package etcd

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"runtime"
	"sync"
	"time"

	"github.com/RichardKnop/machinery/v2/brokers/errs"
	"github.com/RichardKnop/machinery/v2/brokers/iface"
	"github.com/RichardKnop/machinery/v2/common"
	"github.com/RichardKnop/machinery/v2/config"
	"github.com/RichardKnop/machinery/v2/log"
	"github.com/RichardKnop/machinery/v2/tasks"
	clientv3 "go.etcd.io/etcd/client/v3"
	"golang.org/x/sync/errgroup"
)

var haveNoTaskErr = errors.New("have no task")

// Signature ..
type Signature struct {
	*tasks.Signature
	CreateAt time.Time `json:"CreatedAt"`
	Score    int64     `json:"Score"` // 写入时间, 队列排序用
	body     []byte    `json:"-"`     // 序列号后的值
}

func (s *Signature) Body() ([]byte, error) {
	if len(s.body) > 0 {
		return s.body, nil
	}

	body, err := json.Marshal(s)
	if err != nil {
		return nil, err
	}

	s.body = body
	return s.body, nil
}

func (s *Signature) String() string {
	body, _ := s.Body()
	return string(body)
}

type etcdBroker struct {
	common.Broker
	ctx    context.Context
	client *clientv3.Client
	wg     sync.WaitGroup
}

// New ..
func New(ctx context.Context, conf *config.Config) (iface.Broker, error) {
	etcdConf := clientv3.Config{
		Endpoints:   []string{conf.Broker},
		Context:     ctx,
		DialTimeout: time.Second * 5,
	}

	client, err := clientv3.New(etcdConf)
	if err != nil {
		return nil, err
	}

	broker := etcdBroker{
		Broker: common.NewBroker(conf),
		ctx:    ctx,
		client: client,
	}

	return &broker, nil

}

// StartConsuming ..
func (b *etcdBroker) StartConsuming(consumerTag string, concurrency int, taskProcessor iface.TaskProcessor) (bool, error) {
	if concurrency < 1 {
		concurrency = runtime.NumCPU()
	}
	b.Broker.StartConsuming(consumerTag, concurrency, taskProcessor)

	log.INFO.Printf("[*] Waiting for messages, concurrency=%d. To exit press CTRL+C", concurrency)

	// Channel to which we will push tasks ready for processing by worker
	deliveries := make(chan *Signature)

	// A receiving goroutine keeps popping messages from the queue by BLPOP
	// If the message is valid and can be unmarshaled into a proper structure
	// we send it to the deliveries channel
	b.wg.Add(1)
	go func() {
		defer b.wg.Done()

		for {
			select {
			// A way to stop this goroutine from b.StopConsuming
			case <-b.GetStopChan():
				close(deliveries)
				return

			default:
				if !taskProcessor.PreConsumeHandler() {
					continue
				}

				task, err := b.nextTask(getQueue(b.GetConfig(), taskProcessor))
				if err != nil {
					if !errors.Is(err, haveNoTaskErr) {
						log.ERROR.Print(err)
					}
					continue
				}

				if task != nil {
					deliveries <- task
				}
			}
		}
	}()

	// A goroutine to watch for delayed tasks and push them to deliveries
	// channel for consumption by the worker
	b.wg.Add(1)
	go func() {
		defer b.wg.Done()

		for {
			select {
			// A way to stop this goroutine from b.StopConsuming
			case <-b.GetStopChan():
				return

			default:
				task, err := b.nextDelayedTask()
				if err != nil {
					if !errors.Is(err, haveNoTaskErr) {
						log.ERROR.Print(err)
					}
					continue
				}

				if err := b.Publish(context.Background(), task.Signature); err != nil {
					log.ERROR.Print(err)
				}
			}
		}
	}()

	if err := b.consume(deliveries, concurrency, taskProcessor); err != nil {
		return b.GetRetry(), err
	}

	b.wg.Wait()

	return b.GetRetry(), nil
}

// consume takes delivered messages from the channel and manages a worker pool
// to process tasks concurrently
func (b *etcdBroker) consume(deliveries <-chan *Signature, concurrency int, taskProcessor iface.TaskProcessor) error {
	eg, ctx := errgroup.WithContext(context.Background())
	eg.SetLimit(concurrency)

	for i := 0; i < concurrency; i++ {
		eg.Go(func() error {
			for {
				select {
				case <-ctx.Done():
					return ctx.Err()

				case t, ok := <-deliveries:
					if !ok {
						return nil
					}

					if err := b.consumeOne(t, taskProcessor); err != nil {
						return err
					}
				}
			}
		})
	}

	return eg.Wait()

