refactor(web): split TimelineContext into data, view, and display contexts

Reduces unnecessary re-renders by separating the monolithic 20+ property
context into TimelineDataContext, TimelineViewContext, and
TimelineDisplayContext. Panel components now subscribe only to the
slices they need.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/components/timeline/ProjectColorLegend.tsx

@@ -2,12 +2,13 @@
 
 import { clsx } from "clsx";
 import { memo, useMemo, useState } from "react";
-import { useTimelineContext } from "./TimelineContext.js";
+import { useTimelineData, useTimelineView } from "./TimelineContext.js";
 import { getProjectColor } from "~/lib/project-colors.js";
 import { FadeIn } from "~/components/ui/FadeIn.js";
 
 function ProjectColorLegendInner() {
-  const { visibleAssignments, viewMode, projectGroups } = useTimelineContext();
+  const { visibleAssignments, projectGroups } = useTimelineData();
+  const { viewMode } = useTimelineView();
   const [dismissed, setDismissed] = useState(false);
 
   // Collect unique visible projects with their colors
@@ -76,7 +77,13 @@ function ProjectColorLegendInner() {
           )}
           aria-label="Dismiss color legend"
         >
-          <svg className="w-3 h-3" viewBox="0 0 12 12" fill="none" stroke="currentColor" strokeWidth="2">
+          <svg
+            className="w-3 h-3"
+            viewBox="0 0 12 12"
+            fill="none"
+            stroke="currentColor"
+            strokeWidth="2"
+          >
             <path d="M2 2l8 8M10 2l-8 8" />
           </svg>
         </button>

apps/web/src/components/timeline/TimelineContext.tsx

@@ -176,10 +176,9 @@ export type HolidayOverlayEntry = {
   metroCityName?: string | null;
 };
 
-// ─── Context shape ──────────────────────────────────────────────────────────
+// ─── Context shapes ─────────────────────────────────────────────────────────
 
-export interface TimelineContextValue {
+export interface TimelineDataContextValue {
-  // ─ Data
   assignments: TimelineAssignmentEntry[];
   demands: TimelineDemandEntry[];
   visibleAssignments: TimelineAssignmentEntry[];
@@ -190,8 +189,13 @@ export interface TimelineContextValue {
   allocsByResource: Map<string, TimelineAssignmentEntry[]>;
   projectGroups: ProjectGroup[];
   openDemandsByProject: Map<string, TimelineDemandEntry[]>;
+  isLoading: boolean;
+  isInitialLoading: boolean;
+  isEntriesError: boolean;
+  totalAllocCount: number;
+}
 
-  // ─ View state
+export interface TimelineViewContextValue {
   viewStart: Date;
   viewEnd: Date;
   viewDays: number;
@@ -204,32 +208,46 @@ export interface TimelineContextValue {
   viewMode: ViewMode;
   setViewMode: React.Dispatch<React.SetStateAction<ViewMode>>;
   today: Date;
+  activeFilterCount: number;
+}
 
-  // ─ Display preferences
+export interface TimelineDisplayContextValue {
   displayMode: TimelineDisplayMode;
   heatmapScheme: HeatmapColorScheme;
   blinkOverbookedDays: boolean;
-
-  // ─ Loading
-  isLoading: boolean;
-  isInitialLoading: boolean;
-  isEntriesError: boolean;
-  totalAllocCount: number;
-  activeFilterCount: number;
-
-  // ─ SSE is initialized by the provider (no value exposed)
 }
 
-const TimelineContext = createContext<TimelineContextValue | null>(null);
+export type TimelineContextValue = TimelineDataContextValue &
+  TimelineViewContextValue &
+  TimelineDisplayContextValue;
 
-export function useTimelineContext(): TimelineContextValue {
+const TimelineDataContext = createContext<TimelineDataContextValue | null>(null);
-  const ctx = useContext(TimelineContext);
+const TimelineViewContext = createContext<TimelineViewContextValue | null>(null);
-  if (!ctx) {
+const TimelineDisplayContext = createContext<TimelineDisplayContextValue | null>(null);
-    throw new Error("useTimelineContext must be used within a <TimelineProvider>");
+
-  }
+export function useTimelineData(): TimelineDataContextValue {
+  const ctx = useContext(TimelineDataContext);
+  if (!ctx) throw new Error("useTimelineData must be used within a <TimelineProvider>");
   return ctx;
 }
 
