class Minifier

class Minifier {
    
    /**
     * The input javascript to be minified.
     *
     * @var string
     */
    protected $input;
    
    /**
     * Length of input javascript.
     *
     * @var int
     */
    protected $len = 0;
    
    /**
     * The location of the character (in the input string) that is next to be
     * processed.
     *
     * @var int
     */
    protected $index = 0;
    
    /**
     * The first of the characters currently being looked at.
     *
     * @var string
     */
    protected $a = '';
    
    /**
     * The next character being looked at (after a);
     *
     * @var string
     */
    protected $b = '';
    
    /**
     * This character is only active when certain look ahead actions take place.
     *
     *  @var string
     */
    protected $c;
    
    /**
     * Contains the options for the current minification process.
     *
     * @var array
     */
    protected $options;
    
    /**
     * These characters are used to define strings.
     */
    protected $stringDelimiters = [
        '\'' => true,
        '"' => true,
        '`' => true,
    ];
    
    /**
     * Contains the default options for minification. This array is merged with
     * the one passed in by the user to create the request specific set of
     * options (stored in the $options attribute).
     *
     * @var array
     */
    protected static $defaultOptions = [
        'flaggedComments' => true,
    ];
    
    /**
     * Contains lock ids which are used to replace certain code patterns and
     * prevent them from being minified
     *
     * @var array
     */
    protected $locks = [];
    
    /**
     * Takes a string containing javascript and removes unneeded characters in
     * order to shrink the code without altering it's functionality.
     *
     * @param  string      $js      The raw javascript to be minified
     * @param  array       $options Various runtime options in an associative array
     * @throws \Exception
     * @return bool|string
     */
    public static function minify($js, $options = []) {
        try {
            ob_start();
            $jshrink = new Minifier();
            $js = $jshrink->lock($js);
            $jshrink->minifyDirectToOutput($js, $options);
            // Sometimes there's a leading new line, so we trim that out here.
            $js = ltrim(ob_get_clean());
            $js = $jshrink->unlock($js);
            unset($jshrink);
            return $js;
        } catch (\Exception $e) {
            if (isset($jshrink)) {
                // Since the breakdownScript function probably wasn't finished
                // we clean it out before discarding it.
                $jshrink->clean();
                unset($jshrink);
            }
            // without this call things get weird, with partially outputted js.
            ob_end_clean();
            throw $e;
        }
    }
    
    /**
     * Processes a javascript string and outputs only the required characters,
     * stripping out all unneeded characters.
     *
     * @param string $js      The raw javascript to be minified
     * @param array  $options Various runtime options in an associative array
     */
    protected function minifyDirectToOutput($js, $options) {
        $this->initialize($js, $options);
        $this->loop();
        $this->clean();
    }
    
    /**
     *  Initializes internal variables, normalizes new lines,
     *
     * @param string $js      The raw javascript to be minified
     * @param array  $options Various runtime options in an associative array
     */
    protected function initialize($js, $options) {
        $this->options = array_merge(static::$defaultOptions, $options);
        $this->input = str_replace([
            "\r\n",
            '/**/',
            "\r",
        ], [
            "\n",
            "",
            "\n",
        ], $js);
        // We add a newline to the end of the script to make it easier to deal
        // with comments at the bottom of the script- this prevents the unclosed
        // comment error that can otherwise occur.
        $this->input .= PHP_EOL;
        // save input length to skip calculation every time
        $this->len = strlen($this->input);
        // Populate "a" with a new line, "b" with the first character, before
        // entering the loop
        $this->a = "\n";
        $this->b = $this->getReal();
    }
    
    /**
     * Characters that can't stand alone preserve the newline.
     *
     * @var array
     */
    protected $noNewLineCharacters = [
        '(' => true,
        '-' => true,
        '+' => true,
        '[' => true,
        '@' => true,
    ];
    
