package rlepluslazy

type rbitvec struct {
	index int

	bits   uint64
	bitCap byte

	vec []byte
}

func readBitvec(vec []byte) *rbitvec {
	bv := &rbitvec{vec: vec}
	for n := 7; n >= 0; n-- {
		var o uint64
		if len(bv.vec) > n {
			o = uint64(bv.vec[n])
		}

		bv.bits = bv.bits<<8 | o
		bv.index++
	}
	bv.bitCap = 64
	return bv
}

const (
	minCap = 8
)

var bitMasks = [9]byte{
	0x0,
	0x1,
	0x3,
	0x7,
	0xF,
	0x1F,
	0x3F,
	0x7F,
	0xFF,
}

func (bv *rbitvec) Get(count byte) byte {
	res := byte(bv.bits) & bitMasks[count]
	bv.bits = bv.bits >> count
	bv.bitCap = bv.bitCap - count

	if bv.bitCap < minCap {
		var add uint64
		for n := 6; n >= 0; n-- {
			var o uint64
			if len(bv.vec) > bv.index+n {
				o = uint64(bv.vec[bv.index+n])
			}

			add = add<<8 | o
		}
		bv.index = bv.index + 7
		bv.bits = bv.bits | add<<(bv.bitCap)
		bv.bitCap = bv.bitCap + 7*8
	}
	return res
}