// Package variablelengthquantity is for VLQ manipulations.
package variablelengthquantity
import (
	"fmt"
)
// EncodeVarint VLQ encodes input numbers.
func EncodeVarint(input []uint32) []byte {
	out := []byte{}
	for _, val := range input {
		if val == 0 {
			out = append(out, 0x0)
		}
		out = append(out, msb(val)...)
	}
	return out
}
// msb truncates input to 7-bit long pieces.
// Also set the Most Significant Bit for all bytes except the last one.
func msb(input uint32) []byte {
	out := []byte{}
	for input > 0 {
		out = append([]byte{byte(input) & 0x7f}, out...)
		input >>= 7
		if len(out) > 1 { // set MSB except for last one
			out[0] |= 0x80
		}
	}
	return out
}
// DecodeVarint decondes VLQ encoded input.
func DecodeVarint(input []byte) ([]uint32, error) {
	out := []uint32{}
	num := 0
	for i, bt := range input {
		// VSL has 7 useful bit
		num <<= 7
		// set last 7 bits, truncate MSB
		num |= 0x7f & int(bt)
		if (bt & 0x80) == 0 { // MSB is 0, this is the last byte of num
			out = append(out, uint32(num))
			num = 0
		}
		if i == len(input)-1 && (bt&0x80) != 0 {
			return nil, fmt.Errorf("incomplete byte sequence")
		}
	}
	return out, nil
}