refactor(web): Clarify property names in Timeline and Scrubber

Renamed properties across Timeline/Scrubber components for clarity:
  - scrubOverallPercent → timelineScrollPercent
  - scrubberMonthPercent → viewportTopMonthScrollPercent
  - scrubberMonth → viewportTopMonth
  - leadout → isInLeadOutSection

  Additional changes:
  - Updated ScrubberListener signature to accept object parameter
  - Added detailed JSDoc comments for all Scrubber props
  - Fixed callback invocations to use new object syntax
  - Aligned Timeline's local state variables with Scrubber prop names

web/src/lib/components/timeline/Scrubber.svelte

@@ -3,7 +3,7 @@
   import type { ScrubberMonth } from '$lib/managers/timeline-manager/types';
   import { mobileDevice } from '$lib/stores/mobile-device.svelte';
   import { getTabbable } from '$lib/utils/focus-util';
-  import { type ScrubberListener } from '$lib/utils/timeline-util';
+  import { type ScrubberListener, type TimelineYearMonth } from '$lib/utils/timeline-util';
   import { Icon } from '@immich/ui';
   import { mdiPlay } from '@mdi/js';
   import { clamp } from 'lodash-es';
@@ -11,18 +11,31 @@
   import { fade, fly } from 'svelte/transition';
 
   interface Props {
+    /** Offset from the top of the timeline (e.g., for headers) */
     timelineTopOffset?: number;
+    /** Offset from the bottom of the timeline (e.g., for footers) */
     timelineBottomOffset?: number;
+    /** Total height of the scrubber component */
     height?: number;
+    /** Timeline manager instance that controls the timeline state */
     timelineManager: TimelineManager;
-    scrubOverallPercent?: number;
+    /** Overall scroll percentage through the entire timeline (0-1), used when no specific month is targeted */
-    scrubberMonthPercent?: number;
+    timelineScrollPercent?: number;
-    scrubberMonth?: { year: number; month: number };
+    /** The percentage of scroll through the month that is currently intersecting the top boundary of the viewport */
-    leadout?: boolean;
+    viewportTopMonthScrollPercent?: number;
+    /** The year/month of the timeline month at the top of the viewport */
+    viewportTopMonth?: TimelineYearMonth;
+    /** Indicates whether the viewport is currently in the lead-out section (after all months) */
+    isInLeadOutSection?: boolean;
+    /** Width of the scrubber component in pixels (bindable for parent component margin adjustments) */
     scrubberWidth?: number;
+    /** Callback fired when user interacts with the scrubber to navigate */
     onScrub?: ScrubberListener;
+    /** Callback fired when keyboard events occur on the scrubber */
     onScrubKeyDown?: (event: KeyboardEvent, element: HTMLElement) => void;
+    /** Callback fired when scrubbing starts */
     startScrub?: ScrubberListener;
+    /** Callback fired when scrubbing stops */
     stopScrub?: ScrubberListener;
   }
 
@@ -31,10 +44,10 @@
     timelineBottomOffset = 0,
     height = 0,
     timelineManager,
-    scrubOverallPercent = 0,
+    timelineScrollPercent = 0,
-    scrubberMonthPercent = 0,
+    viewportTopMonthScrollPercent = 0,
-    scrubberMonth = undefined,
+    viewportTopMonth = undefined,
-    leadout = false,
+    isInLeadOutSection = false,
     onScrub = undefined,
     onScrubKeyDown = undefined,
     startScrub = undefined,
@@ -100,7 +113,7 @@
         offset += scrubberMonthPercent * relativeBottomOffset;
       }
       return offset;
-    } else if (leadout) {
+    } else if (isInLeadOutSection) {
       let offset = relativeTopOffset;
       for (const segment of segments) {
         offset += segment.height;
@@ -111,7 +124,9 @@
       return scrubOverallPercent * (height - (PADDING_TOP + PADDING_BOTTOM));
     }
   };
-  let scrollY = $derived(toScrollFromMonthGroupPercentage(scrubberMonth, scrubberMonthPercent, scrubOverallPercent));
+  let scrollY = $derived(
+    toScrollFromMonthGroupPercentage(viewportTopMonth, viewportTopMonthScrollPercent, timelineScrollPercent),
+  );
   let timelineFullHeight = $derived(timelineManager.scrubberTimelineHeight + timelineTopOffset + timelineBottomOffset);
   let relativeTopOffset = $derived(toScrollY(timelineTopOffset / timelineFullHeight));
   let relativeBottomOffset = $derived(toScrollY(timelineBottomOffset / timelineFullHeight));
@@ -295,12 +310,24 @@
 
