add comment for hooks

apps/web/src/hooks/use-disable-browser-zoom.ts

@@ -1,13 +1,32 @@
 import { useEffect } from "react";
 
+/**
+ * useDisableBrowserZoom
+ *
+ * This React hook prevents users from zooming in/out the browser window using keyboard shortcuts,
+ * mouse wheel, or gesture events (such as pinch-to-zoom on trackpads or touch devices).
+ *
+ * Typical use case: apps with fixed-size UIs, custom editors, or when zooming would break layout.
+ *
+ * NOTE: Disabling browser zoom may negatively affect accessibility and user experience.
+ * Use with caution, especially for public-facing applications.
+ */
 export const useDisableBrowserZoom = () => {
   useEffect(() => {
+    /**
+     * Prevents browser zoom when user holds Ctrl (or Cmd on Mac) and scrolls the mouse wheel.
+     */
     const handleWheel = (e: WheelEvent) => {
       if (e.ctrlKey) {
         e.preventDefault();
       }
     };
 
+    /**
+     * Prevents browser zoom via keyboard shortcuts:
+     * Ctrl/Cmd + '+', '-', '=', or '0' (reset zoom)
+     * Some keyboards emit '=' for '+' (without Shift).
+     */
     const handleKeyDown = (e: KeyboardEvent) => {
       if (e.ctrlKey) {
         const key = e.key;
@@ -17,23 +36,22 @@ export const useDisableBrowserZoom = () => {
       }
     };
 
+    /**
+     * Prevents pinch-zoom gestures on supported browsers (mainly Safari/macOS/iOS).
+     * gesturestart, gesturechange, and gestureend are non-standard and not supported everywhere.
+     */
     const handleGesture = (e: Event) => {
       e.preventDefault();
     };
 
+    // Attach event listeners (passive: false is required for preventDefault to work)
     window.addEventListener("wheel", handleWheel, { passive: false });
     window.addEventListener("keydown", handleKeyDown, { passive: false });
+    window.addEventListener("gesturestart", handleGesture, { passive: false });
+    window.addEventListener("gesturechange", handleGesture, { passive: false });
+    window.addEventListener("gestureend", handleGesture, { passive: false });
 
-    window.addEventListener("gesturestart", handleGesture, {
+    // Cleanup listeners on unmount to avoid memory leaks
-      passive: false,
-    });
-    window.addEventListener("gesturechange", handleGesture, {
-      passive: false,
-    });
-    window.addEventListener("gestureend", handleGesture, {
-      passive: false,
-    });
-
     return () => {
       window.removeEventListener("wheel", handleWheel);
       window.removeEventListener("keydown", handleKeyDown);

apps/web/src/hooks/use-timeline-playhead.ts

@@ -11,6 +11,13 @@ interface UseTimelinePlayheadProps {
   rulerScrollRef: React.RefObject<HTMLDivElement>;
 }
 
+/**
+ * useTimelinePlayhead
+ *
+ * Custom hook to manage playhead (scrubbing) logic for a timeline editor.
+ * Handles mouse interaction for timeline ruler, calculates time from mouse,
+ * and enables smooth scrubbing without unnecessary re-renders.
+ */
 export function useTimelinePlayhead({
   currentTime,
   duration,
@@ -19,17 +26,35 @@ export function useTimelinePlayhead({
   rulerRef,
   rulerScrollRef,
 }: UseTimelinePlayheadProps) {
+  // Get current project info (especially FPS) from global store
   const { activeProject } = useProjectStore();
 
+  // Ref to track if currently scrubbing
   const isScrubbingRef = useRef(false);
+
+  // Ref to hold the playhead time while scrubbing (does not trigger re-render)
   const scrubTimeRef = useRef<number | null>(null);
+
+  // State to force re-render when scrubbing ends
   const [_, forceRerender] = useState(0);
 
+  /**
+   * Determines the actual playhead position:
+   * - If scrubbing, use the value in scrubTimeRef
+   * - Otherwise, use the currentTime (controlled by external state)
+   */
   const playheadPosition =
     isScrubbingRef.current && scrubTimeRef.current !== null
       ? scrubTimeRef.current
       : currentTime;
 
+  /**
+   * Calculate timeline time (in seconds) based on mouse X position.
+   * - Gets bounding rect of the ruler
+   * - Adjusts for scroll position if ruler is scrollable
+   * - Converts X pixel offset to seconds using current zoom level
+   * - Snaps to nearest frame using FPS
+   */
   const getTimeFromMouse = useCallback(
     (e: MouseEvent | React.MouseEvent) => {
       const ruler = rulerRef.current;
@@ -43,6 +68,7 @@ export function useTimelinePlayhead({
       const scrollLeft = scrollArea.scrollLeft;
       const x = e.clientX - rect.left + scrollLeft;
 
