package fsutil

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

func TestWriteFileAtomic_RoundTripAndDirSync(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "output.md")
	if err := WriteFileAtomic(path, []byte("第一版  \n"), 0o644); err != nil {
		t.Fatal(err)
	}
	if err := WriteFileAtomic(path, []byte("第二版\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	got, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	if string(got) != "第二版\n" {
		t.Fatalf("got %q", got)
	}
}

func TestWriteFileAtomic_RenamesThenSyncsParentDir(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "output.md")
	var synced string
	orig := dirSync
	t.Cleanup(func() { dirSync = orig })
	dirSync = func(d string) error {
		synced = d
		return orig(d)
	}
	if err := WriteFileAtomic(path, []byte("durable\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	if synced != dir {
		t.Fatalf("parent dir sync got %q want %q", synced, dir)
	}
}

func TestWriteFileAtomic_DirSyncUnsupportedIsIgnored(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "output.md")
	orig := dirSync
	t.Cleanup(func() { dirSync = orig })
	dirSync = func(string) error { return syscall.EINVAL }
	if err := WriteFileAtomic(path, []byte("ok\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	got, _ := os.ReadFile(path)
	if string(got) != "ok\n" {
		t.Fatalf("got %q", got)
	}
}

func TestWriteFileAtomic_DirSyncHardErrorSurfacesAfterRename(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "output.md")
	orig := dirSync
	t.Cleanup(func() { dirSync = orig })
	dirSync = func(string) error { return errors.New("sync boom") }
	if err := WriteFileAtomic(path, []byte("kept\n"), 0o644); err == nil {
		t.Fatal("hard dir sync error must surface")
	}
	got, err := os.ReadFile(path)
	if err != nil || string(got) != "kept\n" {
		t.Fatalf("rename must have succeeded before sync error: %q %v", got, err)
	}
}

func TestWriteFileAtomicExclusive_RefusesExisting(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "keep.md")
	if err := WriteFileAtomicExclusive(path, []byte("原备份\n"), 0o644); err != nil {
		t.Fatal(err)
	}
	if err := WriteFileAtomicExclusive(path, []byte("覆盖\n"), 0o644); err == nil {
		t.Fatal("exclusive write must refuse existing backup")
	}
	got, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	if string(got) != "原备份\n" {
		t.Fatalf("existing backup mutated: %q", got)
	}
}

func TestSyncDir_OpensTarget(t *testing.T) {
	dir := t.TempDir()
	if err := SyncDir(dir); err != nil {
		t.Fatal(err)
	}
	if err := SyncDir(filepath.Join(dir, "missing")); err == nil {
		t.Fatal("missing dir must fail")
	}
}

func TestIgnorableDirSync(t *testing.T) {
	if !ignorableDirSync(syscall.EINVAL) || !ignorableDirSync(syscall.ENOTSUP) || !ignorableDirSync(syscall.ENOSYS) {
		t.Fatal("expected compatibility errno to be ignored")
	}
	if ignorableDirSync(errors.New("other")) {
		t.Fatal("hard errors must not be ignored")
	}
}