/* -*- Mode: js; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- /
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
/* global PAGE_INDEX_DEFAULT, InputMethods, KeyEvent, PromiseStorage */

'use strict';

/*
 * This latin input method provides four forms of input assistance:
 *
 * 1) word suggestions
 *
 * 2) auto correction
 *
 * 3) auto capitalization
 *
 * 4) punctuation assistance by converting space space to period space
 *    and by transposing space followed by punctuation.
 *
 * These input modifications are controlled by the type and inputmode
 * properties of the input element that has the focus. If inputmode is
 * "verbatim" then the input method does not modify the user's input in any
 * way. See getInputMode() for a description of input modes.
 *
 * TODO:
 *
 *  when deciding whether to autocorrect, if the first 2 choices are
 *    a prefix of one another, then consider the ratio of 1st to 3rd instead
 *    of 1st to second possibly?  If there different forms of the same word
 *    and that word is the most likely, then substitute it?
 *
 *  add a per-language settings-based list of customizable corrections?
 *
 *  Display an X icon in the suggestions line to give the user a way
 *  to dismiss an autocorrection?  (Easier than space, backspace, space).
 *
 *  Display a + icon in the suggestions line to give the user a way to
 *  add the current input to a personal word list so it doesn't get
 *  auto-corrected?
 *
 *  Use color somehow to indicate that a word is properly spelled?
 *
 *  Make the phone vibrate when it makes an automatic corection?
 */
(function() {
  // Register ourselves in the keyboard's set of input methods
  // The functions used here are all defined below
  InputMethods.latin = {
    init: init,
    activate: activate,
    deactivate: deactivate,
    displaysCandidates: displaysCandidates,
    click: click,
    select: select,
    dismissSuggestions: dismissSuggestions,
    setLayoutPage: setLayoutPage,
    setLayoutParams: setLayoutParams,
    setLanguage: setLanguage,
    stateChange: stateChange,
    generateNearbyKeyMap: findNearbyKeys
  };

  // This is the object that is passed to init().
  // We use the methods of this object to communicate with the keyboard.
  var keyboard;

  // If defined, this is a worker thread that produces word suggestions for us
  var worker;

  // PromiseStorage for access to indexedDB for user dictionary
  var dbStore;

  // These variables are the input method's state. Most of them are
  // passed to the activate() method or are derived in that method.
  var language;           // The user's language
  var inputMode;          // The inputmode we're using: see getInputMode()
  var capitalizing;       // Are we auto-capitalizing for this activation?
  var suggesting;         // Are we offering suggestions for this activation?
  var correcting;         // Are we auto-correcting user input?
  var punctuating;        // Are we offering punctuation assistance?
  var inputText;          // The input text
  var cursor;             // The insertion position
  var selection;          // The end of the selection, if there is one, or 0
  var lastSpaceTimestamp; // If the last key was a space, this is the timestamp
  var layoutParams;       // Parameters passed to setLayoutParams
  var nearbyKeyMap;       // Map keys to nearby keys
  var serializedNearbyKeyMap; // A stringified version of the above
  var idleTimer;          // Used by deactivate
  var suggestionsTimer;   // Used by updateSuggestions;
  var autoCorrection;     // Correction to make if next input is space
  var revertTo;           // Revert to this on backspace after autocorrect
  var revertFrom;         // Revert away from this on backspace
  var disableOnRevert;    // Do we disable auto correction when reverting?
  var correctionDisabled; // Temporarily diabled after reverting?
  var currentPage;        // The current layout page
  var gotNormalKey;       // Indicate if we got a normal key in an alt page

  // Terminate the worker when the keyboard is inactive for this long.
  var WORKER_TIMEOUT = 30000;  // 30 seconds of idle time

  // If we get an autorepeating key is sent to us, don't offer suggestions
  // for this long, until we're pretty certain that the autorepeat
  // has stopped.
  var AUTOREPEAT_DELAY = 250;

  // Some keycodes that we use
  var SPACE = KeyEvent.DOM_VK_SPACE;
  var BACKSPACE = KeyEvent.DOM_VK_BACK_SPACE;
  var RETURN = KeyEvent.DOM_VK_RETURN;
  var PERIOD = 46;
  var QUESTION = 63;
  var EXCLAMATION = 33;
  var COMMA = 44;
  var COLON = 58;
  var SEMICOLON = 59;
  var ATPERSAND = 64;
  var DOUBLEQUOTE = 34;
  var CLOSEPAREN = 41;
  // all whitespace characters
  // U+FFFC place holder is added to white space
  // this enables suggestions
  // when cursor is before place holder.
  var WS = /^[\s\ufffc]+$/;

  // word separator characters
  // U+FFFC is the placeholder character for non-text object
  var WORDSEP = /^[\s.,?!;:\ufffc]+$/;

  var DOUBLE_SPACE_TIME = 700; // ms between spaces to convert to ". "

  // Don't offer to autocorrect unless we're reasonably certain that the
  // user wants this correction. The first suggested word must be at least
  // this much more highly weighted than the second suggested word.
  var AUTO_CORRECT_THRESHOLD = 1.30;

