package bus

import (
	"context"
	"github.com/rs/xid"
	"reflect"
	"sync"
	"time"
)

type Emitter struct {
	mu     sync.RWMutex
	topics map[string][]ListenerObject
}

func New() *Emitter {
	return &Emitter{
		mu:     sync.RWMutex{},
		topics: make(map[string][]ListenerObject),
	}
}

func (e *Emitter) Emit(ctx context.Context, topic string, data any) {
	e.mu.RLock()
	listeners, ok := e.topics[topic]
	e.mu.RUnlock()

	if !ok {
		return
	}

	stop := make(chan struct{})
	txID, _ := ctx.Value("txid-key").(string)
	source, _ := ctx.Value("source-key").(string)
	ctx, cancel := context.WithCancel(ctx)

	if txID == "" {
		txID = xid.New().String()
	}

	event := Event{
		ID:         xid.New().String(),
		TxID:       txID,
		Topic:      topic,
		Source:     source,
		OccurredAt: time.Now(),
		Data:       data,
		stopPropagation: func() {
			select {
			case <-stop:
			default:
				close(stop)
				cancel()
			}
		},
	}

	for _, listener := range listeners {
		select {
		case <-stop:
			return
		default:
			if listener.once != nil {
				listener.once.Do(func() {
					if listener.async {
						go listener.do(ctx, event)
					} else {
						listener.do(ctx, event)
					}
					e.Cancel(topic, listener.do)
				})
			} else if listener.async {
				go listener.do(ctx, event)
			} else {
				listener.do(ctx, event)
			}
		}
	}
}

func (e *Emitter) Listen(topic string, listener Listener, options ...ListenOption) {
	if listener == nil {
		return
	}
	e.mu.Lock()
	defer e.mu.Unlock()
	if e.topics == nil {
		e.topics = make(map[string][]ListenerObject)
	}
	listenerObject := ListenerObject{
		async: false,
		once:  nil,
		do:    listener,
		ptr:   reflect.ValueOf(listener).Pointer(),
	}
	for _, option := range options {
		option(&listenerObject)
	}
	if listeners, has := e.topics[topic]; !has {
		e.topics[topic] = []ListenerObject{listenerObject}
	} else {
		e.topics[topic] = append(listeners, listenerObject)
	}
}

func (e *Emitter) Cancel(topic string, listeners ...Listener) {
	e.mu.Lock()
	defer e.mu.Unlock()
	if e.topics == nil {
		return
	}
	ls, has := e.topics[topic]
	if !has || len(ls) == 0 {
		return
	}
	if len(listeners) == 0 {
		delete(e.topics, topic)
		return
	}
	for _, listener := range listeners {
		for i, l := range ls {
			if l.ptr == 0 {
				l.ptr = reflect.ValueOf(l).Pointer()
			}
			if l.ptr == reflect.ValueOf(listener).Pointer() {
				if i == 0 {
					ls = ls[1:]
				} else if i == len(ls)-1 {
					ls = ls[:i]
				} else {
					ls = append(ls[:i], ls[i+1:]...)
				}
			}
		}
	}
	if len(ls) == 0 {
		delete(e.topics, topic)
	} else {
		e.topics[topic] = ls
	}
}