package storage

import (
    "errors"
	"io"
	"os"
	"pkg/util"
)

func (n *Needle) Append(w io.Writer) uint32 {
	header := make([]byte, 16)
	util.Uint32toBytes(header[0:4], n.Cookie)
	util.Uint64toBytes(header[4:12], n.Id)
	n.Size = uint32(len(n.Data))
	util.Uint32toBytes(header[12:16], n.Size)
	w.Write(header)
	w.Write(n.Data)
	rest := 8 - ((n.Size + 16 + 4) % 8)
	util.Uint32toBytes(header[0:4], n.Checksum.Value())
	w.Write(header[0 : rest+4])
	return n.Size
}
func (n *Needle) Read(r io.Reader, size uint32, version Version) (int, error) {
	if version == Version1 {
		bytes := make([]byte, size+16+4)
		ret, e := r.Read(bytes)
		n.Cookie = util.BytesToUint32(bytes[0:4])
		n.Id = util.BytesToUint64(bytes[4:12])
		n.Size = util.BytesToUint32(bytes[12:16])
		n.Data = bytes[16 : 16+size]
		checksum := util.BytesToUint32(bytes[16+size : 16+size+4])
		if checksum != NewCRC(n.Data).Value() {
			return 0, errors.New("CRC error! Data On Disk Corrupted!")
		}
		return ret, e
	}else if version == Version2 {
	}
	return 0, errors.New("Unsupported Version!")
}
func ReadNeedle(r *os.File) (*Needle, uint32) {
	n := new(Needle)
	bytes := make([]byte, 16)
	count, e := r.Read(bytes)
	if count <= 0 || e != nil {
		return nil, 0
	}
	n.Cookie = util.BytesToUint32(bytes[0:4])
	n.Id = util.BytesToUint64(bytes[4:12])
	n.Size = util.BytesToUint32(bytes[12:16])
	rest := 8 - ((n.Size + 16 + 4) % 8)
	return n, n.Size + 4 + rest
}