  // Append a suffix when a suggestion was picked. In general, we
  // use space in Latin script as word divider.
  var SUGGESTION_SUFFIX = ' ';

  // If the length doesn't match between input and first suggestion.
  // The min. frequency the first suggestion needs to have if we turn it into
  // an autocorrect action
  var MIN_LENGTH_MISMATCH_THRESHOLD = 5;

  var USER_DICT_DB_NAME = 'UserDictLatin';

  // Predictions from user dictionary need to have weight larger than this in
  // order to take precedence over built-in dictionary predictions
  var USER_DICT_PREDICTION_BUMP_THRESHOLD = 1;

  // If this promise exists, that means we are
  // currently loading the new dictionary.
  var getDictionaryDataPromise = null;

  // The promise for getting user dictionary from PromiseStorage
  var getUserDictionaryBlobPromise = null;

  // keyboard.js calls this to pass us the interface object we need
  // to communicate with it
  function init(interfaceObject) {
    keyboard = interfaceObject;

    dbStore = new PromiseStorage(USER_DICT_DB_NAME);
    dbStore.start();
  }

  // Given the type property and inputmode attribute of a form element,
  // this function returns the inputmode that this IM should use. The
  // return value will be one of these strings:
  //
  //   'verbatim': don't alter the user's input at all
  //   'latin': offer word suggestions/corrections, but no capitalization
  //   'latin-prose': offer word suggestions and capitalization
  //
  function getInputMode(type, mode) {
    // For text, textarea and search types, use the requested inputmode
    // if it is valid and supported except numeric/digit mode. For
    // numeric/digit mode, we return verbatim since no typing assitance
    // is required. Otherwise default to latin for text and search and to
    // latin-prose for textarea. For all other form fields, use verbatim mode
    // so we never alter input.
    switch (type) {
      case 'text':
      case 'textarea':
      case 'search':
        switch (mode) {
          case 'verbatim':
          case 'latin':
          case 'latin-prose':
            return mode;
          case 'numeric':
          case 'digit':
            return 'verbatim';
          default:
            return (type === 'textarea') ? 'latin-prose' : 'latin';
        }
        break;
      default:
        return 'verbatim';
    }
  }

  // This gets called whenever the keyboard pops up to tell us everything
  // we need to provide useful typing assistance. It also gets called whenever
  // the user taps on an input field to move the cursor. That means that there
  // may be multiple calls to activate() without calls to deactivate between
  // them.
  function activate(lang, state, options) {
    inputMode = getInputMode(state.type, state.inputmode);
    inputText = state.text;
    cursor = state.selectionStart;
    if (state.selectionEnd > state.selectionStart) {
      selection = state.selectionEnd;
    } else {
      selection = 0;
    }

    // Figure out what kind of input assistance we're providing for this
    // activation.
    capitalizing = punctuating = (inputMode === 'latin-prose');
    suggesting = (options.suggest && inputMode !== 'verbatim');
    correcting = (options.correct && inputMode !== 'verbatim');

    // Some layouts (like French) need to disable punctuation autocorrection
    // all the time.
    if (options.correctPunctuation === false) {
      punctuating = false;
    }

    // Reset our state
    lastSpaceTimestamp = 0;
    autoCorrection = null;
    revertTo = revertFrom = '';
    disableOnRevert = false;
    correctionDisabled = false;
    currentPage = PAGE_INDEX_DEFAULT;
    gotNormalKey = false;

    // The keyboard isn't idle anymore, so clear the timer
    if (idleTimer) {
      clearTimeout(idleTimer);
      idleTimer = null;
    }

    // Start off with the correct capitalization
    updateCapitalization();

    // Get user dictionary blob.
    getUserDictionaryBlobPromise =
      dbStore.getItem('dictblob').then(function(blob) {
      // If worker is there, tell it we have a (new) user dictionary blob,
      // since setLanguage() may be bypassed due to language not changing.
      // (User dictionary is langauge-neutral.)
      // Do pass the argument if blob is undefined (no user dictionary words),
      // Since the worker needs to know if user has deleted all words.
      // Worker will bypass UserDictionary prediction as needed.
      // |undefined| can't be Transferred so we'll need to check for it.
      if (worker) {
        worker.postMessage({
          cmd: 'setUserDictionary',
          args: [blob]
        }, typeof blob === 'undefined' ? undefined : [blob]);
      }

      return blob;
    })['catch'](function(e) {
      e && console.error('latin.js', e);
    });

    // If we are going to offer suggestions, ensure that there is a worker
    // thread created and that it knows what language we're using, and then
    // start things off by requesting a first batch of suggestions.
    if (suggesting || correcting) {
      if (!worker || lang !== language) {
        setLanguage(lang);  // This calls updateSuggestions
      } else {
        updateSuggestions();
      }
    }
  }

  function deactivate() {
    if (!worker || idleTimer) {
      return;
    }
    idleTimer = setTimeout(terminateWorker, WORKER_TIMEOUT);
  }

  function terminateWorker() {
    if (idleTimer) {
      clearTimeout(idleTimer);
      idleTimer = null;
    }
    if (worker) {
      worker.terminate();
      worker = null;
      keyboard.sendCandidates([]); // Clear any displayed suggestions
      autoCorrection = null;       // and forget any pending correction.
    }
  }

  function setLanguage(newlang) {
    // If there is no worker and no language, or if there is a worker and
    // the language has not changed, then there is nothing to do here.
    if ((!worker && !newlang) || (worker && newlang === language)) {
      return;
    }

    language = newlang;

