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+# Phase 7: Mode Switcher + Week Mode - Research
+
+**Researched:** 2026-04-09
+**Domain:** d3.js visualization modes, Tabler UI segmented controls, client-side data aggregation
+**Confidence:** HIGH
+
+## Summary
+
+Phase 7 adds two UI controls (mode switcher and hours/count toggle) and one new renderer (WeekModeRenderer) to the existing strategy-pattern architecture from Phase 6. The infrastructure is solid -- `ModeRenderer` interface, renderer registry, `HeatmapState` with `mode` and `metric` fields, and shared utilities (color scale, tooltip, date-utils) are all in place. The new work is: (1) render two Tabler `nav-segmented` controls in the widget header, (2) wire their click handlers to update `state.mode` and `state.metric` then call `doRender()`, and (3) implement `WeekModeRenderer` that aggregates `DayEntry[]` by weekday and renders 7 colored cells.
+
+Tabler provides a native `nav-segmented` component that matches the "segmented control" design from CONTEXT.md decisions. No custom CSS needed for the control itself -- just Tabler classes. The week-mode renderer is straightforward d3 work: group existing data by day-of-week (0-6), sum hours/count per weekday, render 7 rectangles with the shared `buildColorScale()`. The `getDayLabels()` and weekday-index calculation in `date-utils.ts` already handle start-of-week preference.
+
+**Primary recommendation:** Build controls in JS (not Twig) since they interact with `HeatmapState`; keep the Twig template unchanged. Register `WeekModeRenderer` alongside `YearModeRenderer` at module level.
+
+<user_constraints>
+## User Constraints (from CONTEXT.md)
+
+### Locked Decisions
+- D-01: Segmented control in widget header row (Kimai Tabler card header area), next to title
+- D-02: "Year" and "Week" as the two mode options (Day/Combined in Phase 9)
+- D-03: Active mode highlighted using Kimai/Tabler CSS conventions
+- D-04: Week-mode horizontal layout -- 7 cells, one per weekday, colored by aggregated metric
+- D-05: Day labels alongside cells, respecting user's start-of-week from `state.weekStart`
+- D-06: Client-side aggregation of existing DayEntry[] grouped by weekday (no backend changes)
+- D-07: Tooltip on hover: weekday name + aggregated value
+- D-08: Hours/Count toggle is a separate small segmented control
+- D-09: Placed adjacent to mode switcher in header
+- D-10: Toggles `state.metric` between 'hours' and 'count', triggers re-render without re-fetch
+- D-11: Affects color scale in both year and week modes
+
+### Claude's Discretion
+- Exact sizing/spacing of week-mode cells
+- Whether week-mode cells are clickable (and what click-through shows)
+- Stats row behavior when in week mode
+- Exact Tabler CSS classes for segmented controls
+- Animation/transition when switching modes
+
+### Deferred Ideas (OUT OF SCOPE)
+None
+</user_constraints>
+
+<phase_requirements>
+## Phase Requirements
+
+| ID | Description | Research Support |
+|----|-------------|------------------|
+| VIZ-01 | Mode switcher UI allows toggling between year, week, day, and combined views | Tabler `nav-segmented` component; only Year/Week for this phase per D-02 |
+| VIZ-02 | Week-mode renders day-of-week aggregation showing busiest weekdays | WeekModeRenderer with client-side DayEntry grouping by weekday |
+| VIZ-05 | Hours vs entry-count toggle switches color scale metric across all modes | Separate `nav-segmented` control toggling `state.metric`; `buildColorScale()` already metric-aware |
+| TEST-01 | Vitest tests for mode switcher, each renderer, and display toggle | Test patterns established in existing 9 test files; jsdom environment |
+</phase_requirements>
+
+## Standard Stack
+
+### Core (already installed -- no new packages)
+| Library | Version | Purpose | Why Standard |
+|---------|---------|---------|--------------|
+| d3-selection | ^3.0.0 | DOM manipulation for week cells | Already in use for year renderer |
+| d3-scale | ^4.0.2 | Color scale for week cells | `buildColorScale()` already wraps this |
