# Task 002: Locale-Aware Week Start Implementation
## Feature
Locale-Aware Week Start - Change from hardcoded Sunday to locale-aware using Intl API.
## BDD Scenario
```gherkin
Feature: Locale-Aware Week Start
Scenario: US locale uses Sunday as week start
Given the system locale is "en-US"
And today is Wednesday, January 17, 2024
When getWeekStart() is called
Then the result is Sunday, January 14, 2024
Scenario: Fallback to Sunday when Intl.Locale unavailable
Given Intl.Locale.weekInfo is not available
When getWeekStart() is called
Then Sunday is used as the week start
```
## Files to Modify
| File | Action |
|------|--------|
| `src/utils/dateUtils.ts` | Modify `getWeekStart()` and `getWeekEnd()` functions |
## Implementation Notes
1. Add an optional `locale` parameter to `getWeekStart()` and `getWeekEnd()`
2. Use `Intl.Locale` with `weekInfo` property to get the locale's first day of week:
- `weekInfo.firstDay` returns 1-7 where 1=Monday, 7=Sunday
- Convert to JavaScript's 0-6 format (0=Sunday)
3. Implement fallback to Sunday (0) if:
- `Intl.Locale` is not available
- `weekInfo` property is undefined
- Any error occurs during locale detection
4. Update the date calculation to use the locale-aware first day:
- Calculate days to subtract: `(dayOfWeek - firstDay + 7) % 7`
5. Update JSDoc comments to document locale-aware behavior
## Verification
```bash
# Run the date utils tests
pnpm test -- src/utils/dateUtils.test.ts
# Run date filtering tests to ensure no regressions
pnpm test -- src/utils/dateFiltering.test.ts
# Expected: All tests pass
```
## Dependencies
- **depends-on**: Task 002 Test (task-002-locale-week-start-test.md)
## Commit
```
feat(dateUtils): locale-aware week start using Intl.Locale
```
