<?php
/**
 * JavaScript minifier
 *
 * Please report bugs on https://github.com/matthiasmullie/minify/issues
 *
 * @author Matthias Mullie <minify@mullie.eu>
 * @copyright Copyright (c) 2012, Matthias Mullie. All rights reserved
 * @license MIT License
 */
namespace MatthiasMullie\Minify;

/**
 * JavaScript Minifier Class
 *
 * Please report bugs on https://github.com/matthiasmullie/minify/issues
 *
 * @package Minify
 * @author Matthias Mullie <minify@mullie.eu>
 * @author Tijs Verkoyen <minify@verkoyen.eu>
 * @copyright Copyright (c) 2012, Matthias Mullie. All rights reserved
 * @license MIT License
 */
class JS extends Minify
{
    /**
     * Var-matching regex based on http://stackoverflow.com/a/9337047/802993.
     *
     * Note that regular expressions using that bit must have the PCRE_UTF8
     * pattern modifier (/u) set.
     *
     * @var string
     */
    const REGEX_VARIABLE = 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    /**
     * Full list of JavaScript reserved words.
     * Will be loaded from /data/js/keywords_reserved.txt.
     *
     * @see https://mathiasbynens.be/notes/reserved-keywords
     *
     * @var string[]
     */
    protected $keywordsReserved = array();

    /**
     * List of JavaScript reserved words that accept a <variable, value, ...>
     * after them. Some end of lines are not the end of a statement, like with
     * these keywords.
     *
     * E.g.: we shouldn't insert a ; after this else
     * else
     *     console.log('this is quite fine')
     *
     * Will be loaded from /data/js/keywords_before.txt
     *
     * @var string[]
     */
    protected $keywordsBefore = array();

    /**
     * List of JavaScript reserved words that accept a <variable, value, ...>
     * before them. Some end of lines are not the end of a statement, like when
     * continued by one of these keywords on the newline.
     *
     * E.g.: we shouldn't insert a ; before this instanceof
     * variable
     *     instanceof String
     *
     * Will be loaded from /data/js/keywords_after.txt
     *
     * @var string[]
     */
    protected $keywordsAfter = array();

    /**
     * List of all JavaScript operators.
     *
     * Will be loaded from /data/js/operators.txt
     *
     * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators
     *
     * @var string[]
     */
    protected $operators = array();

    /**
     * List of JavaScript operators that accept a <variable, value, ...> after
     * them. Some end of lines are not the end of a statement, like with these
     * operators.
     *
     * Note: Most operators are fine, we've only removed ++ and --.
     * ++ & -- have to be joined with the value they're in-/decrementing.
     *
     * Will be loaded from /data/js/operators_before.txt
     *
     * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators
     *
     * @var string[]
     */
    protected $operatorsBefore = array();

    /**
     * List of JavaScript operators that accept a <variable, value, ...> before
     * them. Some end of lines are not the end of a statement, like when
     * continued by one of these operators on the newline.
     *
     * Note: Most operators are fine, we've only removed ), ], ++, --, ! and ~.
     * There can't be a newline separating ! or ~ and whatever it is negating.
     * ++ & -- have to be joined with the value they're in-/decrementing.
     * ) & ] are "special" in that they have lots or usecases. () for example
     * is used for function calls, for grouping, in if () and for (), ...
     *
     * Will be loaded from /data/js/operators_after.txt
     *
     * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators
     *
     * @var string[]
     */
    protected $operatorsAfter = array();

    /**
     * {@inheritdoc}
     */
    public function __construct()
    {
        call_user_func_array(array('parent', '__construct'), func_get_args());

        $dataDir = __DIR__.'/../data/js/';
        $options = FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES;
        $this->keywordsReserved = file($dataDir.'keywords_reserved.txt', $options);
        $this->keywordsBefore = file($dataDir.'keywords_before.txt', $options);
        $this->keywordsAfter = file($dataDir.'keywords_after.txt', $options);
        $this->operators = file($dataDir.'operators.txt', $options);
        $this->operatorsBefore = file($dataDir.'operators_before.txt', $options);
        $this->operatorsAfter = file($dataDir.'operators_after.txt', $options);
    }