+| d3-array | ^3.2.4 | `max()` for scale domain | Already in shared/color-scale.ts |
+| vitest | ^4.1.3 | Test runner | Already configured with jsdom |
+
+No new npm packages required. [VERIFIED: package.json in codebase]
+
+### Tabler CSS (bundled with Kimai)
+| Component | Classes | Purpose |
+|-----------|---------|---------|
+| Segmented control | `nav nav-segmented`, `nav-link`, `active` | Mode switcher and metric toggle |
+| Small variant | `nav-sm` | Compact toggle for hours/count |
+
+[CITED: docs.tabler.io/ui/components/segmented-control]
+
+## Architecture Patterns
+
+### Project Structure (new files only)
+```
+assets/
+  src/
+    renderers/
+      week.ts          # NEW: WeekModeRenderer
+    ui/
+      controls.ts      # NEW: mode switcher + metric toggle DOM builders
+  test/
+    week.test.ts       # NEW: WeekModeRenderer tests
+    controls.test.ts   # NEW: UI control interaction tests
+```
+
+### Pattern 1: WeekModeRenderer (Strategy Pattern Extension)
+
+**What:** New renderer implementing `ModeRenderer` interface, registered via `registerRenderer()`.
+
+**When to use:** Rendering the week-mode aggregation view.
+
+**Example:**
+```typescript
+// assets/src/renderers/week.ts
+import type { ModeRenderer, RenderContext } from './types';
+import { registerRenderer } from './registry';
+import { buildColorScale } from '../shared/color-scale';
+import { createTooltip, showTooltip, hideTooltip } from '../shared/tooltip';
+
+interface WeekdayAggregate {
+  dayIndex: number;    // 0-6, relative to weekStart
+  label: string;       // "Mon", "Tue", etc.
+  totalHours: number;
+  totalCount: number;
+  dayCount: number;    // number of occurrences for averaging
+}
+
+export class WeekModeRenderer implements ModeRenderer {
+  readonly mode = 'week';
+  private tooltip: HTMLDivElement | null = null;
+
+  render(ctx: RenderContext): void {
+    // 1. Aggregate DayEntry[] by weekday
+    // 2. Build 7-cell horizontal SVG
+    // 3. Color via buildColorScale() using ctx.state.metric
+    // 4. Attach tooltip handlers
+  }
+
+  destroy(): void {
+    this.tooltip?.remove();
+    this.tooltip = null;
+  }
+}
+
+// Module-level registration
+registerRenderer(new WeekModeRenderer());
+```
+
+### Pattern 2: UI Controls (JS-driven, not Twig)
+
+**What:** Build mode switcher and metric toggle as DOM elements in `heatmap.ts` init, inserted into the widget header area.
+
+**Why JS not Twig:** Controls must interact with `HeatmapState` and call `doRender()`. Putting them in Twig would require a separate event-binding pass and Twig has no knowledge of JS state. Building them in JS during init keeps the coupling clean.
+
+**Example:**
+```typescript
+// assets/src/ui/controls.ts
+export interface ControlCallbacks {
+  onModeChange: (mode: string) => void;
+  onMetricChange: (metric: string) => void;
+}
+
+export function createModeControl(
+  activeMode: string,
+  modes: Array<{ key: string; label: string }>,
+  onChange: (mode: string) => void,
+): HTMLElement {
+  const nav = document.createElement('nav');
+  nav.className = 'nav nav-segmented';
+  nav.setAttribute('role', 'tablist');
+
+  for (const m of modes) {
+    const btn = document.createElement('button');
+    btn.className = 'nav-link' + (m.key === activeMode ? ' active' : '');
+    btn.setAttribute('role', 'tab');
+    btn.textContent = m.label;
+    btn.addEventListener('click', () => {
+      nav.querySelectorAll('.nav-link').forEach(b => b.classList.remove('active'));
+      btn.classList.add('active');
+      onChange(m.key);
+    });
+    nav.appendChild(btn);
+  }
+  return nav;
+}
+
+export function createMetricControl(
+  activeMetric: string,
+  onChange: (metric: string) => void,
+): HTMLElement {
+  // Same pattern, nav-sm for compact size
+  const nav = document.createElement('nav');
+  nav.className = 'nav nav-segmented nav-sm';
+  // ... buttons for 'Hours' and 'Count'
+  return nav;
+}
+```
+
+### Pattern 3: Weekday Aggregation (Client-Side)
+
+**What:** Group `DayEntry[]` by day-of-week index, summing hours and counts.
