// Copyright 2009 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.

// Package sha512 implements the SHA-384, SHA-512, SHA-512/224, and SHA-512/256
// hash algorithms as defined in FIPS 180-4.
package sha512

import (
	"crypto/internal/fips"
	"errors"
	"internal/byteorder"
)

const (
	// size512 is the size, in bytes, of a SHA-512 checksum.
	size512 = 64

	// size224 is the size, in bytes, of a SHA-512/224 checksum.
	size224 = 28

	// size256 is the size, in bytes, of a SHA-512/256 checksum.
	size256 = 32

	// size384 is the size, in bytes, of a SHA-384 checksum.
	size384 = 48

	// blockSize is the block size, in bytes, of the SHA-512/224,
	// SHA-512/256, SHA-384 and SHA-512 hash functions.
	blockSize = 128
)

const (
	chunk     = 128
	init0     = 0x6a09e667f3bcc908
	init1     = 0xbb67ae8584caa73b
	init2     = 0x3c6ef372fe94f82b
	init3     = 0xa54ff53a5f1d36f1
	init4     = 0x510e527fade682d1
	init5     = 0x9b05688c2b3e6c1f
	init6     = 0x1f83d9abfb41bd6b
	init7     = 0x5be0cd19137e2179
	init0_224 = 0x8c3d37c819544da2
	init1_224 = 0x73e1996689dcd4d6
	init2_224 = 0x1dfab7ae32ff9c82
	init3_224 = 0x679dd514582f9fcf
	init4_224 = 0x0f6d2b697bd44da8
	init5_224 = 0x77e36f7304c48942
	init6_224 = 0x3f9d85a86a1d36c8
	init7_224 = 0x1112e6ad91d692a1
	init0_256 = 0x22312194fc2bf72c
	init1_256 = 0x9f555fa3c84c64c2
	init2_256 = 0x2393b86b6f53b151
	init3_256 = 0x963877195940eabd
	init4_256 = 0x96283ee2a88effe3
	init5_256 = 0xbe5e1e2553863992
	init6_256 = 0x2b0199fc2c85b8aa
	init7_256 = 0x0eb72ddc81c52ca2
	init0_384 = 0xcbbb9d5dc1059ed8
	init1_384 = 0x629a292a367cd507
	init2_384 = 0x9159015a3070dd17
	init3_384 = 0x152fecd8f70e5939
	init4_384 = 0x67332667ffc00b31
	init5_384 = 0x8eb44a8768581511
	init6_384 = 0xdb0c2e0d64f98fa7
	init7_384 = 0x47b5481dbefa4fa4
)

// Digest is a SHA-384, SHA-512, SHA-512/224, or SHA-512/256 [hash.Hash]
// implementation.
type Digest struct {
	h    [8]uint64
	x    [chunk]byte
	nx   int
	len  uint64
	size int // size224, size256, size384, or size512
}

func (d *Digest) Reset() {
	switch d.size {
	case size384:
		d.h[0] = init0_384
		d.h[1] = init1_384
		d.h[2] = init2_384
		d.h[3] = init3_384
		d.h[4] = init4_384
		d.h[5] = init5_384
		d.h[6] = init6_384
		d.h[7] = init7_384
	case size224:
		d.h[0] = init0_224
		d.h[1] = init1_224
		d.h[2] = init2_224
		d.h[3] = init3_224
		d.h[4] = init4_224
		d.h[5] = init5_224
		d.h[6] = init6_224
		d.h[7] = init7_224
	case size256:
		d.h[0] = init0_256
		d.h[1] = init1_256
		d.h[2] = init2_256
		d.h[3] = init3_256
		d.h[4] = init4_256
		d.h[5] = init5_256
		d.h[6] = init6_256
		d.h[7] = init7_256
	case size512:
		d.h[0] = init0
		d.h[1] = init1
		d.h[2] = init2
		d.h[3] = init3
		d.h[4] = init4
		d.h[5] = init5
		d.h[6] = init6
		d.h[7] = init7
	default:
		panic("unknown size")
	}
	d.nx = 0
	d.len = 0
}

const (
	magic384      = "sha\x04"
	magic512_224  = "sha\x05"
	magic512_256  = "sha\x06"
	magic512      = "sha\x07"
	marshaledSize = len(magic512) + 8*8 + chunk + 8
)

func (d *Digest) MarshalBinary() ([]byte, error) {
	return d.AppendBinary(make([]byte, 0, marshaledSize))
}

