Add initial SkyElement & city-list example

sky/framework/sky-element/observe.sky

Index: sky/framework/sky-element/observe.sky
diff --git a/sky/framework/sky-element/observe.sky b/sky/framework/sky-element/observe.sky
new file mode 100644
index 0000000000000000000000000000000000000000..23c6fb793586330c9f2faede3c0de6a8995ce6a3
--- /dev/null
+++ b/sky/framework/sky-element/observe.sky
@@ -0,0 +1,1367 @@
+<!--
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+-->
+
+<script>
+function detectEval() {
+  // Don't test for eval if we're running in a Chrome App environment.
+  // We check for APIs set that only exist in a Chrome App context.
+  if (typeof chrome !== 'undefined' && chrome.app && chrome.app.runtime) {
+    return false;
+  }
+
+  // Firefox OS Apps do not allow eval. This feature detection is very hacky
+  // but even if some other platform adds support for this function this code
+  // will continue to work.
+  if (typeof navigator != 'undefined' && navigator.getDeviceStorage) {
+    return false;
+  }
+
+  try {
+    var f = new Function('', 'return true;');
+    return f();
+  } catch (ex) {
+    return false;
+  }
+}
+
+var hasEval = detectEval();
+
+function isIndex(s) {
+  return +s === s >>> 0 && s !== '';
+}
+
+function toNumber(s) {
+  return +s;
+}
+
+function isObject(obj) {
+  return obj === Object(obj);
+}
+
+function areSameValue(left, right) {
+  if (left === right)
+    return left !== 0 || 1 / left === 1 / right;
+  if (Number.isNaN(left) && Number.isNaN(right))
+    return true;
+
+  return left !== left && right !== right;
+}
+
+var createObject = ('__proto__' in {}) ?
+  function(obj) { return obj; } :
+  function(obj) {
+    var proto = obj.__proto__;
+    if (!proto)
+      return obj;
+    var newObject = Object.create(proto);
+    Object.getOwnPropertyNames(obj).forEach(function(name) {
+      Object.defineProperty(newObject, name,
+                           Object.getOwnPropertyDescriptor(obj, name));
+    });
+    return newObject;
+  };
+
+var identStart = '[\$_a-zA-Z]';
+var identPart = '[\$_a-zA-Z0-9]';
+var identRegExp = new RegExp('^' + identStart + '+' + identPart + '*' + '$');
+
+function getPathCharType(char) {
+  if (char === undefined)
+    return 'eof';
+
+  var code = char.charCodeAt(0);
+
+  switch(code) {
+    case 0x5B: // [
+    case 0x5D: // ]
+    case 0x2E: // .
+    case 0x22: // "
+    case 0x27: // '
+    case 0x30: // 0
+      return char;
+
+    case 0x5F: // _
+    case 0x24: // $
+      return 'ident';
+
+    case 0x20: // Space
+    case 0x09: // Tab
+    case 0x0A: // Newline
+    case 0x0D: // Return
+    case 0xA0:  // No-break space
+    case 0xFEFF:  // Byte Order Mark
+    case 0x2028:  // Line Separator
+    case 0x2029:  // Paragraph Separator
+      return 'ws';
+  }
+
+  // a-z, A-Z
+  if ((0x61 <= code && code <= 0x7A) || (0x41 <= code && code <= 0x5A))
+    return 'ident';
+
+  // 1-9
+  if (0x31 <= code && code <= 0x39)
+    return 'number';
+
+  return 'else';
+}
+
+var pathStateMachine = {
+  'beforePath': {
+    'ws': ['beforePath'],
+    'ident': ['inIdent', 'append'],
+    '[': ['beforeElement'],
+    'eof': ['afterPath']
+  },
+
+  'inPath': {
+    'ws': ['inPath'],
+    '.': ['beforeIdent'],
+    '[': ['beforeElement'],
+    'eof': ['afterPath']
+  },
+
+  'beforeIdent': {
+    'ws': ['beforeIdent'],
+    'ident': ['inIdent', 'append']
+  },
+
+  'inIdent': {
+    'ident': ['inIdent', 'append'],
+    '0': ['inIdent', 'append'],
+    'number': ['inIdent', 'append'],
+    'ws': ['inPath', 'push'],
+    '.': ['beforeIdent', 'push'],
+    '[': ['beforeElement', 'push'],
+    'eof': ['afterPath', 'push']
+  },
+
+  'beforeElement': {
+    'ws': ['beforeElement'],
+    '0': ['afterZero', 'append'],
+    'number': ['inIndex', 'append'],
+    "'": ['inSingleQuote', 'append', ''],