+
+**Key detail:** Must respect `state.weekStart`. The existing `date-utils.ts` calculates `dayOfWeek` as `(jsDay + 6) % 7` for Monday start and `jsDay` for Sunday start. Reuse the same logic.
+
+```typescript
+function aggregateByWeekday(
+  days: DayEntry[],
+  weekStart: string,
+): WeekdayAggregate[] {
+  const buckets = new Array(7).fill(null).map((_, i) => ({
+    dayIndex: i,
+    label: '', // filled from getDayLabels or full-name variant
+    totalHours: 0,
+    totalCount: 0,
+    dayCount: 0,
+  }));
+
+  for (const d of days) {
+    const jsDay = new Date(d.date + 'T00:00:00').getDay();
+    const idx = weekStart === 'sunday' ? jsDay : (jsDay + 6) % 7;
+    buckets[idx].totalHours += d.hours;
+    buckets[idx].totalCount += d.count;
+    buckets[idx].dayCount += 1;
+  }
+  return buckets;
+}
+```
+
+### Pattern 4: Control Placement in Widget Header
+
+**What:** Insert controls into the card header alongside the existing title.
+
+**Approach:** The Twig template uses `@theme/embeds/card.html.twig`. The `{% block box_title %}` currently holds just `{{ title }}`. Two options:
+
+1. **Modify Twig** to add a placeholder `<div id="heatmap-controls">` in `box_title` block -- then JS populates it.
+2. **Pure JS** -- find the `.card-header` parent of `#heatmap-container` and inject controls.
+
+**Recommendation:** Option 1 -- add a controls placeholder in Twig. This is cleaner because it ensures the layout structure is correct even before JS loads, and avoids fragile DOM traversal.
+
+```twig
+{% block box_title %}
+    <div style="display: flex; align-items: center; gap: 12px; flex-wrap: wrap;">
+        {{ title }}
+        <div id="heatmap-controls" style="display: flex; gap: 8px; margin-left: auto;"></div>
+    </div>
+{% endblock %}
+```
+
+Then in `heatmap.ts`, build controls and append to `#heatmap-controls`.
+
+### Anti-Patterns to Avoid
+- **Merging mode switcher and metric toggle into one control:** CONTEXT.md D-08 explicitly says separate controls.
+- **Re-fetching data on metric toggle:** D-10 says re-render without re-fetch. The data already has both `hours` and `count` fields.
+- **Building week renderer from scratch without shared utilities:** `buildColorScale()`, tooltip helpers, and `getDayLabels()` are all reusable.
+
+## Don't Hand-Roll
+
+| Problem | Don't Build | Use Instead | Why |
+|---------|-------------|-------------|-----|
+| Segmented control UI | Custom toggle buttons with manual styling | Tabler `nav-segmented` classes | Native Kimai theme integration, accessible markup |
+| Color scale | New scale for week cells | `buildColorScale()` from shared/color-scale.ts | Already metric-aware, consistent across modes |
+| Tooltips | New tooltip logic | `createTooltip/showTooltip/hideTooltip` from shared/tooltip.ts | Consistent behavior, already tested |
+| Weekday ordering | Hard-coded day arrays | Reuse `(jsDay + 6) % 7` pattern from date-utils.ts | Already handles Monday/Sunday start |
+
+## Common Pitfalls
+
+### Pitfall 1: Weekday Index Mismatch Between Aggregation and Labels
+**What goes wrong:** Aggregation uses one weekday ordering, labels use another, so Tuesday's data shows on Monday's cell.
