//go:build windows

package windows

import (
	"context"
	"errors"
	"fmt"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
	"unsafe"

	"golang.org/x/sys/windows"
	"softbox.local/core/application/launch"
)

const seeMaskNoCloseProcess = 0x00000040

var (
	procRtlGetVersion   = windows.NewLazySystemDLL("ntdll.dll").NewProc("RtlGetVersion")
	procShellExecuteExW = windows.NewLazySystemDLL("shell32.dll").NewProc("ShellExecuteExW")
)

type platform struct{}

func newPlatform() Platform {
	return platform{}
}

func (platform) OS() string {
	return "windows"
}

func (platform) Edition() Edition {
	return EditionLegacy
}

func (platform) IsCompatible(minOS string) (bool, error) {
	version, err := currentVersion()
	if err != nil {
		return false, err
	}
	return versionSupports(minOS, version.major, version.minor, version.build, uint32(version.servicePack))
}

func (platform) IsRunning(_ string, entrypoint string) (bool, error) {
	return entrypointIsRunning(entrypoint, func() (processSnapshot, error) {
		return newToolhelpSnapshot(filepath.Base(entrypoint))
	})
}

func (target platform) WaitForExit(ctx context.Context, appID, entrypoint string, timeout time.Duration) error {
	return waitForExit(ctx, timeout, func() (bool, error) {
		return target.IsRunning(appID, entrypoint)
	}, systemExitWaitClock{})
}

func (platform) Start(command launch.Command) (int, error) {
	if !filepath.IsAbs(command.Entrypoint) || !filepath.IsAbs(command.WorkingDirectory) {
		return 0, fmt.Errorf("launch command must contain absolute paths")
	}
	if command.RequiresAdmin {
		return startElevated(command)
	}

	cmd := exec.Command(command.Entrypoint)
	cmd.Dir = command.WorkingDirectory
	if err := cmd.Start(); err != nil {
		return 0, err
	}
	return cmd.Process.Pid, nil
}

type toolhelpSnapshot struct {
	handle     windows.Handle
	targetName string
	entry      windows.ProcessEntry32
	started    bool
}

func newToolhelpSnapshot(targetName string) (processSnapshot, error) {
	handle, err := windows.CreateToolhelp32Snapshot(windows.TH32CS_SNAPPROCESS, 0)
	if err != nil {
		return nil, err
	}
	return &toolhelpSnapshot{handle: handle, targetName: targetName}, nil
}

func (snapshot *toolhelpSnapshot) NextImagePath() (string, bool, error) {
	for {
		var err error
		if !snapshot.started {
			snapshot.entry.Size = uint32(unsafe.Sizeof(snapshot.entry))
			err = windows.Process32First(snapshot.handle, &snapshot.entry)
			snapshot.started = true
		} else {
			err = windows.Process32Next(snapshot.handle, &snapshot.entry)
		}
		if err != nil {
			if errors.Is(err, windows.ERROR_NO_MORE_FILES) {
				return "", false, nil
			}
			return "", false, err
		}
		// ExeFile only narrows the expensive query. The identity decision below
		// always uses QueryFullProcessImageName's normalized full path.
		if !strings.EqualFold(windows.UTF16ToString(snapshot.entry.ExeFile[:]), snapshot.targetName) {
			continue
		}
		path, err := fullProcessImagePath(snapshot.entry.ProcessID)
		if err != nil {
			return "", false, err
		}
		return path, true, nil
	}
}

func (snapshot *toolhelpSnapshot) Close() error {
	return windows.CloseHandle(snapshot.handle)
}

func fullProcessImagePath(pid uint32) (string, error) {
	process, err := windows.OpenProcess(windows.PROCESS_QUERY_LIMITED_INFORMATION, false, pid)
	if err != nil {
		return "", err
	}
	defer windows.CloseHandle(process)

	for size := uint32(260); size <= 32768; size *= 2 {
		buffer := make([]uint16, size)
		length := size
		err = windows.QueryFullProcessImageName(process, 0, &buffer[0], &length)
		if err == nil {
			return windows.UTF16ToString(buffer[:length]), nil
		}
		if !errors.Is(err, windows.ERROR_INSUFFICIENT_BUFFER) {
			return "", err
		}
	}
	return "", fmt.Errorf("process image path exceeds 32768 UTF-16 code units")
}

type rtlOSVersionInfoEx struct {
	size             uint32
	major            uint32
	minor            uint32
	build            uint32
	platformID       uint32
	csdVersion       [128]uint16
	servicePack      uint16
	servicePackMinor uint16
	suiteMask        uint16
	productType      byte
	reserved         byte
}

func currentVersion() (rtlOSVersionInfoEx, error) {
	version := rtlOSVersionInfoEx{size: uint32(unsafe.Sizeof(rtlOSVersionInfoEx{}))}
	status, _, _ := procRtlGetVersion.Call(uintptr(unsafe.Pointer(&version)))
	if status != 0 {
		return rtlOSVersionInfoEx{}, fmt.Errorf("RtlGetVersion failed with status 0x%x", status)
	}
	return version, nil
}

type shellExecuteInfo struct {
	size       uint32
	mask       uint32
	hwnd       uintptr
	verb       *uint16
	file       *uint16
	parameters *uint16
	directory  *uint16
	show       int32
	instance   uintptr
	idList     uintptr
	class      *uint16
	keyClass   uintptr
	hotKey     uint32
	icon       uintptr
	process    windows.Handle
}

func startElevated(command launch.Command) (int, error) {
	verb, err := windows.UTF16PtrFromString("runas")
	if err != nil {
		return 0, err
	}
	file, err := windows.UTF16PtrFromString(command.Entrypoint)
	if err != nil {
		return 0, err
	}
	directory, err := windows.UTF16PtrFromString(command.WorkingDirectory)
	if err != nil {
		return 0, err
	}
	info := shellExecuteInfo{
		size:      uint32(unsafe.Sizeof(shellExecuteInfo{})),
		mask:      seeMaskNoCloseProcess,
		verb:      verb,
		file:      file,
		directory: directory,
		show:      1,
	}
	result, _, callErr := procShellExecuteExW.Call(uintptr(unsafe.Pointer(&info)))
	if result == 0 {
		return 0, fmt.Errorf("ShellExecuteExW failed: %w", callErr)
	}
	if info.process == 0 {
		return 0, fmt.Errorf("ShellExecuteExW did not return a process handle")
	}
	defer windows.CloseHandle(info.process)
	pid, err := windows.GetProcessId(info.process)
	if err != nil {
		return 0, err
	}
	return int(pid), nil
}