package keyedmutex

import (
	"sync"
	"testing"
	"time"
)

func TestLockSerializesSameKey(t *testing.T) {
	var m Mutex
	unlock := m.Lock("a")

	acquired := make(chan struct{})
	go func() {
		u := m.Lock("a")
		close(acquired)
		u()
	}()

	select {
	case <-acquired:
		t.Fatal("second Lock on the same key acquired while the first was held")
	case <-time.After(50 * time.Millisecond):
		// expected: blocked
	}
	unlock()
	select {
	case <-acquired:
		// expected: now acquired
	case <-time.After(time.Second):
		t.Fatal("second Lock did not acquire after release")
	}
}

func TestLockIndependentKeys(t *testing.T) {
	var m Mutex
	unlockA := m.Lock("a")
	defer unlockA()
	// A different key must not block.
	done := make(chan struct{})
	go func() { u := m.Lock("b"); u(); close(done) }()
	select {
	case <-done:
	case <-time.After(time.Second):
		t.Fatal("Lock on an independent key blocked")
	}
}

func TestTryLock(t *testing.T) {
	var m Mutex
	unlock, ok := m.TryLock("a")
	if !ok {
		t.Fatal("TryLock should succeed on a free key")
	}
	if _, ok := m.TryLock("a"); ok {
		t.Fatal("TryLock should fail while the key is held")
	}
	unlock()
	u2, ok := m.TryLock("a")
	if !ok {
		t.Fatal("TryLock should succeed after release")
	}
	u2()
}

func TestConcurrentLockNoRace(t *testing.T) {
	var m Mutex
	var wg sync.WaitGroup
	counter := 0
	for i := 0; i < 50; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			u := m.Lock("shared")
			counter++ // protected by the keyed lock
			u()
		}()
	}
	wg.Wait()
	if counter != 50 {
		t.Errorf("counter = %d, want 50 (lost updates ⇒ lock not serializing)", counter)
	}
}