package main

import (
	"fmt"
	"math/rand"
	"time"
)

const (
	BoatCapacity = 4
	HalfCapacity = BoatCapacity / 2
	MaxDelay     = 250
)

type (
	Hacker struct{}
	Serf   struct{}
)

func sleep() {
	time.Sleep(time.Duration(rand.Intn(MaxDelay)) * time.Millisecond)
}

func genHackers(ch chan<- Hacker) {
	for {
		ch <- Hacker{}
		sleep()
	}
}

func genSerfs(ch chan<- Serf) {
	for {
		ch <- Serf{}
		sleep()
	}
}

func main() {
	hackerCh := make(chan Hacker)
	serfCh := make(chan Serf)

	go genHackers(hackerCh)
	go genSerfs(serfCh)

	for {
		hackers, serfs := 0, 0
		hackerCh, serfCh := hackerCh, serfCh

		for hackers+serfs < BoatCapacity {
			select {
			case <-hackerCh:
				hackers++
			case <-serfCh:
				serfs++
			}

			if hackers+serfs == HalfCapacity+1 {
				switch {
				case hackers == HalfCapacity || serfs == HalfCapacity+1:
					hackerCh = nil
				case hackers == HalfCapacity+1 || serfs == HalfCapacity:
					serfCh = nil
				}
			}
		}

		fmt.Printf("Crossing river with %d hackers and %d serfs\n", hackers, serfs)
	}
}