1 files changed, 171 insertions, 0 deletions
diff --git a/browser/components/urlbar/private/Weather.sys.mjs b/browser/components/urlbar/private/Weather.sys.mjs
new file mode 100644
index 0000000000..611994c8f8
--- /dev/null
+++ b/browser/components/urlbar/private/Weather.sys.mjs
@@ -0,0 +1,171 @@
+/* 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/. */
+
+import { BaseFeature } from "resource:///modules/urlbar/private/BaseFeature.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  clearInterval: "resource://gre/modules/Timer.sys.mjs",
+  MerinoClient: "resource:///modules/MerinoClient.sys.mjs",
+  PromiseUtils: "resource://gre/modules/PromiseUtils.sys.mjs",
+  setInterval: "resource://gre/modules/Timer.sys.mjs",
+  UrlbarPrefs: "resource:///modules/UrlbarPrefs.sys.mjs",
+});
+
+const FETCH_INTERVAL_MS = 30 * 60 * 1000; // 30 minutes
+const MERINO_PROVIDER = "accuweather";
+const MERINO_TIMEOUT_MS = 5000; // 5s
+
+const HISTOGRAM_LATENCY = "FX_URLBAR_MERINO_LATENCY_WEATHER_MS";
+const HISTOGRAM_RESPONSE = "FX_URLBAR_MERINO_RESPONSE_WEATHER";
+
+/**
+ * A feature that periodically fetches weather suggestions from Merino.
+ */
+export class Weather extends BaseFeature {
+  get shouldEnable() {
+    return (
+      lazy.UrlbarPrefs.get("weatherFeatureGate") &&
+      lazy.UrlbarPrefs.get("suggest.weather") &&
+      lazy.UrlbarPrefs.get("merinoEnabled")
+    );
+  }
+
+  get enablingPreferences() {
+    return ["suggest.weather"];
+  }
+
+  /**
+   * @returns {object}
+   *   The last weather suggestion fetched from Merino or null if none.
+   */
+  get suggestion() {
+    return this.#suggestion;
+  }
+
+  enable(enabled) {
+    if (enabled) {
+      this.#init();
+    } else {
+      this.#uninit();
+    }
+  }
+
+  /**
+   * Returns a promise that resolves when all pending fetches finish, if there
+   * are pending fetches. If there aren't, the promise resolves when all pending
+   * fetches starting with the next fetch finish.
+   *
+   * @returns {Promise}
+   */
+  waitForFetches() {
+    if (!this.#waitForFetchesDeferred) {
+      this.#waitForFetchesDeferred = lazy.PromiseUtils.defer();
+    }
+    return this.#waitForFetchesDeferred.promise;
+  }
+
+  #init() {
+    this.#merino = new lazy.MerinoClient(this.constructor.name);
+
+    this.#fetchInterval = lazy.setInterval(
+      () => this.#fetch(),
+      this.#fetchIntervalMs
+    );
+
+    // `#fetch()` is async but there's no need to await it here.
+    this.#fetch();
+  }
+
+  #uninit() {
+    this.#merino = null;
+    this.#suggestion = null;
+    lazy.clearInterval(this.#fetchInterval);
+    this.#fetchInterval = 0;
+  }
+
+  async #fetch() {
+    this.logger.info("Fetching suggestion");
+
+    // This `Weather` instance may be uninitialized while awaiting the fetch or
+    // even uninitialized and re-initialized a number of times. Discard the
+    // fetched suggestion if the `#merino` after the fetch isn't the same as the
+    // one before.
+    let merino = this.#merino;
+
+    let suggestions;
+    this.#pendingFetchCount++;
+    try {
+      suggestions = await merino.fetch({
+        query: "",
+        providers: [MERINO_PROVIDER],
+        timeoutMs: this.#timeoutMs,
+        extraLatencyHistogram: HISTOGRAM_LATENCY,
+        extraResponseHistogram: HISTOGRAM_RESPONSE,
+      });
+    } finally {
+      this.#pendingFetchCount--;
+    }
+
+    // Reset the Merino client's session so different fetches use different
+    // sessions. A single session is intended to represent a single user
+    // engagement in the urlbar, which this is not. Practically this isn't
+    // necessary since the client automatically resets the session on a timer
+    // whose period is much shorter than our fetch period, but there's no reason
+    // to keep it ticking in the meantime.
+    merino.resetSession();
+
+    if (merino != this.#merino) {
+      this.logger.info("Fetch canceled, discarding fetched suggestion, if any");
+    } else {
+      let suggestion = suggestions?.[0];
+      if (!suggestion) {
+        this.logger.info("No suggestion received");
+        this.#suggestion = null;
+      } else {
+        this.logger.info("Got suggestion");
+        this.logger.debug(JSON.stringify({ suggestion }));
+        this.#suggestion = { ...suggestion, source: "merino" };
+      }
+    }
+
+    if (!this.#pendingFetchCount) {
+      this.#waitForFetchesDeferred?.resolve();
+      this.#waitForFetchesDeferred = null;
+    }
+  }
+
+  get _test_merino() {
+    return this.#merino;
+  }
+
+  get _test_fetchInterval() {
+    return this.#fetchInterval;
+  }
+
+  get _test_pendingFetchCount() {
+    return this.#pendingFetchCount;
+  }
+
+  async _test_fetch() {
+    await this.#fetch();
+  }
+
+  _test_setFetchIntervalMs(ms) {
+    this.#fetchIntervalMs = ms < 0 ? FETCH_INTERVAL_MS : ms;
+  }
+
+  _test_setTimeoutMs(ms) {
+    this.#timeoutMs = ms < 0 ? MERINO_TIMEOUT_MS : ms;
+  }
+
+  #merino = null;
+  #suggestion = null;
+  #fetchInterval = 0;
+  #fetchIntervalMs = FETCH_INTERVAL_MS;
+  #timeoutMs = MERINO_TIMEOUT_MS;
+  #waitForFetchesDeferred = null;
+  #pendingFetchCount = 0;
+}