// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This package implements the RIPEMD-160 hash algorithm.
package ripemd160

// RIPEMD-160 is designed by by Hans Dobbertin, Antoon Bosselaers, and Bart
// Preneel with specifications available at:
// http://homes.esat.kuleuven.be/~cosicart/pdf/AB-9601/AB-9601.pdf.

import (
	"hash"
	"os"
)

// The size of the checksum in bytes.
const Size = 20

// The block size of the hash algorithm in bytes.
const BlockSize = 64

const (
	_s0 = 0x67452301
	_s1 = 0xefcdab89
	_s2 = 0x98badcfe
	_s3 = 0x10325476
	_s4 = 0xc3d2e1f0
)

// digest represents the partial evaluation of a checksum.
type digest struct {
	s  [5]uint32       // running context
	x  [BlockSize]byte // temporary buffer
	nx int             // index into x
	tc uint64          // total count of bytes processed
}

func (d *digest) Reset() {
	d.s[0], d.s[1], d.s[2], d.s[3], d.s[4] = _s0, _s1, _s2, _s3, _s4
	d.nx = 0
	d.tc = 0
}

// New returns a new hash.Hash computing the checksum.
func New() hash.Hash {
	result := new(digest)
	result.Reset()
	return result
}

func (d *digest) Size() int { return Size }

func (d *digest) Write(p []byte) (nn int, err os.Error) {
	nn = len(p)
	d.tc += uint64(nn)
	if d.nx > 0 {
		n := len(p)
		if n > BlockSize-d.nx {
			n = BlockSize - d.nx
		}
		for i := 0; i < n; i++ {
			d.x[d.nx+i] = p[i]
		}
		d.nx += n
		if d.nx == BlockSize {
			_Block(d, d.x[0:])
			d.nx = 0
		}
		p = p[n:]
	}
	n := _Block(d, p)
	p = p[n:]
	if len(p) > 0 {
		for i, x := range p {
			d.x[i] = x
		}
		d.nx = len(p)
	}
	return
}

func (d0 *digest) Sum() []byte {
	// Make a copy of d0 so that caller can keep writing and summing.
	d := new(digest)
	*d = *d0

	// Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.
	tc := d.tc
	var tmp [64]byte
	tmp[0] = 0x80
	if tc%64 < 56 {
		d.Write(tmp[0 : 56-tc%64])
	} else {
		d.Write(tmp[0 : 64+56-tc%64])
	}

	// Length in bits.
	tc <<= 3
	for i := uint(0); i < 8; i++ {
		tmp[i] = byte(tc >> (8 * i))
	}
	d.Write(tmp[0:8])

	if d.nx != 0 {
		panic("d.nx != 0")
	}

	p := make([]byte, 20)
	j := 0
	for _, s := range d.s {
		p[j], p[j+1], p[j+2], p[j+3] = byte(s), byte(s>>8), byte(s>>16), byte(s>>24)
		j += 4
	}
	return p
}