+    '"': ['inDoubleQuote', 'append', '']
+  },
+
+  'afterZero': {
+    'ws': ['afterElement', 'push'],
+    ']': ['inPath', 'push']
+  },
+
+  'inIndex': {
+    '0': ['inIndex', 'append'],
+    'number': ['inIndex', 'append'],
+    'ws': ['afterElement'],
+    ']': ['inPath', 'push']
+  },
+
+  'inSingleQuote': {
+    "'": ['afterElement'],
+    'eof': ['error'],
+    'else': ['inSingleQuote', 'append']
+  },
+
+  'inDoubleQuote': {
+    '"': ['afterElement'],
+    'eof': ['error'],
+    'else': ['inDoubleQuote', 'append']
+  },
+
+  'afterElement': {
+    'ws': ['afterElement'],
+    ']': ['inPath', 'push']
+  }
+}
+
+function noop() {}
+
+function parsePath(path) {
+  var keys = [];
+  var index = -1;
+  var c, newChar, key, type, transition, action, typeMap, mode = 'beforePath';
+
+  var actions = {
+    push: function() {
+      if (key === undefined)
+        return;
+
+      keys.push(key);
+      key = undefined;
+    },
+
+    append: function() {
+      if (key === undefined)
+        key = newChar
+      else
+        key += newChar;
+    }
+  };
+
+  function maybeUnescapeQuote() {
+    if (index >= path.length)
+      return;
+
+    var nextChar = path[index + 1];
+    if ((mode == 'inSingleQuote' && nextChar == "'") ||
+        (mode == 'inDoubleQuote' && nextChar == '"')) {
+      index++;
+      newChar = nextChar;
+      actions.append();
+      return true;
+    }
+  }
+
+  while (mode) {
+    index++;
+    c = path[index];
+
+    if (c == '\\' && maybeUnescapeQuote(mode))
+      continue;
+
+    type = getPathCharType(c);
+    typeMap = pathStateMachine[mode];
+    transition = typeMap[type] || typeMap['else'] || 'error';
+
+    if (transition == 'error')
+      return; // parse error;
+
+    mode = transition[0];
+    action = actions[transition[1]] || noop;
+    newChar = transition[2] === undefined ? c : transition[2];
+    action();
+
+    if (mode === 'afterPath') {
+      return keys;
+    }
+  }
+
+  return; // parse error
+}
+
+function isIdent(s) {
+  return identRegExp.test(s);
+}
+
+var constructorIsPrivate = {};
+
+function Path(parts, privateToken) {
+  if (privateToken !== constructorIsPrivate)
+    throw Error('Use Path.get to retrieve path objects');
+
+  for (var i = 0; i < parts.length; i++) {
+    this.push(String(parts[i]));
+  }
+
+  if (hasEval && this.length) {
+    this.getValueFrom = this.compiledGetValueFromFn();
+  }
+}
+
+// TODO(rafaelw): Make simple LRU cache
+var pathCache = {};
+
+function getPath(pathString) {
+  if (pathString instanceof Path)
+    return pathString;
+
+  if (pathString == null || pathString.length == 0)
+    pathString = '';
+
+  if (typeof pathString != 'string') {
+    if (isIndex(pathString.length)) {
+      // Constructed with array-like (pre-parsed) keys
+      return new Path(pathString, constructorIsPrivate);
+    }
+
+    pathString = String(pathString);
+  }
+
+  var path = pathCache[pathString];
+  if (path)
+    return path;
+
+  var parts = parsePath(pathString);
+  if (!parts)
+    return invalidPath;
+
+  var path = new Path(parts, constructorIsPrivate);
+  pathCache[pathString] = path;
+  return path;
+}
+
+Path.get = getPath;
+
+function formatAccessor(key) {
+  if (isIndex(key)) {
+    return '[' + key + ']';
+  } else {
+    return '["' + key.replace(/"/g, '\\"') + '"]';
+  }
+}
+
+Path.prototype = createObject({
+  __proto__: [],
+  valid: true,
+
+  toString: function() {
+    var pathString = '';
+    for (var i = 0; i < this.length; i++) {
+      var key = this[i];
+      if (isIdent(key)) {
+        pathString += i ? '.' + key : key;
+      } else {
+        pathString += formatAccessor(key);
+      }
+    }
+
+    return pathString;
+  },
+
+  getValueFrom: function(obj, directObserver) {
+    for (var i = 0; i < this.length; i++) {
+      if (obj == null)
