package mmap

import (
	"fmt"
	"os"
	"path/filepath"

	"bitbucket.org/anacrolix/go.torrent/mmap_span"
	"github.com/anacrolix/libtorgo/metainfo"
	"launchpad.net/gommap"
)

func TorrentData(md *metainfo.Info, location string) (mms *mmap_span.MMapSpan, err error) {
	mms = &mmap_span.MMapSpan{}
	defer func() {
		if err != nil {
			mms.Close()
			mms = nil
		}
	}()
	for _, miFile := range md.UpvertedFiles() {
		fileName := filepath.Join(append([]string{location, md.Name}, miFile.Path...)...)
		err = os.MkdirAll(filepath.Dir(fileName), 0777)
		if err != nil {
			err = fmt.Errorf("error creating data directory %q: %s", filepath.Dir(fileName), err)
			return
		}
		var file *os.File
		file, err = os.OpenFile(fileName, os.O_CREATE|os.O_RDWR, 0666)
		if err != nil {
			return
		}
		func() {
			defer file.Close()
			var fi os.FileInfo
			fi, err = file.Stat()
			if err != nil {
				return
			}
			if fi.Size() < miFile.Length {
				err = file.Truncate(miFile.Length)
				if err != nil {
					return
				}
			}
			if miFile.Length == 0 {
				// Can't mmap() regions with length 0.
				return
			}
			var mMap gommap.MMap
			mMap, err = gommap.MapRegion(file.Fd(), 0, miFile.Length, gommap.PROT_READ|gommap.PROT_WRITE, gommap.MAP_SHARED)
			if err != nil {
				err = fmt.Errorf("error mapping file %q, length %d: %s", file.Name(), miFile.Length, err)
				return
			}
			if int64(len(mMap)) != miFile.Length {
				panic("mmap has wrong length")
			}
			mms.Append(mMap)
		}()
		if err != nil {
			return
		}
	}
	return
}