diff_match_patch.js

/**
 * This file is a slightly modified version of the Apache-licensed
 * Diff, Match and Patch library. It's modified to not include the diff
 * related functions, as they're already bundled in `component/diff`.
 */

/**
 * Diff Match and Patch
 *
 * Copyright 2006 Google Inc.
 * http://code.google.com/p/google-diff-match-patch/
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @fileoverview Applies the patch onto another text, allowing for errors.
 * @author fraser@google.com (Neil Fraser)
 */

// require the private diff_match_patch constructor from component/diff, to augment it 
// with the match and patch functions.

var diff_match_patch = require('diff/diff_match_patch');

var DIFF_DELETE = -1;
var DIFF_INSERT = 1;
var DIFF_EQUAL = 0;

//  MATCH FUNCTIONS


/**
 * Locate the best instance of 'pattern' in 'text' near 'loc'.
 * @param {string} text The text to search.
 * @param {string} pattern The pattern to search for.
 * @param {number} loc The location to search around.
 * @return {number} Best match index or -1.
 */
diff_match_patch.prototype.match_main = function(text, pattern, loc) {
  // Check for null inputs.
  if (text == null || pattern == null || loc == null) {
    throw new Error('Null input. (match_main)');
  }

  loc = Math.max(0, Math.min(loc, text.length));
  if (text == pattern) {
    // Shortcut (potentially not guaranteed by the algorithm)
    return 0;
  } else if (!text.length) {
    // Nothing to match.
    return -1;
  } else if (text.substring(loc, loc + pattern.length) == pattern) {
    // Perfect match at the perfect spot!  (Includes case of null pattern)
    return loc;
  } else {
    // Do a fuzzy compare.
    return this.match_bitap_(text, pattern, loc);
  }
};


/**
 * Locate the best instance of 'pattern' in 'text' near 'loc' using the
 * Bitap algorithm.
 * @param {string} text The text to search.
 * @param {string} pattern The pattern to search for.
 * @param {number} loc The location to search around.
 * @return {number} Best match index or -1.
 * @private
 */
diff_match_patch.prototype.match_bitap_ = function(text, pattern, loc) {
  if (pattern.length > this.Match_MaxBits) {
    throw new Error('Pattern too long for this browser.');
  }

  // Initialise the alphabet.
  var s = this.match_alphabet_(pattern);

  var dmp = this;  // 'this' becomes 'window' in a closure.

  /**
   * Compute and return the score for a match with e errors and x location.
   * Accesses loc and pattern through being a closure.
   * @param {number} e Number of errors in match.
   * @param {number} x Location of match.
   * @return {number} Overall score for match (0.0 = good, 1.0 = bad).
   * @private
   */
  function match_bitapScore_(e, x) {
    var accuracy = e / pattern.length;
    var proximity = Math.abs(loc - x);
    if (!dmp.Match_Distance) {
      // Dodge divide by zero error.
      return proximity ? 1.0 : accuracy;
    }
    return accuracy + (proximity / dmp.Match_Distance);
  }

  // Highest score beyond which we give up.
  var score_threshold = this.Match_Threshold;
  // Is there a nearby exact match? (speedup)
  var best_loc = text.indexOf(pattern, loc);
  if (best_loc != -1) {
    score_threshold = Math.min(match_bitapScore_(0, best_loc), score_threshold);
    // What about in the other direction? (speedup)
    best_loc = text.lastIndexOf(pattern, loc + pattern.length);
    if (best_loc != -1) {
      score_threshold =
          Math.min(match_bitapScore_(0, best_loc), score_threshold);
    }
  }

