// Rust Bitcoin Library
// Written in 2014 by
//     Andrew Poelstra <apoelstra@wpsoftware.net>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software.
// If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
//

//! Bitcoin Block
//!
//! A block is a bundle of transactions with a proof-of-work attached,
//! which attaches to an earlier block to form the blockchain. This
//! module describes structures and functions needed to describe
//! these blocks and the blockchain.
//!

use util;
use util::Error::{SpvBadTarget, SpvBadProofOfWork};
use util::hash::{BitcoinHash, Sha256dHash};
use util::uint::Uint256;
use consensus::encode::VarInt;
use network::constants::Network;
use blockdata::transaction::Transaction;
use blockdata::constants::max_target;

/// A block header, which contains all the block's information except
/// the actual transactions
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct BlockHeader {
    /// The protocol version. Should always be 1.
    pub version: u32,
    /// Reference to the previous block in the chain
    pub prev_blockhash: Sha256dHash,
    /// The root hash of the merkle tree of transactions in the block
    pub merkle_root: Sha256dHash,
    /// The timestamp of the block, as claimed by the miner
    pub time: u32,
    /// The target value below which the blockhash must lie, encoded as a
    /// a float (with well-defined rounding, of course)
    pub bits: u32,
    /// The nonce, selected to obtain a low enough blockhash
    pub nonce: u32,
    ///	Coinbase transaction that is in the parent block, linking the AuxPOW block to its parent block
    pub coinbase_txn: Transaction,
    /// Hash of the parent_block header
    pub block_hash: Sha256dHash,
    /// The merkle branch linking the coinbase_txn to the parent block's merkle_root
    pub coinbase_branch_hashes: Vec<Sha256dHash>,
    /// Bitmask of which side of the merkle hash function the branch_hash element should go on. Zero means it goes on the right, One means on the left. It is equal to the index of the starting hash within the widest level of the merkle tree for this merkle branch.
    pub coinbase_branch_side_mask: u32,
    /// The merkle branch linking this auxiliary blockchain to the others, when used in a merged mining setup with multiple auxiliary chains
    pub blockchain_branch_hashes: Vec<Sha256dHash>,
    /// Bitmask of which side of the merkle hash function the branch_hash element should go on. Zero means it goes on the right, One means on the left. It is equal to the index of the starting hash within the widest level of the merkle tree for this merkle branch.
    pub blockchain_branch_side_mask: u32,   
    /// Parent block header
    /// The protocol version. Should always be 1.
    pub parent_version: u32,
    /// Reference to the previous block in the chain
    pub parent_prev_blockhash: Sha256dHash,
    /// The root hash of the merkle tree of transactions in the block
    pub parent_merkle_root: Sha256dHash,
    /// The timestamp of the block, as claimed by the miner
    pub parent_time: u32,
    /// The target value below which the blockhash must lie, encoded as a
    /// a float (with well-defined rounding, of course)
    pub parent_bits: u32,
    /// The nonce, selected to obtain a low enough blockhash
    pub parent_nonce: u32
}

/// A Bitcoin block, which is a collection of transactions with an attached
/// proof of work.
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct Block {
    /// The block header
    pub header: BlockHeader,  
    /// List of transactions contained in the block
    pub txdata: Vec<Transaction>
}

/// A block header with txcount attached, which is given in the `headers`
/// network message.
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct LoneBlockHeader {
    /// The actual block header
    pub header: BlockHeader,
    /// The number of transactions in the block. This will always be zero
    /// when the LoneBlockHeader is returned as part of a `headers` message.
    pub tx_count: VarInt
}
/// A legacy header without auxpow
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct BaseHeader {
    /// The protocol version. Should always be 1.
    pub version: u32,
    /// Reference to the previous block in the chain
    pub prev_blockhash: Sha256dHash,
    /// The root hash of the merkle tree of transactions in the block
    pub merkle_root: Sha256dHash,
    /// The timestamp of the block, as claimed by the miner
    pub time: u32,
    /// The target value below which the blockhash must lie, encoded as a
    /// a float (with well-defined rounding, of course)
    pub bits: u32,
    /// The nonce, selected to obtain a low enough blockhash
    pub nonce: u32
}
/// A legacy block without auxpow
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct BaseBlock {
    /// The legacy block header
    pub header: BaseHeader,
    /// List of transactions contained in the block
    pub txdata: Vec<Transaction>
}

impl BlockHeader {
    /// Computes the target [0, T] that a blockhash must land in to be valid
    pub fn target(&self) -> Uint256 {
        // This is a floating-point "compact" encoding originally used by
        // OpenSSL, which satoshi put into consensus code, so we're stuck
        // with it. The exponent needs to have 3 subtracted from it, hence
        // this goofy decoding code:
        let (mant, expt) = {
            let unshifted_expt = self.bits >> 24;
            if unshifted_expt <= 3 {
                ((self.bits & 0xFFFFFF) >> (8 * (3 - unshifted_expt as usize)), 0)
            } else {
                (self.bits & 0xFFFFFF, 8 * ((self.bits >> 24) - 3))
            }
        };

