package bookings

import (
	"crypto/md5"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"strings"
	"time"

	"crussell/auth"
	"crussell/db"
	"crussell/handlers/scheduling"
	"crussell/internal/validators"
	"crussell/mw"
	"net"
)

// ReserveSlotRequest represents the request body for reserving a slot
type ReserveSlotRequest struct {
	StartTime  time.Time `json:"start_time" validate:"required"`
	ServiceIDs []string  `json:"service_ids" validate:"required,min=1"`
}

// ReserveSlotResponse represents the response for a successful reservation
type ReserveSlotResponse struct {
	ID              string    `json:"id"`
	StartTime       time.Time `json:"start_time"`
	DurationMinutes int       `json:"duration_minutes"`
	ExpiresAt       time.Time `json:"expires_at"`
	IsAnonymous     bool      `json:"is_anonymous"`
}

// ReserveSlotHandler creates temporary slot reservations for both logged-in and anonymous users
func ReserveSlotHandler(w http.ResponseWriter, r *http.Request) {
	// a. Parse JSON request body, validate start_time and service_ids are present
	var req ReserveSlotRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		log.Printf("Failed to decode request: %v", err)
		http.Error(w, "Invalid request", http.StatusBadRequest)
		return
	}

	if err := validators.Validate.Struct(&req); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	// M8
	// L5

	if req.StartTime.IsZero() {
		http.Error(w, "start_time is required", http.StatusBadRequest)
		return
	}
	if len(req.ServiceIDs) == 0 {
		http.Error(w, "At least one service is required", http.StatusBadRequest)
		return
	}

	// b. Extract client IP: check CF-Connecting-IP → X-Real-IP → X-Forwarded-For → RemoteAddr
	ip := r.Header.Get("CF-Connecting-IP")
	if ip == "" {
		ip, _, _ = net.SplitHostPort(r.RemoteAddr)
		if ip == "" {
			ip = r.RemoteAddr
		}
	}

	// c. Detect auth: try context first, then parse Bearer token from Authorization header
	userID, hasUser := r.Context().Value(mw.UserIDKey).(string)
	hasAuth := hasUser && userID != ""

	// If no user in context, try to parse token from header
	if !hasAuth {
		authHeader := r.Header.Get("Authorization")
		if strings.HasPrefix(authHeader, "Bearer ") {
			tokenString := strings.TrimPrefix(authHeader, "Bearer ")
			var err error
			userID, _, _, err = auth.VerifyToken(tokenString, r.Context())
			if err != nil {
				// Invalid token - treat as unauthenticated
				userID = ""
			}
			hasAuth = userID != ""
		}
	}

	// d. Calculate total duration: SELECT COALESCE(SUM(duration_minutes), 0) FROM services WHERE id = ANY($1)
	var svcDuration int
	if err := db.Conn.QueryRow(r.Context(), `
		SELECT COALESCE(SUM(duration_minutes), 0) FROM services WHERE id = ANY($1)
	`, req.ServiceIDs).Scan(&svcDuration); err != nil {
		log.Printf("Failed to calculate duration: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	if svcDuration == 0 {
		http.Error(w, "Invalid service IDs", http.StatusBadRequest)
		return
	}

	// e. Validate start_time not in the past
	if req.StartTime.Before(time.Now()) {
		http.Error(w, "Start time cannot be in the past", http.StatusBadRequest)
		return
	}

	// f. Validate working hours: SELECT end_time::text FROM working_hours WHERE weekday = $1
	// DB uses 0=Monday..6=Sunday; Go uses 0=Sunday..6=Saturday. Convert.
	localStart := req.StartTime.In(londonLocation)
	weekday := int((localStart.Weekday() + 6) % 7)
	var closeStr string
	if err := db.Conn.QueryRow(r.Context(), `SELECT end_time FROM working_hours WHERE weekday = $1`, weekday).Scan(&closeStr); err != nil {
		log.Printf("Failed to get hours: %v", err)
		http.Error(w, "Could not verify hours", http.StatusInternalServerError)
		return
	}

	localEnd := localStart.Add(time.Duration(svcDuration) * time.Minute)
	closeTime, _ := time.Parse("15:04:05", closeStr)
	if localEnd.Hour() > closeTime.Hour() || (localEnd.Hour() == closeTime.Hour() && localEnd.Minute() > closeTime.Minute()) {
		http.Error(w, "Cannot book this time - services would extend beyond closing hours", http.StatusBadRequest)
		return
	}

