// Exercise 07 — Fan-in / Merge Channels
//
// ASSIGNMENT
// ----------
// Implement Merge(ctx, chs...):
//
//  1. Returns a single channel carrying every value from every input channel.
//  2. The output channel is CLOSED once all input channels are closed and
//     drained.
//  3. If ctx is cancelled, Merge stops forwarding, and all its internal
//     goroutines exit even if inputs never close and even if nobody reads
//     the output anymore. (No goroutine leaks — the tests count goroutines.)
//  4. Order across inputs is unspecified.
//
// Run the tests:   go test -race ./07-fan-in/
package main

import (
	"context"
	"fmt"
)

// Merge fans in all input channels into one output channel.
// TODO: implement me.
func Merge[T any](ctx context.Context, chs ...<-chan T) <-chan T {
	out := make(chan T)
	// TODO:
	//   - one forwarder goroutine per input channel
	//   - each forward is a select: {out <- v} vs {<-ctx.Done()}
	//   - reading the input must ALSO select on ctx.Done()
	//   - closer goroutine: wg.Wait(); close(out)
	return out
}

func main() {
	gen := func(vals ...int) <-chan int {
		ch := make(chan int)
		go func() {
			defer close(ch)
			for _, v := range vals {
				ch <- v
			}
		}()
		return ch
	}
	for v := range Merge(context.Background(), gen(1, 2, 3), gen(10, 20), gen(100)) {
		fmt.Println(v)
	}
}