add WalletLock class

js/models/core/WalletLock.js

@@ -0,0 +1,47 @@
+'use strict';
+
+var preconditions = require('preconditions').singleton();
+
+function WalletLock(storage, walletId, timeoutMin) {
+  preconditions.checkArgument(storage);
+  preconditions.checkArgument(walletId);
+
+  this.sessionId = storage.getSessionId();
+  this.storage = storage;
+  this.timeoutMin = timeoutMin || 5;
+  this.key = WalletLock._keyFor(walletId);
+  this.keepAlive();
+}
+WalletLock._keyFor = function(walletId) {
+  return 'lock' + '::' + walletId;
+};
+
+WalletLock.prototype._isLockedByOther = function() {
+  var wl = this.storage.getGlobal(this.key);
+
+  if (!wl || wl.expireTs < Date.now() || wl.sessionId === this.sessionId)
+    return false;
+
+  return true;
+};
+
+
+WalletLock.prototype.keepAlive = function() {
+  preconditions.checkState(this.sessionId);
+
+  if (this._isLockedByOther())
+    throw new Error('Could not adquire lock');
+
+  this.storage.setGlobal(this.key, {
+    sessionId: this.sessionId,
+    expireTs: Date.now() + this.timeoutMin * 60 * 1000,
+  });
+};
+
+
+WalletLock.prototype.release = function() {
+  this.storage.removeGlobal(this.key);
+};
+
+
+module.exports = WalletLock;