package mmap

import (
	"fmt"
	"os"
	"syscall"
	"unsafe"

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

func mmapFile(f *os.File, previous *Data) (Data, error) {
	if previous != nil {
		munmapFile(*previous)
	}
	st, err := f.Stat()
	if err != nil {
		return Data{}, err
	}
	size := st.Size()
	if size == 0 {
		return Data{f, nil, nil}, nil
	}

func mmapFile(f *os.File, _ *Data) (Data, error) {
	b, err := io.ReadAll(f)
	if err != nil {
		return Data{}, err
	}
	return Data{f, b, nil}, nil
}

func munmapFile(d Data) error {
	return nil

func Mmap(f *os.File, data *Data) (Data, error) {
	return mmapFile(f, data)
}

// Munmap unmaps the given file from memory.
func Munmap(d *Data) error {
	// d.f.Close() on Windows still gets an error
	return munmapFile(*d)

	if err != nil {
		return Data{}, &fs.PathError{Op: "mmap", Path: f.Name(), Err: err}
	}
	return Data{f, data[:n], nil}, nil
}

func munmapFile(d Data) error {
	if len(d.Data) == 0 {
		return nil
	}
	err := syscall.Munmap(d.Data)
	if err != nil {
		return &fs.PathError{Op: "munmap", Path: d.f.Name(), Err: err}
	}
	return nil