feat: flexible meal planning wizard — plan 1 meal, 1 day, several days, or a week

Backend:
- migration 005: expand menu_items.meal_type CHECK to all 6 types (second_breakfast, afternoon_snack, snack)
- ai/types.go: add Days and MealTypes to MenuRequest for partial generation
- openai/menu.go: parametrize GenerateMenu — use requested meal types and day count; add caloric fractions for all 6 meal types
- menu/repository.go: add UpsertItemsInTx for partial upsert (preserves existing slots); fix meal_type sort order in GetByWeek
- menu/handler.go: add dates+meal_types path to POST /ai/generate-menu; extract fetchImages/saveRecipes helpers; returns {"plans":[...]} for dates mode; backward-compatible with week mode

Client:
- PlanMenuSheet: bottom sheet with 4 planning horizon options
- PlanDatePickerSheet: adaptive sheet with date strip (single day/meal) or custom CalendarRangePicker (multi-day/week); sliding 7-day window for week mode
- menu_service.dart: add generateForDates
- menu_provider.dart: add PlanMenuService (generates + invalidates week providers), lastPlannedDateProvider
- home_screen.dart: add _PlanMenuButton card below quick actions; opens planning wizard
- l10n: 16 new keys for planning UI across all 12 languages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/adapters/ai/types.go

@@ -51,7 +51,7 @@ type NutritionInfo struct {
 	Approximate bool    `json:"approximate"`
 }
 
-// MenuRequest contains parameters for weekly menu generation.
+// MenuRequest contains parameters for menu generation.
 type MenuRequest struct {
 	UserGoal          string
 	DailyCalories     int
@@ -59,6 +59,12 @@ type MenuRequest struct {
 	CuisinePrefs      []string
 	AvailableProducts []string
 	Lang              string // ISO 639-1 target language code, e.g. "en", "ru"
+	// Days specifies which day-of-week slots (1=Monday…7=Sunday) to generate.
+	// When nil, all 7 days are generated.
+	Days []int
+	// MealTypes restricts generation to the listed meal types.
+	// When nil, defaults to ["breakfast","lunch","dinner"].
+	MealTypes []string
 }
 
 // DayPlan is the AI-generated plan for a single day.

backend/internal/adapters/openai/menu.go

@@ -8,72 +8,91 @@ import (
 	"github.com/food-ai/backend/internal/adapters/ai"
 )
 
-// GenerateMenu produces a 7-day × 3-meal plan by issuing three parallel
-// GenerateRecipes calls (one per meal type). This avoids token-limit errors
-// that arise from requesting 21 full recipes in a single prompt.
+// caloricFractions maps each meal type to its share of the daily calorie budget.
+var caloricFractions = map[string]float64{
+	"breakfast":        0.25,
+	"second_breakfast": 0.10,
+	"lunch":            0.35,
+	"afternoon_snack":  0.10,
+	"dinner":           0.20,
+	"snack":            0.10,
+}
+
+// defaultMealTypes is used when MenuRequest.MealTypes is nil.
+var defaultMealTypes = []string{"breakfast", "lunch", "dinner"}
+
+// GenerateMenu produces a meal plan by issuing one parallel GenerateRecipes call per meal
+// type. The number of recipes per type equals the number of days requested.
 func (c *Client) GenerateMenu(ctx context.Context, req ai.MenuRequest) ([]ai.DayPlan, error) {
-	type mealSlot struct {
-		mealType string
-		fraction float64 // share of daily calories
+	mealTypes := req.MealTypes
+	if len(mealTypes) == 0 {
+		mealTypes = defaultMealTypes
 	}
 
