package wire

import (
	"errors"
	"io"
)

// VarIntMaxBytes is the maximum encoded length of a Minecraft VarInt.
const VarIntMaxBytes = 5

var errVarIntTooBig = errors.New("wire: VarInt exceeds 5 bytes")

// ReadVarInt reads a Minecraft-style VarInt from a byte reader.
func ReadVarInt(r io.ByteReader) (int, error) {
	var value, shift int
	for {
		b, err := r.ReadByte()
		if err != nil {
			return 0, err
		}
		value |= int(b&0x7F) << shift
		if b&0x80 == 0 {
			return value, nil
		}
		shift += 7
		if shift >= 32 {
			return 0, errVarIntTooBig
		}
	}
}

// AppendVarInt appends v encoded as a VarInt to dst.
func AppendVarInt(dst []byte, v int) []byte {
	u := uint32(v)
	for u&^uint32(0x7F) != 0 {
		dst = append(dst, byte(u&0x7F)|0x80)
		u >>= 7
	}
	return append(dst, byte(u))
}

// VarIntSize returns the encoded byte length of v.
func VarIntSize(v int) int {
	n := 1
	u := uint32(v)
	for u&^uint32(0x7F) != 0 {
		u >>= 7
		n++
	}
	return n
}