  // Initialise the bit arrays.
  var matchmask = 1 << (pattern.length - 1);
  best_loc = -1;

  var bin_min, bin_mid;
  var bin_max = pattern.length + text.length;
  var last_rd;
  for (var d = 0; d < pattern.length; d++) {
    // Scan for the best match; each iteration allows for one more error.
    // Run a binary search to determine how far from 'loc' we can stray at this
    // error level.
    bin_min = 0;
    bin_mid = bin_max;
    while (bin_min < bin_mid) {
      if (match_bitapScore_(d, loc + bin_mid) <= score_threshold) {
        bin_min = bin_mid;
      } else {
        bin_max = bin_mid;
      }
      bin_mid = Math.floor((bin_max - bin_min) / 2 + bin_min);
    }
    // Use the result from this iteration as the maximum for the next.
    bin_max = bin_mid;
    var start = Math.max(1, loc - bin_mid + 1);
    var finish = Math.min(loc + bin_mid, text.length) + pattern.length;

    var rd = Array(finish + 2);
    rd[finish + 1] = (1 << d) - 1;
    for (var j = finish; j >= start; j--) {
      // The alphabet (s) is a sparse hash, so the following line generates
      // warnings.
      var charMatch = s[text.charAt(j - 1)];
      if (d === 0) {  // First pass: exact match.
        rd[j] = ((rd[j + 1] << 1) | 1) & charMatch;
      } else {  // Subsequent passes: fuzzy match.
        rd[j] = (((rd[j + 1] << 1) | 1) & charMatch) |
                (((last_rd[j + 1] | last_rd[j]) << 1) | 1) |
                last_rd[j + 1];
      }
      if (rd[j] & matchmask) {
        var score = match_bitapScore_(d, j - 1);
        // This match will almost certainly be better than any existing match.
        // But check anyway.
        if (score <= score_threshold) {
          // Told you so.
          score_threshold = score;
          best_loc = j - 1;
          if (best_loc > loc) {
            // When passing loc, don't exceed our current distance from loc.
            start = Math.max(1, 2 * loc - best_loc);
          } else {
            // Already passed loc, downhill from here on in.
            break;
          }
        }
      }
    }
    // No hope for a (better) match at greater error levels.
    if (match_bitapScore_(d + 1, loc) > score_threshold) {
      break;
    }
    last_rd = rd;
  }
  return best_loc;
};


/**
 * Initialise the alphabet for the Bitap algorithm.
 * @param {string} pattern The text to encode.
 * @return {!Object} Hash of character locations.
 * @private
 */
diff_match_patch.prototype.match_alphabet_ = function(pattern) {
  var s = {};
  for (var i = 0; i < pattern.length; i++) {
    s[pattern.charAt(i)] = 0;
  }
  for (var i = 0; i < pattern.length; i++) {
    s[pattern.charAt(i)] |= 1 << (pattern.length - i - 1);
  }
  return s;
};


//  PATCH FUNCTIONS


/**
 * Increase the context until it is unique,
 * but don't let the pattern expand beyond Match_MaxBits.
 * @param {!diff_match_patch.patch_obj} patch The patch to grow.
 * @param {string} text Source text.
 * @private
 */
diff_match_patch.prototype.patch_addContext_ = function(patch, text) {
  if (text.length == 0) {
    return;
  }
  var pattern = text.substring(patch.start2, patch.start2 + patch.length1);
  var padding = 0;

  // Look for the first and last matches of pattern in text.  If two different
  // matches are found, increase the pattern length.
  while (text.indexOf(pattern) != text.lastIndexOf(pattern) &&
         pattern.length < this.Match_MaxBits - this.Patch_Margin -
         this.Patch_Margin) {
    padding += this.Patch_Margin;
    pattern = text.substring(patch.start2 - padding,
                             patch.start2 + patch.length1 + padding);
  }
  // Add one chunk for good luck.
  padding += this.Patch_Margin;

  // Add the prefix.
  var prefix = text.substring(patch.start2 - padding, patch.start2);
  if (prefix) {
    patch.diffs.unshift([DIFF_EQUAL, prefix]);
  }
  // Add the suffix.
  var suffix = text.substring(patch.start2 + patch.length1,
                              patch.start2 + patch.length1 + padding);
  if (suffix) {
    patch.diffs.push([DIFF_EQUAL, suffix]);
  }

  // Roll back the start points.
  patch.start1 -= prefix.length;
  patch.start2 -= prefix.length;
  // Extend the lengths.
  patch.length1 += prefix.length + suffix.length;
  patch.length2 += prefix.length + suffix.length;
};


