enable completing past habit

hooks/useHabits.tsx

@@ -2,7 +2,8 @@ import { useAtom } from 'jotai'
 import { habitsAtom, coinsAtom, settingsAtom } from '@/lib/atoms'
 import { addCoins, removeCoins, saveHabitsData } from '@/app/actions/data'
 import { Habit } from '@/lib/types'
-import { getNowInMilliseconds, getTodayInTimezone, isSameDate, t2d, d2t, getNow, getCompletionsForDate } from '@/lib/utils'
+import { DateTime } from 'luxon'
+import { getNowInMilliseconds, getTodayInTimezone, isSameDate, t2d, d2t, getNow, getCompletionsForDate, getISODate, d2s } from '@/lib/utils'
 import { toast } from '@/hooks/use-toast'
 import { ToastAction } from '@/components/ui/toast'
 import { Undo2 } from 'lucide-react'
@@ -161,10 +162,80 @@ export function useHabits() {
     return updatedHabits
   }
 
+  const completePastHabit = async (habit: Habit, date: DateTime) => {
+    const timezone = settings.system.timezone
+    const dateKey = getISODate({ dateTime: date, timezone })
+
+    // Check if already completed on this date
+    const completionsOnDate = habit.completions.filter(completion =>
+      isSameDate(t2d({ timestamp: completion, timezone }), date)
+    ).length
+    const target = habit.targetCompletions || 1
+
+    if (completionsOnDate >= target) {
+      toast({
+        title: "Already completed",
+        description: `This habit was already completed on ${d2s({ dateTime: date, timezone, format: 'yyyy-MM-dd' })}.`,
+        variant: "destructive",
+      })
+      return null
+    }
+
+    // Use current time but with the past date
+    const now = getNow({ timezone })
+    const completionDateTime = date.set({
+      hour: now.hour,
+      minute: now.minute,
+      second: now.second,
+      millisecond: now.millisecond
+    })
+    const completionTimestamp = d2t({ dateTime: completionDateTime })
+    const updatedHabit = {
+      ...habit,
+      completions: [...habit.completions, completionTimestamp]
+    }
+
+    const updatedHabits = habitsData.habits.map(h =>
+      h.id === habit.id ? updatedHabit : h
+    )
+
+    await saveHabitsData({ habits: updatedHabits })
+    setHabitsData({ habits: updatedHabits })
+
+    // Check if we've now reached the target
+    const isTargetReached = completionsOnDate + 1 === target
+    if (isTargetReached) {
+      const updatedCoins = await addCoins(
+        habit.coinReward,
+        `Completed habit: ${habit.name} on ${d2s({ dateTime: date, timezone, format: 'yyyy-MM-dd' })}`,
+        'HABIT_COMPLETION',
+        habit.id
+      )
+      setCoins(updatedCoins)
+    }
+
+    toast({
+      title: isTargetReached ? "Habit completed!" : "Progress!",
+      description: isTargetReached
+        ? `You earned ${habit.coinReward} coins for ${dateKey}.`
+        : `You've completed ${completionsOnDate + 1}/${target} times on ${dateKey}.`,
+      action: <ToastAction altText="Undo" className="gap-2" onClick={() => undoComplete(updatedHabit)}>
+        <Undo2 className="h-4 w-4" />Undo
+      </ToastAction>
+    })
+
+    return {
+      updatedHabits,
+      newBalance: coins.balance,
+      newTransactions: coins.transactions
+    }
+  }
+
   return {
     completeHabit,
     undoComplete,
     saveHabit,
-    deleteHabit
+    deleteHabit,
+    completePastHabit
   }
 }