    // If there is a worker, and no new language, then kill the worker
    if (worker && !newlang) {
      terminateWorker();
      return;
    }

    // Built-in dictionary is a hard requirement, i.e. if it is undefined, we
    // reset ourselves.
    // User dictionary is not a hard requirement. We swallow any abnormal
    // situation there at activate(), to make sure Promise.all() doesn't fail
    // on its rejection.
    getDictionaryDataPromise = Promise.all([
      keyboard.getData('dictionaries/' + newlang + '.dict'),
      getUserDictionaryBlobPromise
    ]);

    getDictionaryDataPromise
      .then(function(values) {
        getDictionaryDataPromise = null;

        var builtInDict = values[0];
        var userDict = values[1];

        if (!builtInDict) {
          console.error(
            'latin.js: dictionary is specified but can\'t be loaded.');
          language = undefined;

          terminateWorker();
          return;
        }

        setLanguageSync(newlang, builtInDict, userDict);
      })['catch'](function(e) { // workaround gjslint error
        e && console.error('latin.js', e);

        getDictionaryDataPromise = null;
        language = undefined;
        terminateWorker();
      })['catch'](function(e) { e && console.error(e); });
  }

  function setLanguageSync(newlang, dictData, userDict) {
    // If we get here, then we have to create a worker and set its language
    // or change the language of an existing worker.
    if (!worker) {
      // If we haven't created the worker before, do it now
      worker = new Worker('js/imes/latin/worker.js');
      if (layoutParams && nearbyKeyMap) {
        worker.postMessage({ cmd: 'setNearbyKeys', args: [nearbyKeyMap]});
      }

      worker.onmessage = function(e) {
        switch (e.data.cmd) {
        case 'log':
          console.log(e.data.message);
          break;
        case 'error':
          console.error(e.data.message);
          // If the error was a result of our setLanguage call, then
          // kill the worker because it can't do anything without
          // a valid dictionary.
          if (e.data.message.startsWith('setLanguage')) {
            terminateWorker();
          }
          break;
        case 'predictions':
          // The worker is suggesting words: ask the keyboard to display them
          handleSuggestions(e.data.input, e.data.suggestions);
          break;
        }
      };
    }

    // Tell the worker what language we're using and also pass the dictionary
    // data.
    // |undefined| can't be Transferred so we'll need to check for it.
    worker.postMessage({
      cmd: 'setLanguage',
      args: [language, dictData, userDict]
    }, typeof userDict === 'undefined' ? [dictData] : [dictData, userDict]);

    // And now that we've changed the language, ask for new suggestions
    updateSuggestions();
  }

  function displaysCandidates() {
    // If we are suggesting for the language,
    // we should always display the condidate panel.
    return !!(suggesting && language);
  }

  /*
   * The keyboard calls this method to tell us about user input.
   *
   * What we do with the input depends on various things:
   *
   * - whether we are suggesting, correcting, punctuating and/or capitalizing:
   *   these are controlled by settings, input mode and input type
   *
   * - whether there is a selected region in the input field
   *
   * - whether there is an auto-correction ready (when input is space
   *   or punctuation).
   *
   * - whether the last action was an autocorrection (when input is backspace)
   *
   * - the cursor position (affects suggestions, capitalization, etc.)
   *
   * If there is a selection just handle simple insertions and deletions
   * with no extra behavior. (I think)
   *
   * If input is a space or punctuation:
   *
   *  If there is a autocorrection ready, and we are correcting and
   *  the cursor is at the end of a word, make the correction
   *
   *  If the previous character is a space, fix the punctuation. Note that
   *  this only works for a subset of the punctuation characters.
   *
   *  Otherwise just insert it.
   *
   *  If we're correcting and corrections are temporarily diabled, turn them
   *  back on.
   *
   * If input is a backspace:
   *
   *  If we just did an auto-correction, revert it and turn off corrections
   *  until the next space or punctuation character.
   *
   *  If we just inserted a suggested word that the user selected, revert
   *  the insertion, but don't disable autocorrect.
   *
   *  Should we undo punctuation corrections this way, too?
   *
   *  Otherwise, just delete the character before the cursor
   *
   * For any other input character, just insert it.
   *
   * Reset the backspace reversion state
   *
   * Update the capitalization state, if we're capitalizing
   */
  function click(keyCode, repeat) {
    // If the key is anything other than a backspace, forget about any
    // previous changes that we would otherwise revert.
    if (keyCode !== BACKSPACE) {
      revertTo = revertFrom = '';
      disableOnRevert = false;
    }

    var handler;

