package keyedlock

import (
	"context"
	"errors"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

func lockCount(k *Locks) int {
	k.mu.Lock()
	defer k.mu.Unlock()
	return len(k.locks)
}

func TestKeyedLocks_entryRemovedWhenUncontended(t *testing.T) {
	t.Parallel()
	k := New()
	release, err := k.Acquire(context.Background(), "a")
	if err != nil {
		t.Fatalf("acquire error = %v", err)
	}
	if lockCount(k) != 1 {
		t.Errorf("entries while held = %d, want 1", lockCount(k))
	}
	release()
	if lockCount(k) != 0 {
		t.Errorf("entries after release = %d, want 0", lockCount(k))
	}
	if _, err := k.Acquire(context.Background(), "a"); err != nil {
		t.Fatalf("acquire after release error = %v", err)
	}
}

func TestKeyedLocks_waitersShareOneLock(t *testing.T) {
	t.Parallel()
	k := New()
	const n = 20
	var inside, overlaps atomic.Int32
	var wg sync.WaitGroup
	for range n {
		wg.Go(func() {
			release, err := k.Acquire(context.Background(), "shared")
			if err != nil {
				t.Errorf("acquire error = %v", err)
				return
			}
			if inside.Add(1) > 1 {
				overlaps.Add(1)
			}
			time.Sleep(time.Millisecond)
			inside.Add(-1)
			release()
		})
	}
	wg.Wait()
	if overlaps.Load() != 0 {
		t.Errorf("%d holders overlapped on one key", overlaps.Load())
	}
	if lockCount(k) != 0 {
		t.Errorf("entries after every holder released = %d, want 0", lockCount(k))
	}
}

func TestKeyedLocks_waiterGivesUpWithContext(t *testing.T) {
	t.Parallel()
	k := New()
	release, err := k.Acquire(context.Background(), "a")
	if err != nil {
		t.Fatalf("acquire error = %v", err)
	}
	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Millisecond)
	defer cancel()
	start := time.Now()
	if _, err := k.Acquire(ctx, "a"); !errors.Is(err, context.DeadlineExceeded) {
		t.Fatalf("waiter error = %v, want DeadlineExceeded", err)
	}
	if time.Since(start) > time.Second {
		t.Errorf("waiter took %v, want to give up with its ctx", time.Since(start))
	}
	if lockCount(k) != 1 {
		t.Errorf("entries with the holder still in = %d, want 1: the waiter's exit must not drop the holder's entry", lockCount(k))
	}
	release()
	if lockCount(k) != 0 {
		t.Errorf("entries after the holder released = %d, want 0", lockCount(k))
	}
}