+        return;
+      obj = obj[this[i]];
+    }
+    return obj;
+  },
+
+  iterateObjects: function(obj, observe) {
+    for (var i = 0; i < this.length; i++) {
+      if (i)
+        obj = obj[this[i - 1]];
+      if (!isObject(obj))
+        return;
+      observe(obj, this[i]);
+    }
+  },
+
+  compiledGetValueFromFn: function() {
+    var str = '';
+    var pathString = 'obj';
+    str += 'if (obj != null';
+    var i = 0;
+    var key;
+    for (; i < (this.length - 1); i++) {
+      key = this[i];
+      pathString += isIdent(key) ? '.' + key : formatAccessor(key);
+      str += ' &&\n     ' + pathString + ' != null';
+    }
+    str += ')\n';
+
+    var key = this[i];
+    pathString += isIdent(key) ? '.' + key : formatAccessor(key);
+
+    str += '  return ' + pathString + ';\nelse\n  return undefined;';
+    return new Function('obj', str);
+  },
+
+  setValueFrom: function(obj, value) {
+    if (!this.length)
+      return false;
+
+    for (var i = 0; i < this.length - 1; i++) {
+      if (!isObject(obj))
+        return false;
+      obj = obj[this[i]];
+    }
+
+    if (!isObject(obj))
+      return false;
+
+    obj[this[i]] = value;
+    return true;
+  }
+});
+
+var invalidPath = new Path('', constructorIsPrivate);
+invalidPath.valid = false;
+invalidPath.getValueFrom = invalidPath.setValueFrom = function() {};
+
+var MAX_DIRTY_CHECK_CYCLES = 1000;
+
+function dirtyCheck(observer) {
+  var cycles = 0;
+  while (cycles < MAX_DIRTY_CHECK_CYCLES && observer.check_()) {
+    cycles++;
+  }
+
+  return cycles > 0;
+}
+
+function runEOM(fn) {
+  return Promise.resolve().then(fn);
+}
+
+var observedObjectCache = [];
+
+function newObservedObject() {
+  var observer;
+  var object;
+  var discardRecords = false;
+  var first = true;
+
+  function callback(records) {
+    if (observer && observer.state_ === OPENED && !discardRecords)
+      observer.check_(records);
+  }
+
+  return {
+    open: function(obs) {
+      if (observer)
+        throw Error('ObservedObject in use');
+
+      if (!first)
+        Object.deliverChangeRecords(callback);
+
+      observer = obs;
+      first = false;
+    },
+    observe: function(obj, arrayObserve) {
+      object = obj;
+      if (arrayObserve)
+        Array.observe(object, callback);
+      else
+        Object.observe(object, callback);
+    },
+    deliver: function(discard) {
+      discardRecords = discard;
+      Object.deliverChangeRecords(callback);
+      discardRecords = false;
+    },
+    close: function() {
+      observer = undefined;
+      Object.unobserve(object, callback);
+      observedObjectCache.push(this);
+    }
+  };
+}
+
+/*
+ * The observedSet abstraction is a perf optimization which reduces the total
+ * number of Object.observe observations of a set of objects. The idea is that
+ * groups of Observers will have some object dependencies in common and this
+ * observed set ensures that each object in the transitive closure of
+ * dependencies is only observed once. The observedSet acts as a write barrier
+ * such that whenever any change comes through, all Observers are checked for
+ * changed values.
+ *
+ * Note that this optimization is explicitly moving work from setup-time to
+ * change-time.
+ *
+ * TODO(rafaelw): Implement "garbage collection". In order to move work off
+ * the critical path, when Observers are closed, their observed objects are
+ * not Object.unobserve(d). As a result, it's possible that if the observedSet
+ * is kept open, but some Observers have been closed, it could cause "leaks"
+ * (prevent otherwise collectable objects from being collected). At some
+ * point, we should implement incremental "gc" which keeps a list of
+ * observedSets which may need clean-up and does small amounts of cleanup on a
+ * timeout until all is clean.
