// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package bitvector

import (
	"errors"
)

var errInvalidLength = errors.New("invalid length")

// BitVector is a convenience object for manipulating and representing bit vectors
type BitVector struct {
	len int
	b   []byte
}

// New creates a new bit vector with the given length
func New(l int) (bv *BitVector, err error) {
	return NewFromBytes(make([]byte, l/8+1), l)
}

// NewFromBytes creates a bit vector from the passed byte slice.
//
// Leftmost bit in byte slice becomes leftmost bit in bit vector
func NewFromBytes(b []byte, l int) (bv *BitVector, err error) {
	if l <= 0 {
		return nil, errInvalidLength
	}
	if len(b)*8 < l {
		return nil, errInvalidLength
	}
	return &BitVector{
		len: l,
		b:   b,
	}, nil
}

// Get gets the corresponding bit, counted from left to right
func (bv *BitVector) Get(i int) bool {
	bi := i / 8
	return bv.b[bi]&(0x1<<uint(i%8)) != 0
}

// Set sets the bit corresponding to the index in the bitvector, counted from left to right
func (bv *BitVector) set(i int, v bool) {
	bi := i / 8
	cv := bv.Get(i)
	if cv != v {
		bv.b[bi] ^= 0x1 << uint8(i%8)
	}
}

// Set sets the bit corresponding to the index in the bitvector, counted from left to right
func (bv *BitVector) Set(i int) {
	bv.set(i, true)
}

// Unset UNSETS the corresponding bit, counted from left to right
func (bv *BitVector) Unset(i int) {
	bv.set(i, false)
}

// SetBytes sets all bits in the bitvector that are set in the argument
//
// The argument must be the same as the bitvector length
func (bv *BitVector) SetBytes(bs []byte) error {
	if len(bs) != bv.len {
		return errors.New("invalid length")
	}
	for i := 0; i < bv.len*8; i++ {
		bi := i / 8
		if bs[bi]&(0x01<<uint(i%8)) > 0 {
			bv.set(i, true)
		}
	}
	return nil
}

// UnsetBytes UNSETS all bits in the bitvector that are set in the argument
//
// The argument must be the same as the bitvector length
func (bv *BitVector) UnsetBytes(bs []byte) error {
	if len(bs) != bv.len {
		return errors.New("invalid length")
	}
	for i := 0; i < bv.len*8; i++ {
		bi := i / 8
		if bs[bi]&(0x01<<uint(i%8)) > 0 {
			bv.set(i, false)
		}
	}
	return nil
}

// String implements Stringer interface
func (bv *BitVector) String() (s string) {
	for i := 0; i < bv.len*8; i++ {
		if bv.Get(i) {
			s += "1"
		} else {
			s += "0"
		}
	}
	return s
}

// Bytes retrieves the underlying bytes of the bitvector
func (bv *BitVector) Bytes() []byte {
	return bv.b
}