food-ai/backend/internal/gemini/recipe.go

package gemini

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
)

// RecipeGenerator generates recipes using the Gemini AI.
type RecipeGenerator interface {
	GenerateRecipes(ctx context.Context, req RecipeRequest) ([]Recipe, error)
}

// RecipeRequest contains parameters for recipe generation.
type RecipeRequest struct {
	UserGoal          string   // "lose" | "maintain" | "gain"
	DailyCalories     int
	Restrictions      []string // e.g. ["gluten_free", "vegetarian"]
	CuisinePrefs      []string // e.g. ["russian", "asian"]
	Count             int
	AvailableProducts []string // human-readable list of products in user's pantry
	Lang              string   // ISO 639-1 target language code, e.g. "en", "ru"
}

// Recipe is a recipe returned by Gemini.
type Recipe struct {
	Title       string        `json:"title"`
	Description string        `json:"description"`
	Cuisine     string        `json:"cuisine"`
	Difficulty  string        `json:"difficulty"`
	PrepTimeMin int           `json:"prep_time_min"`
	CookTimeMin int           `json:"cook_time_min"`
	Servings    int           `json:"servings"`
	ImageQuery  string        `json:"image_query"`
	ImageURL    string        `json:"image_url"`
	Ingredients []Ingredient  `json:"ingredients"`
	Steps       []Step        `json:"steps"`
	Tags        []string      `json:"tags"`
	Nutrition   NutritionInfo `json:"nutrition_per_serving"`
}

// Ingredient is a single ingredient in a recipe.
type Ingredient struct {
	Name   string  `json:"name"`
	Amount float64 `json:"amount"`
	Unit   string  `json:"unit"`
}

// Step is a single preparation step.
type Step struct {
	Number       int    `json:"number"`
	Description  string `json:"description"`
	TimerSeconds *int   `json:"timer_seconds"`
}

// NutritionInfo contains approximate nutritional information per serving.
type NutritionInfo struct {
	Calories    float64 `json:"calories"`
	ProteinG    float64 `json:"protein_g"`
	FatG        float64 `json:"fat_g"`
	CarbsG      float64 `json:"carbs_g"`
	Approximate bool    `json:"approximate"`
}

// langNames maps ISO 639-1 codes to English language names used in the prompt.
var langNames = map[string]string{
	"en": "English",
	"ru": "Russian",
	"es": "Spanish",
	"de": "German",
	"fr": "French",
	"it": "Italian",
	"pt": "Portuguese",
	"zh": "Chinese (Simplified)",
	"ja": "Japanese",
	"ko": "Korean",
	"ar": "Arabic",
	"hi": "Hindi",
}

// goalNames maps internal goal codes to English descriptions used in the prompt.
var goalNames = map[string]string{
	"lose":     "weight loss",
	"maintain": "weight maintenance",
	"gain":     "muscle gain",
}

// GenerateRecipes generates recipes using the Gemini AI.
// Retries up to maxRetries times only when the response is not valid JSON.
// API-level errors (rate limits, auth, etc.) are returned immediately.
func (c *Client) GenerateRecipes(ctx context.Context, req RecipeRequest) ([]Recipe, error) {
	prompt := buildRecipePrompt(req)

	messages := []map[string]string{
		{"role": "user", "content": prompt},
	}

	var lastErr error
	for attempt := range maxRetries {
		if attempt > 0 {
			messages = []map[string]string{
				{"role": "user", "content": prompt},
				{"role": "user", "content": "Previous response was not valid JSON. Return ONLY a JSON array with no text before or after."},
			}
		}

		text, err := c.generateContent(ctx, messages)
		if err != nil {
			return nil, err
		}

		recipes, err := parseRecipesJSON(text)
		if err != nil {
			lastErr = fmt.Errorf("attempt %d parse JSON: %w", attempt+1, err)
			continue
		}

		for i := range recipes {
			recipes[i].Nutrition.Approximate = true
		}
		return recipes, nil
	}

	return nil, fmt.Errorf("failed to parse valid JSON after %d attempts: %w", maxRetries, lastErr)
}

func buildRecipePrompt(req RecipeRequest) string {
	lang := req.Lang
	if lang == "" {
		lang = "en"
	}
	langName, ok := langNames[lang]
	if !ok {
		langName = "English"
	}

	goal := goalNames[req.UserGoal]
	if goal == "" {
		goal = "weight maintenance"
	}

	restrictions := "none"
	if len(req.Restrictions) > 0 {
		restrictions = strings.Join(req.Restrictions, ", ")
	}

	cuisines := "any"
	if len(req.CuisinePrefs) > 0 {
		cuisines = strings.Join(req.CuisinePrefs, ", ")
	}

	count := req.Count
	if count <= 0 {
		count = 5
	}

	perMealCalories := req.DailyCalories / 3
	if perMealCalories <= 0 {
		perMealCalories = 600
	}

	productsSection := ""
	if len(req.AvailableProducts) > 0 {
		productsSection = "\nAvailable products (⚠ = expiring soon, prioritise these):\n" +
			strings.Join(req.AvailableProducts, "\n") + "\n"
	}

	return fmt.Sprintf(`You are a chef and nutritionist. Generate %d recipes in %s.

User profile:
- Goal: %s
- Daily calories: %d kcal
- Dietary restrictions: %s
- Cuisine preferences: %s
%s
Requirements for each recipe:
- Max %d kcal per serving
- Total cooking time: max 60 minutes
- Include approximate macros per serving

IMPORTANT:
- All text fields (title, description, ingredient names, units, step descriptions, tags) MUST be in %s.
- The "image_query" field MUST always be in English (it is used for stock-photo search).

Return ONLY a valid JSON array without markdown or extra text:
[{
  "title": "...",
  "description": "2-3 sentences",
  "cuisine": "russian|asian|european|mediterranean|american|other",
  "difficulty": "easy|medium|hard",
  "prep_time_min": 10,
  "cook_time_min": 20,
  "servings": 2,
  "image_query": "short English photo-search query",
  "ingredients": [{"name": "...", "amount": 300, "unit": "..."}],
  "steps": [{"number": 1, "description": "...", "timer_seconds": null}],
  "tags": ["..."],
  "nutrition_per_serving": {"calories": 420, "protein_g": 48, "fat_g": 12, "carbs_g": 18}
}]`, count, langName, goal, req.DailyCalories, restrictions, cuisines, productsSection, perMealCalories, langName)
}

func parseRecipesJSON(text string) ([]Recipe, error) {
	text = strings.TrimSpace(text)
	if strings.HasPrefix(text, "```") {
		text = strings.TrimPrefix(text, "```json")
		text = strings.TrimPrefix(text, "```")
		text = strings.TrimSuffix(text, "```")
		text = strings.TrimSpace(text)
	}

	var recipes []Recipe
	if err := json.Unmarshal([]byte(text), &recipes); err != nil {
		return nil, err
	}
	return recipes, nil
}