package main

import (
	"errors"
	"sync"
)

var InsufficientChannelsErr = errors.New("channels count must be >2")

func merge[T any](channels ...<-chan T) (<-chan T, error) {
	out := make(chan T)

	if len(channels) < 2 {
		close(out)

		return out, InsufficientChannelsErr
	}

	var wg sync.WaitGroup
	wg.Add(len(channels))

	for _, c := range channels {
		go func(channel <-chan T) {
			defer wg.Done()

			for v := range channel {
				out <- v
			}
		}(c)
	}

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

	return out, nil
}