    if (selection) {
      // If there is selected text, don't do anything fancy here.
      handler = handleKey(keyCode);
    } else {
      switch (keyCode) {
        case SPACE:     // This list of characters matches the WORDSEP regexp
        case RETURN:
        case PERIOD:
        case QUESTION:
        case EXCLAMATION:
        case COMMA:
        case COLON:
        case SEMICOLON:
        case DOUBLEQUOTE:
        case CLOSEPAREN:
          // These keys may trigger word or punctuation corrections
          handler = handleCorrections(keyCode);
          correctionDisabled = false;
          break;

        case BACKSPACE:
          handler = handleBackspace(repeat);
          break;

        default:
          handler = handleKey(keyCode);
      }
    }

    // After the next key is resolved, we could update the state here.
    return handler.then(function() {
      // handleCorrections() above or it is now out of date, so clear it
      // so it doesn't get used later
      autoCorrection = null;

      // And update the keyboard capitalization state, if necessary
      updateCapitalization();

      // If we're offering suggestions, ask the worker to make them now
      updateSuggestions(repeat);

      // Exit symbol layout mode after space or return key is pressed.
      var isNonDefaultPage = currentPage !== PAGE_INDEX_DEFAULT;
      var isSpace = keyCode === SPACE;
      var isReturn = keyCode === RETURN;
      var isAtpersand = keyCode === ATPERSAND;
      var keyResetLayout = (isSpace && gotNormalKey) || isReturn || isAtpersand;
      if (isNonDefaultPage && keyResetLayout) {
        keyboard.setLayoutPage(PAGE_INDEX_DEFAULT);
      }

      // Next space key will change the layout
      if (keyCode !== SPACE) {
        gotNormalKey = true;
      }

      lastSpaceTimestamp = (keyCode === SPACE) ? Date.now() : 0;
    }, function() {
      // the previous sendKey or replaceSurroundingText has been rejected,
      // No need to update the state.
    })['catch'](function(e) { // ['catch'] for gjslint error
      // Print the error and make sure inputSequencePromise always resolves.
      console.error(e);
    });
  }

  // Handle any key (including backspace) and do the right thing even if
  // there is a selection in the text field. This method does not perform
  // auto-correction or auto-punctuation.
  function handleKey(keycode, repeat) {
    // Generate the key event
    return keyboard.sendKey(keycode, repeat).then(function() {
      // First, update our internal state
      if (keycode === BACKSPACE) {
        if (selection) {
          // backspace while a region is selected erases the selection
          // and leaves the cursor at the selection start
          inputText = inputText.substring(0, cursor) +
            inputText.substring(selection);
          selection = 0;
        } else if (cursor > 0) {
          cursor--;
          inputText = inputText.substring(0, cursor) +
            inputText.substring(cursor + 1);

          // If we have temporarily disabled auto correction for the current
          // word and we've just backspaced over the entire word, then we can
          // re-enabled it again
          if (correctionDisabled && !wordBeforeCursor()) {
            correctionDisabled = false;
          }
        }
      } else {
        if (selection) {
          inputText =
            inputText.substring(0, cursor) +
            String.fromCharCode(keycode) +
            inputText.substring(selection);
          selection = 0;
        } else {
          inputText =
            inputText.substring(0, cursor) +
            String.fromCharCode(keycode) +
            inputText.substring(cursor);
        }
        cursor++;
      }
    }, function() {
      // sendKey got canceled, keep state the same
    });
  }

  // Assuming that the word before the cursor is oldWord, send a
  // minimal number of key events to change it to newWord in the text
  // field. Also update our internal state to match the new textfield
  // content and cursor position.
  function replaceBeforeCursor(oldWord, newWord) {
    var oldWordLen = oldWord.length;
    var replPromise =
      keyboard.replaceSurroundingText(newWord, -oldWordLen, oldWordLen);

    return replPromise.then(function() {
      // Now update internal state
      inputText =
        inputText.substring(0, cursor - oldWordLen) +
        newWord +
        inputText.substring(cursor);
      cursor += newWord.length - oldWordLen;
    });
  }

  // If we just did auto correction or auto punctuation, then backspace
  // should undo it. Otherwise it is just an ordinary backspace.
  function handleBackspace(repeat) {
    // If we made a correction and haven't changed it at all yet,
    // then revert it.
    var len = revertFrom ? revertFrom.length : 0;
    if (len && cursor >= len &&
        inputText.substring(cursor - len, cursor) === revertFrom) {

      // Revert the content of the text field
      return replaceBeforeCursor(revertFrom, revertTo).then(function() {
        // If the change we just reverted was an auto-correction then
        // temporarily disable auto correction until the next space
        if (disableOnRevert) {
          correctionDisabled = true;
        }

        revertFrom = revertTo = '';
        disableOnRevert = false;
      });
    }
    else {
      return handleKey(BACKSPACE, repeat);
    }
  }