/**
 * Compute a list of patches to turn text1 into text2.
 * Use diffs if provided, otherwise compute it ourselves.
 * There are four ways to call this function, depending on what data is
 * available to the caller:
 * Method 1:
 * a = text1, b = text2
 * Method 2:
 * a = diffs
 * Method 3 (optimal):
 * a = text1, b = diffs
 * Method 4 (deprecated, use method 3):
 * a = text1, b = text2, c = diffs
 *
 * @param {string|!Array.<!diff_match_patch.Diff>} a text1 (methods 1,3,4) or
 * Array of diff tuples for text1 to text2 (method 2).
 * @param {string|!Array.<!diff_match_patch.Diff>} opt_b text2 (methods 1,4) or
 * Array of diff tuples for text1 to text2 (method 3) or undefined (method 2).
 * @param {string|!Array.<!diff_match_patch.Diff>} opt_c Array of diff tuples
 * for text1 to text2 (method 4) or undefined (methods 1,2,3).
 * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
 */
diff_match_patch.prototype.patch_make = function(a, opt_b, opt_c) {
  var text1, diffs;
  if (typeof a == 'string' && typeof opt_b == 'string' &&
      typeof opt_c == 'undefined') {
    // Method 1: text1, text2
    // Compute diffs from text1 and text2.
    text1 = /** @type {string} */(a);
    diffs = this.diff_main(text1, /** @type {string} */(opt_b), true);
    if (diffs.length > 2) {
      this.diff_cleanupSemantic(diffs);
      this.diff_cleanupEfficiency(diffs);
    }
  } else if (a && typeof a == 'object' && typeof opt_b == 'undefined' &&
      typeof opt_c == 'undefined') {
    // Method 2: diffs
    // Compute text1 from diffs.
    diffs = /** @type {!Array.<!diff_match_patch.Diff>} */(a);
    text1 = this.diff_text1(diffs);
  } else if (typeof a == 'string' && opt_b && typeof opt_b == 'object' &&
      typeof opt_c == 'undefined') {
    // Method 3: text1, diffs
    text1 = /** @type {string} */(a);
    diffs = /** @type {!Array.<!diff_match_patch.Diff>} */(opt_b);
  } else if (typeof a == 'string' && typeof opt_b == 'string' &&
      opt_c && typeof opt_c == 'object') {
    // Method 4: text1, text2, diffs
    // text2 is not used.
    text1 = /** @type {string} */(a);
    diffs = /** @type {!Array.<!diff_match_patch.Diff>} */(opt_c);
  } else {
    throw new Error('Unknown call format to patch_make.');
  }

  if (diffs.length === 0) {
    return [];  // Get rid of the null case.
  }
  var patches = [];
  var patch = new diff_match_patch.patch_obj();
  var patchDiffLength = 0;  // Keeping our own length var is faster in JS.
  var char_count1 = 0;  // Number of characters into the text1 string.
  var char_count2 = 0;  // Number of characters into the text2 string.
  // Start with text1 (prepatch_text) and apply the diffs until we arrive at
  // text2 (postpatch_text).  We recreate the patches one by one to determine
  // context info.
  var prepatch_text = text1;
  var postpatch_text = text1;
  for (var x = 0; x < diffs.length; x++) {
    var diff_type = diffs[x][0];
    var diff_text = diffs[x][1];

    if (!patchDiffLength && diff_type !== DIFF_EQUAL) {
      // A new patch starts here.
      patch.start1 = char_count1;
      patch.start2 = char_count2;
    }

