package main

import (
	"fmt"
	"sync"
	"time"
)

func worker(id int, readyToProceed chan<- struct{}, startSignal <-chan struct{}) {
	fmt.Printf("Worker %d: Started initial work.
", id)
	time.Sleep(time.Duration(id+1) * 100 * time.Millisecond) // Simulate initial work

	fmt.Printf("Worker %d: Ready to proceed to stage 2.
", id)
	readyToProceed <- struct{}{} // Signal readiness for stage 2

	<-startSignal // Wait for the barrier to lift (channel close or send)

	fmt.Printf("Worker %d: Proceeding with stage 2.
", id)
	time.Sleep(time.Duration(id+1) * 50 * time.Millisecond) // Simulate stage 2 work
	fmt.Printf("Worker %d: Finished stage 2.
", id)
}

func main() {
	const numWorkers = 5
	const barrierThreshold = 3 // We need 3 workers to be ready to proceed

	readyToProceed := make(chan struct{}) // Workers signal readiness here
	startSignal := make(chan struct{})    // Signal for workers to proceed

	var wg sync.WaitGroup

	// Start workers
	for i := 0; i < numWorkers; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			worker(id, readyToProceed, startSignal)
		}(i)
	}

	// Barrier coordinator
	go func() {
		fmt.Printf("Coordinator: Waiting for %d workers to be ready...
", barrierThreshold)
		readyCount := 0
		for range readyToProceed {
			readyCount++
			fmt.Printf("Coordinator: %d workers ready.
", readyCount)
			if readyCount >= barrierThreshold {
				fmt.Println("Coordinator: Barrier reached! Signalling workers to proceed.
")
				close(startSignal) // Close channel to signal all waiting workers
				break
			}
		}
		// If there are more workers than barrierThreshold, they will still send on readyToProceed
		// and block. We need to drain it or close it. For this example, we let it run.
		// In a real application, you might use a buffered channel or a select with a default.
		// Or ensure 'readyToProceed' is closed when all potential signals are sent.
		// For simplicity, we assume workers will proceed after the barrier is lifted.
	}()

	wg.Wait() // Wait for all workers to finish all their stages
	fmt.Println("Main: All workers completed.")
}