<?php
/**
 * Parses unified or context diffs output from eg. the diff utility.
 *
 * Example:
 * <code>
 * $patch = file_get_contents('example.patch');
 * $diff = &new Text_Diff('string', array($patch));
 * $renderer = &new Text_Diff_Renderer_inline();
 * echo $renderer->render($diff);
 * </code>
 *
 * @author    �rjan Persson <o@42mm.org>
 * @copyright Copyright 2005 �rjan Persson
 * @package   Text_Diff
 * @since     0.2.0
 * @access    private
 */
class Text_Diff_Engine_string {

    /**
     * Parses a unified or context diff.
     *
     * First param contains the whole diff and the second can be used to force 
     * a specific diff type. If the second parameter is 'autodetect', the 
     * diff will be examined to find out which type of diff this is.
     * 
     * @param string $diff  The diff content.
     * @param string $mode  The diff mode of the content in $diff. One of
     *                      'context', 'unified', or 'autodetect'.
     *
     * @return array  List of all diff operations.
     */
    function diff($diff, $mode = 'autodetect')
    {
        if ($mode != 'autodetect' && $mode != 'context' && $mode != 'unified') {
            die_friendly('Text_Diff', '<p>Type of diff is unsupported</p>');
        }

        if ($mode == 'autodetect') {
            $context = strpos($diff, '***');
            $unified = strpos($diff, '---');
            if ($context === $unified) {
                die_friendly('Text_Diff', '<p>Type of diff could not be detected</p>');
            } elseif ($context === false || $context === false) {
                $mode = $context !== false ? 'context' : 'unified';
            } else {
                $mode = $context < $unified ? 'context' : 'unified';
            }
        }

        // split by new line and remove the diff header
        $diff = explode("\n", $diff);
        array_shift($diff);
        array_shift($diff);

        if ($mode == 'context') {
            return $this->parseContextDiff($diff);
        } else {
            return $this->parseUnifiedDiff($diff);
        }
    }

    /**
     * Parses an array containing the unified diff.
     *
     * @param array $diff  Array of lines.
     *
     * @return array  List of all diff operations.
     */
    function parseUnifiedDiff($diff)
    {
        $edits = array();
        $end = count($diff) - 1;
        for ($i = 0; $i < $end;) {
            $diff1 = array();
            switch (substr($diff[$i], 0, 1)) {
            case ' ':
                do {
                    $diff1[] = substr($diff[$i], 1);
                } while (++$i < $end && substr($diff[$i], 0, 1) == ' ');
                $edits[] = &new Text_Diff_Op_copy($diff1);
                break;
            case '+':
                // get all new lines
                do {
                    $diff1[] = substr($diff[$i], 1);
                } while (++$i < $end && substr($diff[$i], 0, 1) == '+');
                $edits[] = &new Text_Diff_Op_add($diff1);
                break;
            case '-':
                // get changed or removed lines
                $diff2 = array();
                do {
                    $diff1[] = substr($diff[$i], 1);
                } while (++$i < $end && substr($diff[$i], 0, 1) == '-');
                while ($i < $end && substr($diff[$i], 0, 1) == '+') {
                    $diff2[] = substr($diff[$i++], 1);
                }
                if (count($diff2) == 0) {
                    $edits[] = &new Text_Diff_Op_delete($diff1);
                } else {
                    $edits[] = &new Text_Diff_Op_change($diff1, $diff2);
                }
                break;
            default:
                $i++;
                break;
            }
        }
        return $edits;
    }

    /**
     * Parses an array containing the context diff.
     *
     * @param array $diff  Array of lines.
     *
     * @return array  List of all diff operations.
     */
    function parseContextDiff(&$diff)
    {
        $edits = array();
        $i = $max_i = $j = $max_j = 0;
        $end = count($diff) - 1;
        while ($i < $end && $j < $end) {
            while ($i >= $max_i && $j >= $max_j) {
                // find the boundaries of the diff output of the two files
                for ($i = $j;
                     $i < $end && substr($diff[$i], 0, 3) == '***';
                     $i++);
                for ($max_i = $i;
                     $max_i < $end && substr($diff[$max_i], 0, 3) != '---';
                     $max_i++);
                for ($j = $max_i;
                     $j < $end && substr($diff[$j], 0, 3) == '---';
                     $j++);
                for ($max_j = $j;
                     $max_j < $end && substr($diff[$max_j], 0, 3) != '***';
                     $max_j++);
            }

            // find what hasn't been changed
            $array = array();
            while ($i < $max_i &&
                   $j < $max_j &&
                   strcmp($diff[$i], $diff[$j]) == 0) {
                $array[] = substr($diff[$i], 2);
                $i++;
                $j++;
            }
            while ($i < $max_i && ($max_j-$j) <= 1) {
                if ($diff[$i] != '' && substr($diff[$i], 0, 1) != ' ') {
                    break;
                }
                $array[] = substr($diff[$i++], 2);
            }
            while ($j < $max_j && ($max_i-$i) <= 1) {
                if ($diff[$j] != '' && substr($diff[$j], 0, 1) != ' ') {
                    break;
                }
                $array[] = substr($diff[$j++], 2);
            }
            if (count($array) > 0) {
                $edits[] = &new Text_Diff_Op_copy($array);
            }

            if ($i < $max_i) {
                $diff1 = array();
                switch (substr($diff[$i], 0, 1)) {
                case '!':
                    $diff2 = array();
                    do {
                        $diff1[] = substr($diff[$i], 2);
                        if ($j < $max_j && substr($diff[$j], 0, 1) == '!') {
                            $diff2[] = substr($diff[$j++], 2);
                        }
                    } while (++$i < $max_i && substr($diff[$i], 0, 1) == '!');
                    $edits[] = &new Text_Diff_Op_change($diff1, $diff2);
                    break;
                case '+':
                    do {
                        $diff1[] = substr($diff[$i], 2);
                    } while (++$i < $max_i && substr($diff[$i], 0, 1) == '+');
                    $edits[] = &new Text_Diff_Op_add($diff1);
                    break;
                case '-':
                    do {
                        $diff1[] = substr($diff[$i], 2);
                    } while (++$i < $max_i && substr($diff[$i], 0, 1) == '-');
                    $edits[] = &new Text_Diff_Op_delete($diff1);
                    break;
                }
            }

            if ($j < $max_j) {
                $diff2 = array();
                switch (substr($diff[$j], 0, 1)) {
                case '+':
                    do {
                        $diff2[] = substr($diff[$j++], 2);
                    } while ($j < $max_j && substr($diff[$j], 0, 1) == '+');
                    $edits[] = &new Text_Diff_Op_add($diff2);
                    break;
                case '-':
                    do {
                        $diff2[] = substr($diff[$j++], 2);
                    } while ($j < $max_j && substr($diff[$j], 0, 1) == '-');
                    $edits[] = &new Text_Diff_Op_delete($diff2);
                    break;
                }
            }
        }
        return $edits;
    }
}