// backend/notifications.go

package main

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"sync"
	"time"
)

type Notification struct {
	ID         string          `json:"id"`
	UserID     string          `json:"userId"`
	Type       string          `json:"type"`
	Title      string          `json:"title"`
	Message    string          `json:"message"`
	EntityType string          `json:"entityType"`
	EntityID   string          `json:"entityId"`
	Data       json.RawMessage `json:"data"`
	Silent     bool            `json:"silent"`
	SoundName  string          `json:"soundName,omitempty"`
	ReadAt     *time.Time      `json:"readAt"`
	CreatedAt  time.Time       `json:"createdAt"`
}

type notificationClient struct {
	userID string
	ch     chan Notification
}

type notificationBroker struct {
	mu      sync.RWMutex
	clients map[*notificationClient]struct{}
}

var notificationsBroker = &notificationBroker{
	clients: map[*notificationClient]struct{}{},
}

func (b *notificationBroker) subscribe(userID string) *notificationClient {
	client := &notificationClient{
		userID: userID,
		ch:     make(chan Notification, 16),
	}

	b.mu.Lock()
	b.clients[client] = struct{}{}
	b.mu.Unlock()

	return client
}

func (b *notificationBroker) unsubscribe(client *notificationClient) {
	b.mu.Lock()
	delete(b.clients, client)
	close(client.ch)
	b.mu.Unlock()
}

func (b *notificationBroker) publish(notification Notification) {
	b.mu.RLock()
	defer b.mu.RUnlock()

	for client := range b.clients {
		if client.userID != notification.UserID {
			continue
		}

		select {
		case client.ch <- notification:
		default:
		}
	}
}

func (b *notificationBroker) publishToAll(notification Notification) {
	b.mu.RLock()
	defer b.mu.RUnlock()

	for client := range b.clients {
		select {
		case client.ch <- notification:
		default:
		}
	}
}

func shouldDeliverNotification(
	preferences notificationPreferencesResponse,
	notificationType string,
	entityType string,
) bool {
	if !preferences.InAppEnabled {
		return false
	}

	switch {
	case notificationType == "operation.journal":
		return preferences.OperationJournals

	case strings.HasPrefix(notificationType, "operation.") || entityType == "operation":
		return preferences.OperationUpdates

	case notificationType == "device.journal":
		return preferences.DeviceJournals

	case strings.HasPrefix(notificationType, "device.") || entityType == "device":
		return preferences.DeviceUpdates

	case strings.HasPrefix(notificationType, "system.") || entityType == "system":
		return preferences.SystemMessages

	default:
		return true
	}
}

func notificationSoundName(preferences notificationPreferencesResponse) string {
	if !preferences.SoundEnabled {
		return ""
	}

	return normalizeNotificationSoundName(preferences.SoundName)
}

func (s *Server) createAndPublishNotification(
	ctx context.Context,
	recipientID string,
	notificationType string,
	title string,
	message string,
	entityType string,
	entityID string,
	dataJSON []byte,
	silent bool,
) error {
	preferences, err := s.getNotificationPreferencesOrDefault(ctx, recipientID)
	if err != nil {
		return err
	}

	// Sichtbare Benachrichtigungen respektieren die User-Preferences.
	// Stille Events werden immer erzeugt, weil sie das UI synchronisieren.
	if !silent && !shouldDeliverNotification(preferences, notificationType, entityType) {
		return nil
	}

	var notification Notification
	var rawData []byte

	err = s.db.QueryRow(
		ctx,
		`
		INSERT INTO notifications (
			user_id,
			type,
			title,
			message,
			entity_type,
			entity_id,
			data,
			silent
		)
		VALUES (
			$1,
			$2,
			$3,
			$4,
			$5,
			NULLIF($6, '')::UUID,
			$7::JSONB,
			$8
		)
		RETURNING
			id::TEXT,
			user_id::TEXT,
			type,
			title,
			message,
			entity_type,
			COALESCE(entity_id::TEXT, ''),
			data,
			silent,
			created_at
		`,
		recipientID,
		notificationType,
		title,
		message,
		entityType,
		entityID,
		string(dataJSON),
		silent,
	).Scan(
		&notification.ID,
		&notification.UserID,
		&notification.Type,
		&notification.Title,
		&notification.Message,
		&notification.EntityType,
		&notification.EntityID,
		&rawData,
		&notification.Silent,
		&notification.CreatedAt,
	)
	if err != nil {
		return err
	}

