package serverevents

import (
	"slices"
	"sync"

	"github.com/google/uuid"
)

var emitter *EventEmitter

type Subscription struct {
	id        string
	eventType string
	todo      func(Event)
	emitter   *EventEmitter
}

func (sub Subscription) Unsubscribe() {
	if len(sub.eventType) < 1 {
		emitter.onAllSubscribers = slices.DeleteFunc(emitter.onAllSubscribers, func(existSub Subscription) bool {
			return existSub.id == sub.id
		})
		return
	}
	eventSubscribers := emitter.subscribers[sub.eventType]
	if eventSubscribers == nil || len(eventSubscribers) < 1 {
		return
	}
	emitter.subscribers[sub.eventType] = slices.DeleteFunc(emitter.subscribers[sub.eventType], func(existSub Subscription) bool {
		return existSub.id == sub.id
	})
}

type Event struct {
	Type          string `json:"type"`
	Data          any    `json:"data"`
	IsBackendOnly bool   `json:"-"`
}

type EventEmitter struct {
	subscribers      map[string][]Subscription
	onAllSubscribers []Subscription
	mu               sync.RWMutex
}

func GetEventEmitter() *EventEmitter {
	if emitter == nil {
		emitter = &EventEmitter{
			subscribers:      make(map[string][]Subscription),
			onAllSubscribers: make([]Subscription, 0),
		}
	}
	return emitter
}

func (em *EventEmitter) On(eventType string, do func(Event)) Subscription {
	em.mu.Lock()
	defer em.mu.Unlock()

	if em.subscribers[eventType] == nil {
		em.subscribers[eventType] = make([]Subscription, 0)
	}
	sub := Subscription{
		id:        uuid.NewString(),
		eventType: eventType,
		todo:      do,
		emitter:   em,
	}
	em.subscribers[eventType] = append(em.subscribers[eventType], sub)
	return sub
}

func (em *EventEmitter) OnAll(do func(Event)) Subscription {
	em.mu.Lock()
	defer em.mu.Unlock()

	sub := Subscription{
		id:      uuid.NewString(),
		todo:    do,
		emitter: em,
	}
	em.onAllSubscribers = append(em.onAllSubscribers, sub)
	return sub
}

func (em *EventEmitter) Emit(event Event) {
	executeSubscribers(em.onAllSubscribers, event)
	eventSubscribers := em.subscribers[event.Type]
	if eventSubscribers != nil {
		executeSubscribers(eventSubscribers, event)
	}
}

func executeSubscribers(toDos []Subscription, event Event) {
	for _, sub := range toDos {
		sub.todo(event)
	}
}