Add a class to orchestrate all the collapse behaviours

apps/web/src/viewmodels/structures/auto-collapse/AutoCollapse.ts

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+/*
+ * Copyright 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+import type { PanelImperativeHandle } from "@element-hq/web-shared-components";
+import { CollapseHandler } from "./CollapseHandler";
+import type { BaseCollapseBehaviour } from "./behaviours/BaseCollapseBehaviour";
+import { Behaviours } from "./behaviours/behaviours";
+
+/**
+ * This class orchestrates all the auto-collapse behaviours.
+ */
+export class AutoCollapse {
+    private readonly behaviours: BaseCollapseBehaviour[] = [];
+    private readonly collapseHandler: CollapseHandler;
+
+    public constructor(setCollapsed: (collapsed: boolean) => void) {
+        this.collapseHandler = new CollapseHandler(setCollapsed);
+        for (const Behaviour of Behaviours) {
+            this.behaviours.push(new Behaviour(this.collapseHandler));
+        }
+    }
+
+    /**
+     * When this returns true, any left panel resized events should be ignored.
+     */
+    public get shouldIgnoreResize(): boolean {
+        return this.behaviours.some((b) => b.shouldIgnoreResize);
+    }
+
+    /**
+     * Whether the panel is currently auto-collapsed.
+     */
+    public get isAutoCollapsed(): boolean {
+        return this.collapseHandler.isAutoCollapsed;
+    }
+
+    /**
+     * Returns boolean indicating whether the left panel should be collapsed at app start.
+     */
+    public static shouldStartCollapsed(): boolean {
+        return Behaviours.some((B) => B.shouldStartCollapsed());
+    }
+
+    public dispose = (): void => {
+        for (const behaviour of this.behaviours) {
+            behaviour.dispose();
+        }
+    };
+
+    /**
+     * Make the panel API from react-resizable-panels available to this class.
+     * @param handle The panel handle to access react-resizable-panels API
+     */
+    public setHandle = (handle: PanelImperativeHandle): void => {
+        this.collapseHandler.setHandle(handle);
+    };
+
+    /**
+     * Should be called when the left panel is resized.
+     */
+    public onLeftPanelResized = (): void => {
+        for (const behaviour of this.behaviours) {
+            behaviour.onLeftPanelResized();
+        }
+        this.collapseHandler.isAutoCollapsed = false;
+        this.collapseHandler.updateRestoreWidth();
+    };
+}

apps/web/test/viewmodels/structures/auto-collapse/AutoCollapse-test.ts

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+/*
+ * Copyright 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+import type { PanelImperativeHandle } from "@element-hq/web-shared-components";
+import { AutoCollapse } from "../../../../src/viewmodels/structures/auto-collapse/AutoCollapse";
+import { MockPanelHandle } from "./mocks";
+import type { CollapseHandler } from "../../../../src/viewmodels/structures/auto-collapse/CollapseHandler";
+import { BaseCollapseBehaviour } from "../../../../src/viewmodels/structures/auto-collapse/behaviours/BaseCollapseBehaviour";
+
+let instances: BaseCollapseBehaviour[] = [];
+
+class MockBehaviour extends BaseCollapseBehaviour {
+    public constructor(collapseHandler: CollapseHandler) {
+        super(collapseHandler);
+        instances.push(this);
+    }
+
+    public onLeftPanelResized = jest.fn();
+}
+
+class MockBehaviourWithStartCollapsed extends MockBehaviour {
+    public static shouldStartCollapsed(): boolean {
+        return true;
+    }
+}
+
+class MockBehaviourWithIgnoreResize extends MockBehaviour {
+    public get shouldIgnoreResize(): boolean {
+        return true;
+    }
+}
+
+jest.mock("../../../../src/viewmodels/structures/auto-collapse/behaviours/behaviours", () => {
+    return {
+        // eslint-disable-next-line @typescript-eslint/naming-convention
+        get Behaviours() {
+            return [MockBehaviour, MockBehaviour, MockBehaviourWithIgnoreResize, MockBehaviourWithStartCollapsed];
+        },
+    };
+});
+
+describe("AutoCollapse", () => {
+    beforeEach(() => {
+        instances = [];
+    });
+
+    it("should call onLeftPanelResized of each behaviour", () => {
+        const setCollapsed = jest.fn();
+        const panelHandle = new MockPanelHandle();
+        const autoCollapse = new AutoCollapse(setCollapsed);
+        autoCollapse.setHandle(panelHandle as unknown as PanelImperativeHandle);
+        autoCollapse.onLeftPanelResized();
+        for (const behaviour of instances) {
+            expect(behaviour.onLeftPanelResized).toHaveBeenCalledTimes(1);
+        }
+        expect(autoCollapse.isAutoCollapsed).toBe(false);
+    });
+
+    it("should calculate shouldStartCollapsed correctly", () => {
+        expect(AutoCollapse.shouldStartCollapsed()).toBe(true);
+    });
+
+    it("should calculate shouldIgnoreResize correctly", () => {
+        const setCollapsed = jest.fn();
+        const panelHandle = new MockPanelHandle();
+        const autoCollapse = new AutoCollapse(setCollapsed);
+        autoCollapse.setHandle(panelHandle as unknown as PanelImperativeHandle);
+        expect(autoCollapse.shouldIgnoreResize).toBe(true);
+    });
+});