-	slots := []mealSlot{
-		{"breakfast", 0.25},
-		{"lunch", 0.40},
-		{"dinner", 0.35},
+	days := req.Days
+	if len(days) == 0 {
+		days = make([]int, 7)
+		for dayIndex := range days {
+			days[dayIndex] = dayIndex + 1
+		}
 	}
+	recipeCount := len(days)
 
 	type mealResult struct {
 		recipes []ai.Recipe
 		err     error
 	}
 
-	results := make([]mealResult, len(slots))
+	results := make([]mealResult, len(mealTypes))
 	var wg sync.WaitGroup
 
-	for i, slot := range slots {
+	for slotIndex, mealType := range mealTypes {
 		wg.Add(1)
-		go func(idx int, mealType string, fraction float64) {
+		go func(idx int, mealTypeName string) {
 			defer wg.Done()
-			// Scale daily calories to what this meal should contribute.
-			mealCal := int(float64(req.DailyCalories) * fraction)
-			r, err := c.GenerateRecipes(ctx, ai.RecipeRequest{
+			fraction, ok := caloricFractions[mealTypeName]
+			if !ok {
+				fraction = 0.15
+			}
+			mealCalories := int(float64(req.DailyCalories) * fraction)
+			recipes, generateError := c.GenerateRecipes(ctx, ai.RecipeRequest{
 				UserGoal:          req.UserGoal,
-				DailyCalories:     mealCal * 3, // prompt divides by 3 internally
+				DailyCalories:     mealCalories * recipeCount,
 				Restrictions:      req.Restrictions,
 				CuisinePrefs:      req.CuisinePrefs,
-				Count:             7,
+				Count:             recipeCount,
 				AvailableProducts: req.AvailableProducts,
 				Lang:              req.Lang,
 			})
-			results[idx] = mealResult{r, err}
-		}(i, slot.mealType, slot.fraction)
+			results[idx] = mealResult{recipes, generateError}
+		}(slotIndex, mealType)
 	}
 	wg.Wait()
 
-	for i, res := range results {
-		if res.err != nil {
-			return nil, fmt.Errorf("generate %s: %w", slots[i].mealType, res.err)
+	for slotIndex, result := range results {
+		if result.err != nil {
+			return nil, fmt.Errorf("generate %s: %w", mealTypes[slotIndex], result.err)
 		}
-		if len(res.recipes) == 0 {
-			return nil, fmt.Errorf("no %s recipes returned", slots[i].mealType)
+		if len(result.recipes) == 0 {
+			return nil, fmt.Errorf("no %s recipes returned", mealTypes[slotIndex])
 		}
-		// Pad to exactly 7 by repeating the last recipe.
-		for len(results[i].recipes) < 7 {
-			results[i].recipes = append(results[i].recipes, results[i].recipes[len(results[i].recipes)-1])
+		// Pad to exactly recipeCount by repeating the last recipe.
+		for len(results[slotIndex].recipes) < recipeCount {
+			last := results[slotIndex].recipes[len(results[slotIndex].recipes)-1]
+			results[slotIndex].recipes = append(results[slotIndex].recipes, last)
 		}
 	}
 
-	days := make([]ai.DayPlan, 7)
-	for day := range 7 {
-		days[day] = ai.DayPlan{
-			Day: day + 1,
-			Meals: []ai.MealEntry{
-				{MealType: slots[0].mealType, Recipe: results[0].recipes[day]},
-				{MealType: slots[1].mealType, Recipe: results[1].recipes[day]},
-				{MealType: slots[2].mealType, Recipe: results[2].recipes[day]},
-			},
+	dayPlans := make([]ai.DayPlan, recipeCount)
+	for dayIndex, dayOfWeek := range days {
+		meals := make([]ai.MealEntry, len(mealTypes))
+		for slotIndex, mealType := range mealTypes {
+			meals[slotIndex] = ai.MealEntry{
+				MealType: mealType,
+				Recipe:   results[slotIndex].recipes[dayIndex],
+			}
 		}
+		dayPlans[dayIndex] = ai.DayPlan{Day: dayOfWeek, Meals: meals}
 	}
-	return days, nil
+	return dayPlans, nil
 }