// SPDX-License-Identifier: Apache-2.0
//
// Copyright The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build windows

package ntdll

import (
	"fmt"
	"time"
	"unsafe"

	"golang.org/x/sys/windows"
)

// SystemTimeOfDayInformation is the SYSTEM_TIMEOFDAY_INFORMATION structure.
// The times are in 100-nanosecond intervals since January 1, 1601 (UTC).
type SystemTimeOfDayInformation struct {
	BootTime      int64
	CurrentTime   int64
	TimeZoneBias  int64
	TimeZoneID    uint32
	Reserved      uint32
	BootTimeBias  uint64
	SleepTimeBias uint64
}

// BootTime returns the time the system booted.
//
// The kernel moves the boot time along when the system time is set, so it
// stays correct after a clock correction.
func BootTime() (time.Time, error) {
	var info SystemTimeOfDayInformation

	err := windows.NtQuerySystemInformation(
		windows.SystemTimeOfDayInformation,
		unsafe.Pointer(&info),
		uint32(unsafe.Sizeof(info)),
		nil,
	)
	if err != nil {
		return time.Time{}, fmt.Errorf("NtQuerySystemInformation(SystemTimeOfDayInformation): %w", err)
	}

	ft := windows.Filetime{
		LowDateTime:  uint32(info.BootTime),
		HighDateTime: uint32(info.BootTime >> 32),
	}

	return time.Unix(0, ft.Nanoseconds()), nil
}