}

// consumeOne processes a single message using TaskProcessor
func (b *etcdBroker) consumeOne(signature *Signature, taskProcessor iface.TaskProcessor) error {
	// If the task is not registered, we requeue it,
	// there might be different workers for processing specific tasks
	if !b.IsTaskRegistered(signature.Name) {
		if signature.IgnoreWhenTaskNotRegistered {
			return nil
		}
		log.INFO.Printf("Task not registered with this worker. Requeuing message: %s", signature)
		b.requeueMessage(signature, taskProcessor)
		return nil
	}

	log.DEBUG.Printf("Received new message: %s", signature)

	return taskProcessor.Process(signature.Signature)
}

// StopConsuming 停止
func (b *etcdBroker) StopConsuming() {
	b.Broker.StopConsuming()

	b.wg.Wait()
}

// Publish put kvs to etcd stor
func (b *etcdBroker) Publish(ctx context.Context, signature *tasks.Signature) error {
	// Adjust routing key (this decides which queue the message will be published to)
	b.Broker.AdjustRoutingKey(signature)

	now := time.Now()
	s := Signature{
		Signature: signature,
		CreateAt:  now,
		Score:     now.UnixMilli(),
	}

	msg, err := json.Marshal(s)
	if err != nil {
		return fmt.Errorf("JSON marshal error: %s", err)
	}

	key := fmt.Sprintf("/machinery/v2/broker/pending_tasks/%s/%s", s.RoutingKey, s.UUID)

	// Check the ETA signature field, if it is set and it is in the future,
	// delay the task
	if s.ETA != nil {
		if s.ETA.After(now) {
			key = fmt.Sprintf("/machinery/v2/broker/delayed_tasks/t%d-%s", s.ETA.UnixNano(), s.UUID)
			_, err = b.client.Put(ctx, key, string(msg))
			return err
		}
	}

	_, err = b.client.Put(ctx, key, string(msg))
	return err
}

func (b *etcdBroker) getTasks(ctx context.Context, key string) ([]*Signature, error) {
	resp, err := b.client.Get(ctx, key, clientv3.WithPrefix())
	if err != nil {
		return nil, err
	}

	result := make([]*Signature, 0, len(resp.Kvs))
	for _, kvs := range resp.Kvs {
		signature := new(Signature)
		decoder := json.NewDecoder(bytes.NewReader(kvs.Value))
		decoder.UseNumber()
		if err := decoder.Decode(signature); err != nil {
			return nil, errs.NewErrCouldNotUnmarshalTaskSignature(kvs.Value, err)
		}

		result = append(result, signature)
	}

	return result, nil
}

// GetPendingTasks 获取执行队列, 任务统计可使用
func (b *etcdBroker) GetPendingTasks(queue string) ([]*tasks.Signature, error) {
	if queue == "" {
		queue = b.GetConfig().DefaultQueue
	}

	key := fmt.Sprintf("/machinery/v2/broker/pending_tasks/%s", queue)
	items, err := b.getTasks(context.Background(), key)
	if err != nil {
		return nil, err
	}

	rawTasks := make([]*tasks.Signature, 0, len(items))
	for _, v := range items {
		rawTasks = append(rawTasks, v.Signature)
	}

	return rawTasks, nil
}

// GetDelayedTasks 任务统计可使用
func (b *etcdBroker) GetDelayedTasks() ([]*tasks.Signature, error) {
	key := "/machinery/v2/broker/delayed_tasks"

	items, err := b.getTasks(context.Background(), key)
	if err != nil {
		return nil, err
	}

	rawTasks := make([]*tasks.Signature, 0, len(items))
	for _, v := range items {
		rawTasks = append(rawTasks, v.Signature)
	}

	return rawTasks, nil
}

func (b *etcdBroker) nextTask(queue string) (*Signature, error) {
	keyPrefix := fmt.Sprintf("/machinery/v2/broker/pending_tasks/%s", queue)
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
	defer cancel()

	item, err := getFirstItem(ctx, b.client, keyPrefix)
	if err != nil {
		return nil, err
	}

	signature := new(Signature)
	decoder := json.NewDecoder(bytes.NewReader(item))
	decoder.UseNumber()
	if err := decoder.Decode(signature); err != nil {
		return nil, errs.NewErrCouldNotUnmarshalTaskSignature(item, err)
	}

	return signature, nil
}

func (b *etcdBroker) nextDelayedTask() (*Signature, error) {
	keyPrefix := "/machinery/v2/broker/delayed_tasks"
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
	defer cancel()

	item, err := getFirstETAItem(ctx, b.client, keyPrefix)
	if err != nil {
		return nil, err
	}

	signature := new(Signature)
	decoder := json.NewDecoder(bytes.NewReader(item))
	decoder.UseNumber()
	if err := decoder.Decode(signature); err != nil {
		return nil, errs.NewErrCouldNotUnmarshalTaskSignature(item, err)
	}

	return signature, nil
}

func (b *etcdBroker) requeueMessage(delivery *Signature, taskProcessor iface.TaskProcessor) {
	queue := getQueue(b.GetConfig(), taskProcessor)
	key := fmt.Sprintf("/machinery/v2/broker/pending_tasks/%s", queue)
	now := time.Now()
	s := Signature{
		Signature: delivery.Signature,
		CreateAt:  now,
		Score:     now.UnixMilli(),
	}
	body, err := json.Marshal(s)
	if err != nil {
		log.ERROR.Print(err)
		return
	}

	_, err = b.client.KV.Put(b.ctx, key, string(body))
	if err != nil {
		log.ERROR.Print(err)
	}
}

func getQueue(config *config.Config, taskProcessor iface.TaskProcessor) string {
	customQueue := taskProcessor.CustomQueue()
	if customQueue == "" {
		return config.DefaultQueue
	}
	return customQueue
}