+ */
+
+function getObservedObject(observer, object, arrayObserve) {
+  var dir = observedObjectCache.pop() || newObservedObject();
+  dir.open(observer);
+  dir.observe(object, arrayObserve);
+  return dir;
+}
+
+var observedSetCache = [];
+
+function newObservedSet() {
+  var observerCount = 0;
+  var observers = [];
+  var objects = [];
+  var rootObj;
+  var rootObjProps;
+
+  function observe(obj, prop) {
+    if (!obj)
+      return;
+
+    if (obj === rootObj)
+      rootObjProps[prop] = true;
+
+    if (objects.indexOf(obj) < 0) {
+      objects.push(obj);
+      Object.observe(obj, callback);
+    }
+
+    observe(Object.getPrototypeOf(obj), prop);
+  }
+
+  function allRootObjNonObservedProps(recs) {
+    for (var i = 0; i < recs.length; i++) {
+      var rec = recs[i];
+      if (rec.object !== rootObj ||
+          rootObjProps[rec.name] ||
+          rec.type === 'setPrototype') {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  function callback(recs) {
+    if (allRootObjNonObservedProps(recs))
+      return;
+
+    var observer;
+    for (var i = 0; i < observers.length; i++) {
+      observer = observers[i];
+      if (observer.state_ == OPENED) {
+        observer.iterateObjects_(observe);
+      }
+    }
+
+    for (var i = 0; i < observers.length; i++) {
+      observer = observers[i];
+      if (observer.state_ == OPENED) {
+        observer.check_();
+      }
+    }
+  }
+
+  var record = {
+    objects: objects,
+    get rootObject() { return rootObj; },
+    set rootObject(value) {
+      rootObj = value;
+      rootObjProps = {};
+    },
+    open: function(obs, object) {
+      observers.push(obs);
+      observerCount++;
+      obs.iterateObjects_(observe);
+    },
+    close: function(obs) {
+      observerCount--;
+      if (observerCount > 0) {
+        return;
+      }
+
+      for (var i = 0; i < objects.length; i++) {
+        Object.unobserve(objects[i], callback);
+        Observer.unobservedCount++;
+      }
+
+      observers.length = 0;
+      objects.length = 0;
+      rootObj = undefined;
+      rootObjProps = undefined;
+      observedSetCache.push(this);
+      if (lastObservedSet === this)
+        lastObservedSet = null;
+    },
+  };
+
+  return record;
+}
+
+var lastObservedSet;
+
+function getObservedSet(observer, obj) {
+  if (!lastObservedSet || lastObservedSet.rootObject !== obj) {
+    lastObservedSet = observedSetCache.pop() || newObservedSet();
+    lastObservedSet.rootObject = obj;
+  }
+  lastObservedSet.open(observer, obj);
+  return lastObservedSet;
+}
+
+var UNOPENED = 0;
+var OPENED = 1;
+var CLOSED = 2;
+var RESETTING = 3;
+
+var nextObserverId = 1;
+
+function Observer() {
+  this.state_ = UNOPENED;
+  this.callback_ = undefined;
+  this.target_ = undefined; // TODO(rafaelw): Should be WeakRef
+  this.directObserver_ = undefined;
+  this.value_ = undefined;
+  this.id_ = nextObserverId++;
+}
+
+Observer.prototype = {
+  open: function(callback, target) {
+    if (this.state_ != UNOPENED)
+      throw Error('Observer has already been opened.');
+
+    this.callback_ = callback;
+    this.target_ = target;
+    this.connect_();
+    this.state_ = OPENED;
+    return this.value_;
+  },
+
+  close: function() {
+    if (this.state_ != OPENED)
+      return;
+
+    this.disconnect_();
+    this.value_ = undefined;
+    this.callback_ = undefined;
+    this.target_ = undefined;
+    this.state_ = CLOSED;
+  },
+
+  deliver: function() {
+    if (this.state_ != OPENED)
+      return;
+
+    dirtyCheck(this);
+  },
+
+  report_: function(changes) {
+    try {
+      this.callback_.apply(this.target_, changes);
+    } catch (ex) {
+      Observer._errorThrownDuringCallback = true;
+      console.error('Exception caught during observer callback: ' +
+                     (ex.stack || ex));
+    }
+  },
+
+  discardChanges: function() {
+    this.check_(undefined, true);
+    return this.value_;
+  }
+}
+
+function ArrayObserver(array) {
+  if (!Array.isArray(array))
+    throw Error('Provided object is not an Array');
+  Observer.call(this);
+  this.value_ = array;
+  this.oldObject_ = undefined;
+}
+
+ArrayObserver.prototype = createObject({
+
+  __proto__: Observer.prototype,
+
+  connect_: function(callback, target) {
+    this.directObserver_ = getObservedObject(this, this.value_,
+                                             true /* arrayObserve */);
+  },
+
+  copyObject: function(arr) {
+    return arr.slice();
+  },
+
+  check_: function(changeRecords) {
+    var splices;
+    if (!changeRecords)
+      return false;
+    splices = projectArraySplices(this.value_, changeRecords);
+
+    if (!splices || !splices.length)
+      return false;
+
+    this.report_([splices]);
+    return true;
+  },
+
+  disconnect_: function() {
+    this.directObserver_.close();
+    this.directObserver_ = undefined;
+  },
+
+  deliver: function() {
+    if (this.state_ != OPENED)
+      return;
+
+    this.directObserver_.deliver(false);
+  },
+
+  discardChanges: function() {
+    if (this.directObserver_)
+      this.directObserver_.deliver(true);
+    else
