//go:build linux

package processlock

import (
	"errors"
	"os"
	"path/filepath"
	"testing"
)

func TestLockUsesKernelOwnershipAndLeavesFileInPlace(t *testing.T) {
	t.Parallel()
	path := filepath.Join(t.TempDir(), "serve.lock")
	first, err := Acquire(path)
	if err != nil {
		t.Fatalf("acquire first lock: %v", err)
	}
	second, err := Acquire(path)
	if !errors.Is(err, ErrAlreadyLocked) || second != nil {
		t.Fatalf("expected second acquire to fail with lock ownership, lock=%v err=%v", second, err)
	}
	metadata, err := os.ReadFile(path)
	if err != nil || len(metadata) == 0 {
		t.Fatalf("read diagnostic PID: data=%q err=%v", metadata, err)
	}
	if err := first.Close(); err != nil {
		t.Fatalf("release first lock: %v", err)
	}
	if _, err := os.Stat(path); err != nil {
		t.Fatalf("lock file should remain after release: %v", err)
	}
	third, err := Acquire(path)
	if err != nil {
		t.Fatalf("reacquire existing lock file: %v", err)
	}
	if err := third.Close(); err != nil {
		t.Fatalf("release reacquired lock: %v", err)
	}
}