Minimalist Habit Tracker

AI Prompts to Build This

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1. 1. Offline-First PWA

   Create a Next.js 14 App Router PWA for habit tracking. Offline-first with IndexedDB; sync to Supabase.
   
   Schema (Supabase Postgres):
   - users(id, email, plan ENUM[free,pro,lifetime,family], stripe_customer_id, timezone, created_at)
   - habits(id, user_id, name, icon, color, frequency ENUM[daily,weekly,xdays], target_count_per_period INT, shared_with_partner_id, archived bool, created_at)
   - checkins(id, habit_id, date, value INT, source ENUM[manual,healthkit,google_fit], created_at)
   - partners(id, user_a_id, user_b_id, status ENUM[invited,accepted,declined], created_at)
   - partner_nudges(id, sender_user_id, receiver_user_id, habit_id, sent_at)
   
   RLS: users see own. Habits: viewable by owner, and by partner if habits.shared_with_partner_id = partner.user_x_id and status=accepted.
   
   Offline storage:
   - IndexedDB via Dexie.js: mirror habits and today's checkins.
   - On check-in: write to IndexedDB immediately, show UI update. Enqueue sync operation in a pending-queue. Service worker processes queue when online.
   - Conflict resolution: last-write-wins per (habit_id, date); server timestamp authoritative.
   
   Routes:
   - / (marketing, see heatmap of anonymized user for demo)
   - /app (authed: today's habits grid, tap to check)
   - /habits (list, reorder, archive)
   - /history (year-view heatmap, longest streak, current streak per habit)
   - /partner (invite flow, shared-habit picker, nudge history)
   - /settings (notifications, integrations, billing)
   
   Heatmap: react-calendar-heatmap or custom SVG; 365-day grid colored by completion rate.

2. 2. Health Integration Bridge

   Implement the Apple HealthKit (via iOS Shortcut) and Google Fit auto-log bridges.
   
   Apple HealthKit flow (iOS only):
   1. On iOS, user visits /integrations/healthkit. Show a button: "Add to Shortcuts."
   2. Deep link to a pre-built iCloud Shortcut: https://www.icloud.com/shortcuts/{uuid}.
   3. Shortcut definition:
      - Get today's HKQuantityType samples (stepCount, distanceWalkingRunning, mindfulSession, sleepAnalysis).
      - Filter by user's configured habit mappings (stored in Shortcut input from user's account).
      - For each match, POST to https://product.com/api/healthkit-sync with signed request: {user_api_key, date, habit_mappings: [{habit_id, value}]}.
   4. User schedules the Shortcut via Personal Automation: daily at 11:59pm local. One-time setup.
   
   On server side /api/healthkit-sync:
   - Authenticate request via user_api_key (32-char random, stored in user profile).
   - Upsert checkins rows with source='healthkit'. Replace manual check-ins for the same (habit, date) if healthkit value >= configured threshold.
   
   Google Fit flow (cross-platform):
   1. User clicks 'Connect Google Fit' → OAuth flow with scope fitness.activity.read.
   2. Store refresh_token encrypted.
   3. Nightly cron (Vercel Cron):
      - For each user with Google Fit connected: refresh access token, query Google Fit Aggregate API for yesterday's activities.
      - Match to habits by activity type + duration threshold (e.g., "Run 3 miles" habit triggers if running distance >= 4828 meters).
      - Insert checkins with source='google_fit'.
   
   Conflict rule: healthkit/google_fit can add a check-in; they never remove. Manual takes precedence if user explicitly un-checks.

3. 3. Accountability Partner Loop

   Build the partner invitation and nudge system. This is the retention moat.
   
   Invite flow:
   1. /partner → 'Invite a partner' button. User enters email.
   2. Server creates partners(user_a_id=current, user_b_id=NULL, invited_email, invite_token, status='invited').
   3. Resend sends email with link https://product.com/partner/accept/{invite_token} and friendly copy.
   4. Recipient clicks link, signs up or logs in, /partner/accept resolves user_b_id, sets status='accepted'.
   5. Both users now see partner section populated.
   
   Share a habit:
   1. In /habits/:id/settings → 'Share with partner' toggle (only if partner exists).
   2. Sets habits.shared_with_partner_id = partner.user_b_id (or user_a_id depending on who is sharing).
   3. RLS policy allows partner to SELECT this habit + associated checkins.
   
   Nudge logic (daily cron):
   - For each (habit, partner) where shared AND habit's streak broken yesterday (no checkin, frequency=daily):
     - Check partner_nudges WHERE habit_id=X AND sender=partner AND receiver=owner AND sent_at > NOW() - INTERVAL '7 days'. If exists, skip (rate limit).
     - Send Web Push notification to partner: 'Chris didn't check in Meditate yesterday. Want to send a nudge?'
     - Partner taps → sends thoughtful pre-written nudge email to owner ('Hey, just checking in on meditation — no pressure, just thinking of you').
     - Record partner_nudges row with sent_at.
   
   Crucial UX: partner CANNOT see habit data, only streak status (unbroken/broken). Owner can revoke partner visibility at any time. Streak visibility is opt-in per-habit.
   
   Privacy settings: /partner/privacy explicitly lists what the partner sees and what they don't.