    /**
     * The primary action occurs here. This function loops through the input string,
     * outputting anything that's relevant and discarding anything that is not.
     */
    protected function loop() {
        while ($this->a !== false && !is_null($this->a) && $this->a !== '') {
            switch ($this->a) {
                // new lines
                case "\n":
                    // if the next line is something that can't stand alone preserve the newline
                    if ($this->b !== false && isset($this->noNewLineCharacters[$this->b])) {
                        echo $this->a;
                        $this->saveString();
                        break;
                    }
                    // if B is a space we skip the rest of the switch block and go down to the
                    // string/regex check below, resetting $this->b with getReal
                    if ($this->b === ' ') {
                        break;
                    }
                // otherwise we treat the newline like a space
                // no break
                case ' ':
                    if (static::isAlphaNumeric($this->b)) {
                        echo $this->a;
                    }
                    $this->saveString();
                    break;
                default:
                    switch ($this->b) {
                        case "\n":
                            if (strpos('}])+-"\'', $this->a) !== false) {
                                echo $this->a;
                                $this->saveString();
                                break;
                            }
                            else {
                                if (static::isAlphaNumeric($this->a)) {
                                    echo $this->a;
                                    $this->saveString();
                                }
                            }
                            break;
                        case ' ':
                            if (!static::isAlphaNumeric($this->a)) {
                                break;
                            }
                        // no break
                        default:
                            // check for some regex that breaks stuff
                            if ($this->a === '/' && ($this->b === '\'' || $this->b === '"')) {
                                $this->saveRegex();
                                continue 3;
                            }
                            echo $this->a;
                            $this->saveString();
                            break;
                    }
            }
            // do reg check of doom
            $this->b = $this->getReal();
            if ($this->b == '/' && strpos('(,=:[!&|?', $this->a) !== false) {
                $this->saveRegex();
            }
        }
    }
    
    /**
     * Resets attributes that do not need to be stored between requests so that
     * the next request is ready to go. Another reason for this is to make sure
     * the variables are cleared and are not taking up memory.
     */
    protected function clean() {
        unset($this->input);
        $this->len = 0;
        $this->index = 0;
        $this->a = $this->b = '';
        unset($this->c);
        unset($this->options);
    }
    
    /**
     * Returns the next string for processing based off of the current index.
     *
     * @return string
     */
    protected function getChar() {
        // Check to see if we had anything in the look ahead buffer and use that.
        if (isset($this->c)) {
            $char = $this->c;
            unset($this->c);
        }
        else {
            // Otherwise we start pulling from the input.
            $char = $this->index < $this->len ? $this->input[$this->index] : false;
            // If the next character doesn't exist return false.
            if (isset($char) && $char === false) {
                return false;
            }
            // Otherwise increment the pointer and use this char.
            $this->index++;
        }
        // Normalize all whitespace except for the newline character into a
        // standard space.
        if ($char !== "\n" && $char < " ") {
            return ' ';
        }
        return $char;
    }
    
    /**
     * This function gets the next "real" character. It is essentially a wrapper
     * around the getChar function that skips comments. This has significant
     * performance benefits as the skipping is done using native functions (ie,
     * c code) rather than in script php.
     *
     *
     * @return string            Next 'real' character to be processed.
     * @throws \RuntimeException
     */
    protected function getReal() {
        $startIndex = $this->index;
        $char = $this->getChar();
        // Check to see if we're potentially in a comment
        if ($char !== '/') {
            return $char;
        }
        $this->c = $this->getChar();
        if ($this->c === '/') {
            $this->processOneLineComments($startIndex);
            return $this->getReal();
        }
        elseif ($this->c === '*') {
            $this->processMultiLineComments($startIndex);
            return $this->getReal();
        }
        return $char;
    }
    
    /**
     * Removed one line comments, with the exception of some very specific types of
     * conditional comments.
     *
     * @param  int  $startIndex The index point where "getReal" function started
     * @return void
     */
    protected function processOneLineComments($startIndex) {
        $thirdCommentString = $this->index < $this->len ? $this->input[$this->index] : false;
        // kill rest of line
        $this->getNext("\n");
        unset($this->c);
        if ($thirdCommentString == '@') {
            $endPoint = $this->index - $startIndex;
            $this->c = "\n" . substr($this->input, $startIndex, $endPoint);
        }
    }
    
    /**
     * Skips multiline comments where appropriate, and includes them where needed.
     * Conditional comments and "license" style blocks are preserved.
     *
     * @param  int               $startIndex The index point where "getReal" function started
     * @return void
     * @throws \RuntimeException Unclosed comments will throw an error
     */
    protected function processMultiLineComments($startIndex) {
        $this->getChar();
        // current C
        $thirdCommentString = $this->getChar();
        // kill everything up to the next */ if it's there
        if ($this->getNext('*/')) {
            $this->getChar();
            // get *
            $this->getChar();
            // get /
            $char = $this->getChar();
            // get next real character
            // Now we reinsert conditional comments and YUI-style licensing comments
            if ($this->options['flaggedComments'] && $thirdCommentString === '!' || $thirdCommentString === '@') {
                // If conditional comments or flagged comments are not the first thing in the script
                // we need to echo a and fill it with a space before moving on.
                if ($startIndex > 0) {
                    echo $this->a;
                    $this->a = " ";
                    // If the comment started on a new line we let it stay on the new line
                    if ($this->input[$startIndex - 1] === "\n") {
                        echo "\n";
                    }
                }
                $endPoint = $this->index - 1 - $startIndex;
                echo substr($this->input, $startIndex, $endPoint);
                $this->c = $char;
                return;
            }
        }
        else {
            $char = false;
        }
        if ($char === false) {
            throw new \RuntimeException('Unclosed multiline comment at position: ' . ($this->index - 2));
        }
        // if we're here c is part of the comment and therefore tossed
        $this->c = $char;
    }
    