+      this.oldObject_ = this.copyObject(this.value_);
+
+    return this.value_;
+  }
+});
+
+ArrayObserver.applySplices = function(previous, current, splices) {
+  splices.forEach(function(splice) {
+    var spliceArgs = [splice.index, splice.removed.length];
+    var addIndex = splice.index;
+    while (addIndex < splice.index + splice.addedCount) {
+      spliceArgs.push(current[addIndex]);
+      addIndex++;
+    }
+
+    Array.prototype.splice.apply(previous, spliceArgs);
+  });
+};
+
+function PathObserver(object, path) {
+  Observer.call(this);
+
+  this.object_ = object;
+  this.path_ = getPath(path);
+  this.directObserver_ = undefined;
+}
+
+PathObserver.prototype = createObject({
+  __proto__: Observer.prototype,
+
+  get path() {
+    return this.path_;
+  },
+
+  connect_: function() {
+    this.directObserver_ = getObservedSet(this, this.object_);
+    this.check_(undefined, true);
+  },
+
+  disconnect_: function() {
+    this.value_ = undefined;
+
+    if (this.directObserver_) {
+      this.directObserver_.close(this);
+      this.directObserver_ = undefined;
+    }
+  },
+
+  iterateObjects_: function(observe) {
+    this.path_.iterateObjects(this.object_, observe);
+  },
+
+  check_: function(changeRecords, skipChanges) {
+    var oldValue = this.value_;
+    this.value_ = this.path_.getValueFrom(this.object_);
+    if (skipChanges || areSameValue(this.value_, oldValue))
+      return false;
+
+    this.report_([this.value_, oldValue, this]);
+    return true;
+  },
+
+  setValue: function(newValue) {
+    if (this.path_)
+      this.path_.setValueFrom(this.object_, newValue);
+  }
+});
+
+function CompoundObserver(reportChangesOnOpen) {
+  Observer.call(this);
+
+  this.reportChangesOnOpen_ = reportChangesOnOpen;
+  this.value_ = [];
+  this.directObserver_ = undefined;
+  this.observed_ = [];
+}
+
+var observerSentinel = {};
+
+CompoundObserver.prototype = createObject({
+  __proto__: Observer.prototype,
+
+  connect_: function() {
+    var object;
+    var needsDirectObserver = false;
+    for (var i = 0; i < this.observed_.length; i += 2) {
+      object = this.observed_[i]
+      if (object !== observerSentinel) {
+        needsDirectObserver = true;
+        break;
+      }
+    }
+
+    if (needsDirectObserver)
+      this.directObserver_ = getObservedSet(this, object);
+
+    this.check_(undefined, !this.reportChangesOnOpen_);
+  },
+
+  disconnect_: function() {
+    for (var i = 0; i < this.observed_.length; i += 2) {
+      if (this.observed_[i] === observerSentinel)
+        this.observed_[i + 1].close();
+    }
+    this.observed_.length = 0;
+    this.value_.length = 0;
+
+    if (this.directObserver_) {
+      this.directObserver_.close(this);
+      this.directObserver_ = undefined;
+    }
+  },
+
+  addPath: function(object, path) {
+    if (this.state_ != UNOPENED && this.state_ != RESETTING)
+      throw Error('Cannot add paths once started.');
+
+    var path = getPath(path);
+    this.observed_.push(object, path);
+    if (!this.reportChangesOnOpen_)
+      return;
+    var index = this.observed_.length / 2 - 1;
+    this.value_[index] = path.getValueFrom(object);
+  },
+
+  addObserver: function(observer) {
+    if (this.state_ != UNOPENED && this.state_ != RESETTING)
+      throw Error('Cannot add observers once started.');
+
+    this.observed_.push(observerSentinel, observer);
+    if (!this.reportChangesOnOpen_)
+      return;
+    var index = this.observed_.length / 2 - 1;
+    this.value_[index] = observer.open(this.deliver, this);
+  },
+
+  startReset: function() {
+    if (this.state_ != OPENED)
+      throw Error('Can only reset while open');
+
+    this.state_ = RESETTING;
+    this.disconnect_();
+  },
+
+  finishReset: function() {
+    if (this.state_ != RESETTING)
+      throw Error('Can only finishReset after startReset');
+    this.state_ = OPENED;
+    this.connect_();
+
+    return this.value_;
+  },
+
+  iterateObjects_: function(observe) {
+    var object;
+    for (var i = 0; i < this.observed_.length; i += 2) {
+      object = this.observed_[i]
+      if (object !== observerSentinel)
+        this.observed_[i + 1].iterateObjects(object, observe)
+    }
+  },
+
+  check_: function(changeRecords, skipChanges) {
+    var oldValues;
+    for (var i = 0; i < this.observed_.length; i += 2) {
+      var object = this.observed_[i];
+      var path = this.observed_[i+1];
+      var value;
+      if (object === observerSentinel) {
+        var observable = path;
+        value = this.state_ === UNOPENED ?
+            observable.open(this.deliver, this) :
+            observable.discardChanges();
+      } else {
+        value = path.getValueFrom(object);
+      }
+
+      if (skipChanges) {
+        this.value_[i / 2] = value;
+        continue;
+      }
+
+      if (areSameValue(value, this.value_[i / 2]))
+        continue;
+
+      oldValues = oldValues || [];
+      oldValues[i / 2] = this.value_[i / 2];
+      this.value_[i / 2] = value;
+    }
+
+    if (!oldValues)
+      return false;
+
+    // TODO(rafaelw): Having observed_ as the third callback arg here is
+    // pretty lame API. Fix.
