feat: show habit history in details

frontend/src/lib/mvp-utils.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { archivePanelFlags, calendarModeLabel, changedHabitFields, clampFabPosition, countdownDayText, countdownKindLabel, dateKey, defaultView, formatArchivedAt, formatAuditAction, formatAuditEntity, formatHabitApiError, formatLocalShortDateTime, formatUserAgent, habitActionState, habitButtonNotice, habitButtonValue, habitWeek, invalidateHabitGridCache, isFabDrag, isHabitComplete, isHabitScheduledToday, isTaskView, nextHabitSwipeValue, nextTotalAfterLocalTaskAdd, nextTotalAfterLocalTaskRemoval, snapFabPosition, normalizeRequiredName, numericHabitInputValue, performHabitRestore, performTrashMutation, previousHabitSwipeValue, quickTaskFields, readCountdownCache, readHabitGridCache, readStoredBoolean, readStoredNavigation, shouldToggleRowSwipe, validateHabitForm, writeCountdownCache, writeHabitGridCache, writeStoredBoolean, writeStoredNavigation } from './mvp-utils'
+import { archivePanelFlags, calendarModeLabel, changedHabitFields, clampFabPosition, countdownDayText, countdownKindLabel, dateKey, dayBefore, defaultView, formatArchivedAt, formatAuditAction, formatAuditEntity, formatHabitApiError, formatHabitHistoryNumber, formatLocalShortDateTime, formatUserAgent, habitActionState, habitButtonNotice, habitButtonValue, habitHistoryWindow, habitWeek, invalidateHabitGridCache, isFabDrag, isHabitComplete, isHabitScheduledToday, isTaskView, mergeHabitHistory, nextHabitSwipeValue, nextTotalAfterLocalTaskAdd, nextTotalAfterLocalTaskRemoval, snapFabPosition, normalizeRequiredName, numericHabitInputValue, performHabitRestore, performTrashMutation, previousHabitSwipeValue, quickTaskFields, readCountdownCache, readHabitGridCache, readStoredBoolean, readStoredNavigation, shouldToggleRowSwipe, validateHabitForm, writeCountdownCache, writeHabitGridCache, writeStoredBoolean, writeStoredNavigation } from './mvp-utils'
 
 describe('MVP view utilities', () => {
   it('formats a local date as YYYY-MM-DD', () => {
@@ -71,6 +71,25 @@ describe('MVP view utilities', () => {
     expect(readStoredNavigation(fakeStorage, 'dodo.navigation')).toEqual({ view: 'today', listId: '' })
   })
 
+  it('builds non-overlapping 90-day habit history windows', () => {
+    expect(habitHistoryWindow('2026-09-15')).toEqual({ from: '2026-06-18', to: '2026-09-15' })
+    expect(dayBefore('2026-06-18')).toBe('2026-06-17')
+    expect(habitHistoryWindow('2026-01-01', 2)).toEqual({ from: '2025-12-31', to: '2026-01-01' })
+  })
+
+  it('merges habit history by day, coerces API values, and keeps newest first', () => {
+    expect(mergeHabitHistory(
+      [{ day: '2026-09-14', value: 1 }, { day: '2026-09-13', value: 2 }],
+      [{ day: '2026-09-15', value: 3 }, { day: '2026-09-14', value: 4 }],
+    )).toEqual([
+      { day: '2026-09-15', value: 3 },
+      { day: '2026-09-14', value: 4 },
+      { day: '2026-09-13', value: 2 },
+    ])
+    expect(formatHabitHistoryNumber(8)).toBe('8')
+    expect(formatHabitHistoryNumber(1.25)).toBe('1.25')
+  })
+
   it('only completes numeric habits when progress reaches the target', () => {
     expect(isHabitComplete('numeric', 3, 5)).toBe(false)
     expect(isHabitComplete('numeric', 5, 5)).toBe(true)

frontend/src/lib/mvp-utils.ts

@@ -80,6 +80,33 @@ export function isHabitComplete(kind: string | undefined, value: number | boolea
   return Boolean(value)
 }
 
+export type HabitHistoryLog = { day: string; value: number }
+
+export function habitHistoryWindow(toDay: string, size = 90) {
+  const [year, month, day] = toDay.split('-').map(Number)
+  const to = new Date(year, month - 1, day)
+  const from = new Date(to)
+  from.setDate(from.getDate() - (size - 1))
+  return { from: dateKey(from), to: dateKey(to) }
+}
+
+export function dayBefore(day: string) {
+  const [year, month, date] = day.split('-').map(Number)
+  const value = new Date(year, month - 1, date)
+  value.setDate(value.getDate() - 1)
+  return dateKey(value)
+}
+
+export function mergeHabitHistory(previous: HabitHistoryLog[], incoming: HabitHistoryLog[]) {
+  const merged = new Map(previous.map((item) => [item.day, item]))
+  for (const item of incoming) merged.set(item.day, { day: item.day, value: Number(item.value) })
+  return [...merged.values()].sort((a, b) => b.day.localeCompare(a.day))
+}
+
+export function formatHabitHistoryNumber(value: number) {
+  return Number.isInteger(value) ? String(value) : String(Number(value.toFixed(6)))
+}
+
 type HabitSchedule = {
   kind?: string
   cells?: Array<{ day: string; scheduled?: boolean; paused?: boolean; value?: number | boolean }>