package units

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

	"github.com/food-ai/backend/internal/infra/locale"
	"github.com/food-ai/backend/internal/infra/middleware"
	"github.com/jackc/pgx/v5/pgxpool"
)

type unitItem struct {
	Code string `json:"code"`
	Name string `json:"name"`
}

// NewListHandler returns an http.HandlerFunc for GET /units.
// It queries the database directly, resolving translations via COALESCE.
func NewListHandler(pool *pgxpool.Pool) http.HandlerFunc {
	return func(responseWriter http.ResponseWriter, request *http.Request) {
		lang := locale.FromContext(request.Context())

		rows, queryError := pool.Query(request.Context(), `
			SELECT u.code, COALESCE(ut.name, u.code) AS name
			FROM units u
			LEFT JOIN unit_translations ut ON ut.unit_code = u.code AND ut.lang = $1
			ORDER BY u.sort_order`, lang)
		if queryError != nil {
			slog.ErrorContext(request.Context(), "list units", "err", queryError)
			writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to load units")
			return
		}
		defer rows.Close()

		items := make([]unitItem, 0)
		for rows.Next() {
			var item unitItem
			if scanError := rows.Scan(&item.Code, &item.Name); scanError != nil {
				slog.ErrorContext(request.Context(), "scan unit row", "err", scanError)
				writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to load units")
				return
			}
			items = append(items, item)
		}
		if rowsError := rows.Err(); rowsError != nil {
			slog.ErrorContext(request.Context(), "iterate unit rows", "err", rowsError)
			writeErrorJSON(responseWriter, request, http.StatusInternalServerError, "failed to load units")
			return
		}

		responseWriter.Header().Set("Content-Type", "application/json")
		_ = json.NewEncoder(responseWriter).Encode(map[string]any{"units": items})
	}
}

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(map[string]any{"error": msg, "request_id": middleware.RequestIDFromCtx(request.Context())})
}