package sync

import (
	"context"
	"sync"
)

func FanOut[T any](ctx context.Context, in <-chan T, channelCount int, buffer int) []<-chan T {
	if in == nil {
		// we only expect this to happen during development
		panic("in-channel is nil")
	}
	if channelCount < 1 {
		channelCount = 1
	}
	if buffer < 0 {
		buffer = 0
	}

	chs := make([]chan T, channelCount)
	for i := range channelCount {
		chs[i] = make(chan T, buffer)
	}

	go func() {
		defer func() {
			for _, out := range chs {
				close(out)
			}
		}()

		for v := range OrDone(ctx, in) {
			for _, out := range chs {
				// N.b. this will block if *any* of the out channels has a full buffer
				if !CancelOrSend(ctx, out, v) {
					return
				}
			}
		}
	}()

	outs := make([]<-chan T, channelCount)
	for i, out := range chs {
		outs[i] = out
	}

	return outs
}

func FanIn[T any](ctx context.Context, buffer int, ins ...<-chan T) <-chan T {
	if buffer < 0 {
		buffer = 0
	}

	wg := sync.WaitGroup{}

	out := make(chan T, buffer)

	for _, in := range ins {
		wg.Go(func() {
			if in == nil {
				return
			}

			for v := range OrDone(ctx, in) {
				if !CancelOrSend(ctx, out, v) {
					return
				}
			}
		})
	}

	go func() {
		wg.Wait()
		close(out)
	}()

	return out
}