// Copyright (c) 2013-2015 The btcsuite developers
// Copyright (c) 2015 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package wire

import (
	"bytes"
	"io"
	"time"

	"github.com/decred/dcrd/chaincfg/chainhash"
)

// MaxBlockHeaderPayload is the max size of the header which comes from:
// Version 4 bytes + Bits 4 bytes + PrevBlock and MerkleRoot hashes + 32 StakeRoot
// bytes + 2 VoteBits bytes + 6 FinalState bytes + 2 Voters bytes +
// 1 FreshStake byte + 1 Revocations byte + 8 SBits bytes + 4 PoolSize bytes +
// 4 Height bytes + 4 Size bytes + Timestamp 4 bytes + 4 bytes nonce.
// --> Total 180 bytes.
const MaxBlockHeaderPayload = 16 + (chainhash.HashSize * 2) + 64 + 36

// BlockHeader defines information about a block and is used in the decred
// block (MsgBlock) and headers (MsgHeaders) messages.
type BlockHeader struct {
	// Version of the block.  This is not the same as the protocol version.
	Version int32

	// Hash of the previous block in the block chain.
	PrevBlock chainhash.Hash

	// Merkle tree reference to hash of all transactions for the block.
	MerkleRoot chainhash.Hash

	// Merkle tree reference to hash of all stake transactions for the block.
	StakeRoot chainhash.Hash

	// Votes on the previous merkleroot and yet undecided parameters. (TODO)
	VoteBits uint16

	// Final state of the PRNG used for ticket selection in the lottery.
	FinalState [6]byte

	// Number of participating voters for this block.
	Voters uint16

	// Number of new sstx in this block.
	FreshStake uint8

	// Number of ssrtx present in this block.
	Revocations uint8

	// Size of the ticket pool.
	PoolSize uint32

	// Difficulty target for the block.
	Bits uint32

	// Stake difficulty target.
	SBits int64

	// Height is the block height in the block chain.
	Height uint32

	// Size is the size of the serialized block in its entirety.
	Size uint32

	// Time the block was created.  This is, unfortunately, encoded as a
	// uint32 on the wire and therefore is limited to 2106.
	Timestamp time.Time

	// Nonce is technically a part of ExtraData, but we use it as the
	// classical 4-byte nonce here.
	Nonce uint32

	// ExtraData is used to encode the nonce or any other extra data
	// that might be used later on in consensus.
	ExtraData [36]byte
}

// blockHeaderLen is a constant that represents the number of bytes for a block
// header.
const blockHeaderLen = 180

// BlockSha computes the block identifier hash for the given block header.
func (h *BlockHeader) BlockSha() chainhash.Hash {
	// Encode the header and hash256 everything prior to the number of
	// transactions.  Ignore the error returns since there is no way the
	// encode could fail except being out of memory which would cause a
	// run-time panic.
	var buf bytes.Buffer
	_ = writeBlockHeader(&buf, 0, h)

	return chainhash.HashFuncH(buf.Bytes())
}

// Deserialize decodes a block header from r into the receiver using a format
// that is suitable for long-term storage such as a database while respecting
// the Version field.
func (h *BlockHeader) Deserialize(r io.Reader) error {
	// At the current time, there is no difference between the wire encoding
	// at protocol version 0 and the stable long-term storage format.  As
	// a result, make use of readBlockHeader.
	return readBlockHeader(r, 0, h)
}

// Serialize encodes a block header from r into the receiver using a format
// that is suitable for long-term storage such as a database while respecting
// the Version field.
func (h *BlockHeader) Serialize(w io.Writer) error {
	// At the current time, there is no difference between the wire encoding
	// at protocol version 0 and the stable long-term storage format.  As
	// a result, make use of writeBlockHeader.
	return writeBlockHeader(w, 0, h)
}

// Bytes returns a byte slice containing the serialized contents of the block
// header.
func (h *BlockHeader) Bytes() ([]byte, error) {
	// Serialize the MsgBlock.
	var w bytes.Buffer
	err := h.Serialize(&w)
	if err != nil {
		return nil, err
	}
	serializedBlockHeader := w.Bytes()

	// Cache the serialized bytes and return them.
	return serializedBlockHeader, nil
}

// NewBlockHeader returns a new BlockHeader using the provided previous block
// hash, merkle root hash, difficulty bits, and nonce used to generate the
// block with defaults for the remaining fields.
func NewBlockHeader(version int32, prevHash *chainhash.Hash,
	merkleRootHash *chainhash.Hash, stakeRoot *chainhash.Hash, voteBits uint16,
	finalState [6]byte, voters uint16, freshStake uint8, revocations uint8,
	poolsize uint32, bits uint32, sbits int64, height uint32, size uint32,
	nonce uint32, extraData [36]byte) *BlockHeader {

	// Limit the timestamp to one second precision since the protocol
	// doesn't support better.
	return &BlockHeader{
		Version:     version,
		PrevBlock:   *prevHash,
		MerkleRoot:  *merkleRootHash,
		StakeRoot:   *stakeRoot,
		VoteBits:    voteBits,
		FinalState:  finalState,
		Voters:      voters,
		FreshStake:  freshStake,
		Revocations: revocations,
		PoolSize:    poolsize,
		Bits:        bits,
		SBits:       sbits,
		Height:      height,
		Size:        size,
		Timestamp:   time.Unix(time.Now().Unix(), 0),
		Nonce:       nonce,
		ExtraData:   extraData,
	}
}

// readBlockHeader reads a decred block header from r.  See Deserialize for
// decoding block headers stored to disk, such as in a database, as opposed to
// decoding from the wire.
func readBlockHeader(r io.Reader, pver uint32, bh *BlockHeader) error {
	var sec uint32
	err := readElements(
		r,
		&bh.Version,
		&bh.PrevBlock,
		&bh.MerkleRoot,
		&bh.StakeRoot,
		&bh.VoteBits,
		&bh.FinalState,
		&bh.Voters,
		&bh.FreshStake,
		&bh.Revocations,
		&bh.PoolSize,
		&bh.Bits,
		&bh.SBits,
		&bh.Height,
		&bh.Size,
		&sec,
		&bh.Nonce,
		&bh.ExtraData)
	if err != nil {
		return err
	}
	bh.Timestamp = time.Unix(int64(sec), 0)

	return nil
}

// writeBlockHeader writes a decred block header to w.  See Serialize for
// encoding block headers to be stored to disk, such as in a database, as
// opposed to encoding for the wire.
// TODO: make sure serializing/writing is actually correct w/r/t dereferencing
func writeBlockHeader(w io.Writer, pver uint32, bh *BlockHeader) error {
	sec := uint32(bh.Timestamp.Unix())
	err := writeElements(
		w,
		bh.Version,
		&bh.PrevBlock,
		&bh.MerkleRoot,
		&bh.StakeRoot,
		bh.VoteBits,
		bh.FinalState,
		bh.Voters,
		bh.FreshStake,
		bh.Revocations,
		bh.PoolSize,
		bh.Bits,
		bh.SBits,
		bh.Height,
		bh.Size,
		sec,
		bh.Nonce,
		bh.ExtraData)
	if err != nil {
		return err
	}

	return nil
}