func (d *Digest) AppendBinary(b []byte) ([]byte, error) {
	switch d.size {
	case size384:
		b = append(b, magic384...)
	case size224:
		b = append(b, magic512_224...)
	case size256:
		b = append(b, magic512_256...)
	case size512:
		b = append(b, magic512...)
	default:
		panic("unknown size")
	}
	b = byteorder.BeAppendUint64(b, d.h[0])
	b = byteorder.BeAppendUint64(b, d.h[1])
	b = byteorder.BeAppendUint64(b, d.h[2])
	b = byteorder.BeAppendUint64(b, d.h[3])
	b = byteorder.BeAppendUint64(b, d.h[4])
	b = byteorder.BeAppendUint64(b, d.h[5])
	b = byteorder.BeAppendUint64(b, d.h[6])
	b = byteorder.BeAppendUint64(b, d.h[7])
	b = append(b, d.x[:d.nx]...)
	b = append(b, make([]byte, len(d.x)-d.nx)...)
	b = byteorder.BeAppendUint64(b, d.len)
	return b, nil
}

func (d *Digest) UnmarshalBinary(b []byte) error {
	if len(b) < len(magic512) {
		return errors.New("crypto/sha512: invalid hash state identifier")
	}
	switch {
	case d.size == size384 && string(b[:len(magic384)]) == magic384:
	case d.size == size224 && string(b[:len(magic512_224)]) == magic512_224:
	case d.size == size256 && string(b[:len(magic512_256)]) == magic512_256:
	case d.size == size512 && string(b[:len(magic512)]) == magic512:
	default:
		return errors.New("crypto/sha512: invalid hash state identifier")
	}
	if len(b) != marshaledSize {
		return errors.New("crypto/sha512: invalid hash state size")
	}
	b = b[len(magic512):]
	b, d.h[0] = consumeUint64(b)
	b, d.h[1] = consumeUint64(b)
	b, d.h[2] = consumeUint64(b)
	b, d.h[3] = consumeUint64(b)
	b, d.h[4] = consumeUint64(b)
	b, d.h[5] = consumeUint64(b)
	b, d.h[6] = consumeUint64(b)
	b, d.h[7] = consumeUint64(b)
	b = b[copy(d.x[:], b):]
	b, d.len = consumeUint64(b)
	d.nx = int(d.len % chunk)
	return nil
}

func consumeUint64(b []byte) ([]byte, uint64) {
	return b[8:], byteorder.BeUint64(b)
}

// New returns a new Digest computing the SHA-512 hash.
func New() *Digest {
	d := &Digest{size: size512}
	d.Reset()
	return d
}

// New512_224 returns a new Digest computing the SHA-512/224 hash.
func New512_224() *Digest {
	d := &Digest{size: size224}
	d.Reset()
	return d
}

// New512_256 returns a new Digest computing the SHA-512/256 hash.
func New512_256() *Digest {
	d := &Digest{size: size256}
	d.Reset()
	return d
}

// New384 returns a new Digest computing the SHA-384 hash.
func New384() *Digest {
	d := &Digest{size: size384}
	d.Reset()
	return d
}

func (d *Digest) Size() int {
	return d.size
}

func (d *Digest) BlockSize() int { return blockSize }

func (d *Digest) Write(p []byte) (nn int, err error) {
	nn = len(p)
	d.len += uint64(nn)
	if d.nx > 0 {
		n := copy(d.x[d.nx:], p)
		d.nx += n
		if d.nx == chunk {
			block(d, d.x[:])
			d.nx = 0
		}
		p = p[n:]
	}
	if len(p) >= chunk {
		n := len(p) &^ (chunk - 1)
		block(d, p[:n])
		p = p[n:]
	}
	if len(p) > 0 {
		d.nx = copy(d.x[:], p)
	}
	return
}

func (d *Digest) Sum(in []byte) []byte {
	fips.RecordApproved()
	// Make a copy of d so that caller can keep writing and summing.
	d0 := new(Digest)
	*d0 = *d
	hash := d0.checkSum()
	return append(in, hash[:d.size]...)
}

func (d *Digest) checkSum() [size512]byte {
	// Padding. Add a 1 bit and 0 bits until 112 bytes mod 128.
	len := d.len
	var tmp [128 + 16]byte // padding + length buffer
	tmp[0] = 0x80
	var t uint64
	if len%128 < 112 {
		t = 112 - len%128
	} else {
		t = 128 + 112 - len%128
	}

	// Length in bits.
	len <<= 3
	padlen := tmp[:t+16]
	// Upper 64 bits are always zero, because len variable has type uint64,
	// and tmp is already zeroed at that index, so we can skip updating it.
	// byteorder.BePutUint64(padlen[t+0:], 0)
	byteorder.BePutUint64(padlen[t+8:], len)
	d.Write(padlen)

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

	var digest [size512]byte
	byteorder.BePutUint64(digest[0:], d.h[0])
	byteorder.BePutUint64(digest[8:], d.h[1])
	byteorder.BePutUint64(digest[16:], d.h[2])
	byteorder.BePutUint64(digest[24:], d.h[3])
	byteorder.BePutUint64(digest[32:], d.h[4])
	byteorder.BePutUint64(digest[40:], d.h[5])
	if d.size != size384 {
		byteorder.BePutUint64(digest[48:], d.h[6])
		byteorder.BePutUint64(digest[56:], d.h[7])
	}

	return digest
}