food-ai/backend/internal/recommendation/handler.go

package recommendation

import (
	"context"
	"encoding/json"
	"log/slog"
	"net/http"
	"strconv"
	"sync"

	"github.com/food-ai/backend/internal/gemini"
	"github.com/food-ai/backend/internal/middleware"
	"github.com/food-ai/backend/internal/user"
)

// PhotoSearcher can search for a photo by text query.
type PhotoSearcher interface {
	SearchPhoto(ctx context.Context, query string) (string, error)
}

// UserLoader can load a user profile by ID.
type UserLoader interface {
	GetByID(ctx context.Context, id string) (*user.User, error)
}

// ProductLister returns a human-readable list of user's products for the AI prompt.
type ProductLister interface {
	ListForPrompt(ctx context.Context, userID string) ([]string, error)
}

// userPreferences is the shape of user.Preferences JSONB.
type userPreferences struct {
	Cuisines     []string `json:"cuisines"`
	Restrictions []string `json:"restrictions"`
}

// Handler handles GET /recommendations.
type Handler struct {
	gemini        *gemini.Client
	pexels        PhotoSearcher
	userLoader    UserLoader
	productLister ProductLister
}

// NewHandler creates a new Handler.
func NewHandler(geminiClient *gemini.Client, pexels PhotoSearcher, userLoader UserLoader, productLister ProductLister) *Handler {
	return &Handler{
		gemini:        geminiClient,
		pexels:        pexels,
		userLoader:    userLoader,
		productLister: productLister,
	}
}

// GetRecommendations handles GET /recommendations?count=5.
func (h *Handler) GetRecommendations(w http.ResponseWriter, r *http.Request) {
	userID := middleware.UserIDFromCtx(r.Context())
	if userID == "" {
		writeErrorJSON(w, http.StatusUnauthorized, "unauthorized")
		return
	}

	count := 5
	if s := r.URL.Query().Get("count"); s != "" {
		if n, err := strconv.Atoi(s); err == nil && n > 0 && n <= 20 {
			count = n
		}
	}

	u, err := h.userLoader.GetByID(r.Context(), userID)
	if err != nil {
		slog.Error("load user for recommendations", "user_id", userID, "err", err)
		writeErrorJSON(w, http.StatusInternalServerError, "failed to load user profile")
		return
	}

	req := buildRecipeRequest(u, count)

	// Attach available products to personalise the prompt.
	if products, err := h.productLister.ListForPrompt(r.Context(), userID); err == nil {
		req.AvailableProducts = products
	} else {
		slog.Warn("load products for recommendations", "user_id", userID, "err", err)
	}

	recipes, err := h.gemini.GenerateRecipes(r.Context(), req)
	if err != nil {
		slog.Error("generate recipes", "user_id", userID, "err", err)
		writeErrorJSON(w, http.StatusServiceUnavailable, "recipe generation failed, please try again")
		return
	}

	// Fetch Pexels photos in parallel — each goroutine owns a distinct index.
	var wg sync.WaitGroup
	for i := range recipes {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			imageURL, err := h.pexels.SearchPhoto(r.Context(), recipes[i].ImageQuery)
			if err != nil {
				slog.Warn("pexels photo search failed", "query", recipes[i].ImageQuery, "err", err)
			}
			recipes[i].ImageURL = imageURL
		}(i)
	}
	wg.Wait()

	writeJSON(w, http.StatusOK, recipes)
}

func buildRecipeRequest(u *user.User, count int) gemini.RecipeRequest {
	req := gemini.RecipeRequest{
		Count:         count,
		DailyCalories: 2000, // sensible default
	}

	if u.Goal != nil {
		req.UserGoal = *u.Goal
	}
	if u.DailyCalories != nil && *u.DailyCalories > 0 {
		req.DailyCalories = *u.DailyCalories
	}

	if len(u.Preferences) > 0 {
		var prefs userPreferences
		if err := json.Unmarshal(u.Preferences, &prefs); err == nil {
			req.CuisinePrefs = prefs.Cuisines
			req.Restrictions = prefs.Restrictions
		}
	}
	return req
}

type errorResponse struct {
	Error string `json:"error"`
}

func writeErrorJSON(w http.ResponseWriter, status int, msg string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(errorResponse{Error: msg}); err != nil {
		slog.Error("write error response", "err", err)
	}
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if err := json.NewEncoder(w).Encode(v); err != nil {
		slog.Error("write JSON response", "err", err)
	}
}