# Phase 8 — Meal Planning & Waste Reduction

**Goal**: Enable weekly meal planning with automatic nutrition tracking vs targets. The core feature is a **suggestion engine** that recommends recipes prioritizing ingredients already in the pantry (especially those expiring soon), reducing food waste while maintaining nutritional balance.

**Depends on**: Phase 5 (products), Phase 6 (recipes), Phase 7 (pantry)

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## Implementation Workflow (Vertical Slice)

Following the project's standard workflow, Phase 8 will be implemented in the following order:

### 8.1 — Shared Layer: Types & Validation
- **Types**: Define `MealPlan` and `NutritionTarget` in `packages/shared/src/types/`.
- **Enums**: Define `MealType` and `MealPlanStatus` in `packages/shared/src/enums/`.
- **Validation**: Create Zod schemas in `packages/shared/src/validation/`:
  - `CreateMealPlanSchema`: Ensures 7 days, valid `weekStartDate`.
  - `UpdateMealPlanSchema`: Supports granular updates (add/move/remove meal).
  - `NutritionTargetSchema`: Validates daily macros and calorie goals.
- **Unit Tests**: Test Zod schemas for all edge cases (e.g., negative calories, overlapping weeks).

### 8.2 — Database Layer: Repositories
- **MealPlanRepository**:
  - `findByHousehold(householdId, weekStartDate)`: Unique constraint per household per week.
  - `findCurrent(householdId)`: Returns the plan for the current calendar week.
  - `updateMeal(id, dayIndex, mealId, data)`: Granular update for a specific meal slot.
- **NutritionTargetRepository**:
  - `findByUser(userId, householdId)`: Get active targets for a specific user.
  - `upsert(userId, householdId, data)`: Update or create targets.
- **Integration Tests**: Verify MongoDB unique indexes and household scoping.

### 8.3 — Service Layer: Suggestion Engine & Planning
- **MealPlanService**:
  - Manage CRUD operations and status transitions (Draft -> Active).
  - Compute `dailyNutritionTotal` dynamically using the `NutritionCalculatorService` from Phase 6.
- **NutritionTargetService**:
  - Manage user-specific nutritional goals and presets (Maintenance, Loss, Gain).
- **SuggestionEngineService** (Core Algorithm):
  - **Scoring Algorithm**:
    - `IngredientCoverage` (40%): Matches recipe ingredients vs current pantry items.
    - `FreshnessUrgency` (30%): Bonus for using items with `urgency: urgent` or `expiringSoon`.
    - `NutritionBalance` (20%): Complements existing meals in the day vs user targets.
    - `Variety` (10%): Penalizes recipes used in the last 14 days.
  - Uses `RecipesService` to fetch catalog and `PantryService` to fetch current inventory.
- **ShoppingGapService**:
  - Analyze meal plans vs pantry to identify missing ingredients for Phase 9 integration.
- **Unit Tests**: Test scoring weights and ingredient matching logic (100% coverage required).

### 8.4 — Route Layer: API Endpoints
- **MealPlanRoutes**:
  - `GET /api/v1/households/:householdId/meal-plans`: List plans.
  - `GET /api/v1/households/:householdId/meal-plans/current`: Get current week.
  - `POST /api/v1/households/:householdId/meal-plans`: Create plan.
  - `PATCH /api/v1/households/:householdId/meal-plans/:id`: Update structure.
  - `GET /api/v1/households/:householdId/meal-plans/suggestions`: Get algorithmic suggestions.
- **NutritionTargetRoutes**:
  - `GET /api/v1/households/:householdId/nutrition-targets`: Get user targets.
  - `POST /api/v1/households/:householdId/nutrition-targets`: Set targets.
- **Integration Tests**: Verify all endpoints return correctly shaped responses (using `toProductResponse` style mappers).

### 8.5 — Web Layer: API Client & Components
- **API Client**: Implement `meal-plans.ts` and `nutrition-targets.ts` in `packages/web/src/services/`.
- **Hooks**: Create `useMealPlan` and `useSuggestions` hooks for state management.
- **Components**:
  - `CalendarGrid`: Weekly view using CSS Grid and drag-and-drop.
  - `NutritionProgress`: Daily progress bars vs targets.
  - `SuggestionPanel`: Sidebar showing ranked recipes with "reasoning" tooltips.
  - `ShoppingGapView`: Breakdown of missing items.
- **Component Tests**: Use React Testing Library to verify drag-and-drop and progress bar calculations.

### 8.6 — Verification Gate
- `npm run build`
- `npm run test:cov` (100% API/Shared, 90% Web thresholds)
- `npm run lint`

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## Technical Details

### Scoring Algorithm Constants
```typescript
const WEIGHTS = {
  COVERAGE: 0.4,   // Do I have the items?
  URGENCY: 0.3,    // Should I use these items now?
  NUTRITION: 0.2,  // Does it fit my macros?
  VARIETY: 0.1     // Have I eaten this too much?
};
```

### Integration Points
- **PantryService**: Fetch items where `status` is `sealed` or `opened`.
- **RecipesService**: Fetch recipes and their computed nutrition/ingredients.
- **NutritionCalculator**: Reuse for summing daily plan totals.

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## Acceptance Criteria
- [ ] Weekly meal plans can be created and managed via a calendar UI.
- [ ] Drag-and-drop allows moving recipes between days and meal types.
- [ ] The suggestion engine prioritizes recipes using urgent pantry items.
- [ ] Daily nutrition bars reflect progress against user-defined macro targets.
- [ ] Shopping gap analysis identifies missing ingredients for the planned week.
- [ ] Full unit and integration test coverage as per project standards.
- [ ] Build, Lint, and Coverage checks all pass.