package util

import (
	"sync"
	"time"
)

// Deduplicated (debounced) channel. To close the channel, call `close(dchan.In())`.
type DChan[T comparable] struct {
	inChan        chan T
	outChan       chan T
	existingElems map[T]struct{}
	mtx           sync.Mutex
}

func NewDChan[T comparable](capacity int) *DChan[T] {
	dchan := &DChan[T]{
		inChan:        make(chan T, capacity),
		outChan:       make(chan T),
		existingElems: make(map[T]struct{}),
	}
	go func() {
		defer close(dchan.outChan)
		for elem := range dchan.inChan {
			dchan.mtx.Lock()
			if _, ok := dchan.existingElems[elem]; !ok {
				// Send the element to the output channel.
				dchan.existingElems[elem] = struct{}{}
				dchan.mtx.Unlock()
				dchan.outChan <- elem
			} else {
				// Deduplicate the element.
				dchan.mtx.Unlock()
			}
		}
	}()
	return dchan
}

func (dc *DChan[T]) In() chan<- T {
	return dc.inChan
}

func (dc *DChan[T]) Out() <-chan T {
	return dc.outChan
}

// Marks an element as read (stops deduplication), so that it can be sent and received again.
func (dc *DChan[T]) MarkElemReadDone(elem T) {
	dc.mtx.Lock()
	delete(dc.existingElems, elem)
	dc.mtx.Unlock()
}

// Checks if an element is in the channel.
func (dc *DChan[T]) Contains(elem T) bool {
	dc.mtx.Lock()
	_, ok := dc.existingElems[elem]
	dc.mtx.Unlock()
	return ok
}

// Writes an element to the input channel.
func (dc *DChan[T]) Write(elem T) {
	dc.inChan <- elem
}

// Queues an element to be written to the input channel after a delay. If already in the channel, the delay is ignored.
func (dc *DChan[T]) DelayedWrite(elem T, delay time.Duration) {
	if delay <= 0 {
		dc.inChan <- elem
		return
	}

	// Check if the element is already in the channel.
	dc.mtx.Lock()
	if _, ok := dc.existingElems[elem]; ok {
		// Existing element, abort.
		dc.mtx.Unlock()
		return
	} else {
		// New element, queue it.
		dc.existingElems[elem] = struct{}{}
		dc.mtx.Unlock()
	}

	// Write the element after the delay.
	go func() {
		time.Sleep(delay)
		// HACK!
		dc.MarkElemReadDone(elem)
		dc.inChan <- elem
	}()
}