        // The mantissa is signed but may not be negative
        if mant > 0x7FFFFF {
            Default::default()
        } else {
            Uint256::from_u64(mant as u64).unwrap() << (expt as usize)
        }
    }

    /// Computes the target value in float format from Uint256 format.
    pub fn compact_target_from_u256(value: &Uint256) -> u32 {
        let mut size = (value.bits() + 7) / 8;
        let mut compact = if size <= 3 {
            (value.low_u64() << (8 * (3 - size))) as u32
        } else {
            let bn = *value >> (8 * (size - 3));
            bn.low_u32()
        };

        if (compact & 0x00800000) != 0 {
            compact >>= 8;
            size += 1;
        }

        compact | (size << 24) as u32
    }

    /// Compute the popular "difficulty" measure for mining
    pub fn difficulty(&self, network: Network) -> u64 {
        (max_target(network) / self.target()).low_u64()
    }

    /// Performs an SPV validation of a block, which confirms that the proof-of-work
    /// is correct, but does not verify that the transactions are valid or encoded
    /// correctly.
    pub fn spv_validate(&self, required_target: &Uint256) -> Result<(), util::Error> {
        let target = &self.target();
        if target != required_target {
            return Err(SpvBadTarget);
        }
        let hash = &self.bitcoin_hash().into_le();
        if hash <= target { Ok(()) } else { Err(SpvBadProofOfWork) }
    }

    /// Returns the total work of the block
    pub fn work(&self) -> Uint256 {
        // 2**256 / (target + 1) == ~target / (target+1) + 1    (eqn shamelessly stolen from bitcoind)
        let mut ret = !self.target();
        let mut ret1 = self.target();
        ret1.increment();
        ret = ret / ret1;
        ret.increment();
        ret
    }
}
impl BitcoinHash for BlockHeader {
    fn bitcoin_hash(&self) -> Sha256dHash {
        use consensus::encode::serialize;
        Sha256dHash::from_data(&serialize(self))
    }
}
impl BitcoinHash for BaseHeader {
    fn bitcoin_hash(&self) -> Sha256dHash {
        use consensus::encode::serialize;
        Sha256dHash::from_data(&serialize(self))
    }
}
impl BitcoinHash for Block {
    fn bitcoin_hash(&self) -> Sha256dHash {
        self.header.bitcoin_hash()
    }
}

impl_consensus_encoding!(BlockHeader, version, prev_blockhash, merkle_root, time, bits, nonce, coinbase_txn, block_hash, coinbase_branch_hashes, coinbase_branch_side_mask, blockchain_branch_hashes, blockchain_branch_side_mask, parent_version, parent_prev_blockhash, parent_merkle_root, parent_time, parent_bits, parent_nonce);
impl_consensus_encoding!(Block, header, txdata);
impl_consensus_encoding!(BaseHeader, version, prev_blockhash, merkle_root, time, bits, nonce);
impl_consensus_encoding!(BaseBlock, header, txdata);

impl_consensus_encoding!(LoneBlockHeader, header, tx_count);

#[cfg(test)]
mod tests {
    use hex::decode as hex_decode;

    use blockdata::block::{Block, BlockHeader};
    use consensus::encode::{deserialize, serialize};

    #[test]
    fn block_test() {
        let some_block = hex_decode("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").unwrap();
        let cutoff_block = hex_decode("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").unwrap();
        let prevhash = hex_decode("6f378876737d2a2bfffd51ca4c7e3d6281dad5fbd0b8ce61cde88674440f0000").unwrap();
        let merkle = hex_decode("aaa7bee217ab6c525b55734dfb013e6e7b7bb70848adb50407b6cc74fbf2011e").unwrap();
        let decode: Result<Block, _> = deserialize(&some_block);
        let bad_decode: Result<Block, _> = deserialize(&cutoff_block);

        assert!(decode.is_ok());
        assert!(bad_decode.is_err());
        let real_decode = decode.unwrap();
        assert_eq!(real_decode.header.version, 268435716);
        assert_eq!(serialize(&real_decode.header.prev_blockhash), prevhash);
        // [test] TODO: actually compute the merkle root
        assert_eq!(serialize(&real_decode.header.merkle_root), merkle);
        assert_eq!(real_decode.header.time, 1548886497);
        assert_eq!(real_decode.header.bits, 504365040);
        assert_eq!(real_decode.header.nonce, 0);
        // [test] TODO: check the transaction data
    
        assert_eq!(serialize(&real_decode), some_block);
    }
    
    #[test]
    fn compact_roundrtip_test() {
        let some_header = hex_decode("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").unwrap();

        let header: BlockHeader = deserialize(&some_header).expect("Can't deserialize correct block header");

        assert_eq!(header.bits, BlockHeader::compact_target_from_u256(&header.target()));

    }
}