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diff --git a/toolkit/components/satchel/megalist/MegalistViewModel.sys.mjs b/toolkit/components/satchel/megalist/MegalistViewModel.sys.mjs
new file mode 100644
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+++ b/toolkit/components/satchel/megalist/MegalistViewModel.sys.mjs
@@ -0,0 +1,291 @@
+/* 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 { DefaultAggregator } from "resource://gre/modules/megalist/aggregator/DefaultAggregator.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  OSKeyStore: "resource://gre/modules/OSKeyStore.sys.mjs",
+});
+
+/**
+ * View Model for Megalist.
+ *
+ * Responsible for filtering, grouping, moving selection, editing.
+ * Refers to the same MegalistAggregator in the parent process to access data.
+ * Paired to exactly one MegalistView in the child process to present to the user.
+ * Receives user commands from MegalistView.
+ *
+ * There can be multiple snapshots of the same line displayed in different contexts.
+ *
+ * snapshotId - an id for a snapshot of a line used between View Model and View.
+ */
+export class MegalistViewModel {
+  /**
+   *
+   * View Model prepares snapshots in the parent process to be displayed
+   * by the View in the child process. View gets the firstSnapshotId + length of the
+   * list. Making it a very short message for each time we filter or refresh data.
+   *
+   * View requests line data by providing snapshotId = firstSnapshotId + index.
+   *
+   */
+  #firstSnapshotId = 0;
+  #snapshots = [];
+  #selectedIndex = 0;
+  #searchText = "";
+  #messageToView;
+  static #aggregator = new DefaultAggregator();
+
+  constructor(messageToView) {
+    this.#messageToView = messageToView;
+    MegalistViewModel.#aggregator.attachViewModel(this);
+  }
+
+  willDestroy() {
+    MegalistViewModel.#aggregator.detachViewModel(this);
+  }
+
+  refreshAllLinesOnScreen() {
+    this.#rebuildSnapshots();
+  }
+
+  refreshSingleLineOnScreen(line) {
+    if (this.#searchText) {
+      // Data is filtered, which may require rebuilding the whole list
+      //@sg check if current filter would affected by this line
+      //@sg throttle refresh operation
+      this.#rebuildSnapshots();
+    } else {
+      const snapshotIndex = this.#snapshots.indexOf(line);
+      if (snapshotIndex >= 0) {
+        const snapshotId = snapshotIndex + this.#firstSnapshotId;
+        this.#sendSnapshotToView(snapshotId, line);
+      }
+    }
+  }
+
+  /**
+   *
+   * Send snapshot of necessary line data across parent-child boundary.
+   *
+   * @param {number} snapshotId
+   * @param {object} snapshotData
+   */
+  async #sendSnapshotToView(snapshotId, snapshotData) {
+    if (!snapshotData) {
+      return;
+    }
+
+    // Only usable set of fields is sent over to the View.
+    // Line object may contain other data used by the Data Source.
+    const snapshot = {
+      label: snapshotData.label,
+      value: await snapshotData.value,
+    };
+    if ("template" in snapshotData) {
+      snapshot.template = snapshotData.template;
+    }
+    if ("start" in snapshotData) {
+      snapshot.start = snapshotData.start;
+    }
+    if ("end" in snapshotData) {
+      snapshot.end = snapshotData.end;
+    }
+    if ("commands" in snapshotData) {
+      snapshot.commands = snapshotData.commands;
+    }
+    if ("valueIcon" in snapshotData) {
+      snapshot.valueIcon = snapshotData.valueIcon;
+    }
+    if ("href" in snapshotData) {
+      snapshot.href = snapshotData.href;
+    }
+    if (snapshotData.stickers) {
+      for (const sticker of snapshotData.stickers) {
+        snapshot.stickers ??= [];
+        snapshot.stickers.push(sticker);
+      }
+    }
+
+    this.#messageToView("Snapshot", { snapshotId, snapshot });
+  }
+
+  receiveRequestSnapshot({ snapshotId }) {
+    const snapshotIndex = snapshotId - this.#firstSnapshotId;
+    const snapshot = this.#snapshots[snapshotIndex];
+    if (!snapshot) {
+      // Ignore request for unknown line index or outdated list
+      return;
+    }
+
+    if (snapshot.lineIsReady()) {
+      this.#sendSnapshotToView(snapshotId, snapshot);
+    }
+  }
+
+  handleViewMessage({ name, data }) {
+    const handlerName = `receive${name}`;
+    if (!(handlerName in this)) {
+      throw new Error(`Received unknown message "${name}"`);
+    }
+    return this[handlerName](data);
+  }
+
+  receiveRefresh() {
+    this.#rebuildSnapshots();
+  }
+
+  #rebuildSnapshots() {
+    // Remember current selection to attempt to restore it later
