var keyCodes = { ESC: 27, backspace: 8, deleteKey: 46, enter: 13, space: 32, shiftKey: 16, f1: 112, f12: 123};
var keyNames = { 37: "left", 38: "up", 39: "right", 40: "down" }

// This is a mapping of the incorrect keyIdentifiers generated by Webkit on Windows during keydown events to
// the correct identifiers, which are correctly generated on Mac. We require this mapping to properly handle
// these keys on Windows. See https://bugs.webkit.org/show_bug.cgi?id=19906 for more details.
var keyIdentifierCorrectionMap = {
  "U+00C0": ["U+0060", "U+007E"], // `~
  "U+00BD": ["U+002D", "U+005F"], // -_
  "U+00BB": ["U+003D", "U+002B"], // =+
  "U+00DB": ["U+005B", "U+007B"], // [{
  "U+00DD": ["U+005D", "U+007D"], // ]}
  "U+00DC": ["U+005C", "U+007C"], // \|
  "U+00BA": ["U+003B", "U+003A"], // ;:
  "U+00DE": ["U+0027", "U+0022"], // '"
  "U+00BC": ["U+002C", "U+003C"], // ,<
  "U+00BE": ["U+002E", "U+003E"], // .>
  "U+00BF": ["U+002F", "U+003F"] // /?
};

var platform;
if (navigator.userAgent.indexOf("Mac") != -1)
  platform = "Mac";
else if (navigator.userAgent.indexOf("Linux") != -1)
  platform = "Linux";
else
  platform = "Windows";

function getKeyChar(event) {
    // Not a letter
    if (event.keyIdentifier.slice(0, 2) != "U+") {
        // Named key
        if (keyNames[event.keyCode]) {
          return keyNames[event.keyCode];
        }
        // F-key
        if (event.keyCode >= keyCodes.f1 && event.keyCode <= keyCodes.f12) {
          return "f" + (1 + event.keyCode - keyCodes.f1);
        }
        return "";
    }
    var keyIdentifier = event.keyIdentifier;
    // On Windows, the keyIdentifiers for non-letter keys are incorrect. See
    // https://bugs.webkit.org/show_bug.cgi?id=19906 for more details.
    if ((platform == "Windows" || platform == "Linux") && keyIdentifierCorrectionMap[keyIdentifier]) {
      correctedIdentifiers = keyIdentifierCorrectionMap[keyIdentifier];
      keyIdentifier = event.shiftKey ? correctedIdentifiers[0] : correctedIdentifiers[1];
    }
    var unicodeKeyInHex = "0x" + keyIdentifier.substring(2);
    return String.fromCharCode(parseInt(unicodeKeyInHex)).toLowerCase();
}

function isPrimaryModifierKey(event) {
  if (platform == "Mac")
    return event.metaKey;
  else
    return event.ctrlKey;
}

function isEscape(event) {
  return event.keyCode == keyCodes.ESC ||
    (event.ctrlKey && getKeyChar(event) == '['); // c-[ is mapped to ESC in Vim by default.
}