package main

import (
	"fmt"
	"syscall"
	"unicode/utf16"
	"unsafe"
)

var (
	comdlg32            = syscall.NewLazyDLL("Comdlg32.dll")
	procGetOpenFileName = comdlg32.NewProc("GetOpenFileNameW")
)

var (
	Err_No_File_Chosen = fmt.Errorf("no file was chosen")
)

func OpenFileDialog(title string) (filepath string, err error) {

	type OPENFILENAMEW struct {
		LStructSize   uint32
		HwndOwner     syscall.Handle
		HInstance     syscall.Handle
		Filter        *uint16
		CustomFilter  *uint16
		MaxCustFilter uint32
		FilterIndex   uint32
		File          *uint16
		MaxFile       uint32
		FileTitle     *uint16
		MaxFileTitle  uint32
		InitialDir    *uint16
		Title         *uint16
		Flags         uint32
		FileOffset    uint16
		FileExtension uint16
		DefExt        *uint16
		CustData      uintptr
		FnHook        syscall.Handle
		TemplateName  *uint16
		PvReserved    uintptr
		DwReserved    uint32
		FlagsEx       uint32
	}

	titleByteArr := utf16.Encode([]rune(title + "\x00"))
	filterByteArr := utf16.Encode([]rune("All Files (*.*)\x00*.*\x00Text Files (*.txt)\x00*.txt\x00\x00"))

	filenameByteArr := make([]uint16, syscall.MAX_LONG_PATH)

	ofn := &OPENFILENAMEW{
		HwndOwner:   0,
		HInstance:   0,
		LStructSize: uint32(unsafe.Sizeof(OPENFILENAMEW{})),
		Title:       &titleByteArr[0],
		Filter:      &filterByteArr[0],
		File:        &filenameByteArr[0],
		MaxFile:     syscall.MAX_LONG_PATH,
		// OFN_FILEMUSTEXIST
		Flags: 0x00001000,
	}

	ret, _, _ := procGetOpenFileName.Call(uintptr(unsafe.Pointer(ofn)))
	if ret == 0 {
		return "", Err_No_File_Chosen
	}

	filepath = syscall.UTF16ToString(filenameByteArr)
	return filepath, nil
}