+export function useTimelineView(): TimelineViewContextValue {
+  const ctx = useContext(TimelineViewContext);
+  if (!ctx) throw new Error("useTimelineView must be used within a <TimelineProvider>");
+  return ctx;
+}
+
+export function useTimelineDisplay(): TimelineDisplayContextValue {
+  const ctx = useContext(TimelineDisplayContext);
+  if (!ctx) throw new Error("useTimelineDisplay must be used within a <TimelineProvider>");
+  return ctx;
+}
+
+/** Combined hook — use the specific hooks above to avoid unnecessary re-renders. */
+export function useTimelineContext(): TimelineContextValue {
+  return { ...useTimelineData(), ...useTimelineView(), ...useTimelineDisplay() };
+}
+
 // ─── Provider ───────────────────────────────────────────────────────────────
 
 interface TimelineProviderProps {
@@ -752,7 +770,7 @@ export function TimelineProvider({
     filters.projectIds.length +
     filters.countryCodes.length;
 
-  const value = useMemo<TimelineContextValue>(
+  const dataValue = useMemo<TimelineDataContextValue>(
     () => ({
       assignments,
       demands,
@@ -764,26 +782,10 @@ export function TimelineProvider({
       allocsByResource,
       projectGroups,
       openDemandsByProject,
-      viewStart,
-      viewEnd,
-      viewDays,
-      setViewStart,
-      setViewDays,
-      filters,
-      setFilters,
-      filterOpen,
-      setFilterOpen,
-      viewMode,
-      setViewMode,
-      today,
-      displayMode,
-      heatmapScheme,
-      blinkOverbookedDays,
       isLoading,
       isInitialLoading,
       isEntriesError,
       totalAllocCount,
-      activeFilterCount,
     }),
     [
       assignments,
@@ -796,23 +798,44 @@ export function TimelineProvider({
       allocsByResource,
       projectGroups,
       openDemandsByProject,
-      viewStart,
-      viewEnd,
-      viewDays,
-      filters,
-      filterOpen,
-      viewMode,
-      today,
-      displayMode,
-      heatmapScheme,
-      blinkOverbookedDays,
       isLoading,
       isInitialLoading,
       isEntriesError,
       totalAllocCount,
-      activeFilterCount,
     ],
   );
 
-  return <TimelineContext.Provider value={value}>{children}</TimelineContext.Provider>;
+  const viewValue = useMemo<TimelineViewContextValue>(
+    () => ({
+      viewStart,
+      viewEnd,
+      viewDays,
+      setViewStart,
+      setViewDays,
+      filters,
+      setFilters,
+      filterOpen,
+      setFilterOpen,
+      viewMode,
+      setViewMode,
+      today,
+      activeFilterCount,
+    }),
+    [viewStart, viewEnd, viewDays, filters, filterOpen, viewMode, today, activeFilterCount],
+  );
+
+  const displayValue = useMemo<TimelineDisplayContextValue>(
+    () => ({ displayMode, heatmapScheme, blinkOverbookedDays }),
+    [displayMode, heatmapScheme, blinkOverbookedDays],
+  );
+
+  return (
+    <TimelineDataContext.Provider value={dataValue}>
+      <TimelineViewContext.Provider value={viewValue}>
+        <TimelineDisplayContext.Provider value={displayValue}>
+          {children}
+        </TimelineDisplayContext.Provider>
+      </TimelineViewContext.Provider>
+    </TimelineDataContext.Provider>
+  );
 }

apps/web/src/components/timeline/TimelineProjectPanel.tsx

@@ -5,7 +5,9 @@ import { memo, startTransition, useCallback, useEffect, useMemo, useRef, useStat
 import { useVirtualizer } from "@tanstack/react-virtual";
 import type { CSSProperties } from "react";
 import {
-  useTimelineContext,
+  useTimelineData,
+  useTimelineView,
+  useTimelineDisplay,
   type TimelineAssignmentEntry,
   type TimelineDemandEntry,
 } from "./TimelineContext.js";
@@ -32,7 +34,12 @@ import {
   ORDER_TYPE_COLORS,
 } from "./timelineConstants.js";
 import { getProjectColor } from "~/lib/project-colors.js";
-import type { DragState, AllocDragState, RangeState, MultiSelectState } from "~/hooks/useTimelineDrag.js";
+import type {
+  DragState,
+  AllocDragState,
+  RangeState,
+  MultiSelectState,
+} from "~/hooks/useTimelineDrag.js";
 import type { AllocMouseDownInfo, RowMouseDownInfo } from "./TimelineResourcePanel.js";
 import {
   buildVacationBlocksByResource,
@@ -50,10 +57,7 @@ import {
 } from "./timelineHover.js";
 import { buildResourceHeatmapSeries } from "./timelineHeatmap.js";
 import { buildResourceCapacitySeries } from "./timelineCapacity.js";
-import {
+import { buildProjectRowMetrics, type ProjectDayMetric } from "./timelineProjectMetrics.js";
-  buildProjectRowMetrics,
-  type ProjectDayMetric,
-} from "./timelineProjectMetrics.js";
 import {
   buildProjectFlatRows,
   estimateProjectRowHeight,
@@ -147,18 +151,10 @@ function TimelineProjectPanelInner({
   gridLines,
   xToDate,
 }: TimelineProjectPanelProps) {
-  const {
+  const { projectGroups, openDemandsByProject, allocsByResource, vacationsByResource } =
-    projectGroups,
+    useTimelineData();
-    openDemandsByProject,
+  const { filters, activeFilterCount, today } = useTimelineView();
-    allocsByResource,
+  const { displayMode, heatmapScheme, blinkOverbookedDays } = useTimelineDisplay();
-    vacationsByResource,
-    filters,
-    displayMode,
-    heatmapScheme,
-    blinkOverbookedDays,
-    activeFilterCount,
-    today,
-  } = useTimelineContext();
 
