package orchestration

import (
	"context"
	"errors"
	"strconv"
	"time"

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

type LeaseRecord struct {
	ConversationID string
	DeviceID       string
	SequenceNo     int64
	Status         string
	ExpiresAt      time.Time
	ObservedAt     time.Time
}

type LeaseCache interface {
	Refresh(context.Context, LeaseRecord) error
	End(context.Context, string, string, time.Time) error
}

type RedisLeaseCache struct {
	client *redis.Client
	prefix string
}

var refreshLeaseScript = redis.NewScript(`
local current = redis.call('HGET', KEYS[1], 'sequence_no')
if current and tonumber(current) >= tonumber(ARGV[1]) then
  return 0
end
redis.call('HSET', KEYS[1],
  'sequence_no', ARGV[1], 'status', ARGV[2], 'device_id', ARGV[3],
  'lease_expires_at', ARGV[4], 'observed_at', ARGV[5])
redis.call('PEXPIRE', KEYS[1], ARGV[6])
redis.call('HSET', KEYS[2],
  'online', 'true', 'conversation_id', ARGV[7], 'sequence_no', ARGV[1],
  'last_seen_at', ARGV[5])
redis.call('PEXPIRE', KEYS[2], ARGV[8])
return 1
`)

func NewRedisLeaseCache(client *redis.Client, prefix string) (*RedisLeaseCache, error) {
	if client == nil || prefix == "" {
		return nil, errors.New("redis client and lease key prefix are required")
	}
	return &RedisLeaseCache{client: client, prefix: prefix}, nil
}

func (c *RedisLeaseCache) Refresh(ctx context.Context, record LeaseRecord) error {
	ttl := time.Until(record.ExpiresAt)
	if ttl <= 0 || record.SequenceNo < 1 || record.ConversationID == "" || record.DeviceID == "" {
		return errors.New("active lease record is invalid or already expired")
	}
	presenceTTL := ttl * 2
	_, err := refreshLeaseScript.Run(ctx, c.client, []string{
		c.prefix + ":conversation:lease:" + record.ConversationID,
		c.prefix + ":device:presence:" + record.DeviceID,
	},
		strconv.FormatInt(record.SequenceNo, 10), record.Status, record.DeviceID,
		record.ExpiresAt.UTC().Format(time.RFC3339Nano), record.ObservedAt.UTC().Format(time.RFC3339Nano),
		ttl.Milliseconds(), record.ConversationID, presenceTTL.Milliseconds(),
	).Result()
	return err
}

func (c *RedisLeaseCache) End(ctx context.Context, conversationID, deviceID string, observedAt time.Time) error {
	if conversationID == "" || deviceID == "" {
		return errors.New("conversation and device identifiers are required")
	}
	leaseKey := c.prefix + ":conversation:lease:" + conversationID
	presenceKey := c.prefix + ":device:presence:" + deviceID
	pipe := c.client.TxPipeline()
	pipe.Del(ctx, leaseKey)
	pipe.HSet(ctx, presenceKey, "conversation_id", "", "status", "idle", "last_seen_at", observedAt.UTC().Format(time.RFC3339Nano))
	_, err := pipe.Exec(ctx)
	return err
}