+      // Calculate how many pixels represent one second, depending on zoom
       const pixelsPerSecond = 50 * zoomLevel;
       const rawTime = Math.max(0, Math.min(duration, x / pixelsPerSecond));
       const time = snapTimeToFrame(rawTime, activeProject?.fps || 30);
@@ -51,6 +77,13 @@ export function useTimelinePlayhead({
     [rulerRef, rulerScrollRef, duration, zoomLevel, activeProject?.fps]
   );
 
+  /**
+   * Handle mouse down event on the ruler:
+   * - Starts scrubbing and updates playhead immediately
+   * - Registers mousemove/mouseup events to allow scrubbing
+   * - Updates time as mouse moves and seeks to new time
+   * - Cleans up listeners and triggers re-render when scrubbing ends
+   */
   const handleRulerMouseDown = useCallback(
     (e: React.MouseEvent) => {
       e.preventDefault();
@@ -61,6 +94,7 @@ export function useTimelinePlayhead({
       scrubTimeRef.current = time;
       seek(time);
 
+      // Mouse move handler: update playhead and seek to new time
       const onMouseMove = (e: MouseEvent) => {
         const t = getTimeFromMouse(e);
         if (t !== scrubTimeRef.current) {
@@ -69,6 +103,7 @@ export function useTimelinePlayhead({
         }
       };
 
+      // Mouse up handler: stop scrubbing, cleanup, and force re-render
       const onMouseUp = () => {
         isScrubbingRef.current = false;
         window.removeEventListener("mousemove", onMouseMove);
@@ -76,6 +111,7 @@ export function useTimelinePlayhead({
         forceRerender((v) => v + 1);
       };
 
+      // Attach listeners to window for drag outside the ruler area
       window.addEventListener("mousemove", onMouseMove);
       window.addEventListener("mouseup", onMouseUp);
     },
@@ -83,7 +119,7 @@ export function useTimelinePlayhead({
   );
 
   return {
-    playheadPosition,
+    playheadPosition, // Current playhead position (real-time while scrubbing)
-    handleRulerMouseDown,
+    handleRulerMouseDown, // Attach to the ruler's onMouseDown
   };
 }

apps/web/src/hooks/use-timeline-zoom.ts

@@ -15,15 +15,30 @@ interface UseTimelineZoomReturn {
   handleWheel: (e: React.WheelEvent) => void;
 }
 
+/**
+ * useTimelineZoom
+ *
+ * Custom hook to manage zoom logic for a timeline component.
+ * Handles zoom state, step calculation, level changes, and mouse wheel zooming (with ctrl/meta).
+ */
 export function useTimelineZoom(): UseTimelineZoomReturn {
+  // Current zoom level (1 = default)
   const [zoomLevel, setZoomLevel] = useState(1);
 
+  /**
+   * Calculate the current zoom step based on the zoom level and a base step constant.
+   * Ensures minimum step is 1 (prevents zero or negative step).
+   */
   const zoomStep = useMemo(
     () =>
       Math.max(1, Math.round(zoomLevel / TIMELINE_CONSTANTS.ZOOM_STEP_BASE)),
     [zoomLevel]
   );
 
+  /**
+   * Update the zoom level using a given step.
+   * The zoom level is clamped to a minimum value defined in constants.
+   */
   const handleChangeZoomStep = useCallback((newStep: number) => {
     setZoomLevel(
       Math.max(
@@ -33,6 +48,10 @@ export function useTimelineZoom(): UseTimelineZoomReturn {
     );
   }, []);
 
+  /**
+   * Update the zoom level directly.
+   * The new value is clamped between the defined minimum and maximum levels.
+   */
   const handleChangeZoomLevel = useCallback((newLevel: number) => {
     setZoomLevel(
       Math.max(
@@ -42,7 +61,10 @@ export function useTimelineZoom(): UseTimelineZoomReturn {
     );
   }, []);
 
-  // Mouse wheel zoom, ctrl/meta gesture
+  /**
+   * Handle zooming using mouse wheel + ctrl/meta key (like browser zoom).
+   * Prevents default browser behavior and updates zoom level accordingly.
+   */
   const handleWheel = useCallback((e: React.WheelEvent) => {
     if (e.ctrlKey || e.metaKey) {
       e.preventDefault?.();
@@ -59,12 +81,13 @@ export function useTimelineZoom(): UseTimelineZoomReturn {
     }
   }, []);
 
+  // Return all handlers and state values for use in timeline components
   return {
-    zoomLevel,
+    zoomLevel, // Current zoom level
-    zoomStep,
+    zoomStep, // Current zoom step (calculated from zoomLevel)
-    setZoomLevel,
+    setZoomLevel, // Directly set the zoom level (accepts value or updater function)
-    handleChangeZoomStep,
+    handleChangeZoomStep, // Change zoom by step value
-    handleChangeZoomLevel,
+    handleChangeZoomLevel, // Change zoom by level value
-    handleWheel,
+    handleWheel, // Handler for mouse wheel zooming
   };
 }