+    const prevSelected = this.#snapshots[this.#selectedIndex];
+
+    // Rebuild snapshots
+    this.#firstSnapshotId += this.#snapshots.length;
+    this.#snapshots = Array.from(
+      MegalistViewModel.#aggregator.enumerateLines(this.#searchText)
+    );
+
+    // Update snapshots on screen
+    this.#messageToView("ShowSnapshots", {
+      firstSnapshotId: this.#firstSnapshotId,
+      count: this.#snapshots.length,
+    });
+
+    // Restore selection
+    const usedToBeSelectedNewIndex = this.#snapshots.findIndex(
+      snapshot => snapshot == prevSelected
+    );
+    if (usedToBeSelectedNewIndex >= 0) {
+      this.#selectSnapshotByIndex(usedToBeSelectedNewIndex);
+    } else {
+      // Make sure selection is within visible lines
+      this.#selectSnapshotByIndex(
+        Math.min(this.#selectedIndex, this.#snapshots.length - 1)
+      );
+    }
+  }
+
+  receiveUpdateFilter({ searchText } = { searchText: "" }) {
+    if (this.#searchText != searchText) {
+      this.#searchText = searchText;
+      this.#messageToView("MegalistUpdateFilter", { searchText });
+      this.#rebuildSnapshots();
+    }
+  }
+
+  async receiveCommand({ commandId, snapshotId, value } = {}) {
+    const index = snapshotId
+      ? snapshotId - this.#firstSnapshotId
+      : this.#selectedIndex;
+    const snapshot = this.#snapshots[index];
+    if (snapshot) {
+      commandId = commandId ?? snapshot.commands[0]?.id;
+      const mustVerify = snapshot.commands.find(c => c.id == commandId)?.verify;
+      if (!mustVerify || (await this.#verifyUser())) {
+        // TODO:Enter the prompt message and pref for #verifyUser()
+        await snapshot[`execute${commandId}`]?.(value);
+      }
+    }
+  }
+
+  receiveSelectSnapshot({ snapshotId }) {
+    const index = snapshotId - this.#firstSnapshotId;
+    if (index >= 0) {
+      this.#selectSnapshotByIndex(index);
+    }
+  }
+
+  receiveSelectNextSnapshot() {
+    this.#selectSnapshotByIndex(this.#selectedIndex + 1);
+  }
+
+  receiveSelectPreviousSnapshot() {
+    this.#selectSnapshotByIndex(this.#selectedIndex - 1);
+  }
+
+  receiveSelectNextGroup() {
+    let i = this.#selectedIndex + 1;
+    while (i < this.#snapshots.length - 1 && !this.#snapshots[i].start) {
+      i += 1;
+    }
+    this.#selectSnapshotByIndex(i);
+  }
+
+  receiveSelectPreviousGroup() {
+    let i = this.#selectedIndex - 1;
+    while (i >= 0 && !this.#snapshots[i].start) {
+      i -= 1;
+    }
+    this.#selectSnapshotByIndex(i);
+  }
+
+  #selectSnapshotByIndex(index) {
+    if (index >= 0 && index < this.#snapshots.length) {
+      this.#selectedIndex = index;
+      const selectedIndex = this.#selectedIndex;
+      this.#messageToView("UpdateSelection", { selectedIndex });
+    }
+  }
+
+  async #verifyUser(promptMessage, prefName) {
+    if (!this.getOSAuthEnabled(prefName)) {
+      promptMessage = false;
+    }
+    let result = await lazy.OSKeyStore.ensureLoggedIn(promptMessage);
+    return result.authenticated;
+  }
+
+  /**
+   * Get the decrypted value for a string pref.
+   *
+   * @param {string} prefName -> The pref whose value is needed.
+   * @param {string} safeDefaultValue -> Value to be returned incase the pref is not yet set.
+   * @returns {string}
+   */
+  #getSecurePref(prefName, safeDefaultValue) {
+    try {
+      let encryptedValue = Services.prefs.getStringPref(prefName, "");
+      return this._crypto.decrypt(encryptedValue);
+    } catch {
+      return safeDefaultValue;
+    }
+  }
+
+  /**
+   * Set the pref to the encrypted form of the value.
+   *
+   * @param {string} prefName -> The pref whose value is to be set.
+   * @param {string} value -> The value to be set in its encryoted form.
+   */
+  #setSecurePref(prefName, value) {
+    let encryptedValue = this._crypto.encrypt(value);
+    Services.prefs.setStringPref(prefName, encryptedValue);
+  }
+
+  /**
+   * Get whether the OSAuth is enabled or not.
+   *
+   * @param {string} prefName -> The name of the pref (creditcards or addresses)
+   * @returns {boolean}
+   */
+  getOSAuthEnabled(prefName) {
+    return this.#getSecurePref(prefName, "") !== "opt out";
+  }
+
+  /**
+   * Set whether the OSAuth is enabled or not.
+   *
+   * @param {string} prefName -> The pref to encrypt.
+   * @param {boolean} enable -> Whether the pref is to be enabled.
+   */
+  setOSAuthEnabled(prefName, enable) {
+    if (enable) {
+      Services.prefs.clearUserPref(prefName);
+    } else {
+      this.#setSecurePref(prefName, "opt out");
+    }
+  }
+}