    switch (diff_type) {
      case DIFF_INSERT:
        patch.diffs[patchDiffLength++] = diffs[x];
        patch.length2 += diff_text.length;
        postpatch_text = postpatch_text.substring(0, char_count2) + diff_text +
                         postpatch_text.substring(char_count2);
        break;
      case DIFF_DELETE:
        patch.length1 += diff_text.length;
        patch.diffs[patchDiffLength++] = diffs[x];
        postpatch_text = postpatch_text.substring(0, char_count2) +
                         postpatch_text.substring(char_count2 +
                             diff_text.length);
        break;
      case DIFF_EQUAL:
        if (diff_text.length <= 2 * this.Patch_Margin &&
            patchDiffLength && diffs.length != x + 1) {
          // Small equality inside a patch.
          patch.diffs[patchDiffLength++] = diffs[x];
          patch.length1 += diff_text.length;
          patch.length2 += diff_text.length;
        } else if (diff_text.length >= 2 * this.Patch_Margin) {
          // Time for a new patch.
          if (patchDiffLength) {
            this.patch_addContext_(patch, prepatch_text);
            patches.push(patch);
            patch = new diff_match_patch.patch_obj();
            patchDiffLength = 0;
            // Unlike Unidiff, our patch lists have a rolling context.
            // http://code.google.com/p/google-diff-match-patch/wiki/Unidiff
            // Update prepatch text & pos to reflect the application of the
            // just completed patch.
            prepatch_text = postpatch_text;
            char_count1 = char_count2;
          }
        }
        break;
    }

    // Update the current character count.
    if (diff_type !== DIFF_INSERT) {
      char_count1 += diff_text.length;
    }
    if (diff_type !== DIFF_DELETE) {
      char_count2 += diff_text.length;
    }
  }
  // Pick up the leftover patch if not empty.
  if (patchDiffLength) {
    this.patch_addContext_(patch, prepatch_text);
    patches.push(patch);
  }

  return patches;
};


/**
 * Given an array of patches, return another array that is identical.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
 */
diff_match_patch.prototype.patch_deepCopy = function(patches) {
  // Making deep copies is hard in JavaScript.
  var patchesCopy = [];
  for (var x = 0; x < patches.length; x++) {
    var patch = patches[x];
    var patchCopy = new diff_match_patch.patch_obj();
    patchCopy.diffs = [];
    for (var y = 0; y < patch.diffs.length; y++) {
      patchCopy.diffs[y] = patch.diffs[y].slice();
    }
    patchCopy.start1 = patch.start1;
    patchCopy.start2 = patch.start2;
    patchCopy.length1 = patch.length1;
    patchCopy.length2 = patch.length2;
    patchesCopy[x] = patchCopy;
  }
  return patchesCopy;
};


/**
 * Merge a set of patches onto the text.  Return a patched text, as well
 * as a list of true/false values indicating which patches were applied.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @param {string} text Old text.
 * @return {!Array.<string|!Array.<boolean>>} Two element Array, containing the
 *      new text and an array of boolean values.
 */
diff_match_patch.prototype.patch_apply = function(patches, text) {
  if (patches.length == 0) {
    return [text, []];
  }

  // Deep copy the patches so that no changes are made to originals.
  patches = this.patch_deepCopy(patches);

  var nullPadding = this.patch_addPadding(patches);
  text = nullPadding + text + nullPadding;

