1 files changed, 142 insertions, 0 deletions
diff --git a/comm/calendar/base/src/CalMetronome.jsm b/comm/calendar/base/src/CalMetronome.jsm
new file mode 100644
index 0000000000..b675e5bc0a
--- /dev/null
+++ b/comm/calendar/base/src/CalMetronome.jsm
@@ -0,0 +1,142 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const EXPORTED_SYMBOLS = ["CalMetronome"];
+
+const { cal } = ChromeUtils.import("resource:///modules/calendar/calUtils.jsm");
+const { EventEmitter } = ChromeUtils.importESModule("resource://gre/modules/EventEmitter.sys.mjs");
+
+const MINUTE_IN_MS = 60000;
+const HOUR_IN_MS = 3600000;
+const DAY_IN_MS = 86400000;
+
+/**
+ * Keeps calendar UI/components in sync by ticking regularly. Fires a "minute"
+ * event every minute on the minute, an "hour" event on the hour, and a "day"
+ * event at midnight. Each event also fires if longer than the time period in
+ * question has elapsed since the last event, e.g. because the computer has
+ * been asleep.
+ *
+ * It automatically corrects clock skew: if a minute event is more than one
+ * second late, the time to the next event is recalculated and should fire a
+ * few milliseconds late at worst.
+ *
+ * @implements nsIObserver
+ * @implements EventEmitter
+ */
+var CalMetronome = {
+  QueryInterface: ChromeUtils.generateQI(["nsIObserver"]),
+
+  /**
+   * The time when the minute event last fired, in milliseconds since the epoch.
+   *
+   * @type integer
+   */
+  _lastFireTime: 0,
+
+  /**
+   * The last minute for which the minute event fired.
+   *
+   * @type integer (0-59)
+   */
+  _lastMinute: -1,
+
+  /**
+   * The last hour for which the hour event fired.
+   *
+   * @type integer (0-23)
+   */
+  _lastHour: -1,
+
+  /**
+   * The last day of the week for which the day event fired.
+   *
+   * @type integer (0-7)
+   */
+  _lastDay: -1,
+
+  /**
+   * The timer running everything.
+   *
+   * @type nsITimer
+   */
+  _timer: Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer),
+
+  init() {
+    let now = new Date();
+    this._lastFireTime = now.valueOf();
+    this._lastHour = now.getHours();
+    this._lastDay = now.getDay();
+
+    EventEmitter.decorate(this);
+
+    Services.obs.addObserver(this, "wake_notification");
+    Services.obs.addObserver(this, "quit-application");
+    this._startNext();
+  },
+
+  observe(subject, topic, data) {
+    if (topic == "wake_notification") {
+      cal.LOGverbose("[CalMetronome] Observed wake_notification");
+      this.notify();
+    } else if (topic == "quit-application") {
+      this._timer.cancel();
+      Services.obs.removeObserver(this, "wake_notification");
+      Services.obs.removeObserver(this, "quit-application");
+    }
+  },
+
+  _startNext() {
+    this._timer.cancel();
+
+    let now = new Date();
+    let next = new Date(
+      now.getFullYear(),
+      now.getMonth(),
+      now.getDate(),
+      now.getHours(),
+      now.getMinutes() + 1,
+      0
+    );
+    cal.LOGverbose(`[CalMetronome] Scheduling one-off event in ${next - now}ms`);
+    this._timer.initWithCallback(this, next - now, Ci.nsITimer.TYPE_ONE_SHOT);
+  },
+
+  _startRepeating() {
+    cal.LOGverbose(`[CalMetronome] Starting repeating events`);
+    this._timer.initWithCallback(this, MINUTE_IN_MS, Ci.nsITimer.TYPE_REPEATING_SLACK);
+  },
+
+  notify() {
+    let now = new Date();
+    let elapsedSinceLastFire = now.valueOf() - this._lastFireTime;
+    this._lastFireTime = now.valueOf();
+
+    let minute = now.getMinutes();
+    if (minute != this._lastMinute || elapsedSinceLastFire > MINUTE_IN_MS) {
+      this._lastMinute = minute;
+      this.emit("minute", now);
+    }
+
+    let hour = now.getHours();
+    if (hour != this._lastHour || elapsedSinceLastFire > HOUR_IN_MS) {
+      this._lastHour = hour;
+      this.emit("hour", now);
+    }
+
+    let day = now.getDay();
+    if (day != this._lastDay || elapsedSinceLastFire > DAY_IN_MS) {
+      this._lastDay = day;
+      this.emit("day", now);
+    }
+
+    let slack = now.getSeconds();
+    if (slack >= 1 && slack < 59) {
+      this._startNext();
+    } else if (this._timer.type == Ci.nsITimer.TYPE_ONE_SHOT) {
+      this._startRepeating();
+    }
+  },
+};
+CalMetronome.init();