SimpleFinanceDash/.planning/phases/04-chart-polish-and-bug-fixes/04-01-SUMMARY.md

phase, plan, subsystem, tags, requires, provides, affects, tech-stack, key-files, key-decisions, patterns-established, requirements-completed, duration, completed

phase	plan	subsystem	tags	requires	provides	affects	tech-stack	key-files	key-decisions	patterns-established	requirements-completed	duration	completed
04-chart-polish-and-bug-fixes	01	ui	intl locale currency formatting typescript vitest		Locale-aware formatCurrency(amount, currency, locale='en') with 'en' default Unit tests covering English, German, USD, zero, negative, and empty-string edge cases	04-02-chart-tooltips any component calling formatCurrency	added patterns Intl.NumberFormat locale parameter passed from call site — no hardcoded locale in utility functions	created modified frontend/src/lib/format.test.ts frontend/src/lib/format.ts	formatCurrency third parameter defaults to 'en', replacing hardcoded 'de-DE' — all existing 2-arg call sites now produce English formatting (FIX-01) Defensive locale || 'en' guard prevents RangeError when empty string is passed	TDD pattern: write failing test first (RED commit), then implement (GREEN commit) — verified by vitest run between steps	FIX-01	5min	2026-03-12

Phase 4 Plan 01: Locale-Aware formatCurrency Summary

Intl.NumberFormat locale parameter added to formatCurrency with 'en' default, replacing hardcoded 'de-DE' — English users now see 1,234.56 instead of 1.234,56

Performance

• Duration: 5 min
• Started: 2026-03-12T08:23:13Z
• Completed: 2026-03-12T08:28:00Z
• Tasks: 2 (TDD RED + TDD GREEN)
• Files modified: 2

Accomplishments

• Added optional locale parameter to formatCurrency with 'en' as the default
• Removed the hardcoded 'de-DE' locale that was forcing German number formatting for all users
• Defensive locale || 'en' guard prevents RangeError on empty string input
• 8 unit tests cover English formatting, German formatting, USD, zero, negative amounts, and edge cases
• All 51 frontend tests pass with no regressions

Task Commits

Each task was committed atomically:

1. TDD RED: Failing tests for locale-aware formatCurrency - 6ffce76 (test)
2. TDD GREEN: Implement locale parameter - eb1bb8a (feat)

Note: TDD tasks have two commits (test → feat). No refactor needed.

Files Created/Modified

• frontend/src/lib/format.test.ts - 8 unit tests for locale behavior, defaults, and edge cases
• frontend/src/lib/format.ts - Updated function signature with locale: string = 'en' parameter

Decisions Made

• Third parameter defaults to 'en' (not 'en-US' or 'de-DE') — bare 'en' is a valid BCP 47 tag and produces comma-grouped, period-decimal output consistent with user expectations for English locale
• locale || 'en' fallback is intentional — empty string is not a valid BCP 47 locale and Intl.NumberFormat('') throws RangeError in some environments

Deviations from Plan

None - plan executed exactly as written.

Issues Encountered

None. Pre-existing act(...) warnings in unrelated test files (InlineEditCell.test.tsx, CategoriesPage.test.tsx) were observed but are out of scope per deviation rules — logged to deferred items.

User Setup Required

None - no external service configuration required.

Next Phase Readiness

• formatCurrency(amount, currency, locale) is ready for use in chart tooltips (04-02)
• All call sites currently pass 2 args and will automatically receive English formatting
• Callers can pass user's preferred_locale from API response as the third arg

Self-Check: PASSED

• frontend/src/lib/format.ts — FOUND
• frontend/src/lib/format.test.ts — FOUND
• 04-01-SUMMARY.md — FOUND
• Commit 6ffce76 (test RED) — FOUND
• Commit eb1bb8a (feat GREEN) — FOUND

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Phase: 04-chart-polish-and-bug-fixes Completed: 2026-03-12