;
        $this->output = '';
        $this->build = [];
        $this->skip = 0;
        $this->skipName = '';
        $this->head = false;
        $this->elements = [
            'skip' => [
                'code',
                'pre',
                'script',
                'textarea',
            ],
            'inline' => [
                'a',
                'abbr',
                'acronym',
                'b',
                'bdo',
                'big',
                'br',
                'cite',
                'code',
                'dfn',
                'em',
                'i',
                'img',
                'kbd',
                'map',
                'object',
                'samp',
                'small',
                'span',
                'strong',
                'sub',
                'sup',
                'tt',
                'var',
                'q',
            ],
            'hard' => [
                '!doctype',
                'body',
                'html',
            ]
        ];
    }

    // Run minifier
    public function minify(string $html) : string
    {
        if (!isset($this->options['disable_comments']) ||
            !$this->options['disable_comments']) {
            $html = $this->removeComments($html);
        }

        $rest = $html;

        while (!empty($rest)) {
            $parts = explode('<', $rest, 2);
            $this->walk($parts[0]);
            $rest = (isset($parts[1])) ? $parts[1] : '';
        }

        return $this->output;
    }

    // Walk trough html
    private function walk(&$part)
    {
        $tag_parts = explode('>', $part);
        $tag_content = $tag_parts[0];

        if (!empty($tag_content)) {
            $name = $this->findName($tag_content);
            $element = $this->toElement($tag_content, $part, $name);
            $type = $this->toType($element);

            if ($name == 'head') {
                $this->head = $type === 'open';
            }

            $this->build[] = [
                'name' => $name,
                'content' => $element,
                'type' => $type
            ];

            $this->setSkip($name, $type);

            if (!empty($tag_content)) {
                $content = (isset($tag_parts[1])) ? $tag_parts[1] : '';
                if ($content !== '') {
                    $this->build[] = [
                        'content' => $this->compact($content, $name, $element),
                        'type' => 'content'
                    ];
                }
            }

            $this->buildHtml();
        }
    }

    // Remove comments
    private function removeComments($content = '')
    {
        return preg_replace('/(?=<!--)([\s\S]*?)-->/', '', $content);
    }

    // Check if string contains string
    private function contains($needle, $haystack)
    {
        return strpos($haystack, $needle) !== false;
    }

    // Return type of element
    private function toType($element)
    {
        return (substr($element, 1, 1) == '/') ? 'close' : 'open';
    }

    // Create element
    private function toElement($element, $noll, $name)
    {
        $element = $this->stripWhitespace($element);
        $element = $this->addChevrons($element, $noll);
        $element = $this->removeSelfSlash($element);
        $element = $this->removeMeta($element, $name);
        return $element;
    }

    // Remove unneeded element meta
    private function removeMeta($element, $name)
    {
        if ($name == 'style') {
            $element = str_replace(
                [
                    ' type="text/css"',
                    "' type='text/css'"
                ],
                ['', ''],
                $element
            );
        } elseif ($name == 'script') {
            $element = str_replace(
                [
                    ' type="text/javascript"',
                    " type='text/javascript'"
                ],
                ['', ''],
                $element
            );
        }
        return $element;
    }

    // Strip whitespace from element
    private function stripWhitespace($element)
    {
        if ($this->skip == 0) {
            $element = preg_replace('/\s+/', ' ', $element);
        }
        return trim($element);
    }

    // Add chevrons around element
    private function addChevrons($element, $noll)
    {
        if (empty($element)) {
            return $element;
        }
        $char = ($this->contains('>', $noll)) ? '>' : '';
        $element = '<' . $element . $char;
        return $element;
    }

    // Remove unneeded self slash
    private function removeSelfSlash($element)
    {
        if (substr($element, -3) == ' />') {
            $element = substr($element, 0, -3) . '>';
        }
        return $element;
    }

    // Compact content
    private function compact($content, $name, $element)
    {
        if ($this->skip != 0) {
            $name = $this->skipName;
        } else {
            $content = preg_replace('/\s+/', ' ', $content);
        }

        if (in_array($name, $this->elements['skip'])) {
            return $content;
        } elseif (in_array($name, $this->elements['hard']) ||
            $this->head) {
            return $this->minifyHard($content);
        } else {
            return $this->minifyKeepSpaces($content);
        }
    }

    // Build html
    private function buildHtml()
    {
        foreach ($this->build as $build) {

            if (!empty($this->options['collapse_whitespace'])) {

                if (strlen(trim($build['content'])) == 0)
                    continue;

                elseif ($build['type'] != 'content' && !in_array($build['name'], $this->elements['inline']))
                    trim($build['content']);

            }

            $this->output .= $build['content'];
        }

        $this->build = [];
    }

    // Find name by part
    private function findName($part)
    {
        $name_cut = explode(" ", $part, 2)[0];
        $name_cut = explode(">", $name_cut, 2)[0];
        $name_cut = explode("\n", $name_cut, 2)[0];
        $name_cut = preg_replace('/\s+/', '', $name_cut);
        $name_cut = strtolower(str_replace('/', '', $name_cut));
        return $name_cut;
    }

    // Set skip if elements are blocked from minification
    private function setSkip($name, $type)
    {
        foreach ($this->elements['skip'] as $element) {
            if ($element == $name && $this->skip == 0) {
                $this->skipName = $name;
            }
        }
        if (in_array($name, $this->elements['skip'])) {
            if ($type == 'open') {
                $this->skip++;
            }
            if ($type == 'close') {
                $this->skip--;
            }
        }
    }

    // Minify all, even spaces between elements
    private function minifyHard($element)
    {
        $element = preg_replace('!\s+!', ' ', $element);
        $element = trim($element);
        return trim($element);
    }

    // Strip but keep one space
    private function minifyKeepSpaces($element)
    {
        return preg_replace('!\s+!', ' ', $element);
    }
}