    /**
     * Pushes the index ahead to the next instance of the supplied string. If it
     * is found the first character of the string is returned and the index is set
     * to it's position.
     *
     * @param  string       $string
     * @return string|false Returns the first character of the string or false.
     */
    protected function getNext($string) {
        // Find the next occurrence of "string" after the current position.
        $pos = strpos($this->input, $string, $this->index);
        // If it's not there return false.
        if ($pos === false) {
            return false;
        }
        // Adjust position of index to jump ahead to the asked for string
        $this->index = $pos;
        // Return the first character of that string.
        return $this->index < $this->len ? $this->input[$this->index] : false;
    }
    
    /**
     * When a javascript string is detected this function crawls for the end of
     * it and saves the whole string.
     *
     * @throws \RuntimeException Unclosed strings will throw an error
     */
    protected function saveString() {
        $startpos = $this->index;
        // saveString is always called after a gets cleared, so we push b into
        // that spot.
        $this->a = $this->b;
        // If this isn't a string we don't need to do anything.
        if (!isset($this->stringDelimiters[$this->a])) {
            return;
        }
        // String type is the quote used, " or '
        $stringType = $this->a;
        // Echo out that starting quote
        echo $this->a;
        // Loop until the string is done
        // Grab the very next character and load it into a
        while (($this->a = $this->getChar()) !== false) {
            switch ($this->a) {
                // If the string opener (single or double quote) is used
                // output it and break out of the while loop-
                // The string is finished!
                case $stringType:
                    break 2;
                // New lines in strings without line delimiters are bad- actual
                // new lines will be represented by the string \n and not the actual
                // character, so those will be treated just fine using the switch
                // block below.
                case "\n":
                    if ($stringType === '`') {
                        echo $this->a;
                    }
                    else {
                        throw new \RuntimeException('Unclosed string at position: ' . $startpos);
                    }
                    break;
                // Escaped characters get picked up here. If it's an escaped new line it's not really needed
                case '\\':
                    // a is a slash. We want to keep it, and the next character,
                    // unless it's a new line. New lines as actual strings will be
                    // preserved, but escaped new lines should be reduced.
                    $this->b = $this->getChar();
                    // If b is a new line we discard a and b and restart the loop.
                    if ($this->b === "\n") {
                        break;
                    }
                    // echo out the escaped character and restart the loop.
                    echo $this->a . $this->b;
                    break;
                // Since we're not dealing with any special cases we simply
                // output the character and continue our loop.
                default:
                    echo $this->a;
            }
        }
    }
    
    /**
     * When a regular expression is detected this function crawls for the end of
     * it and saves the whole regex.
     *
     * @throws \RuntimeException Unclosed regex will throw an error
     */
    protected function saveRegex() {
        echo $this->a . $this->b;
        while (($this->a = $this->getChar()) !== false) {
            if ($this->a === '/') {
                break;
            }
            if ($this->a === '\\') {
                echo $this->a;
                $this->a = $this->getChar();
            }
            if ($this->a === "\n") {
                throw new \RuntimeException('Unclosed regex pattern at position: ' . $this->index);
            }
            echo $this->a;
        }
        $this->b = $this->getReal();
    }
    
    /**
     * Checks to see if a character is alphanumeric.
     *
     * @param  string $char Just one character
     * @return bool
     */
    protected static function isAlphaNumeric($char) {
        return preg_match('/^[\\w\\$\\pL]$/', $char) === 1 || $char == '/';
    }
    
    /**
     * Replace patterns in the given string and store the replacement
     *
     * @param  string $js The string to lock
     * @return bool
     */
    protected function lock($js) {
        
        /* lock things like <code>"asd" + ++x;</code> */
        $lock = '"LOCK---' . crc32(time()) . '"';
        $matches = [];
        preg_match('/([+-])(\\s+)([+-])/S', $js, $matches);
        if (empty($matches)) {
            return $js;
        }
        $this->locks[$lock] = $matches[2];
        $js = preg_replace('/([+-])\\s+([+-])/S', "\$1{$lock}\$2", $js);
        
        /* -- */
        return $js;
    }
    
    /**
     * Replace "locks" with the original characters
     *
     * @param  string $js The string to unlock
     * @return bool
     */
    protected function unlock($js) {
        if (empty($this->locks)) {
            return $js;
        }
        foreach ($this->locks as $lock => $replacement) {
            $js = str_replace($lock, $replacement, $js);
        }
        return $js;
    }

}