     const scrollPercent = toTimelineY(hoverY);
     if (wasDragging === false && isDragging) {
-      void startScrub?.(segmentDate!, scrollPercent, monthGroupPercentY);
+      void startScrub?.({
-      void onScrub?.(segmentDate!, scrollPercent, monthGroupPercentY);
+        scrubberMonth: segmentDate!,
+        overallScrollPercent: scrollPercent,
+        scrubberMonthScrollPercent: monthGroupPercentY,
+      });
+      void onScrub?.({
+        scrubberMonth: segmentDate!,
+        overallScrollPercent: scrollPercent,
+        scrubberMonthScrollPercent: monthGroupPercentY,
+      });
     }
 
     if (wasDragging && !isDragging) {
-      void stopScrub?.(segmentDate!, scrollPercent, monthGroupPercentY);
+      void stopScrub?.({
+        scrubberMonth: segmentDate!,
+        overallScrollPercent: scrollPercent,
+        scrubberMonthScrollPercent: monthGroupPercentY,
+      });
       return;
     }
 
@@ -308,7 +335,11 @@
       return;
     }
 
-    void onScrub?.(segmentDate!, scrollPercent, monthGroupPercentY);
+    void onScrub?.({
+      scrubberMonth: segmentDate!,
+      overallScrollPercent: scrollPercent,
+      scrubberMonthScrollPercent: monthGroupPercentY,
+    });
   };
   /* eslint-disable tscompat/tscompat */
   const getTouch = (event: TouchEvent) => {
@@ -412,7 +443,11 @@
       }
       if (next) {
         event.preventDefault();
-        void onScrub?.({ year: next.year, month: next.month }, -1, 0);
+        void onScrub?.({
+          scrubberMonth: { year: next.year, month: next.month },
+          overallScrollPercent: -1,
+          scrubberMonthScrollPercent: 0,
+        });
         return true;
       }
     }
@@ -422,7 +457,11 @@
         const next = segments[idx + 1];
         if (next) {
           event.preventDefault();
-          void onScrub?.({ year: next.year, month: next.month }, -1, 0);
+          void onScrub?.({
+            scrubberMonth: { year: next.year, month: next.month },
+            overallScrollPercent: -1,
+            scrubberMonthScrollPercent: 0,
+          });
           return true;
         }
       }

web/src/lib/components/timeline/Timeline.svelte

@@ -110,14 +110,19 @@
   let timelineElement: HTMLElement | undefined = $state();
   let showSkeleton = $state(true);
   let isShowSelectDate = $state(false);
-  let scrubberMonthPercent = $state(0);
+  // The percentage of scroll through the month that is currently intersecting the top boundary of the viewport.
-  let scrubberMonth: { year: number; month: number } | undefined = $state(undefined);
+  // Note: There may be multiple months visible within the viewport at any given time.
-  let scrubOverallPercent: number = $state(0);
+  let viewportTopMonthScrollPercent = $state(0);
+  // The timeline month intersecting the top position of the viewport
+  let viewportTopMonth: { year: number; month: number } | undefined = $state(undefined);
+  // Overall scroll percentage through the entire timeline (0-1)
+  let timelineScrollPercent: number = $state(0);
   let scrubberWidth = $state(0);
 
   // 60 is the bottom spacer element at 60px
   let bottomSectionHeight = 60;
-  let leadout = $state(false);
+  // Indicates whether the viewport is currently in the lead-out section (after all months)
+  let isInLeadOutSection = $state(false);
 
   const maxMd = $derived(mobileDevice.maxMd);
   const usingMobileDevice = $derived(mobileDevice.pointerCoarse);
@@ -301,20 +306,19 @@
     scrollTop(scrollToTop);
   };
 
-  // note: don't throttle, debounch, or otherwise make this function async - it causes flicker
+  // note: don't throttle, debounce, or otherwise make this function async - it causes flicker
-  const onScrub: ScrubberListener = (
+  // this function scrolls the timeline to the specified month group and offset, based on scrubber interaction
-    scrubMonth: { year: number; month: number },
+  const onScrub: ScrubberListener = (scrubberData) => {
-    overallScrollPercent: number,
+    const { scrubberMonth, overallScrollPercent, scrubberMonthScrollPercent } = scrubberData;
-    scrubberMonthScrollPercent: number,
+
-  ) => {
+    if (!scrubberMonth || timelineManager.timelineHeight < timelineManager.viewportHeight * 2) {
-    if (!scrubMonth || timelineManager.timelineHeight < timelineManager.viewportHeight * 2) {
       // edge case - scroll limited due to size of content, must adjust - use use the overall percent instead
       const maxScroll = getMaxScroll();
       const offset = maxScroll * overallScrollPercent;
       scrollTop(offset);
     } else {
       const monthGroup = timelineManager.months.find(
-        ({ yearMonth: { year, month } }) => year === scrubMonth.year && month === scrubMonth.month,
+        ({ yearMonth: { year, month } }) => year === scrubberMonth.year && month === scrubberMonth.month,
       );
       if (!monthGroup) {
         return;
@@ -325,7 +329,7 @@
 