+**Why it happens:** JS `Date.getDay()` returns 0=Sunday. The existing code remaps for Monday-start. If aggregation and label generation use different mappings, they desync.
+**How to avoid:** Use the exact same index formula as `generateCells()` in date-utils.ts: `weekStart === 'sunday' ? jsDay : (jsDay + 6) % 7`. Map labels using the same index.
+**Warning signs:** Tests with known weekday data showing wrong labels.
+
+### Pitfall 2: Empty Aggregate Buckets Confuse Color Scale
+**What goes wrong:** Weekdays with zero entries get passed to `buildColorScale()` which sets domain `[0, maxVal]`, and zero values map to the lowest color bucket instead of showing as empty.
+**Why it happens:** `buildColorScale` maps any value in `[0, maxVal]` to a color. Zero is technically in-domain.
+**How to avoid:** Either (a) filter out zero-value weekdays before passing to color scale and render them as empty cells, or (b) treat weekdays with `dayCount === 0` as empty (no fill), similar to how year-mode handles null entries.
+**Warning signs:** All 7 cells colored even when user tracked on only 3 weekdays.
+
+### Pitfall 3: Controls Not Reflecting State After Re-render
+**What goes wrong:** Mode or metric changes correctly, but if `doRender()` rebuilds the entire container, controls get destroyed.
+**Why it happens:** `heatmap.ts`'s `doRender()` calls `renderer.render(ctx)` which does `ctx.container.innerHTML = ''` on the SVG area. If controls are inside the SVG area, they vanish.
+**How to avoid:** Controls live outside the SVG area container (in the card header via `#heatmap-controls`). The renderer only clears `svgArea`, not the card header.
+**Warning signs:** Controls disappear after first interaction.
+
+### Pitfall 4: Stats Row Showing Year-Specific Data in Week Mode
+**What goes wrong:** Streak counter and "busiest day" stats show in week mode where they don't make contextual sense.
+**Why it happens:** `renderStats()` is called unconditionally after every `doRender()`.
+**How to avoid:** Either skip `renderStats()` when mode is 'week', or show week-appropriate stats (e.g., busiest weekday, average per weekday). Simplest: hide stats in week mode for now.
+**Warning signs:** "Busiest: Mon, Jan 13" showing below a weekday aggregation view.
+
+## Code Examples
+
+### Weekday Aggregation with Full Labels
+```typescript
+// Full weekday names for tooltips (D-07 wants "Monday: 42.5h")
+const WEEKDAY_NAMES_MONDAY = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'];
+const WEEKDAY_NAMES_SUNDAY = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
+
+function getWeekdayNames(weekStart: string): string[] {
+  return weekStart === 'sunday' ? WEEKDAY_NAMES_SUNDAY : WEEKDAY_NAMES_MONDAY;
+}
+```
+
+### Week-Mode SVG Layout (7 horizontal cells)
+```typescript
+// Larger cells since only 7 vs 365
+const cellWidth = 60;
+const cellHeight = 40;
+const cellGap = 4;
+const labelWidth = 50; // space for "Mon", "Tue" labels
+const svgWidth = labelWidth + 7 * (cellWidth + cellGap);
+const svgHeight = cellHeight + 20; // room for value text below
+
+// Layout: label | rect | label | rect | ...