	notification.Data = json.RawMessage(rawData)

	if !notification.Silent {
		notification.SoundName = notificationSoundName(preferences)
	}

	notificationsBroker.publish(notification)

	return nil
}

func (s *Server) handleNotificationEvents(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("X-Accel-Buffering", "no")

	flusher, ok := w.(http.Flusher)
	if !ok {
		writeError(w, http.StatusInternalServerError, "Streaming wird nicht unterstützt")
		return
	}

	client := notificationsBroker.subscribe(user.ID)
	defer notificationsBroker.unsubscribe(client)

	fmt.Fprintf(w, "event: connected\n")
	fmt.Fprintf(w, "data: {}\n\n")
	flusher.Flush()

	for {
		select {
		case <-r.Context().Done():
			return

		case notification := <-client.ch:
			payload, err := json.Marshal(notification)
			if err != nil {
				continue
			}

			eventName := "notification"

			if notification.Silent {
				switch notification.EntityType {
				case "operation":
					eventName = "operation-event"
				case "device":
					eventName = "device-event"
				case "user":
					eventName = "user-event"
				default:
					eventName = "notification-event"
				}
			}

			fmt.Fprintf(w, "event: %s\n", eventName)
			fmt.Fprintf(w, "data: %s\n\n", payload)
			flusher.Flush()
		}
	}
}

func (s *Server) handleListNotifications(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	rows, err := s.db.Query(
		r.Context(),
		`
		SELECT
			id::TEXT,
			user_id::TEXT,
			type,
			title,
			message,
			entity_type,
			COALESCE(entity_id::TEXT, ''),
			data,
			silent,
			read_at,
			created_at
		FROM notifications
		WHERE user_id = $1
			AND silent = false
		ORDER BY created_at DESC
		LIMIT 50
		`,
		user.ID,
	)

	if err != nil {
		writeError(w, http.StatusInternalServerError, "Benachrichtigungen konnten nicht geladen werden")
		return
	}
	defer rows.Close()

	notifications := []Notification{}

	for rows.Next() {
		var notification Notification
		var readAt sql.NullTime
		var data []byte

		if err := rows.Scan(
			&notification.ID,
			&notification.UserID,
			&notification.Type,
			&notification.Title,
			&notification.Message,
			&notification.EntityType,
			&notification.EntityID,
			&data,
			&notification.Silent,
			&readAt,
			&notification.CreatedAt,
		); err != nil {
			writeError(w, http.StatusInternalServerError, "Benachrichtigungen konnten nicht gelesen werden")
			return
		}

		if readAt.Valid {
			notification.ReadAt = &readAt.Time
		}

		notification.Data = json.RawMessage(data)
		notifications = append(notifications, notification)
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"notifications": notifications,
	})
}

func (s *Server) handleMarkNotificationRead(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	notificationID := strings.TrimSpace(r.PathValue("id"))
	if notificationID == "" {
		writeError(w, http.StatusBadRequest, "Benachrichtigungs-ID fehlt")
		return
	}

	_, err := s.db.Exec(
		r.Context(),
		`
		UPDATE notifications
		SET read_at = COALESCE(read_at, now())
		WHERE id = $1 AND user_id = $2
		`,
		notificationID,
		user.ID,
	)

	if err != nil {
		writeError(w, http.StatusInternalServerError, "Benachrichtigung konnte nicht aktualisiert werden")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"ok": true,
	})
}

func (s *Server) handleMarkAllNotificationsRead(w http.ResponseWriter, r *http.Request) {
	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	_, err := s.db.Exec(
		r.Context(),
		`
		UPDATE notifications
		SET read_at = COALESCE(read_at, now())
		WHERE user_id = $1 AND read_at IS NULL
		`,
		user.ID,
	)

	if err != nil {
		writeError(w, http.StatusInternalServerError, "Benachrichtigungen konnten nicht aktualisiert werden")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"ok": true,
	})
}

func (s *Server) createOperationNotification(
	ctx context.Context,
	actor User,
	operation Operation,
	notificationType string,
	title string,
	message string,
	data map[string]any,
) error {
	dataJSON, err := json.Marshal(data)
	if err != nil {
		return err
	}

	rows, err := s.db.Query(
		ctx,
		`
		SELECT id::TEXT
		FROM users
		WHERE id <> $1
		  AND (
			'admin' = ANY(rights)
			OR 'operations:read' = ANY(rights)
		  )
		`,
		actor.ID,
	)
	if err != nil {
		return err
	}
	defer rows.Close()