   // note: don't throttle, debounch, or otherwise make this function async - it causes flicker
   const handleTimelineScroll = () => {
-    leadout = false;
+    isInLeadOutSection = false;
 
     if (!element) {
       return;
@@ -334,19 +338,19 @@
     if (timelineManager.timelineHeight < timelineManager.viewportHeight * 2) {
       // edge case - scroll limited due to size of content, must adjust -  use the overall percent instead
       const maxScroll = getMaxScroll();
-      scrubOverallPercent = Math.min(1, element.scrollTop / maxScroll);
+      timelineScrollPercent = Math.min(1, element.scrollTop / maxScroll);
 
-      scrubberMonth = undefined;
+      viewportTopMonth = undefined;
-      scrubberMonthPercent = 0;
+      viewportTopMonthScrollPercent = 0;
     } else {
       let top = element.scrollTop;
       if (top < timelineManager.topSectionHeight) {
         // in the lead-in area
-        scrubberMonth = undefined;
+        viewportTopMonth = undefined;
-        scrubberMonthPercent = 0;
+        viewportTopMonthScrollPercent = 0;
         const maxScroll = getMaxScroll();
 
-        scrubOverallPercent = Math.min(1, element.scrollTop / maxScroll);
+        timelineScrollPercent = Math.min(1, element.scrollTop / maxScroll);
         return;
       }
 
@@ -371,15 +375,15 @@
         let next = top - monthGroupHeight * maxScrollPercent;
         // instead of checking for < 0, add a little wiggle room for subpixel resolution
         if (next < -1 && monthGroup) {
-          scrubberMonth = monthGroup;
+          viewportTopMonth = monthGroup;
 
           // allowing next to be at least 1 may cause percent to go negative, so ensure positive percentage
-          scrubberMonthPercent = Math.max(0, top / (monthGroupHeight * maxScrollPercent));
+          viewportTopMonthScrollPercent = Math.max(0, top / (monthGroupHeight * maxScrollPercent));
 
           // compensate for lost precision/rounding errors advance to the next bucket, if present
-          if (scrubberMonthPercent > 0.9999 && i + 1 < monthsLength - 1) {
+          if (viewportTopMonthScrollPercent > 0.9999 && i + 1 < monthsLength - 1) {
-            scrubberMonth = timelineManager.months[i + 1].yearMonth;
+            viewportTopMonth = timelineManager.months[i + 1].yearMonth;
-            scrubberMonthPercent = 0;
+            viewportTopMonthScrollPercent = 0;
           }
 
           found = true;
@@ -388,10 +392,10 @@
         top = next;
       }
       if (!found) {
-        leadout = true;
+        isInLeadOutSection = true;
-        scrubberMonth = undefined;
+        viewportTopMonth = undefined;
-        scrubberMonthPercent = 0;
+        viewportTopMonthScrollPercent = 0;
-        scrubOverallPercent = 1;
+        timelineScrollPercent = 1;
       }
     }
   };
@@ -854,10 +858,10 @@
     height={timelineManager.viewportHeight}
     timelineTopOffset={timelineManager.topSectionHeight}
     timelineBottomOffset={bottomSectionHeight}
-    {leadout}
+    {isInLeadOutSection}
-    {scrubOverallPercent}
+    {timelineScrollPercent}
-    {scrubberMonthPercent}
+    {viewportTopMonthScrollPercent}
-    {scrubberMonth}
+    {viewportTopMonth}
     {onScrub}
     bind:scrubberWidth
     onScrubKeyDown={(evt) => {

web/src/lib/utils/timeline-util.ts

@@ -23,11 +23,11 @@ export type TimelineDateTime = TimelineDate & {
   millisecond: number;
 };
 
-export type ScrubberListener = (
+export type ScrubberListener = (scrubberData: {
-  scrubberMonth: { year: number; month: number },
+  scrubberMonth: { year: number; month: number };
-  overallScrollPercent: number,
+  overallScrollPercent: number;
-  scrubberMonthScrollPercent: number,
+  scrubberMonthScrollPercent: number;
-) => void | Promise<void>;
+}) => void | Promise<void>;
 
 // used for AssetResponseDto.dateTimeOriginal, amongst others
 export const fromISODateTime = (isoDateTime: string, timeZone: string): DateTime<true> =>