  this.patch_splitMax(patches);
  // delta keeps track of the offset between the expected and actual location
  // of the previous patch.  If there are patches expected at positions 10 and
  // 20, but the first patch was found at 12, delta is 2 and the second patch
  // has an effective expected position of 22.
  var delta = 0;
  var results = [];
  for (var x = 0; x < patches.length; x++) {
    var expected_loc = patches[x].start2 + delta;
    var text1 = this.diff_text1(patches[x].diffs);
    var start_loc;
    var end_loc = -1;
    if (text1.length > this.Match_MaxBits) {
      // patch_splitMax will only provide an oversized pattern in the case of
      // a monster delete.
      start_loc = this.match_main(text, text1.substring(0, this.Match_MaxBits),
                                  expected_loc);
      if (start_loc != -1) {
        end_loc = this.match_main(text,
            text1.substring(text1.length - this.Match_MaxBits),
            expected_loc + text1.length - this.Match_MaxBits);
        if (end_loc == -1 || start_loc >= end_loc) {
          // Can't find valid trailing context.  Drop this patch.
          start_loc = -1;
        }
      }
    } else {
      start_loc = this.match_main(text, text1, expected_loc);
    }
    if (start_loc == -1) {
      // No match found.  :(
      results[x] = false;
      // Subtract the delta for this failed patch from subsequent patches.
      delta -= patches[x].length2 - patches[x].length1;
    } else {
      // Found a match.  :)
      results[x] = true;
      delta = start_loc - expected_loc;
      var text2;
      if (end_loc == -1) {
        text2 = text.substring(start_loc, start_loc + text1.length);
      } else {
        text2 = text.substring(start_loc, end_loc + this.Match_MaxBits);
      }
      if (text1 == text2) {
        // Perfect match, just shove the replacement text in.
        text = text.substring(0, start_loc) +
               this.diff_text2(patches[x].diffs) +
               text.substring(start_loc + text1.length);
      } else {
        // Imperfect match.  Run a diff to get a framework of equivalent
        // indices.
        var diffs = this.diff_main(text1, text2, false);
        if (text1.length > this.Match_MaxBits &&
            this.diff_levenshtein(diffs) / text1.length >
            this.Patch_DeleteThreshold) {
          // The end points match, but the content is unacceptably bad.
          results[x] = false;
        } else {
          this.diff_cleanupSemanticLossless(diffs);
          var index1 = 0;
          var index2;
          for (var y = 0; y < patches[x].diffs.length; y++) {
            var mod = patches[x].diffs[y];
            if (mod[0] !== DIFF_EQUAL) {
              index2 = this.diff_xIndex(diffs, index1);
            }
            if (mod[0] === DIFF_INSERT) {  // Insertion
              text = text.substring(0, start_loc + index2) + mod[1] +
                     text.substring(start_loc + index2);
            } else if (mod[0] === DIFF_DELETE) {  // Deletion
              text = text.substring(0, start_loc + index2) +
                     text.substring(start_loc + this.diff_xIndex(diffs,
                         index1 + mod[1].length));
            }
            if (mod[0] !== DIFF_DELETE) {
              index1 += mod[1].length;
            }
          }
        }
      }
    }
  }
  // Strip the padding off.
  text = text.substring(nullPadding.length, text.length - nullPadding.length);
  return [text, results];
};


/**
 * Add some padding on text start and end so that edges can match something.
 * Intended to be called only from within patch_apply.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @return {string} The padding string added to each side.
 */
diff_match_patch.prototype.patch_addPadding = function(patches) {
  var paddingLength = this.Patch_Margin;
  var nullPadding = '';
  for (var x = 1; x <= paddingLength; x++) {
    nullPadding += String.fromCharCode(x);
  }

  // Bump all the patches forward.
  for (var x = 0; x < patches.length; x++) {
    patches[x].start1 += paddingLength;
    patches[x].start2 += paddingLength;
  }

  // Add some padding on start of first diff.
  var patch = patches[0];
  var diffs = patch.diffs;
  if (diffs.length == 0 || diffs[0][0] != DIFF_EQUAL) {
    // Add nullPadding equality.
    diffs.unshift([DIFF_EQUAL, nullPadding]);
    patch.start1 -= paddingLength;  // Should be 0.
    patch.start2 -= paddingLength;  // Should be 0.
    patch.length1 += paddingLength;
    patch.length2 += paddingLength;
  } else if (paddingLength > diffs[0][1].length) {
    // Grow first equality.
    var extraLength = paddingLength - diffs[0][1].length;
    diffs[0][1] = nullPadding.substring(diffs[0][1].length) + diffs[0][1];
    patch.start1 -= extraLength;
    patch.start2 -= extraLength;
    patch.length1 += extraLength;
    patch.length2 += extraLength;
  }

  // Add some padding on end of last diff.
  patch = patches[patches.length - 1];
  diffs = patch.diffs;
  if (diffs.length == 0 || diffs[diffs.length - 1][0] != DIFF_EQUAL) {
    // Add nullPadding equality.
    diffs.push([DIFF_EQUAL, nullPadding]);
    patch.length1 += paddingLength;
    patch.length2 += paddingLength;
  } else if (paddingLength > diffs[diffs.length - 1][1].length) {
    // Grow last equality.
    var extraLength = paddingLength - diffs[diffs.length - 1][1].length;
    diffs[diffs.length - 1][1] += nullPadding.substring(0, extraLength);
    patch.length1 += extraLength;
    patch.length2 += extraLength;
  }

  return nullPadding;
};