	// g. Check existing booking overlap (same query as CreateBookingHandler)
	endTime := req.StartTime.Add(time.Duration(svcDuration) * time.Minute)
	var cnt int
	if err := db.Conn.QueryRow(r.Context(), `
		SELECT COUNT(*) FROM bookings WHERE status IN ('pending','confirmed','in_progress','completed')
		AND start_time < $2
		AND end_time > $1
	`, req.StartTime, endTime).Scan(&cnt); err != nil {
		log.Printf("Failed to check overlap: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	if cnt > 0 {
		http.Error(w, "Cannot book this time - slot overlaps with an existing booking", http.StatusConflict)
		return
	}

	// h. Check time blocker overlap using scheduling.CheckTimeBlockerOverlap
	blockerOverlap, _, err := scheduling.CheckTimeBlockerOverlap(r.Context(), req.StartTime, endTime)
	if err != nil {
		log.Printf("Failed to check time blocker overlap: %v", err)
	} else if blockerOverlap {
		http.Error(w, "Cannot book this time - slot is blocked", http.StatusConflict)
		return
	}

	// j. Branch on auth
	var reservationID string
	var createdAt time.Time

	if hasAuth {
		tx, err := db.Conn.Begin(r.Context())
		if err != nil {
			log.Printf("Failed to start transaction: %v", err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}
		defer tx.Rollback(r.Context())

		// LOGGED IN: Delete existing reservation
		_, err = tx.Exec(r.Context(), `
			DELETE FROM time_blockers
			WHERE created_by = $1 AND description LIKE 'RESERVATION:user:%'
		`, userID)
		if err != nil {
			log.Printf("Failed to delete existing reservation: %v", err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}

		// Insert new reservation
		description := fmt.Sprintf("RESERVATION:user:%s:%d", userID, time.Now().UnixNano())
		err = tx.QueryRow(r.Context(), `
			INSERT INTO time_blockers (start_time, duration_minutes, description, created_by)
			VALUES ($1, $2, $3, $4)
			RETURNING id, created_at
		`, req.StartTime, svcDuration, description, userID).Scan(&reservationID, &createdAt)
		if err != nil {
			log.Printf("Failed to create reservation: %v", err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}

		if err := tx.Commit(r.Context()); err != nil {
			log.Printf("Failed to commit transaction: %v", err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}
	} else {
		// ANONYMOUS: Check cap (50 in 10 minutes)
		tenMinutesAgo := time.Now().Add(-10 * time.Minute)
		var anonCount int
		if err := db.Conn.QueryRow(r.Context(), `
			SELECT COUNT(*) FROM time_blockers
			WHERE description LIKE 'RESERVATION:anon:%' AND created_at > $1
		`, tenMinutesAgo).Scan(&anonCount); err != nil {
			log.Printf("Failed to check anon cap: %v", err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}

		if anonCount >= 50 {
			http.Error(w, "Too many active reservations. Please wait or log in.", http.StatusTooManyRequests)
			return
		}

		// Calculate ipHash: first 8 chars of md5 hex of the IP string
		ipHash := fmt.Sprintf("%x", md5.Sum([]byte(ip)))[:8]
		description := fmt.Sprintf("RESERVATION:anon:%s:%d", ipHash, time.Now().UnixNano())

		// Insert new reservation with created_by = NULL
		err = db.Conn.QueryRow(r.Context(), `
			INSERT INTO time_blockers (start_time, duration_minutes, description, created_by)
			VALUES ($1, $2, $3, NULL)
			RETURNING id, created_at
		`, req.StartTime, svcDuration, description).Scan(&reservationID, &createdAt)
		if err != nil {
			log.Printf("Failed to create reservation: %v", err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}
	}

	// k. Calculate expires_at: logged-in = created_at + 1 hour, anon = created_at + 10 minutes
	var expiresAt time.Time
	if hasAuth {
		expiresAt = createdAt.Add(1 * time.Hour)
	} else {
		expiresAt = createdAt.Add(10 * time.Minute)
	}

	// l. Return 201 with JSON response
	response := ReserveSlotResponse{
		ID:              reservationID,
		StartTime:       req.StartTime,
		DurationMinutes: svcDuration,
		ExpiresAt:       expiresAt,
		IsAnonymous:     !hasAuth,
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusCreated)
	json.NewEncoder(w).Encode(response)
}