    /**
     * Minify the data.
     * Perform JS optimizations.
     *
     * @param string[optional] $path Path to write the data to
     *
     * @return string The minified data
     */
    public function execute($path = null)
    {
        $content = '';

        /*
         * Let's first take out strings, comments and regular expressions.
         * All of these can contain JS code-like characters, and we should make
         * sure any further magic ignores anything inside of these.
         *
         * Consider this example, where we should not strip any whitespace:
         * var str = "a   test";
         *
         * Comments will be removed altogether, strings and regular expressions
         * will be replaced by placeholder text, which we'll restore later.
         */
        $this->extractStrings('\'"`');
        $this->stripComments();
        $this->extractRegex();

        // loop files
        foreach ($this->data as $source => $js) {
            // take out strings, comments & regex (for which we've registered
            // the regexes just a few lines earlier)
            $js = $this->replace($js);

            $js = $this->propertyNotation($js);
            $js = $this->shortenBools($js);
            $js = $this->stripWhitespace($js);

            // combine js: separating the scripts by a ;
            $content .= $js.";";
        }

        // clean up leftover `;`s from the combination of multiple scripts
        $content = ltrim($content, ';');
        $content = substr($content, 0, -1);

        /*
         * Earlier, we extracted strings & regular expressions and replaced them
         * with placeholder text. This will restore them.
         */
        $content = $this->restoreExtractedData($content);

        return $content;
    }

    /**
     * Strip comments from source code.
     */
    protected function stripComments()
    {
        // single-line comments
        $this->registerPattern('/\/\/.*$/m', '');

        // multi-line comments
        $this->registerPattern('/\/\*.*?\*\//s', '');
    }

    /**
     * JS can have /-delimited regular expressions, like: /ab+c/.match(string).
     *
     * The content inside the regex can contain characters that may be confused
     * for JS code: e.g. it could contain whitespace it needs to match & we
     * don't want to strip whitespace in there.
     *
     * The regex can be pretty simple: we don't have to care about comments,
     * (which also use slashes) because stripComments() will have stripped those
     * already.
     *
     * This method will replace all string content with simple REGEX#
     * placeholder text, so we've rid all regular expressions from characters
     * that may be misinterpreted. Original regex content will be saved in
     * $this->extracted and after doing all other minifying, we can restore the
     * original content via restoreRegex()
     */
    protected function extractRegex()
    {
        // PHP only supports $this inside anonymous functions since 5.4
        $minifier = $this;
        $callback = function ($match) use ($minifier) {
            $count = count($minifier->extracted);
            $placeholder = '"'.$count.'"';
            $minifier->extracted[$placeholder] = $match[0];

            return $placeholder;
        };

        // match all chars except `/` and `\`
        // `\` is allowed though, along with whatever char follows (which is the
        // one being escaped)
        // this should allow all chars, except for an unescaped `/` (= the one
        // closing the regex)
        // then also ignore bare `/` inside `[]`, where they don't need to be
        // escaped: anything inside `[]` can be ignored safely
        $pattern = '\\/(?:[^\\[\\/\\\\]+|(?:\\\\.)+|(?:\\[(?:[^\\]\\\\]+|(?:\\\\.)+)+\\])+)++\\/[gimy]*';

        // a regular expression can only be followed by a few operators or some
        // of the RegExp methods (a `\` followed by a variable or value is
        // likely part of a division, not a regex)
        $keywords = array('do', 'in', 'new', 'else', 'throw', 'yield', 'delete', 'return',  'typeof');
        $before = '([=:,;\+\-\*\/\}\(\{\[&\|!\)]|^|'.implode('|', $keywords).')\s*';
        $propertiesAndMethods = array(
            // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp#Properties_2
            'constructor',
            'flags',
            'global',
            'ignoreCase',
            'multiline',
            'source',
            'sticky',
            'unicode',
            // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp#Methods_2
            'compile(',
            'exec(',
            'test(',
            'toSource(',
            'toString(',
        );
        $delimiters = array_fill(0, count($propertiesAndMethods), '/');
        $propertiesAndMethods = array_map('preg_quote', $propertiesAndMethods, $delimiters);
        $after = '(?=\s*[\.,;\)\}&\|+]|\/\/|$|\.('.implode('|', $propertiesAndMethods).'))';
        $this->registerPattern('/'.$before.'\K'.$pattern.$after.'/', $callback);

