package storage

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"filefast/backend/internal/config"
	"filefast/backend/internal/model"

	"github.com/redis/go-redis/v9"
)

const (
	RedisRealtimeRelayChannel    = "filefast:ws:relay"
	RedisRealtimePresenceChannel = "filefast:ws:presence"
)

type RedisClient struct {
	client *redis.Client
}

type RealtimeMessage struct {
	Channel string
	Payload []byte
}

func NewRedisClient(cfg config.RedisConfig) *RedisClient {
	client := redis.NewClient(&redis.Options{
		Addr:         cfg.Addr,
		Password:     cfg.Password,
		DB:           cfg.DB,
		MaxRetries:   1,
		DialTimeout:  3 * time.Second,
		ReadTimeout:  3 * time.Second,
		WriteTimeout: 3 * time.Second,
	})

	return &RedisClient{client: client}
}

func (c *RedisClient) Ping(ctx context.Context) error {
	if !c.available() {
		return redis.ErrClosed
	}
	return c.client.Ping(ctx).Err()
}

func (c *RedisClient) SaveAdminSession(ctx context.Context, session model.AdminSession, ttl time.Duration) error {
	if !c.available() {
		return redis.ErrClosed
	}

	payload, err := json.Marshal(session)
	if err != nil {
		return err
	}

	return c.client.Set(ctx, adminSessionKey(session.Token), payload, ttl).Err()
}

func (c *RedisClient) HasAdminSession(ctx context.Context, token string) (bool, error) {
	if !c.available() {
		return false, redis.ErrClosed
	}

	result, err := c.client.Exists(ctx, adminSessionKey(token)).Result()
	if err != nil {
		return false, err
	}

	return result > 0, nil
}

func (c *RedisClient) SaveDeviceSession(ctx context.Context, session model.DeviceSession, ttl time.Duration) error {
	if !c.available() {
		return redis.ErrClosed
	}

	return c.client.Set(ctx, deviceSessionKey(session.DeviceID), session.Token, ttl).Err()
}

func (c *RedisClient) ValidateDeviceSession(ctx context.Context, deviceID, token string) (bool, error) {
	if !c.available() {
		return false, redis.ErrClosed
	}

	value, err := c.client.Get(ctx, deviceSessionKey(deviceID)).Result()
	if err != nil {
		if err == redis.Nil {
			return false, nil
		}
		return false, err
	}

	return value == token, nil
}

func (c *RedisClient) SetDevicePresence(ctx context.Context, deviceID string, online bool, lastSeen time.Time, ttl time.Duration) error {
	if !c.available() {
		return redis.ErrClosed
	}

	key := devicePresenceKey(deviceID)
	if !online {
		return c.client.Del(ctx, key).Err()
	}

	return c.client.Set(ctx, key, lastSeen.UTC().Format(time.RFC3339Nano), ttl).Err()
}

func (c *RedisClient) GetDevicePresence(ctx context.Context, deviceIDs []string) (map[string]bool, error) {
	if !c.available() {
		return nil, redis.ErrClosed
	}

	statuses := make(map[string]bool, len(deviceIDs))
	if len(deviceIDs) == 0 {
		return statuses, nil
	}

	keys := make([]string, 0, len(deviceIDs))
	for _, id := range deviceIDs {
		keys = append(keys, devicePresenceKey(id))
	}

	values, err := c.client.MGet(ctx, keys...).Result()
	if err != nil {
		return nil, err
	}

	for index, id := range deviceIDs {
		statuses[id] = values[index] != nil
	}

	return statuses, nil
}

func (c *RedisClient) PublishRealtime(ctx context.Context, channel string, payload []byte) error {
	if !c.available() {
		return redis.ErrClosed
	}
	return c.client.Publish(ctx, channel, payload).Err()
}

func (c *RedisClient) SubscribeRealtime(ctx context.Context, channels ...string) (<-chan RealtimeMessage, error) {
	if !c.available() {
		return nil, redis.ErrClosed
	}

	pubsub := c.client.Subscribe(ctx, channels...)
	if _, err := pubsub.Receive(ctx); err != nil {
		_ = pubsub.Close()
		return nil, err
	}

	source := pubsub.Channel()
	messages := make(chan RealtimeMessage, 64)

	go func() {
		defer close(messages)
		defer pubsub.Close()

		for {
			select {
			case <-ctx.Done():
				return
			case message, ok := <-source:
				if !ok {
					return
				}
				messages <- RealtimeMessage{
					Channel: message.Channel,
					Payload: []byte(message.Payload),
				}
			}
		}
	}()

	return messages, nil
}

func (c *RedisClient) Close() error {
	if !c.available() {
		return nil
	}
	return c.client.Close()
}

func (c *RedisClient) available() bool {
	return c != nil && c.client != nil
}

func adminSessionKey(token string) string {
	return fmt.Sprintf("filefast:admin:session:%s", token)
}

func devicePresenceKey(deviceID string) string {
	return fmt.Sprintf("filefast:device:online:%s", deviceID)
}

func deviceSessionKey(deviceID string) string {
	return fmt.Sprintf("filefast:device:session:%s", deviceID)
}