	for rows.Next() {
		var recipientID string

		if err := rows.Scan(&recipientID); err != nil {
			return err
		}

		if err := s.createAndPublishNotification(
			ctx,
			recipientID,
			notificationType,
			title,
			message,
			"operation",
			operation.ID,
			dataJSON,
			false,
		); err != nil {
			return err
		}
	}

	return rows.Err()
}

func (s *Server) createOperationCreatedEvent(
	ctx context.Context,
	actor User,
	operation Operation,
	data map[string]any,
) error {
	dataJSON, err := json.Marshal(data)
	if err != nil {
		return err
	}

	rows, err := s.db.Query(
		ctx,
		`
		SELECT id::TEXT
		FROM users
		WHERE id <> $1
		  AND (
		    'admin' = ANY(rights)
		    OR 'operations:read' = ANY(rights)
		  )
		`,
		actor.ID,
	)
	if err != nil {
		return err
	}
	defer rows.Close()

	for rows.Next() {
		var recipientID string

		if err := rows.Scan(&recipientID); err != nil {
			return err
		}

		if err := s.createAndPublishNotification(
			ctx,
			recipientID,
			"operation.created",
			"Einsatz erstellt",
			"",
			"operation",
			operation.ID,
			dataJSON,
			true,
		); err != nil {
			return err
		}
	}

	return rows.Err()
}

func (s *Server) createOperationUpdateEvent(
	ctx context.Context,
	actor User,
	operation Operation,
	data map[string]any,
) error {
	dataJSON, err := json.Marshal(data)
	if err != nil {
		return err
	}

	rows, err := s.db.Query(
		ctx,
		`
		SELECT id::TEXT
		FROM users
		WHERE id <> $1
		  AND (
		    'admin' = ANY(rights)
		    OR 'operations:read' = ANY(rights)
		  )
		`,
		actor.ID,
	)
	if err != nil {
		return err
	}
	defer rows.Close()

	for rows.Next() {
		var recipientID string

		if err := rows.Scan(&recipientID); err != nil {
			return err
		}

		if err := s.createAndPublishNotification(
			ctx,
			recipientID,
			"operation.updated",
			"Einsatz geändert",
			"",
			"operation",
			operation.ID,
			dataJSON,
			true,
		); err != nil {
			return err
		}
	}

	return rows.Err()
}

func (s *Server) createOperationJournalEvent(
	ctx context.Context,
	actor User,
	operation Operation,
	data map[string]any,
) error {
	dataJSON, err := json.Marshal(data)
	if err != nil {
		return err
	}

	rows, err := s.db.Query(
		ctx,
		`
		SELECT id::TEXT
		FROM users
		WHERE id <> $1
		`,
		actor.ID,
	)
	if err != nil {
		return err
	}
	defer rows.Close()

	for rows.Next() {
		var recipientID string

		if err := rows.Scan(&recipientID); err != nil {
			return err
		}

		if err := s.createAndPublishNotification(
			ctx,
			recipientID,
			"operation.journal",
			"Journal aktualisiert",
			"Ein Journal-Eintrag wurde aktualisiert.",
			"operation",
			operation.ID,
			dataJSON,
			true,
		); err != nil {
			return err
		}
	}

	return rows.Err()
}

func (s *Server) createDeviceJournalEvent(
	ctx context.Context,
	actor User,
	device Device,
	data map[string]any,
) error {
	dataJSON, err := json.Marshal(data)
	if err != nil {
		return err
	}

	rows, err := s.db.Query(
		ctx,
		`
		SELECT id::TEXT
		FROM users
		WHERE id <> $1
		  AND (
		    'admin' = ANY(rights)
		    OR 'devices:read' = ANY(rights)
		  )
		`,
		actor.ID,
	)
	if err != nil {
		return err
	}
	defer rows.Close()

	for rows.Next() {
		var recipientID string

		if err := rows.Scan(&recipientID); err != nil {
			return err
		}

		if err := s.createAndPublishNotification(
			ctx,
			recipientID,
			"device.journal",
			"Geräte-Journal aktualisiert",
			"Ein Geräte-Journal-Eintrag wurde hinzugefügt.",
			"device",
			device.ID,
			dataJSON,
			true,
		); err != nil {
			return err
		}
	}

	return rows.Err()
}