   const visualAllocsByResource = useMemo(() => {
     if (optimisticAllocations.size === 0) return allocsByResource;
@@ -171,13 +167,14 @@ function TimelineProjectPanelInner({
   }, [allocsByResource, optimisticAllocations]);
 
   const visualProjectGroups = useMemo(
-    () => projectGroups.map((project) => ({
+    () =>
-      ...project,
+      projectGroups.map((project) => ({
-      resourceRows: project.resourceRows.map((row) => ({
+        ...project,
-        ...row,
+        resourceRows: project.resourceRows.map((row) => ({
-        allocs: applyVisualOverrides(row.allocs, optimisticAllocations),
+          ...row,
+          allocs: applyVisualOverrides(row.allocs, optimisticAllocations),
+        })),
       })),
-    })),
     [projectGroups, optimisticAllocations],
   );
 
@@ -224,7 +221,15 @@ function TimelineProjectPanelInner({
         totalCanvasWidth,
         filters.showWeekends,
       ),
-    [CELL_WIDTH, filters.showVacations, filters.showWeekends, toLeft, toWidth, totalCanvasWidth, vacationsByResource],
+    [
+      CELL_WIDTH,
+      filters.showVacations,
+      filters.showWeekends,
+      toLeft,
+      toWidth,
+      totalCanvasWidth,
+      vacationsByResource,
+    ],
   );
 
   const projectRowMetrics = useMemo(() => {
@@ -262,10 +267,7 @@ function TimelineProjectPanelInner({
 
       const rect = e.currentTarget.getBoundingClientRect();
       const dayIndex = Math.floor((e.clientX - rect.left) / CELL_WIDTH);
-      if (
+      if (dayIndex === lastHeatmapDayRef.current && resourceId === lastHeatmapResourceRef.current)
-        dayIndex === lastHeatmapDayRef.current &&
-        resourceId === lastHeatmapResourceRef.current
-      )
         return;
 
       pendingHeatmapRef.current = { clientX: e.clientX, rect, resourceId };
@@ -310,7 +312,14 @@ function TimelineProjectPanelInner({
         return;
       }
 
-      updateTooltipPosition(vacationTooltipPosRef, vacationTooltipRef, e.clientX, e.clientY, 14, -8);
+      updateTooltipPosition(
+        vacationTooltipPosRef,
+        vacationTooltipRef,
+        e.clientX,
+        e.clientY,
+        14,
+        -8,
+      );
       scheduleVacationHoverUpdate({
         frameRef: vacationHoverRafRef,
         hoveredKeyRef: hoveredVacationKeyRef,
@@ -350,16 +359,13 @@ function TimelineProjectPanelInner({
     }
   }, [demandHover]);
 
-  const handleDemandHoverMove = useCallback(
+  const handleDemandHoverMove = useCallback((e: React.MouseEvent, demand: TimelineDemandEntry) => {
-    (e: React.MouseEvent, demand: TimelineDemandEntry) => {
+    updateTooltipPosition(demandTooltipPosRef, demandTooltipRef, e.clientX, e.clientY, 16, -36);
-      updateTooltipPosition(demandTooltipPosRef, demandTooltipRef, e.clientX, e.clientY, 16, -36);
 