  // This function is called when the user types space, return or a punctuation
  // character. It performs auto correction or auto punctuation or just
  // inserts the character.
  function handleCorrections(keycode) {
    if (correcting && autoCorrection && !correctionDisabled && atWordEnd() &&
        wordBeforeCursor() !== autoCorrection) {
      return autoCorrect(keycode);
    }
    else if (punctuating && cursor >= 2 &&
             isWhiteSpace(inputText[cursor - 1]) &&
             inputText[cursor - 1].charCodeAt(0) !== KeyEvent.DOM_VK_RETURN &&
             !WORDSEP.test(inputText[cursor - 2]))
    {
      return autoPunctuate(keycode);
    }
    else {
      return handleKey(keycode);
    }
  }

  // Perform an autocorrection. Assumes that all pre-conditions for
  // auto-correction have been met.
  function autoCorrect(keycode) {
    // Get the word before the cursor
    var currentWord = wordBeforeCursor();

    // Figure out the auto correction text
    var newWord = autoCorrection;

    // Make the correction
    return replaceBeforeCursor(currentWord, newWord).then(function() {
      // Remember the change we just made so we can revert it if the
      // user types backspace
      revertTo = currentWord;
      revertFrom = newWord;
      disableOnRevert = true;
    }).then(function() {
      // Send the keycode as separate key event because it may get canceled
      return handleKey(keycode).then(function() {
        revertFrom += String.fromCharCode(keycode);
      });
    });
  }

  // Auto punctuate, converting space punctuation to punctuation space
  // or converting space space to period space if the two spaces were
  // close enough together. Assumes that pre-conditions for auto punctuation
  // have been met.
  function autoPunctuate(keycode) {
    switch (keycode) {
    case SPACE:
      if (Date.now() - lastSpaceTimestamp < DOUBLE_SPACE_TIME) {
        return fixPunctuation(PERIOD, SPACE);
      } else {
        return handleKey(keycode);
      }
      break;

    case PERIOD:
    case QUESTION:
    case EXCLAMATION:
    case COMMA:
      return fixPunctuation(keycode);

    default:
      // colon and semicolon don't auto-punctuate because they're
      // used after spaces for smileys.
      return handleKey(keycode);
    }

    // In both the space space and the space period case we call this function
    // Second argument is the character reverting to if cancelling auto
    // punctuation
    // If the second argument is omitted, assume it is the same as the first
    function fixPunctuation(keycode, revertToKeycode) {
      return keyboard.sendKey(BACKSPACE)
        .then(function() {
          return keyboard.sendKey(keycode);
        })
        .then(function() {
          return keyboard.sendKey(SPACE);
        })
        .then(function() {
          var newtext = String.fromCharCode(keycode) + ' ';
          inputText = inputText.substring(0, cursor - 1) +
            newtext +
            inputText.substring(cursor);
          cursor++;

          // Remember this change so we can revert it on backspace
          revertTo = ' ' + String.fromCharCode(revertToKeycode || keycode);
          revertFrom = newtext;
          disableOnRevert = false;
        });
    }
  }

  // When the worker thread sends us a batch of suggestions, deal
  // with them here.
  function handleSuggestions(input, suggestions) {
    // If we didn't get any suggestions just send the empty array to
    // clear any suggestions that are currently displayed. Do the same
    // if the word before the cursor has changed since we requested
    // these suggestions. That is, if the user has typed faster than we could
    // offer suggestions, ignore them.
    if (suggestions.length === 0 || wordBeforeCursor() !== input) {
      keyboard.sendCandidates([]); // Clear any displayed suggestions
      return;
    }

    // If input is ucase, then make all suggestions ucase as well.
    // Ignore input.length of 1, it never gets autocorrected anyway
    if (input.length > 1 && isUpperCase(input)) {
      for (var ix = 0; ix < suggestions.length; ix++) {
        suggestions[ix][0] = suggestions[ix][0].toUpperCase();
      }
    }

    // We show no more than 3 suggestions; but we'd like to keep at least one
    // suggestion from user dictionary, if its weight is less than 1. However,
    // that suggestion can still be dropped if it matches the user input.
    // User dictionary suggestion is identified by suggestion[2] === true.

    var inputDefinedInUserDict = false;
    // See if the user's input is a valid word on the list of suggestions
    var inputIsSuggestion = false;
    var inputWeight = 0;
    var inputIndex;
    for (inputIndex = 0; inputIndex < suggestions.length; inputIndex++) {
      if (suggestions[inputIndex][0] === input) {
        inputIsSuggestion = true;
        inputDefinedInUserDict = !!suggestions[inputIndex][2];
        inputWeight = suggestions[inputIndex][1];
        break;
      }
    }

    // We never want to display the user's input as a suggestion so
    // remove it from the list if it is there.
    if (inputIsSuggestion) {
      suggestions.splice(inputIndex, 1);
    }

    // If we don't have any suggestions we're done
    if (suggestions.length === 0) {
      keyboard.sendCandidates([]); // Clear any displayed suggestions
      return;
    }