        // 1 more edge case: a regex can be followed by a lot more operators or
        // keywords if there's a newline (ASI) in between, where the operator
        // actually starts a new statement
        // (https://github.com/matthiasmullie/minify/issues/56)
        $operators = $this->getOperatorsForRegex($this->operatorsBefore, '/');
        $operators += $this->getOperatorsForRegex($this->keywordsReserved, '/');
        $after = '(?=\s*\n\s*('.implode('|', $operators).'))';
        $this->registerPattern('/'.$pattern.$after.'/', $callback);
    }

    /**
     * Strip whitespace.
     *
     * We won't strip *all* whitespace, but as much as possible. The thing that
     * we'll preserve are newlines we're unsure about.
     * JavaScript doesn't require statements to be terminated with a semicolon.
     * It will automatically fix missing semicolons with ASI (automatic semi-
     * colon insertion) at the end of line causing errors (without semicolon.)
     *
     * Because it's sometimes hard to tell if a newline is part of a statement
     * that should be terminated or not, we'll just leave some of them alone.
     *
     * @param string $content The content to strip the whitespace for
     *
     * @return string
     */
    protected function stripWhitespace($content)
    {
        // uniform line endings, make them all line feed
        $content = str_replace(array("\r\n", "\r"), "\n", $content);

        // collapse all non-line feed whitespace into a single space
        $content = preg_replace('/[^\S\n]+/', ' ', $content);

        // strip leading & trailing whitespace
        $content = str_replace(array(" \n", "\n "), "\n", $content);

        // collapse consecutive line feeds into just 1
        $content = preg_replace('/\n+/', "\n", $content);

        $operatorsBefore = $this->getOperatorsForRegex($this->operatorsBefore, '/');
        $operatorsAfter = $this->getOperatorsForRegex($this->operatorsAfter, '/');
        $operators = $this->getOperatorsForRegex($this->operators, '/');
        $keywordsBefore = $this->getKeywordsForRegex($this->keywordsBefore, '/');
        $keywordsAfter = $this->getKeywordsForRegex($this->keywordsAfter, '/');

        // strip whitespace that ends in (or next line begin with) an operator
        // that allows statements to be broken up over multiple lines
        unset($operatorsBefore['+'], $operatorsBefore['-'], $operatorsAfter['+'], $operatorsAfter['-']);
        $content = preg_replace(
            array(
                '/('.implode('|', $operatorsBefore).')\s+/',
                '/\s+('.implode('|', $operatorsAfter).')/',
            ), '\\1', $content
        );

        // make sure + and - can't be mistaken for, or joined into ++ and --
        $content = preg_replace(
            array(
                '/(?<![\+\-])\s*([\+\-])(?![\+\-])/',
                '/(?<![\+\-])([\+\-])\s*(?![\+\-])/',
            ), '\\1', $content
        );

        // collapse whitespace around reserved words into single space
        $content = preg_replace('/(^|[;\}\s])\K('.implode('|', $keywordsBefore).')\s+/', '\\2 ', $content);
        $content = preg_replace('/\s+('.implode('|', $keywordsAfter).')(?=([;\{\s]|$))/', ' \\1', $content);

        /*
         * We didn't strip whitespace after a couple of operators because they
         * could be used in different contexts and we can't be sure it's ok to
         * strip the newlines. However, we can safely strip any non-line feed
         * whitespace that follows them.
         */
        $operatorsDiffBefore = array_diff($operators, $operatorsBefore);
        $operatorsDiffAfter = array_diff($operators, $operatorsAfter);
        $content = preg_replace('/('.implode('|', $operatorsDiffBefore).')[^\S\n]+/', '\\1', $content);
        $content = preg_replace('/[^\S\n]+('.implode('|', $operatorsDiffAfter).')/', '\\1', $content);

        /*
         * Whitespace after `return` can be omitted in a few occasions
         * (such as when followed by a string or regex)
         */
        $content = preg_replace('/\breturn\s+(["\'\/\+\-])/', 'return$1', $content);

