package home

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"time"

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

// Handler handles GET /home/summary.
type Handler struct {
	pool *pgxpool.Pool
}

// NewHandler creates a new Handler.
func NewHandler(pool *pgxpool.Pool) *Handler {
	return &Handler{pool: pool}
}

// GetSummary handles GET /home/summary.
func (h *Handler) GetSummary(w http.ResponseWriter, r *http.Request) {
	userID := middleware.UserIDFromCtx(r.Context())
	if userID == "" {
		writeError(w, http.StatusUnauthorized, "unauthorized")
		return
	}

	ctx := r.Context()
	now := time.Now().UTC()
	todayStr := now.Format("2006-01-02")

	// ISO day of week: Monday=1 … Sunday=7.
	wd := int(now.Weekday())
	if wd == 0 {
		wd = 7
	}

	// Monday of the current ISO week.
	year, week := now.ISOWeek()
	weekStart := mondayOfISOWeek(year, week).Format("2006-01-02")

	// Daily calorie goal from user profile.
	dailyGoal := h.getDailyGoal(ctx, userID)

	summary := Summary{
		Today: TodaySummary{
			Date:           todayStr,
			DailyGoal:      dailyGoal,
			LoggedCalories: h.getLoggedCalories(ctx, userID, todayStr),
			Plan:           h.getTodayPlan(ctx, userID, weekStart, wd),
		},
		ExpiringSoon:    h.getExpiringSoon(ctx, userID),
		Recommendations: h.getRecommendations(ctx, userID),
	}

	writeJSON(w, http.StatusOK, summary)
}

// getDailyGoal returns the user's daily_calories setting (default 2000).
func (h *Handler) getDailyGoal(ctx context.Context, userID string) int {
	var goal int
	err := h.pool.QueryRow(ctx,
		`SELECT COALESCE(daily_calories, 2000) FROM users WHERE id = $1`,
		userID,
	).Scan(&goal)
	if err != nil {
		slog.Warn("home: get daily goal", "user_id", userID, "err", err)
		return 2000
	}
	return goal
}

// getLoggedCalories returns total calories logged in meal_diary for today.
func (h *Handler) getLoggedCalories(ctx context.Context, userID, date string) float64 {
	var total float64
	_ = h.pool.QueryRow(ctx,
		`SELECT COALESCE(SUM(calories * portions), 0)
		 FROM meal_diary
		 WHERE user_id = $1 AND date::text = $2`,
		userID, date,
	).Scan(&total)
	return total
}

// getTodayPlan returns the three meal slots planned for today.
// If no menu exists, all three slots are returned with nil recipe fields.
func (h *Handler) getTodayPlan(ctx context.Context, userID, weekStart string, dow int) []MealPlan {
	const q = `
		SELECT mi.meal_type,
		       sr.title,
		       sr.image_url,
		       (sr.nutrition->>'calories')::float
		FROM menu_plans mp
		JOIN menu_items mi ON mi.menu_plan_id = mp.id
		LEFT JOIN saved_recipes sr ON sr.id = mi.recipe_id
		WHERE mp.user_id = $1
		  AND mp.week_start::text = $2
		  AND mi.day_of_week = $3`

	rows, err := h.pool.Query(ctx, q, userID, weekStart, dow)
	if err != nil {
		slog.Warn("home: get today plan", "err", err)
		return defaultPlan()
	}
	defer rows.Close()

	found := map[string]MealPlan{}
	for rows.Next() {
		var mealType string
		var title, imageURL *string
		var calories *float64
		if err := rows.Scan(&mealType, &title, &imageURL, &calories); err != nil {
			continue
		}
		found[mealType] = MealPlan{
			MealType:       mealType,
			RecipeTitle:    title,
			RecipeImageURL: imageURL,
			Calories:       calories,
		}
	}

	// Always return all three meal types in order.
	mealTypes := []string{"breakfast", "lunch", "dinner"}
	plan := make([]MealPlan, 0, 3)
	for _, mt := range mealTypes {
		if mp, ok := found[mt]; ok {
			plan = append(plan, mp)
		} else {
			plan = append(plan, MealPlan{MealType: mt})
		}
	}
	return plan
}

// defaultPlan returns three empty meal slots.
func defaultPlan() []MealPlan {
	return []MealPlan{
		{MealType: "breakfast"},
		{MealType: "lunch"},
		{MealType: "dinner"},
	}
}

// getExpiringSoon returns products expiring within the next 3 days.
func (h *Handler) getExpiringSoon(ctx context.Context, userID string) []ExpiringSoon {
	rows, err := h.pool.Query(ctx, `
		WITH p AS (
			SELECT name, quantity, unit,
			       (added_at + storage_days * INTERVAL '1 day') AS expires_at
			FROM products
			WHERE user_id = $1
		)
		SELECT name, quantity, unit,
		       GREATEST(0, EXTRACT(EPOCH FROM (expires_at - now())) / 86400)::int
		FROM p
		WHERE expires_at > now()
		  AND expires_at <= now() + INTERVAL '3 days'
		ORDER BY expires_at
		LIMIT 5`,
		userID,
	)
	if err != nil {
		slog.Warn("home: get expiring soon", "err", err)
		return nil
	}
	defer rows.Close()

	var result []ExpiringSoon
	for rows.Next() {
		var name, unit string
		var quantity float64
		var daysLeft int
		if err := rows.Scan(&name, &quantity, &unit, &daysLeft); err != nil {
			continue
		}
		result = append(result, ExpiringSoon{
			Name:          name,
			ExpiresInDays: daysLeft,
			Quantity:      fmt.Sprintf("%.0f %s", quantity, unit),
		})
	}
	return result
}

// getRecommendations returns the 3 most recently generated recipe recommendations.
func (h *Handler) getRecommendations(ctx context.Context, userID string) []Recommendation {
	rows, err := h.pool.Query(ctx, `
		SELECT id, title, COALESCE(image_url, ''),
		       (nutrition->>'calories')::float
		FROM saved_recipes
		WHERE user_id = $1 AND source = 'recommendation'
		ORDER BY saved_at DESC
		LIMIT 3`,
		userID,
	)
	if err != nil {
		slog.Warn("home: get recommendations", "err", err)
		return nil
	}
	defer rows.Close()

	var result []Recommendation
	for rows.Next() {
		var rec Recommendation
		var cal *float64
		if err := rows.Scan(&rec.ID, &rec.Title, &rec.ImageURL, &cal); err != nil {
			continue
		}
		rec.Calories = cal
		result = append(result, rec)
	}
	return result
}

// mondayOfISOWeek returns the Monday of the given ISO year/week.
func mondayOfISOWeek(year, week int) time.Time {
	jan4 := time.Date(year, time.January, 4, 0, 0, 0, 0, time.UTC)
	wd := int(jan4.Weekday())
	if wd == 0 {
		wd = 7
	}
	monday1 := jan4.AddDate(0, 0, 1-wd)
	return monday1.AddDate(0, 0, (week-1)*7)
}

func writeError(w http.ResponseWriter, status int, msg string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(map[string]string{"error": msg})
}

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