+    this.report_([this.value_, oldValues, this.observed_]);
+    return true;
+  }
+});
+
+function identFn(value) { return value; }
+
+function ObserverTransform(observable, getValueFn, setValueFn,
+                           dontPassThroughSet) {
+  this.callback_ = undefined;
+  this.target_ = undefined;
+  this.value_ = undefined;
+  this.observable_ = observable;
+  this.getValueFn_ = getValueFn || identFn;
+  this.setValueFn_ = setValueFn || identFn;
+  // TODO(rafaelw): This is a temporary hack. PolymerExpressions needs this
+  // at the moment because of a bug in it's dependency tracking.
+  this.dontPassThroughSet_ = dontPassThroughSet;
+}
+
+ObserverTransform.prototype = {
+  open: function(callback, target) {
+    this.callback_ = callback;
+    this.target_ = target;
+    this.value_ =
+        this.getValueFn_(this.observable_.open(this.observedCallback_, this));
+    return this.value_;
+  },
+
+  observedCallback_: function(value) {
+    value = this.getValueFn_(value);
+    if (areSameValue(value, this.value_))
+      return;
+    var oldValue = this.value_;
+    this.value_ = value;
+    this.callback_.call(this.target_, this.value_, oldValue);
+  },
+
+  discardChanges: function() {
+    this.value_ = this.getValueFn_(this.observable_.discardChanges());
+    return this.value_;
+  },
+
+  deliver: function() {
+    return this.observable_.deliver();
+  },
+
+  setValue: function(value) {
+    value = this.setValueFn_(value);
+    if (!this.dontPassThroughSet_ && this.observable_.setValue)
+      return this.observable_.setValue(value);
+  },
+
+  close: function() {
+    if (this.observable_)
+      this.observable_.close();
+    this.callback_ = undefined;
+    this.target_ = undefined;
+    this.observable_ = undefined;
+    this.value_ = undefined;
+    this.getValueFn_ = undefined;
+    this.setValueFn_ = undefined;
+  }
+}
+
+function newSplice(index, removed, addedCount) {
+  return {
+    index: index,
+    removed: removed,
+    addedCount: addedCount
+  };
+}
+
+var EDIT_LEAVE = 0;
+var EDIT_UPDATE = 1;
+var EDIT_ADD = 2;
+var EDIT_DELETE = 3;
+
+function ArraySplice() {}
+
+ArraySplice.prototype = {
+
+  // Note: This function is *based* on the computation of the Levenshtein
+  // "edit" distance. The one change is that "updates" are treated as two
+  // edits - not one. With Array splices, an update is really a delete
+  // followed by an add. By retaining this, we optimize for "keeping" the
+  // maximum array items in the original array. For example:
+  //
+  //   'xxxx123' -> '123yyyy'
+  //
+  // With 1-edit updates, the shortest path would be just to update all seven
+  // characters. With 2-edit updates, we delete 4, leave 3, and add 4. This
+  // leaves the substring '123' intact.
+  calcEditDistances: function(current, currentStart, currentEnd,
+                              old, oldStart, oldEnd) {
+    // "Deletion" columns
+    var rowCount = oldEnd - oldStart + 1;
+    var columnCount = currentEnd - currentStart + 1;
+    var distances = new Array(rowCount);
+
+    // "Addition" rows. Initialize null column.
+    for (var i = 0; i < rowCount; i++) {
+      distances[i] = new Array(columnCount);
+      distances[i][0] = i;
+    }
+
+    // Initialize null row
+    for (var j = 0; j < columnCount; j++)
+      distances[0][j] = j;
+
+    for (var i = 1; i < rowCount; i++) {
+      for (var j = 1; j < columnCount; j++) {
+        if (this.equals(current[currentStart + j - 1], old[oldStart + i - 1]))
+          distances[i][j] = distances[i - 1][j - 1];
+        else {
+          var north = distances[i - 1][j] + 1;
+          var west = distances[i][j - 1] + 1;
+          distances[i][j] = north < west ? north : west;
+        }
+      }
+    }
+
+    return distances;
+  },
+
+  // This starts at the final weight, and walks "backward" by finding
+  // the minimum previous weight recursively until the origin of the weight
+  // matrix.