        /*
         * Get rid of double semicolons, except where they can be used like:
         * "for(v=1,_=b;;)", "for(v=1;;v++)" or "for(;;ja||(ja=true))".
         * I'll safeguard these double semicolons inside for-loops by
         * temporarily replacing them with an invalid condition: they won't have
         * a double semicolon and will be easy to spot to restore afterwards.
         */
        $content = preg_replace('/\bfor\(([^;]*);;([^;]*)\)/', 'for(\\1;-;\\2)', $content);
        $content = preg_replace('/;+/', ';', $content);
        $content = preg_replace('/\bfor\(([^;]*);-;([^;]*)\)/', 'for(\\1;;\\2)', $content);

        /*
         * Next, we'll be removing all semicolons where ASI kicks in.
         * for-loops however, can have an empty body (ending in only a
         * semicolon), like: `for(i=1;i<3;i++);`, of `for(i in list);`
         * Here, nothing happens during the loop; it's just used to keep
         * increasing `i`. With that ; omitted, the next line would be expected
         * to be the for-loop's body... Same goes for while loops.
         * I'm going to double that semicolon (if any) so after the next line,
         * which strips semicolons here & there, we're still left with this one.
         */
        $content = preg_replace('/(for\([^;\{]*;[^;\{]*;[^;\{]*\));(\}|$)/s', '\\1;;\\2', $content);
        $content = preg_replace('/(for\([^;\{]+\s+in\s+[^;\{]+\));(\}|$)/s', '\\1;;\\2', $content);
        /*
         * Below will also keep `;` after a `do{}while();` along with `while();`
         * While these could be stripped after do-while, detecting this
         * distinction is cumbersome, so I'll play it safe and make sure `;`
         * after any kind of `while` is kept.
         */
        $content = preg_replace('/(while\([^;\{]+\));(\}|$)/s', '\\1;;\\2', $content);

        /*
         * We also can't strip empty else-statements. Even though they're
         * useless and probably shouldn't be in the code in the first place, we
         * shouldn't be stripping the `;` that follows it as it breaks the code.
         * We can just remove those useless else-statements completely.
         *
         * @see https://github.com/matthiasmullie/minify/issues/91
         */
        $content = preg_replace('/else;/s', '', $content);

        /*
         * We also don't really want to terminate statements followed by closing
         * curly braces (which we've ignored completely up until now) or end-of-
         * script: ASI will kick in here & we're all about minifying.
         * Semicolons at beginning of the file don't make any sense either.
         */
        $content = preg_replace('/;(\}|$)/s', '\\1', $content);
        $content = ltrim($content, ';');

        // get rid of remaining whitespace af beginning/end
        return trim($content);
    }

    /**
     * We'll strip whitespace around certain operators with regular expressions.
     * This will prepare the given array by escaping all characters.
     *
     * @param string[] $operators
     * @param string   $delimiter
     *
     * @return string[]
     */
    protected function getOperatorsForRegex(array $operators, $delimiter = '/')
    {
        // escape operators for use in regex
        $delimiters = array_fill(0, count($operators), $delimiter);
        $escaped = array_map('preg_quote', $operators, $delimiters);

        $operators = array_combine($operators, $escaped);

        // ignore + & - for now, they'll get special treatment
        unset($operators['+'], $operators['-']);

        // dot can not just immediately follow a number; it can be confused for
        // decimal point, or calling a method on it, e.g. 42 .toString()
        $operators['.'] = '(?<![0-9]\s)\.';

        // don't confuse = with other assignment shortcuts (e.g. +=)
        $chars = preg_quote('+-*\=<>%&|', $delimiter);
        $operators['='] = '(?<!['.$chars.'])\=';

        return $operators;
    }

    /**
     * We'll strip whitespace around certain keywords with regular expressions.
     * This will prepare the given array by escaping all characters.
     *
     * @param string[] $keywords
     * @param string   $delimiter
     *
     * @return string[]
     */
    protected function getKeywordsForRegex(array $keywords, $delimiter = '/')
    {
        // escape keywords for use in regex
        $delimiter = array_fill(0, count($keywords), $delimiter);
        $escaped = array_map('preg_quote', $keywords, $delimiter);

        // add word boundaries
        array_walk($keywords, function ($value) {
            return '\b'.$value.'\b';
        });