/**
 * Look through the patches and break up any which are longer than the maximum
 * limit of the match algorithm.
 * Intended to be called only from within patch_apply.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 */
diff_match_patch.prototype.patch_splitMax = function(patches) {
  var patch_size = this.Match_MaxBits;
  for (var x = 0; x < patches.length; x++) {
    if (patches[x].length1 <= patch_size) {
      continue;
    }
    var bigpatch = patches[x];
    // Remove the big old patch.
    patches.splice(x--, 1);
    var start1 = bigpatch.start1;
    var start2 = bigpatch.start2;
    var precontext = '';
    while (bigpatch.diffs.length !== 0) {
      // Create one of several smaller patches.
      var patch = new diff_match_patch.patch_obj();
      var empty = true;
      patch.start1 = start1 - precontext.length;
      patch.start2 = start2 - precontext.length;
      if (precontext !== '') {
        patch.length1 = patch.length2 = precontext.length;
        patch.diffs.push([DIFF_EQUAL, precontext]);
      }
      while (bigpatch.diffs.length !== 0 &&
             patch.length1 < patch_size - this.Patch_Margin) {
        var diff_type = bigpatch.diffs[0][0];
        var diff_text = bigpatch.diffs[0][1];
        if (diff_type === DIFF_INSERT) {
          // Insertions are harmless.
          patch.length2 += diff_text.length;
          start2 += diff_text.length;
          patch.diffs.push(bigpatch.diffs.shift());
          empty = false;
        } else if (diff_type === DIFF_DELETE && patch.diffs.length == 1 &&
                   patch.diffs[0][0] == DIFF_EQUAL &&
                   diff_text.length > 2 * patch_size) {
          // This is a large deletion.  Let it pass in one chunk.
          patch.length1 += diff_text.length;
          start1 += diff_text.length;
          empty = false;
          patch.diffs.push([diff_type, diff_text]);
          bigpatch.diffs.shift();
        } else {
          // Deletion or equality.  Only take as much as we can stomach.
          diff_text = diff_text.substring(0,
              patch_size - patch.length1 - this.Patch_Margin);
          patch.length1 += diff_text.length;
          start1 += diff_text.length;
          if (diff_type === DIFF_EQUAL) {
            patch.length2 += diff_text.length;
            start2 += diff_text.length;
          } else {
            empty = false;
          }
          patch.diffs.push([diff_type, diff_text]);
          if (diff_text == bigpatch.diffs[0][1]) {
            bigpatch.diffs.shift();
          } else {
            bigpatch.diffs[0][1] =
                bigpatch.diffs[0][1].substring(diff_text.length);
          }
        }
      }
      // Compute the head context for the next patch.
      precontext = this.diff_text2(patch.diffs);
      precontext =
          precontext.substring(precontext.length - this.Patch_Margin);
      // Append the end context for this patch.
      var postcontext = this.diff_text1(bigpatch.diffs)
                            .substring(0, this.Patch_Margin);
      if (postcontext !== '') {
        patch.length1 += postcontext.length;
        patch.length2 += postcontext.length;
        if (patch.diffs.length !== 0 &&
            patch.diffs[patch.diffs.length - 1][0] === DIFF_EQUAL) {
          patch.diffs[patch.diffs.length - 1][1] += postcontext;
        } else {
          patch.diffs.push([DIFF_EQUAL, postcontext]);
        }
      }
      if (!empty) {
        patches.splice(++x, 0, patch);
      }
    }
  }
};


/**
 * Take a list of patches and return a textual representation.
 * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
 * @return {string} Text representation of patches.
 */
diff_match_patch.prototype.patch_toText = function(patches) {
  var text = [];
  for (var x = 0; x < patches.length; x++) {
    text[x] = patches[x];
  }
  return text.join('');
};