-      startTransition(() => {
+    startTransition(() => {
-        setDemandHover(buildDemandHoverData(demand));
+      setDemandHover(buildDemandHoverData(demand));
-      });
+    });
-    },
+  }, []);
-    [],
-  );
 
   useEffect(
     () => () => {
@@ -432,8 +438,14 @@ function TimelineProjectPanelInner({
                 return (
                   <div
                     data-project-group="true"
-                    className={clsx("flex border-b border-gray-200 dark:border-gray-700 group/proj", colors.light)}
+                    className={clsx(
-                    style={{ height: PROJECT_HEADER_HEIGHT, borderLeft: `4px solid ${customColor ?? projectColor.hex}` }}
+                      "flex border-b border-gray-200 dark:border-gray-700 group/proj",
+                      colors.light,
+                    )}
+                    style={{
+                      height: PROJECT_HEADER_HEIGHT,
+                      borderLeft: `4px solid ${customColor ?? projectColor.hex}`,
+                    }}
                   >
                     <div
                       className={clsx(
@@ -570,7 +582,9 @@ function TimelineProjectPanelInner({
                     <div className="text-xs font-medium text-gray-800 dark:text-gray-200 truncate cursor-pointer hover:text-brand-600 dark:hover:text-brand-400 transition-colors">
                       {row.resource.displayName}
                     </div>
-                    <div className="text-[10px] text-gray-400 dark:text-gray-500 truncate">{row.resource.eid}</div>
+                    <div className="text-[10px] text-gray-400 dark:text-gray-500 truncate">
+                      {row.resource.eid}
+                    </div>
                   </div>
                 </div>
 
@@ -721,7 +735,9 @@ function renderOpenDemandRow(
             ?
           </div>
           <div className="min-w-0">
-            <div className="text-xs font-medium text-amber-700 dark:text-amber-400 truncate">Open demand</div>
+            <div className="text-xs font-medium text-amber-700 dark:text-amber-400 truncate">
+              Open demand
+            </div>
             <div className="text-[10px] text-amber-500 dark:text-amber-600 truncate">
               {openDemandCount} open demand{openDemandCount > 1 ? "s" : ""}
             </div>
@@ -741,19 +757,23 @@ function renderOpenDemandRow(
           const allocStart = new Date(alloc.startDate);
           const allocEnd = new Date(alloc.endDate);
 
-          const isAllocDragged = allocDragState.isActive && allocDragState.allocationId === alloc.id;
+          const isAllocDragged =
+            allocDragState.isActive && allocDragState.allocationId === alloc.id;
           const dispStart =
             isAllocDragged && allocDragState.currentStartDate
               ? allocDragState.currentStartDate
               : allocStart;
           const dispEnd =
-            isAllocDragged && allocDragState.currentEndDate ? allocDragState.currentEndDate : allocEnd;
+            isAllocDragged && allocDragState.currentEndDate
+              ? allocDragState.currentEndDate
+              : allocEnd;
 
           // Multi-drag visual offset
           const isMultiDragTarget =
-            multiSelectState.isMultiDragging &&
+            multiSelectState.isMultiDragging && selectedAllocationSet.has(alloc.id);
-            selectedAllocationSet.has(alloc.id);
+          const multiDragPx = isMultiDragTarget
-          const multiDragPx = isMultiDragTarget ? multiSelectState.multiDragDaysDelta * CELL_WIDTH : 0;
+            ? multiSelectState.multiDragDaysDelta * CELL_WIDTH
+            : 0;
           const multiDragMode = multiSelectState.multiDragMode;
 
           let left = toLeft(dispStart);
@@ -838,9 +858,12 @@ function renderOpenDemandRow(
                 border: `2px dashed ${roleColor}B3`,
                 ...((multiDragPx && multiDragMode === "move") || dragTransform
                   ? {
-                      transform: [dragTransform, multiDragPx && multiDragMode === "move"
+                      transform: [
-                        ? `translateX(${multiDragPx}px)`
+                        dragTransform,
-                        : null]
+                        multiDragPx && multiDragMode === "move"
+                          ? `translateX(${multiDragPx}px)`
+                          : null,
+                      ]
                         .filter(Boolean)
                         .join(" "),
                     }
@@ -964,18 +987,18 @@ function renderProjectUtilOverlay(
     const projPct = (projH / capacityH) * 100;
     const totalPct = (totalH / capacityH) * 100;
     const projColor = useHeatmapColors
-      ? heatmapColor(
+      ? (heatmapColor(
           projPct,
           heatmapScheme as import("~/hooks/useAppPreferences.js").HeatmapColorScheme,
           "bar",
-        ) ?? "rgba(59,130,246,0.8)"
+        ) ?? "rgba(59,130,246,0.8)")
       : "rgba(96,165,250,0.8)";
     const totalColor = useHeatmapColors
-      ? heatmapColor(
+      ? (heatmapColor(
           totalPct,
           heatmapScheme as import("~/hooks/useAppPreferences.js").HeatmapColorScheme,
           "bar",
-        ) ?? "rgba(156,163,175,0.5)"
+        ) ?? "rgba(156,163,175,0.5)")
       : isOver
         ? "rgba(252,211,77,0.8)"
         : "rgba(209,213,219,0.8)";
@@ -1081,8 +1104,7 @@ function renderProjectDragHandles(
 