        $keywords = array_combine($keywords, $escaped);

        return $keywords;
    }

    /**
     * Replaces all occurrences of array['key'] by array.key.
     *
     * @param string $content
     *
     * @return string
     */
    protected function propertyNotation($content)
    {
        // PHP only supports $this inside anonymous functions since 5.4
        $minifier = $this;
        $keywords = $this->keywordsReserved;
        $callback = function ($match) use ($minifier, $keywords) {
            $property = trim($minifier->extracted[$match[1]], '\'"');

            /*
             * Check if the property is a reserved keyword. In this context (as
             * property of an object literal/array) it shouldn't matter, but IE8
             * freaks out with "Expected identifier".
             */
            if (in_array($property, $keywords)) {
                return $match[0];
            }

            /*
             * See if the property is in a variable-like format (e.g.
             * array['key-here'] can't be replaced by array.key-here since '-'
             * is not a valid character there.
             */
            if (!preg_match('/^'.$minifier::REGEX_VARIABLE.'$/u', $property)) {
                return $match[0];
            }

            return '.'.$property;
        };

        /*
         * Figure out if previous character is a variable name (of the array
         * we want to use property notation on) - this is to make sure
         * standalone ['value'] arrays aren't confused for keys-of-an-array.
         * We can (and only have to) check the last character, because PHP's
         * regex implementation doesn't allow unfixed-length look-behind
         * assertions.
         */
        preg_match('/(\[[^\]]+\])[^\]]*$/', static::REGEX_VARIABLE, $previousChar);
        $previousChar = $previousChar[1];

        /*
         * Make sure word preceding the ['value'] is not a keyword, e.g.
         * return['x']. Because -again- PHP's regex implementation doesn't allow
         * unfixed-length look-behind assertions, I'm just going to do a lot of
         * separate look-behind assertions, one for each keyword.
         */
        $keywords = $this->getKeywordsForRegex($keywords);
        $keywords = '(?<!'.implode(')(?<!', $keywords).')';

        return preg_replace_callback('/(?<='.$previousChar.'|\])'.$keywords.'\[\s*(([\'"])[0-9]+\\2)\s*\]/u', $callback, $content);
    }

    /**
     * Replaces true & false by !0 and !1.
     *
     * @param string $content
     *
     * @return string
     */
    protected function shortenBools($content)
    {
        /*
         * 'true' or 'false' could be used as property names (which may be
         * followed by whitespace) - we must not replace those!
         * Since PHP doesn't allow variable-length (to account for the
         * whitespace) lookbehind assertions, I need to capture the leading
         * character and check if it's a `.`
         */
        $callback = function ($match) {
            if (trim($match[1]) === '.') {
                return $match[0];
            }

            return $match[1].($match[2] === 'true' ? '!0' : '!1');
        };
        $content = preg_replace_callback('/(^|.\s*)\b(true|false)\b(?!:)/', $callback, $content);

        // for(;;) is exactly the same as while(true), but shorter :)
        $content = preg_replace('/\bwhile\(!0\){/', 'for(;;){', $content);

        // now make sure we didn't turn any do ... while(true) into do ... for(;;)
        preg_match_all('/\bdo\b/', $content, $dos, PREG_OFFSET_CAPTURE | PREG_SET_ORDER);

        // go backward to make sure positional offsets aren't altered when $content changes
        $dos = array_reverse($dos);
        foreach ($dos as $do) {
            $offsetDo = $do[0][1];

            // find all `while` (now `for`) following `do`: one of those must be
            // associated with the `do` and be turned back into `while`
            preg_match_all('/\bfor\(;;\)/', $content, $whiles, PREG_OFFSET_CAPTURE | PREG_SET_ORDER, $offsetDo);
            foreach ($whiles as $while) {
                $offsetWhile = $while[0][1];

                $open = substr_count($content, '{', $offsetDo, $offsetWhile - $offsetDo);
                $close = substr_count($content, '}', $offsetDo, $offsetWhile - $offsetDo);
                if ($open === $close) {
                    // only restore `while` if amount of `{` and `}` are the same;
                    // otherwise, that `for` isn't associated with this `do`
                    $content = substr_replace($content, 'while(!0)', $offsetWhile, strlen('for(;;)'));
                    break;
                }
            }
        }

        return $content;
    }
}
