1 files changed, 78 insertions, 0 deletions
diff --git a/toolkit/components/satchel/megalist/aggregator/Aggregator.sys.mjs b/toolkit/components/satchel/megalist/aggregator/Aggregator.sys.mjs
new file mode 100644
index 0000000000..e101fadd16
--- /dev/null
+++ b/toolkit/components/satchel/megalist/aggregator/Aggregator.sys.mjs
@@ -0,0 +1,78 @@
+/* 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/. */
+
+/**
+ * Connects multiple Data Sources with multiple View Models.
+ * Aggregator owns Data Sources.
+ * Aggregator weakly refers to View Models.
+ */
+export class Aggregator {
+  #sources = [];
+  #attachedViewModels = [];
+
+  attachViewModel(viewModel) {
+    // Weak reference the View Model so we do not keep it in memory forever
+    this.#attachedViewModels.push(new WeakRef(viewModel));
+  }
+
+  detachViewModel(viewModel) {
+    for (let i = this.#attachedViewModels.length - 1; i >= 0; i--) {
+      const knownViewModel = this.#attachedViewModels[i].deref();
+      if (viewModel == knownViewModel || !knownViewModel) {
+        this.#attachedViewModels.splice(i, 1);
+      }
+    }
+  }
+
+  /**
+   * Run action on each of the alive attached view models.
+   * Remove dead consumers.
+   *
+   * @param {Function} action to perform on each alive consumer
+   */
+  forEachViewModel(action) {
+    for (let i = this.#attachedViewModels.length - 1; i >= 0; i--) {
+      const viewModel = this.#attachedViewModels[i].deref();
+      if (viewModel) {
+        action(viewModel);
+      } else {
+        this.#attachedViewModels.splice(i, 1);
+      }
+    }
+  }
+
+  *enumerateLines(searchText) {
+    for (let source of this.#sources) {
+      yield* source.enumerateLines(searchText);
+    }
+  }
+
+  /**
+   *
+   * @param {Function} createSourceFn (aggregatorApi) used to create Data Source.
+   *                   aggregatorApi is the way for Data Source to push data
+   *                   to the Aggregator.
+   */
+  addSource(createSourceFn) {
+    const api = this.#apiForDataSource();
+    const source = createSourceFn(api);
+    this.#sources.push(source);
+  }
+
+  /**
+   * Exposes interface for a datasource to communicate with Aggregator.
+   */
+  #apiForDataSource() {
+    const aggregator = this;
+    return {
+      refreshSingleLineOnScreen(line) {
+        aggregator.forEachViewModel(vm => vm.refreshSingleLineOnScreen(line));
+      },
+
+      refreshAllLinesOnScreen() {
+        aggregator.forEachViewModel(vm => vm.refreshAllLinesOnScreen());
+      },
+    };
+  }
+}