package snapshot

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

func TestFileCTime_RealFile(t *testing.T) {
	// Create a temporary file
	dir := t.TempDir()
	path := filepath.Join(dir, "testfile.txt")

	if err := os.WriteFile(path, []byte("hello"), 0644); err != nil {
		t.Fatal(err)
	}

	info, err := os.Stat(path)
	if err != nil {
		t.Fatal(err)
	}

	ctime := fileCTime(info)

	// ctime should be a valid time (not zero)
	if ctime.IsZero() {
		t.Fatal("fileCTime returned zero time")
	}

	// ctime should be close to now (within a few seconds)
	diff := time.Since(ctime)
	if diff < 0 || diff > 5*time.Second {
		t.Fatalf("fileCTime returned unexpected time: %v (diff from now: %v)", ctime, diff)
	}

	// ctime should not equal mtime exactly in all cases, but for a freshly
	// created file they should be very close
	mtime := info.ModTime()
	ctimeMtimeDiff := ctime.Sub(mtime)
	if ctimeMtimeDiff < 0 {
		ctimeMtimeDiff = -ctimeMtimeDiff
	}
	// For a freshly created file, ctime and mtime should be within 1 second
	if ctimeMtimeDiff > time.Second {
		t.Fatalf("ctime and mtime differ by too much for a new file: ctime=%v, mtime=%v, diff=%v",
			ctime, mtime, ctimeMtimeDiff)
	}
}

func TestFileCTime_AfterMtimeChange(t *testing.T) {
	// Create a temporary file
	dir := t.TempDir()
	path := filepath.Join(dir, "testfile.txt")

	if err := os.WriteFile(path, []byte("hello"), 0644); err != nil {
		t.Fatal(err)
	}

	// Get initial ctime
	info1, err := os.Stat(path)
	if err != nil {
		t.Fatal(err)
	}
	ctime1 := fileCTime(info1)

	// Change mtime to a time in the past
	pastTime := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
	if err := os.Chtimes(path, pastTime, pastTime); err != nil {
		t.Fatal(err)
	}

	// Get new stats
	info2, err := os.Stat(path)
	if err != nil {
		t.Fatal(err)
	}
	ctime2 := fileCTime(info2)
	mtime2 := info2.ModTime()

	// mtime should now be in the past
	if mtime2.Year() != 2020 {
		t.Fatalf("mtime not set correctly: %v", mtime2)
	}

	// On macOS: ctime (birth time) should remain unchanged since birth time
	// doesn't change when mtime is updated.
	// On Linux: ctime (inode change time) will be updated to ~now because
	// changing mtime is a metadata change.
	// Either way, ctime should NOT equal the past mtime we just set.
	if ctime2.Equal(pastTime) {
		t.Fatal("ctime should not equal the artificially set past mtime")
	}

	// ctime should still be a recent time (the original creation time or
	// the metadata change time, depending on platform)
	_ = ctime1 // used for reference; both platforms will have a recent ctime2
	if time.Since(ctime2) > 10*time.Second {
		t.Fatalf("ctime is unexpectedly old: %v", ctime2)
	}
}

// TestFileCTime_NonSyscallFileInfo verifies the fallback to mtime when
// the FileInfo doesn't have a *syscall.Stat_t (e.g. afero.MemMapFs).
type mockFileInfo struct {
	name    string
	size    int64
	mode    os.FileMode
	modTime time.Time
	isDir   bool
}

func (m *mockFileInfo) Name() string       { return m.name }
func (m *mockFileInfo) Size() int64        { return m.size }
func (m *mockFileInfo) Mode() os.FileMode  { return m.mode }
func (m *mockFileInfo) ModTime() time.Time { return m.modTime }
func (m *mockFileInfo) IsDir() bool        { return m.isDir }
func (m *mockFileInfo) Sys() interface{}   { return nil } // No syscall.Stat_t

func TestFileCTime_FallbackToMtime(t *testing.T) {
	now := time.Now().UTC().Truncate(time.Second)
	info := &mockFileInfo{
		name:    "test.txt",
		size:    100,
		mode:    0644,
		modTime: now,
	}

	ctime := fileCTime(info)
	if !ctime.Equal(now) {
		t.Fatalf("expected fallback to mtime %v, got %v", now, ctime)
	}
}