/**
 * Parse a textual representation of patches and return a list of Patch objects.
 * @param {string} textline Text representation of patches.
 * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
 * @throws {!Error} If invalid input.
 */
diff_match_patch.prototype.patch_fromText = function(textline) {
  var patches = [];
  if (!textline) {
    return patches;
  }
  var text = textline.split('\n');
  var textPointer = 0;
  var patchHeader = /^@@ -(\d+),?(\d*) \+(\d+),?(\d*) @@$/;
  while (textPointer < text.length) {
    var m = text[textPointer].match(patchHeader);
    if (!m) {
      throw new Error('Invalid patch string: ' + text[textPointer]);
    }
    var patch = new diff_match_patch.patch_obj();
    patches.push(patch);
    patch.start1 = parseInt(m[1], 10);
    if (m[2] === '') {
      patch.start1--;
      patch.length1 = 1;
    } else if (m[2] == '0') {
      patch.length1 = 0;
    } else {
      patch.start1--;
      patch.length1 = parseInt(m[2], 10);
    }

    patch.start2 = parseInt(m[3], 10);
    if (m[4] === '') {
      patch.start2--;
      patch.length2 = 1;
    } else if (m[4] == '0') {
      patch.length2 = 0;
    } else {
      patch.start2--;
      patch.length2 = parseInt(m[4], 10);
    }
    textPointer++;

    while (textPointer < text.length) {
      var sign = text[textPointer].charAt(0);
      try {
        var line = decodeURI(text[textPointer].substring(1));
      } catch (ex) {
        // Malformed URI sequence.
        throw new Error('Illegal escape in patch_fromText: ' + line);
      }
      if (sign == '-') {
        // Deletion.
        patch.diffs.push([DIFF_DELETE, line]);
      } else if (sign == '+') {
        // Insertion.
        patch.diffs.push([DIFF_INSERT, line]);
      } else if (sign == ' ') {
        // Minor equality.
        patch.diffs.push([DIFF_EQUAL, line]);
      } else if (sign == '@') {
        // Start of next patch.
        break;
      } else if (sign === '') {
        // Blank line?  Whatever.
      } else {
        // WTF?
        throw new Error('Invalid patch mode "' + sign + '" in: ' + line);
      }
      textPointer++;
    }
  }
  return patches;
};


/**
 * Class representing one patch operation.
 * @constructor
 */
diff_match_patch.patch_obj = function() {
  /** @type {!Array.<!diff_match_patch.Diff>} */
  this.diffs = [];
  /** @type {?number} */
  this.start1 = null;
  /** @type {?number} */
  this.start2 = null;
  /** @type {number} */
  this.length1 = 0;
  /** @type {number} */
  this.length2 = 0;
};


/**
 * Emmulate GNU diff's format.
 * Header: @@ -382,8 +481,9 @@
 * Indicies are printed as 1-based, not 0-based.
 * @return {string} The GNU diff string.
 */
diff_match_patch.patch_obj.prototype.toString = function() {
  var coords1, coords2;
  if (this.length1 === 0) {
    coords1 = this.start1 + ',0';
  } else if (this.length1 == 1) {
    coords1 = this.start1 + 1;
  } else {
    coords1 = (this.start1 + 1) + ',' + this.length1;
  }
  if (this.length2 === 0) {
    coords2 = this.start2 + ',0';
  } else if (this.length2 == 1) {
    coords2 = this.start2 + 1;
  } else {
    coords2 = (this.start2 + 1) + ',' + this.length2;
  }
  var text = ['@@ -' + coords1 + ' +' + coords2 + ' @@\n'];
  var op;
  // Escape the body of the patch with %xx notation.
  for (var x = 0; x < this.diffs.length; x++) {
    switch (this.diffs[x][0]) {
      case DIFF_INSERT:
        op = '+';
        break;
      case DIFF_DELETE:
        op = '-';
        break;
      case DIFF_EQUAL:
        op = ' ';
        break;
    }
    text[x + 1] = op + encodeURI(this.diffs[x][1]) + '\n';
  }
  return text.join('').replace(/%20/g, ' ');
};

module.exports = diff_match_patch;