    //
    // If there was an exact match for the user input in the suggestions
    // it has already been removed. Now we need to loop through again
    // looking for approximate matches and bump those to the start of the
    // list. A word is an approximate match if all the letters match
    // when we ignore case, apostrophes and hyphens. The assumption here
    // is that the user is not expected to have to use the shift key or
    // the alternate forms menu or the punctuation menus. If they type all
    // the right letters, a matching word should have higher priority than
    // a non-matching word. In particular this code ensures that "im" gets
    // autocorrected to "I'm" instead of "in" and "id" gets autocorrected to
    // "I'd" instead of "is". (Bug 1164421)
    //
    // XXX In English, apostrophes and hyphens are the only punctuation that
    // commonly occurs within words. If other wordlists include other
    // punctuation, we may need to add them to the regular expression below.
    //
    // XXX In the future, we might want to generalize this to consider
    // accented forms when looking for approximate matches. If "jose"
    // was autocorrecting to "hose" instead of "José", for example, then
    // we might need to extend the definition of an approximate match here.
    // For now, I don't have any examples of corrections that are coming
    // out incorrectly for accented letters, though, so am keeping this
    // simple.
    //
    // We loop backward through the suggestions, bumping any approximate
    // match to the start of the list. This ensures that the highest ranked
    // approximate match comes before lower ranked approximate matches,
    // and all approximate matches come before non-matching suggestions.
    //
    var i = suggestions.length - 1;
    var approximateMatches = 0;  // how many approximate matches we've bumped
    var lcInput = input.toLowerCase();
    while(i > approximateMatches) {
      if (suggestions[i][0].toLowerCase().replace(/[-']/g, '') === lcInput) {
        // If this suggestion was an approximate match for the users input..
        var match = suggestions[i];  // get the match,
        suggestions.splice(i, 1);    // remove it,
        suggestions.unshift(match);  // and put it back at the start.
        approximateMatches++;        // Increment this instead of i-- here.
      }
      else {
        i--;       // if not an approximate match move to next suggestion
      }
    }

    // Make sure we have no more than three words
    if (suggestions.length > 3) {
      // We want to keep at least a user dictionary word here (if the heighest
      // user dictionary word has weight >= 1).
      // If for the first two suggestions we see one from user dictionary, or
      // if we dropped a user dict suggestion above (matching user input),
      // we can just append the third suggestion.
      // Otherwise, we'll need to search through the remaining suggestions and
      // append the first user-dict suggestion we find (that has weight >= 1);
      // if we can't find any suitable user-dict suggestions, we just append
      // the third suggestion (i.e. whatever that has the largest frequency
      // in the remaining suggestions).

      var trimmedSuggestions = suggestions.slice(0, 2);

      var userDictionaryWordEncountered =
        inputDefinedInUserDict ||
        (!!suggestions[0][2]) ||
        (!!suggestions[1][2]);

      if (userDictionaryWordEncountered) {
        trimmedSuggestions.push(suggestions[2]);
      } else {
        userDictionaryWordEncountered =
          suggestions.slice(2).some(function(suggestion) {
            if (suggestion[2] && suggestion[1] >=
                USER_DICT_PREDICTION_BUMP_THRESHOLD) {
              trimmedSuggestions.push(suggestion);
              return true;
            } else {
              return false;
            }
          });

        if (!userDictionaryWordEncountered) {
          trimmedSuggestions.push(suggestions[2]);
        }
      }

      suggestions = trimmedSuggestions;
    }

    // Now get an array of just the suggested words
    var words = suggestions.map(function(x) { return x[0]; });

    // see whether words[0] and input have same length
    var lengthMismatch;
    switch (Math.abs(input.length - words[0].length)) {
    case 0:
      lengthMismatch = false;
      break;
    case 1:
      lengthMismatch = suggestions[0][1] < MIN_LENGTH_MISMATCH_THRESHOLD;
      break;
    default:
      lengthMismatch = true;
      break;
    }

    // Decide whether the first word is going to be an autocorrection.
    // If the user's input is already a valid word, then don't
    // autocorrect unless the first suggested word is more common than
    // the input.  Note that if the first suggested word has a higher
    // weight even after whatever penalty is applied for not matching
    // exactly, then it is significantly more common than the actual input.
    // (This rule means that "ill" will autocorrect to "I'll",
    // "wont" to "won't", etc.)
    // Also, don't autocorrect if the input is a single letter and
    // the first word is more than a single letter. (But still autocorrect
    // "i" to "I")
    if (correcting &&
        !correctionDisabled &&
        (!inputIsSuggestion ||
          suggestions[0][1] > inputWeight * AUTO_CORRECT_THRESHOLD) &&
        (input.length > 1 || words[0].length === 1) &&
        !lengthMismatch) {
      // Remember the word to use if the next character is a space.
      autoCorrection = words[0];
      // Mark the auto-correction so the renderer can highlight it
      words[0] = '*' + words[0];
    }
    else {
      autoCorrection = null;
    }

    keyboard.sendCandidates(words);
  }

  //
  // If the user selects one of the suggestions offered by this input method
  // the keyboard calls this method to tell us it has been selected.
  // We have to delete the current word, insert this new word, and
  // update our internal state to match.
  //   word: the text displayed as the suggestion, might contain ellipsis
  //   data: the actual data we need to output
  //
  function select(word, data) {
    var oldWord = wordBeforeCursor();
    // A word divider is expected to append to the word when the
    // suggestion is selected.
    var newWord = data + SUGGESTION_SUFFIX;