     // Multi-drag visual offset
     const isMultiDragTarget =
-      multiSelectState.isMultiDragging &&
+      multiSelectState.isMultiDragging && selectedAllocationSet.has(alloc.id);
-      selectedAllocationSet.has(alloc.id);
     const multiDragPx = isMultiDragTarget ? multiSelectState.multiDragDaysDelta * CELL_WIDTH : 0;
     const multiDragMode = multiSelectState.multiDragMode;
 
@@ -1132,9 +1154,7 @@ function renderProjectDragHandles(
             ? {
                 transform: [
                   dragTransform,
-                  multiDragPx && multiDragMode === "move"
+                  multiDragPx && multiDragMode === "move" ? `translateX(${multiDragPx}px)` : null,
-                    ? `translateX(${multiDragPx}px)`
-                    : null,
                 ]
                   .filter(Boolean)
                   .join(" "),

apps/web/src/components/timeline/TimelineResourcePanel.tsx

@@ -3,7 +3,12 @@
 import { clsx } from "clsx";
 import { memo, startTransition, useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { useVirtualizer } from "@tanstack/react-virtual";
-import { useTimelineContext, type TimelineAssignmentEntry } from "./TimelineContext.js";
+import {
+  useTimelineData,
+  useTimelineView,
+  useTimelineDisplay,
+  type TimelineAssignmentEntry,
+} from "./TimelineContext.js";
 import { applyVisualOverrides, type TimelineVisualOverrides } from "./allocationVisualState.js";
 import { ConflictOverlay } from "./ConflictOverlay.js";
 import { computeSubLanes } from "./utils.js";
@@ -117,18 +122,9 @@ function TimelineResourcePanelInner({
   gridLines,
   xToDate,
 }: TimelineResourcePanelProps) {
-  const {
+  const { resources, allocsByResource, vacationsByResource } = useTimelineData();
-    resources,
+  const { filters, viewStart, viewEnd, activeFilterCount } = useTimelineView();
-    allocsByResource,
+  const { displayMode, heatmapScheme, blinkOverbookedDays } = useTimelineDisplay();
-    vacationsByResource,
-    filters,
-    viewStart,
-    viewEnd,
-    displayMode,
-    heatmapScheme,
-    blinkOverbookedDays,
-    activeFilterCount,
-  } = useTimelineContext();
 
   // ─── Heatmap hover state ────────────────────────────────────────────────────
   const heatmapRafRef = useRef<number | null>(null);

apps/web/src/components/timeline/TimelineView.tsx

@@ -28,7 +28,8 @@ import { HEADER_DAY_HEIGHT, HEADER_MONTH_HEIGHT, LABEL_WIDTH } from "./timelineC
 import { formatDateShort } from "~/lib/format.js";
 import {
   TimelineProvider,
-  useTimelineContext,
+  useTimelineData,
+  useTimelineView,
   type TimelineAssignmentEntry,
 } from "./TimelineContext.js";
 import { TimelineResourcePanel } from "./TimelineResourcePanel.js";
@@ -339,17 +340,22 @@ function TimelineViewContent({
   undo: () => Promise<void>;
   redo: () => Promise<void>;
 }) {
-  const ctx = useTimelineContext();
   const {
     resources,
     projectGroups,
     allocsByResource,
     openDemandsByProject,
+    visibleAssignments,
+    visibleDemands,
+    isLoading,
+    isInitialLoading,
+    isEntriesError,
+    totalAllocCount,
+  } = useTimelineData();
+  const {
     viewStart,
     viewEnd,
     viewDays,
-    visibleAssignments,
-    visibleDemands,
     setViewStart,
     setViewDays,
     filters,
@@ -359,11 +365,7 @@ function TimelineViewContent({
     viewMode,
     setViewMode,
     today,
-    isLoading,
+  } = useTimelineView();
-    isInitialLoading,
-    isEntriesError,
-    totalAllocCount,
-  } = ctx;
 
   const scrollContainerRef = useRef<HTMLDivElement>(null);
   const canvasRef = useRef<HTMLDivElement>(null);