+  spliceOperationsFromEditDistances: function(distances) {
+    var i = distances.length - 1;
+    var j = distances[0].length - 1;
+    var current = distances[i][j];
+    var edits = [];
+    while (i > 0 || j > 0) {
+      if (i == 0) {
+        edits.push(EDIT_ADD);
+        j--;
+        continue;
+      }
+      if (j == 0) {
+        edits.push(EDIT_DELETE);
+        i--;
+        continue;
+      }
+      var northWest = distances[i - 1][j - 1];
+      var west = distances[i - 1][j];
+      var north = distances[i][j - 1];
+
+      var min;
+      if (west < north)
+        min = west < northWest ? west : northWest;
+      else
+        min = north < northWest ? north : northWest;
+
+      if (min == northWest) {
+        if (northWest == current) {
+          edits.push(EDIT_LEAVE);
+        } else {
+          edits.push(EDIT_UPDATE);
+          current = northWest;
+        }
+        i--;
+        j--;
+      } else if (min == west) {
+        edits.push(EDIT_DELETE);
+        i--;
+        current = west;
+      } else {
+        edits.push(EDIT_ADD);
+        j--;
+        current = north;
+      }
+    }
+
+    edits.reverse();
+    return edits;
+  },
+
+  /**
+   * Splice Projection functions:
+   *
+   * A splice map is a representation of how a previous array of items
+   * was transformed into a new array of items. Conceptually it is a list of
+   * tuples of
+   *
+   *   <index, removed, addedCount>
+   *
+   * which are kept in ascending index order of. The tuple represents that at
+   * the |index|, |removed| sequence of items were removed, and counting forward
+   * from |index|, |addedCount| items were added.
+   */
+
+  /**
+   * Lacking individual splice mutation information, the minimal set of
+   * splices can be synthesized given the previous state and final state of an
+   * array. The basic approach is to calculate the edit distance matrix and
+   * choose the shortest path through it.
+   *
+   * Complexity: O(l * p)
+   *   l: The length of the current array
+   *   p: The length of the old array
+   */
+  calcSplices: function(current, currentStart, currentEnd,
+                        old, oldStart, oldEnd) {
+    var prefixCount = 0;
+    var suffixCount = 0;
+
+    var minLength = Math.min(currentEnd - currentStart, oldEnd - oldStart);
+    if (currentStart == 0 && oldStart == 0)
+      prefixCount = this.sharedPrefix(current, old, minLength);
+
+    if (currentEnd == current.length && oldEnd == old.length)
+      suffixCount = this.sharedSuffix(current, old, minLength - prefixCount);
+
+    currentStart += prefixCount;
+    oldStart += prefixCount;
+    currentEnd -= suffixCount;
+    oldEnd -= suffixCount;
+
+    if (currentEnd - currentStart == 0 && oldEnd - oldStart == 0)
+      return [];
+
+    if (currentStart == currentEnd) {
+      var splice = newSplice(currentStart, [], 0);
+      while (oldStart < oldEnd)
+        splice.removed.push(old[oldStart++]);
+
+      return [ splice ];
+    } else if (oldStart == oldEnd)
+      return [ newSplice(currentStart, [], currentEnd - currentStart) ];
+
+    var ops = this.spliceOperationsFromEditDistances(
+        this.calcEditDistances(current, currentStart, currentEnd,
+                               old, oldStart, oldEnd));
+
+    var splice = undefined;
+    var splices = [];
+    var index = currentStart;
+    var oldIndex = oldStart;
+    for (var i = 0; i < ops.length; i++) {
+      switch(ops[i]) {
+        case EDIT_LEAVE:
+          if (splice) {
+            splices.push(splice);
+            splice = undefined;
+          }
+
+          index++;
+          oldIndex++;
+          break;
+        case EDIT_UPDATE:
+          if (!splice)
+            splice = newSplice(index, [], 0);
+
+          splice.addedCount++;
+          index++;
+
+          splice.removed.push(old[oldIndex]);
+          oldIndex++;
+          break;
+        case EDIT_ADD:
+          if (!splice)
+            splice = newSplice(index, [], 0);
+
+          splice.addedCount++;
+          index++;
+          break;
+        case EDIT_DELETE:
+          if (!splice)
+            splice = newSplice(index, [], 0);
+
+          splice.removed.push(old[oldIndex]);
+          oldIndex++;
+          break;
+      }
+    }
+
+    if (splice) {
+      splices.push(splice);
+    }
+    return splices;
+  },
+
+  sharedPrefix: function(current, old, searchLength) {
+    for (var i = 0; i < searchLength; i++)
+      if (!this.equals(current[i], old[i]))
+        return i;
+    return searchLength;
+  },
+
+  sharedSuffix: function(current, old, searchLength) {
+    var index1 = current.length;
+    var index2 = old.length;
+    var count = 0;
+    while (count < searchLength &&
+           this.equals(current[--index1], old[--index2])) {
+      count++;
+    }
+
+    return count;
+  },
+
+  calculateSplices: function(current, previous) {
+    return this.calcSplices(current, 0, current.length, previous, 0,
+                            previous.length);
+  },
+
+  equals: function(currentValue, previousValue) {