    // The user has selected a suggestion, so we don't need to display
    // them anymore. Note that calling this function resets all the
    // autocorrect state. We'll reset much of that state below after
    // the word has been replace with the new one.
    dismissSuggestions();

    return replaceBeforeCursor(oldWord, newWord).then(function() {
      // Remember the change we just made so we can revert it if the
      // next key is a backspace. If the word is reverted we disable
      // autocorrection for this word.
      revertFrom = newWord;
      revertTo = oldWord;

      // And update the keyboard capitalization state, if necessary
      updateCapitalization();
    });
  }

  function dismissSuggestions() {
    // Clear the list of candidates
    keyboard.sendCandidates([]);

    // Get rid of any autocorrection that is pending and reset the rest
    // of our state, too.
    lastSpaceTimestamp = 0;
    autoCorrection = null;
    revertTo = revertFrom = '';
    disableOnRevert = false;
    correctionDisabled = false;
  }

  function setLayoutPage(page) {
    if (currentPage === PAGE_INDEX_DEFAULT) {
      // we don't want to reset gotNormalKey if we're already in an alternative
      // layout.
      gotNormalKey = false;
    }

    currentPage = page;
  }

  function setLayoutParams(params) {
    layoutParams = params;

    // We don't need to update the nearbyKeys when using number/digit layout.
    if (inputMode === 'verbatim') {
      return;
    }

    // XXX We call nearbyKeys() every time the keyboard pops up.
    // Maybe it would be better to compute it once in keyboard.js and
    // cache it.

    // We get called every time the keyboard case changes. Don't bother
    // passing this data to the prediction engine if nothing has changed.
    var newmap = findNearbyKeys(params);
    var serialized = JSON.stringify(newmap);
    if (serialized === serializedNearbyKeyMap) {
      return;
    }

    nearbyKeyMap = newmap;
    serializedNearbyKeyMap = serialized;
    if (worker) {
      worker.postMessage({ cmd: 'setNearbyKeys', args: [nearbyKeyMap]});
      // Ask for new suggestions since the new layout may affect them.
      // (When switching from QWERTY to Dvorak, e.g.)
      updateSuggestions();
    }
  }

  function findNearbyKeys(layout) {
    var nearbyKeys = {};
    var keys = layout.keyArray;

    // Make sure that all the keycodes are lowercase, not uppercase
    for (var p = 0; p < keys.length; ++p) {
      keys[p].code =
        String.fromCharCode(keys[p].code).toLowerCase().charCodeAt(0);
    }

    // For each key, calculate the keys nearby.
    for (var n = 0; n < keys.length; ++n) {
      var key1 = keys[n];
      if (SpecialKey(key1)) {
        continue;
      }
      var nearby = {};
      for (var m = 0; m < keys.length; ++m) {
        if (m === n) {
          continue; // don't compare a key to itself
        }
        var key2 = keys[m];
        if (SpecialKey(key2)) {
          continue;
        }
        var d = distance(key1, key2);
        if (d !== 0) {
          nearby[key2.code] = d;
        }
      }
      nearbyKeys[key1.code] = nearby;
    }

    return nearbyKeys;

    // Compute the inverse square distance between the center point of
    // two keys, using the radius of the key (where radius is defined
    // as the distance from the center of key1 to a corner of key1)
    // as the unit of measure. If the distance is greater than 2.5
    // times the radius return 0 instead.
    function distance(key1, key2) {
      var cx1 = key1.x + key1.width / 2;
      var cy1 = key1.y + key1.height / 2;
      var cx2 = key2.x + key2.width / 2;
      var cy2 = key2.y + key2.height / 2;
      var radius = Math.sqrt(key1.width * key1.width / 4 +
                             key1.height * key1.height / 4);

      var dx = (cx1 - cx2) / radius;
      var dy = (cy1 - cy2) / radius;
      // We calculate distance from center to center, but this gives
      // too high of a penalty to vertical keys, so normalize dx/dy
      dy /= (key1.height / key1.width);
      var distanceSquared = dx * dx + dy * dy;

      if (distanceSquared < 1) {
        console.warn('Keys too close',
                     JSON.stringify(key1), JSON.stringify(key2));
        return 0;
      }

      if (distanceSquared > 2.5 * 2.5) {
        return 0;
      } else {
        return 1 / distanceSquared;
      }
    }

    // Determine whether the key is a special character or a regular letter.
    // Special characters include backspace (8), return (13), and space (32).
    function SpecialKey(key) {
      switch (key.code) {
      case 0:
      case KeyEvent.DOM_VK_BACK_SPACE:
      case KeyEvent.DOM_VK_CAPS_LOCK:
      case KeyEvent.DOM_VK_RETURN:
      case KeyEvent.DOM_VK_ALT:
      case KeyEvent.DOM_VK_SPACE:
        return true;
      default: // anything else is not special
        return false;
      }
    }
  }

  function updateSuggestions(repeat) {
    // If the user hasn't enabled suggestions, or if they're not appropriate
    // for this input type, or are turned off by the input mode, do nothing
    if (!suggesting && !correcting) {
      return;
    }