+// Or: 7 rects in a row with labels below/beside
+```
+
+### Wiring Controls to State in heatmap.ts
+```typescript
+// In init(), after building wrapper:
+const controlsContainer = document.getElementById('heatmap-controls');
+if (controlsContainer) {
+  const modeControl = createModeControl(state.mode, [
+    { key: 'year', label: 'Year' },
+    { key: 'week', label: 'Week' },
+  ], (mode) => {
+    state.mode = mode as HeatmapMode;
+    doRender();
+  });
+
+  const metricControl = createMetricControl(state.metric, (metric) => {
+    state.metric = metric as DisplayMetric;
+    doRender();
+  });
+
+  controlsContainer.appendChild(modeControl);
+  controlsContainer.appendChild(metricControl);
+}
+```
+
+## Validation Architecture
+
+### Test Framework
+| Property | Value |
+|----------|-------|
+| Framework | Vitest 4.1.3 + jsdom |
+| Config file | `vitest.config.ts` |
+| Quick run command | `npm test` |
+| Full suite command | `npm test` |
+
+### Phase Requirements to Test Map
+| Req ID | Behavior | Test Type | Automated Command | File Exists? |
+|--------|----------|-----------|-------------------|-------------|
+| VIZ-01 | Mode switcher renders Year/Week buttons, click changes active state | unit | `npx vitest run assets/test/controls.test.ts` | Wave 0 |
+| VIZ-02 | Week renderer aggregates by weekday, renders 7 cells with correct colors | unit | `npx vitest run assets/test/week.test.ts` | Wave 0 |
+| VIZ-05 | Metric toggle switches state.metric, re-renders with different color values | unit | `npx vitest run assets/test/controls.test.ts` | Wave 0 |
+| TEST-01 | All mode/renderer/toggle tests pass | suite | `npm test` | Wave 0 |
+
+### Sampling Rate
+- **Per task commit:** `npm test`
+- **Per wave merge:** `npm test` (single suite)
+- **Phase gate:** Full suite green before `/gsd-verify-work`
+
+### Wave 0 Gaps
+- [ ] `assets/test/week.test.ts` -- WeekModeRenderer rendering and aggregation tests
+- [ ] `assets/test/controls.test.ts` -- mode switcher and metric toggle interaction tests
+
+## Security Domain
+
+No security-relevant ASVS categories apply to this phase. It is purely client-side UI rendering with no authentication, input handling from users, cryptography, or access control changes. Data comes from the existing authenticated API endpoint.
+
+## Assumptions Log
+
+| # | Claim | Section | Risk if Wrong |
+|---|-------|---------|---------------|
+| A1 | Tabler `nav-segmented` classes are available in Kimai's bundled Tabler version | Architecture Patterns | Controls would need custom CSS; verify in running Kimai instance |
+| A2 | The `card-header` area in Kimai's card embed template has enough space for controls next to the title | Architecture Patterns | May need to adjust Twig layout or use a different placement |
+
+## Open Questions
+
+1. **Stats row in week mode**
+   - What we know: Year-mode shows streak, total hours, avg hours, busiest day
+   - What's unclear: Whether these make sense in week mode (streak is year-concept)
+   - Recommendation: Hide stats in week mode initially; can add week-specific stats later if wanted
+
+2. **Week-mode cell click behavior**
+   - What we know: Year-mode clicks navigate to timesheet for that date
+   - What's unclear: What clicking "Monday" in week-mode should do (filter timesheet by weekday? no-op?)
+   - Recommendation: No click handler for week cells initially -- the aggregation isn't tied to a single date
+
+## Sources
+
+### Primary (HIGH confidence)
+- Codebase: `assets/src/renderers/types.ts`, `registry.ts`, `year.ts` -- ModeRenderer contract and reference implementation
+- Codebase: `assets/src/state.ts`, `assets/src/types.ts` -- HeatmapState with mode/metric fields already defined
+- Codebase: `assets/src/shared/color-scale.ts` -- buildColorScale already metric-aware
+- Codebase: `assets/src/shared/date-utils.ts` -- weekday index calculation with start-of-week support
+
+### Secondary (MEDIUM confidence)
+- [Tabler segmented control docs](https://docs.tabler.io/ui/components/segmented-control) -- `nav nav-segmented` markup pattern [CITED: docs.tabler.io/ui/components/segmented-control]
+
+### Tertiary (LOW confidence)
+- None
+
+## Metadata
+
+**Confidence breakdown:**
+- Standard stack: HIGH -- no new packages, all already installed and tested
+- Architecture: HIGH -- extends well-established strategy pattern from Phase 6
+- Pitfalls: HIGH -- based on direct codebase analysis of existing patterns
+
+**Research date:** 2026-04-09
+**Valid until:** 2026-05-09 (stable -- no external dependency changes expected)