// Copyright 2024 GoEdge CDN goedge.cdn@gmail.com. All rights reserved. Official site: https://goedge.cn .
//go:build plus && !windows

package mmap

import (
	"fmt"
	fsutils "github.com/TeaOSLab/EdgeNode/internal/utils/fs"
	"io"
	"os"
	"runtime"
	"sync/atomic"
	"syscall"
)

var totalMMAPFileSize int64

func TotalMMAPFileSize() int64 {
	return atomic.LoadInt64(&totalMMAPFileSize)
}

// OpenFile memory-maps the file pointer for reading.
func OpenFile(f *os.File, size int64) (r *ReaderAt, err error) {
	// update stat
	atomic.AddInt64(&totalMMAPFileSize, size)

	defer func() {
		if r == nil {
			atomic.AddInt64(&totalMMAPFileSize, -size)
		}
	}()

	defer func() {
		_ = f.Close()
	}()

	if size == 0 {
		return &ReaderAt{
			data: make([]byte, 0),
		}, nil
	}
	if size < 0 {
		return nil, fmt.Errorf("mmap: file %q has negative size", f.Name())
	}
	if size != int64(int(size)) {
		return nil, fmt.Errorf("mmap: file %q is too large", f.Name())
	}

	fsutils.ReaderLimiter.Ack()
	data, err := syscall.Mmap(int(f.Fd()), 0, int(size), syscall.PROT_READ, MMAPReadFlags)
	fsutils.ReaderLimiter.Release()
	if err != nil {
		return nil, err
	}
	r = &ReaderAt{
		data: data,
		size: size,
	}
	runtime.SetFinalizer(r, (*ReaderAt).Close)
	return r, nil
}

func (r *ReaderAt) Write(writer io.Writer, offset int) (int, error) {
	var l = len(r.data)
	const segmentSize = 16 << 10

	if l-offset <= segmentSize {
		return writer.Write(r.data[offset:])
	}

	var n int

	for {
		var n1 int
		var err error
		fsutils.ReaderLimiter.Ack()
		if offset+segmentSize <= l {
			n1, err = writer.Write(r.data[offset : offset+segmentSize])
		} else {
			n1, err = writer.Write(r.data[offset:])
		}
		fsutils.ReaderLimiter.Release()
		n += n1
		offset += n1
		if err != nil {
			return n, err
		}

		if offset >= l {
			break
		}
	}

	return n, nil
}