package fileutil

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

func TestCopyFile(t *testing.T) {
	dir := t.TempDir()
	src := filepath.Join(dir, "src.txt")
	dst := filepath.Join(dir, "dst.txt")

	content := []byte("hello world")
	if err := os.WriteFile(src, content, 0o644); err != nil {
		t.Fatal(err)
	}

	if err := CopyFile(src, dst); err != nil {
		t.Fatalf("CopyFile: %v", err)
	}

	got, err := os.ReadFile(dst)
	if err != nil {
		t.Fatalf("reading dst: %v", err)
	}
	if string(got) != string(content) {
		t.Fatalf("got %q, want %q", got, content)
	}
}

func TestCopyFileMissingSrc(t *testing.T) {
	dir := t.TempDir()
	err := CopyFile(filepath.Join(dir, "nonexistent"), filepath.Join(dir, "dst"))
	if err == nil {
		t.Fatal("expected error for missing source")
	}
}

func TestCopyFileOverwrite(t *testing.T) {
	dir := t.TempDir()
	src := filepath.Join(dir, "src.txt")
	dst := filepath.Join(dir, "dst.txt")

	os.WriteFile(src, []byte("new"), 0o644)
	os.WriteFile(dst, []byte("old"), 0o644)

	if err := CopyFile(src, dst); err != nil {
		t.Fatalf("CopyFile: %v", err)
	}

	got, _ := os.ReadFile(dst)
	if string(got) != "new" {
		t.Fatalf("got %q, want %q", got, "new")
	}
}

func TestCopyFileEmptyFile(t *testing.T) {
	dir := t.TempDir()
	src := filepath.Join(dir, "empty.txt")
	dst := filepath.Join(dir, "dst.txt")

	os.WriteFile(src, []byte{}, 0o644)

	if err := CopyFile(src, dst); err != nil {
		t.Fatalf("CopyFile: %v", err)
	}

	got, _ := os.ReadFile(dst)
	if len(got) != 0 {
		t.Fatalf("expected empty file, got %d bytes", len(got))
	}
}