+    return currentValue === previousValue;
+  }
+};
+
+var arraySplice = new ArraySplice();
+
+function calcSplices(current, currentStart, currentEnd,
+                     old, oldStart, oldEnd) {
+  return arraySplice.calcSplices(current, currentStart, currentEnd,
+                                 old, oldStart, oldEnd);
+}
+
+function intersect(start1, end1, start2, end2) {
+  // Disjoint
+  if (end1 < start2 || end2 < start1)
+    return -1;
+
+  // Adjacent
+  if (end1 == start2 || end2 == start1)
+    return 0;
+
+  // Non-zero intersect, span1 first
+  if (start1 < start2) {
+    if (end1 < end2)
+      return end1 - start2; // Overlap
+    else
+      return end2 - start2; // Contained
+  } else {
+    // Non-zero intersect, span2 first
+    if (end2 < end1)
+      return end2 - start1; // Overlap
+    else
+      return end1 - start1; // Contained
+  }
+}
+
+function mergeSplice(splices, index, removed, addedCount) {
+
+  var splice = newSplice(index, removed, addedCount);
+
+  var inserted = false;
+  var insertionOffset = 0;
+
+  for (var i = 0; i < splices.length; i++) {
+    var current = splices[i];
+    current.index += insertionOffset;
+
+    if (inserted)
+      continue;
+
+    var intersectCount = intersect(splice.index,
+                                   splice.index + splice.removed.length,
+                                   current.index,
+                                   current.index + current.addedCount);
+
+    if (intersectCount >= 0) {
+      // Merge the two splices
+
+      splices.splice(i, 1);
+      i--;
+
+      insertionOffset -= current.addedCount - current.removed.length;
+
+      splice.addedCount += current.addedCount - intersectCount;
+      var deleteCount = splice.removed.length +
+                        current.removed.length - intersectCount;
+
+      if (!splice.addedCount && !deleteCount) {
+        // merged splice is a noop. discard.
+        inserted = true;
+      } else {
+        var removed = current.removed;
+
+        if (splice.index < current.index) {
+          // some prefix of splice.removed is prepended to current.removed.
+          var prepend = splice.removed.slice(0, current.index - splice.index);
+          Array.prototype.push.apply(prepend, removed);
+          removed = prepend;
+        }
+
+        if (splice.index + splice.removed.length >
+            current.index + current.addedCount) {
+          // some suffix of splice.removed is appended to current.removed.
+          var append = splice.removed.slice(
+              current.index + current.addedCount - splice.index);
+          Array.prototype.push.apply(removed, append);
+        }
+
+        splice.removed = removed;
+        if (current.index < splice.index) {
+          splice.index = current.index;
+        }
+      }
+    } else if (splice.index < current.index) {
+      // Insert splice here.
+
+      inserted = true;
+
+      splices.splice(i, 0, splice);
+      i++;
+
+      var offset = splice.addedCount - splice.removed.length
+      current.index += offset;
+      insertionOffset += offset;
+    }
+  }
+
+  if (!inserted)
+    splices.push(splice);
+}
+
+function createInitialSplices(array, changeRecords) {
+  var splices = [];
+
+  for (var i = 0; i < changeRecords.length; i++) {
+    var record = changeRecords[i];
+    switch(record.type) {
+      case 'splice':
+        mergeSplice(splices, record.index, record.removed.slice(),
+                    record.addedCount);
+        break;
+      case 'add':
+      case 'update':
+      case 'delete':
+        if (!isIndex(record.name))
+          continue;
+        var index = toNumber(record.name);
+        if (index < 0)
+          continue;
+        mergeSplice(splices, index, [record.oldValue], 1);
+        break;
+      default:
+        console.error('Unexpected record type: ' + JSON.stringify(record));
+        break;
+    }
+  }
+
+  return splices;
+}
+
+function projectArraySplices(array, changeRecords) {
+  var splices = [];
+
+  createInitialSplices(array, changeRecords).forEach(function(splice) {
+    if (splice.addedCount == 1 && splice.removed.length == 1) {
+      if (splice.removed[0] !== array[splice.index])
+        splices.push(splice);
+
+      return
+    };
+
+    splices = splices.concat(calcSplices(array, splice.index,
+                                         splice.index + splice.addedCount,
+                                         splice.removed,
+                                         0,
+                                         splice.removed.length));
+  });
+
+  return splices;
+}
+
+ArrayObserver.calculateSplices = function(current, previous) {
+  return arraySplice.calculateSplices(current, previous);
+};
+
+module.exports = {
+  Observer: Observer,
+  runEOM_: runEOM,
+  observerSentinel_: observerSentinel,
+  PathObserver: PathObserver,
+  ArrayObserver: ArrayObserver,
+  ArraySplice: ArraySplice,
+  CompoundObserver: CompoundObserver,
+  Path: Path,
+  ObserverTransform: ObserverTransform
+}
+</script>