package product

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

	"github.com/go-chi/chi/v5"
	"github.com/food-ai/backend/internal/infra/middleware"
)

// ProductSearcher is the data layer interface used by Handler for search.
type ProductSearcher interface {
	Search(ctx context.Context, query string, limit int) ([]*Product, error)
	GetByBarcode(ctx context.Context, barcode string) (*Product, error)
	UpsertByBarcode(ctx context.Context, catalogProduct *Product) (*Product, error)
}

// OpenFoodFactsClient fetches product data from Open Food Facts.
type OpenFoodFactsClient interface {
	Fetch(requestContext context.Context, barcode string) (*Product, error)
}

// Handler handles catalog product HTTP requests.
type Handler struct {
	repo           ProductSearcher
	openFoodFacts  OpenFoodFactsClient
}

// NewHandler creates a new Handler.
func NewHandler(repo ProductSearcher, openFoodFacts OpenFoodFactsClient) *Handler {
	return &Handler{repo: repo, openFoodFacts: openFoodFacts}
}

// Search handles GET /products/search?q=&limit=10.
func (handler *Handler) Search(responseWriter http.ResponseWriter, request *http.Request) {
	query := request.URL.Query().Get("q")
	if query == "" {
		responseWriter.Header().Set("Content-Type", "application/json")
		_, _ = responseWriter.Write([]byte("[]"))
		return
	}

	limit := 10
	if limitStr := request.URL.Query().Get("limit"); limitStr != "" {
		if parsedLimit, parseError := strconv.Atoi(limitStr); parseError == nil && parsedLimit > 0 && parsedLimit <= 50 {
			limit = parsedLimit
		}
	}

	products, searchError := handler.repo.Search(request.Context(), query, limit)
	if searchError != nil {
		slog.ErrorContext(request.Context(), "search catalog products", "q", query, "err", searchError)
		responseWriter.Header().Set("Content-Type", "application/json")
		responseWriter.WriteHeader(http.StatusInternalServerError)
		_, _ = responseWriter.Write([]byte(`{"error":"search failed"}`))
		return
	}

	if products == nil {
		products = []*Product{}
	}

	responseWriter.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(responseWriter).Encode(products)
}

// GetByBarcode handles GET /products/barcode/{barcode}.
// Checks the database first; on miss, fetches from Open Food Facts and caches the result.
func (handler *Handler) GetByBarcode(responseWriter http.ResponseWriter, request *http.Request) {
	barcode := chi.URLParam(request, "barcode")
	if barcode == "" {
		writeErrorJSON(responseWriter, request, http.StatusBadRequest, "barcode is required")
		return
	}

	// Check the local catalog first.
	catalogProduct, lookupError := handler.repo.GetByBarcode(request.Context(), barcode)
	if lookupError != nil {
		slog.ErrorContext(request.Context(), "lookup product by barcode", "barcode", barcode, "err", lookupError)
		writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "lookup failed")
		return
	}
	if catalogProduct != nil {
		writeJSON(responseWriter, http.StatusOK, catalogProduct)
		return
	}

	// Not in catalog — fetch from Open Food Facts.
	fetchedProduct, fetchError := handler.openFoodFacts.Fetch(request.Context(), barcode)
	if fetchError != nil {
		slog.WarnContext(request.Context(), "open food facts fetch failed", "barcode", barcode, "err", fetchError)
		writeErrorJSON(responseWriter, request, http.StatusNotFound, "product not found")
		return
	}

	// Persist the fetched product so subsequent lookups are served from the DB.
	savedProduct, upsertError := handler.repo.UpsertByBarcode(request.Context(), fetchedProduct)
	if upsertError != nil {
		slog.WarnContext(request.Context(), "upsert product from open food facts", "barcode", barcode, "err", upsertError)
		// Return the fetched data even if we could not cache it.
		writeJSON(responseWriter, http.StatusOK, fetchedProduct)
		return
	}
	writeJSON(responseWriter, http.StatusOK, savedProduct)
}

type errorResponse struct {
	Error     string `json:"error"`
	RequestID string `json:"request_id,omitempty"`
}

func writeErrorJSON(responseWriter http.ResponseWriter, request *http.Request, status int, msg string) {
	responseWriter.Header().Set("Content-Type", "application/json")
	responseWriter.WriteHeader(status)
	_ = json.NewEncoder(responseWriter).Encode(errorResponse{
		Error:     msg,
		RequestID: middleware.RequestIDFromCtx(request.Context()),
	})
}

func writeJSON(responseWriter http.ResponseWriter, status int, value any) {
	responseWriter.Header().Set("Content-Type", "application/json")
	responseWriter.WriteHeader(status)
	_ = json.NewEncoder(responseWriter).Encode(value)
}