package systemtime

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

func TestOSApplierAppliesAndRollsBackTimezoneFile(t *testing.T) {
	root := t.TempDir()
	zoneRoot := filepath.Join(root, "zoneinfo")
	localtime := filepath.Join(root, "etc", "localtime")
	if err := os.MkdirAll(filepath.Join(zoneRoot, "Asia"), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.MkdirAll(filepath.Dir(localtime), 0o755); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(filepath.Join(zoneRoot, "Asia", "Seoul"), []byte("new-zone"), 0o644); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(localtime, []byte("old-zone"), 0o640); err != nil {
		t.Fatal(err)
	}
	applier, err := NewOSApplier(zoneRoot, localtime)
	if err != nil {
		t.Fatal(err)
	}

	rollback, err := applier.ApplyTimezone(context.Background(), "Asia/Seoul")
	if err != nil {
		t.Fatalf("ApplyTimezone() error = %v", err)
	}
	content, _ := os.ReadFile(localtime)
	if string(content) != "new-zone" {
		t.Fatalf("localtime = %q, want new-zone", content)
	}
	if err := rollback(); err != nil {
		t.Fatalf("rollback() error = %v", err)
	}
	content, _ = os.ReadFile(localtime)
	if string(content) != "old-zone" {
		t.Fatalf("restored localtime = %q, want old-zone", content)
	}
}

func TestNewOSApplierRequiresAbsolutePaths(t *testing.T) {
	if _, err := NewOSApplier("zoneinfo", "/etc/localtime"); err == nil {
		t.Fatal("NewOSApplier accepted a relative zoneinfo root")
	}
	if _, err := NewOSApplier("/usr/share/zoneinfo", "localtime"); err == nil {
		t.Fatal("NewOSApplier accepted a relative localtime path")
	}
}