package asynq

import (
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"strconv"
	"time"

	"github.com/go-redis/redis/v7"
)

// Redis keys
const (
	queuePrefix  = "asynq:queues:"         // LIST - asynq:queues:<qname>
	defaultQueue = queuePrefix + "default" // LIST
	allQueues    = "asynq:queues"          // SET
	scheduled    = "asynq:scheduled"       // ZSET
	retry        = "asynq:retry"           // ZSET
	dead         = "asynq:dead"            // ZSET
	inProgress   = "asynq:in_progress"     // SET
)

var (
	errQueuePopTimeout = errors.New("blocking queue pop operation timed out")
	errSerializeTask   = errors.New("could not encode task message into json")
	errDeserializeTask = errors.New("could not decode task message from json")
)

// rdb encapsulates the interactions with redis server.
type rdb struct {
	client *redis.Client
}

func newRDB(client *redis.Client) *rdb {
	return &rdb{client}
}

// enqueue inserts the given task to the end of the queue.
// It also adds the queue name to the "all-queues" list.
func (r *rdb) enqueue(msg *taskMessage) error {
	bytes, err := json.Marshal(msg)
	if err != nil {
		return fmt.Errorf("could not encode task into JSON: %v", err)
	}
	qname := queuePrefix + msg.Queue
	pipe := r.client.Pipeline()
	pipe.SAdd(allQueues, qname)
	pipe.LPush(qname, string(bytes))
	_, err = pipe.Exec()
	if err != nil {
		return fmt.Errorf("could not enqueue task %+v to %q: %v",
			msg, qname, err)
	}
	return nil
}

// dequeue blocks until there is a task available to be processed,
// once a task is available, it adds the task to "in progress" list
// and returns the task.
func (r *rdb) dequeue(qname string, timeout time.Duration) (*taskMessage, error) {
	data, err := r.client.BRPopLPush(qname, inProgress, timeout).Result()
	if err != nil {
		if err != redis.Nil {
			return nil, fmt.Errorf("command BRPOPLPUSH %q %q %v failed: %v", qname, inProgress, timeout, err)
		}
		return nil, errQueuePopTimeout
	}
	var msg taskMessage
	err = json.Unmarshal([]byte(data), &msg)
	if err != nil {
		return nil, errDeserializeTask
	}
	fmt.Printf("[DEBUG] perform task %+v from %s\n", msg, qname)
	return &msg, nil
}

func (r *rdb) lrem(key string, msg *taskMessage) error {
	bytes, err := json.Marshal(msg)
	if err != nil {
		return fmt.Errorf("could not encode task into JSON: %v", err)
	}
	// NOTE: count ZERO means "remove all elements equal to val"
	err = r.client.LRem(key, 0, string(bytes)).Err()
	if err != nil {
		return fmt.Errorf("command LREM %s 0 %s failed: %v", key, string(bytes), err)
	}
	return nil
}

// zadd adds the taskMessage to the specified zset (sorted set) with the given score.
func (r *rdb) zadd(zset string, zscore float64, msg *taskMessage) error {
	bytes, err := json.Marshal(msg)
	if err != nil {
		return fmt.Errorf("could not encode task into JSON: %v", err)
	}
	err = r.client.ZAdd(zset, &redis.Z{Member: string(bytes), Score: zscore}).Err()
	if err != nil {
		return fmt.Errorf("command ZADD %s %.1f %s failed: %v",
			zset, zscore, string(bytes), err)
	}
	return nil
}

func (r *rdb) zRangeByScore(key string, opt *redis.ZRangeBy) ([]*taskMessage, error) {
	jobs, err := r.client.ZRangeByScore(key, opt).Result()
	if err != nil {
		return nil, fmt.Errorf("command ZRANGEBYSCORE %s %v failed: %v", key, opt, err)
	}
	var msgs []*taskMessage
	for _, j := range jobs {
		fmt.Printf("[debug] j = %v\n", j)
		var msg taskMessage
		err = json.Unmarshal([]byte(j), &msg)
		if err != nil {
			log.Printf("[WARNING] could not unmarshal task data %s: %v\n", j, err)
			continue
		}
		msgs = append(msgs, &msg)
	}
	return msgs, nil
}

// move moves taskMessage from zfrom to the specified queue.
func (r *rdb) move(from string, msg *taskMessage) error {
	// TODO(hibiken): Lua script, make this atomic.
	bytes, err := json.Marshal(msg)
	if err != nil {
		return errSerializeTask
	}
	if r.client.ZRem(from, string(bytes)).Val() > 0 {
		err = r.enqueue(msg)
		if err != nil {
			log.Printf("[SERVERE ERROR] could not push task to queue %q: %v\n",
				msg.Queue, err)
			// TODO(hibiken): Handle this error properly.
			// Add back to zfrom?
			return fmt.Errorf("could not push task %v from %q: %v", msg, msg.Queue, err)
		}
	}
	return nil
}

const maxDeadTask = 100
const deadExpirationInDays = 90

// kill sends the taskMessage to "dead" set.
// It also trims the sorted set by timestamp and set size.
func (r *rdb) kill(msg *taskMessage) error {
	bytes, err := json.Marshal(msg)
	if err != nil {
		return fmt.Errorf("could not encode task into JSON: %v", err)
	}
	now := time.Now()
	pipe := r.client.Pipeline()
	pipe.ZAdd(dead, &redis.Z{Member: string(bytes), Score: float64(now.Unix())})
	limit := now.AddDate(0, 0, -deadExpirationInDays).Unix() // 90 days ago
	pipe.ZRemRangeByScore(dead, "-inf", strconv.Itoa(int(limit)))
	pipe.ZRemRangeByRank(dead, 0, -maxDeadTask) // trim the set to 100
	_, err = pipe.Exec()
	return err
}

// listQueues returns the list of all queues.
// NOTE: Add default to the slice if empty because
// BLPOP will error out if empty list is passed.
func (r *rdb) listQueues() []string {
	queues := r.client.SMembers(allQueues).Val()
	if len(queues) == 0 {
		queues = append(queues, queuePrefix+"default")
	}
	return queues
}

// moveAll moves all tasks from src list to dst list.
func (r *rdb) moveAll(src, dst string) error {
	// TODO(hibiken): Lua script
	txf := func(tx *redis.Tx) error {
		length := tx.LLen(src).Val()
		for i := 0; i < int(length); i++ {
			tx.RPopLPush(src, dst)
		}
		return nil
	}
	return r.client.Watch(txf, src)
}

// forward moves all tasks with a score less than the current unix time
// from the given zset to the default queue.
func (r *rdb) forward(from string) error {
	script := redis.NewScript(`
	local msgs = redis.call("ZRANGEBYSCORE", KEYS[1], "-inf", ARGV[1])
	for _, msg in ipairs(msgs) do
		redis.call("ZREM", KEYS[1], msg)
		redis.call("SADD", KEYS[2], KEYS[3])
		redis.call("LPUSH", KEYS[3], msg)
	end
	return msgs
	`)
	now := float64(time.Now().Unix())
	_, err := script.Run(r.client, []string{from, allQueues, defaultQueue}, now).Result()
	return err
}