    // If there is no dictionary language, do nothing
    if (!language) {
      return;
    }

    // If we are still loading the dictionary, do nothing
    if (getDictionaryDataPromise) {
      return;
    }

    // This shouldn't happen -- we previously allow layout to be selected
    // without the dictionary, but the build script has since prevent that.
    if (!worker) {
      console.error('latin.js: called updateSuggestions() w/o an worker.');

      return;
    }

    // If we deferred suggestions because of a key repeat, clear that timer
    if (suggestionsTimer) {
      clearTimeout(suggestionsTimer);
      suggestionsTimer = null;
    }

    // If we're still repeating, reset the repeat timer.
    if (repeat) {
      suggestionsTimer = setTimeout(updateSuggestions, AUTOREPEAT_DELAY);
      return;
    }

    // If we're not at the end of a word, we want to clear any suggestions
    // that might already be there
    if (!atWordEnd()) {
      if (suggesting) {
        keyboard.sendCandidates([]);
      }
      return;
    }

    var word = wordBeforeCursor();
    if (word) { // Defend against bug 879572 even though I can't reproduce it
      worker.postMessage({cmd: 'predict', args: [word]});
    }
  }

  function updateCapitalization() {
    // If either the input mode or the input type is one that doesn't
    // want capitalization, then don't alter the state of the keyboard.
    // We however want to reset the shift key state triggered by the user,
    // regardless of the layout page the user is currently on.
    if (!capitalizing) {
      keyboard.setUpperCase({
        isUpperCase: false
      });
      return;
    }

    // Set the keyboard to uppercase or lowercase depending
    // on the text around the cursor:
    //
    // 1) If the cursor is at the start of the field: uppercase
    //
    // 2) If there is a non space character immediately before the cursor:
    //    lowercase
    //
    // 3) If the first non-space character before the cursor is . ? or !:
    //    uppercase
    //
    // 4) Otherwise: lowercase
    //
    if (cursor === 0) {
      keyboard.setUpperCase({
        isUpperCase: true
      });
    }
    else if (!isWhiteSpace(inputText.substring(cursor - 1, cursor))) {
      keyboard.setUpperCase({
        isUpperCase: false
      });
    }
    else if (atSentenceStart()) {
      keyboard.setUpperCase({
        isUpperCase: true
      });
    }
    else {
      keyboard.setUpperCase({
        isUpperCase: false
      });
    }
  }

  // Return true if all characters of s are uppercase. A character
  // is uppercase if toLowerCase() on that character is returns something
  // different than the character
  function isUpperCase(s) {
    var lc = s.toLowerCase();
    for (var i = 0, n = s.length; i < n; i++) {
      if (s[i] === lc[i]) {
        return false;
      }
    }
    return true;
  }

  function isWhiteSpace(s) {
    return WS.test(s);
  }

  // We only offer suggestions if the cursor is at the end of a word
  // The character before the cursor must be a word character and
  // the cursor must be at the end of the input or the character after
  // must be whitespace.  If there is a selection we never return true.
  function atWordEnd() {
    // If there is a selection we never want suggestions
    if (selection) {
      return false;
    }

    // If we're not at the end of the line and the character after the
    // cursor is not whitespace, don't offer a suggestion
    // Note that we purposely use WS here, not WORDSEP.
    if (cursor < inputText.length && !WS.test(inputText[cursor])) {
      return false;
    }

    // If the cursor is at position 0 then we're not at the end of a word
    if (cursor <= 0) {
      return false;
    }

    // We're at the end of a word if the character before the cursor is
    // not a word separator character
    var c = inputText[cursor - 1];
    return !WORDSEP.test(c);
  }

  // Get the word before the cursor. Assumes that atWordEnd() is true
  function wordBeforeCursor() {
    for (var firstletter = cursor - 1; firstletter >= 0; firstletter--) {
      if (WORDSEP.test(inputText[firstletter])) {
        break;
      }
    }
    firstletter++;

    // firstletter is now the position of the start of the word and cursor is
    // the end of the word
    return inputText.substring(firstletter, cursor);
  }

  function atSentenceStart() {
    var i = cursor - 1;

    if (i === -1) {   // This is the empty string case
      return true;
    }

    // Verify that the position before the cursor is whitespace
    if (!isWhiteSpace(inputText[i--])) {
      return false;
    }
    // Now skip any additional whitespace before that
    while (i >= 0 && isWhiteSpace(inputText[i])) {
      i--;
    }

    if (i < 0) {    // whitespace all the way back to the end of the string
      return true;
    }

    var c = inputText[i];
    return c === '.' || c === '?' || c === '!';
  }

  function stateChange(state) {
    // TODO: Remove this and actually compare the state properties with
    // the internal states.
    if (state.ownAction) {
      return;
    }

    cursor = state.selectionStart;
    selection = (state.selectionEnd > state.selectionStart) ?
      state.selectionEnd : 0;
    inputText = state.text;

    dismissSuggestions();
    updateSuggestions();
  }

  if (!('PAGE_INDEX_DEFAULT' in window)) {
    window.PAGE_INDEX_DEFAULT = null;
  }
}());