// 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 crate::clarity::util::uint::Uint256;

use crate::clarity::util::bitcoin::blockdata::constants::max_target;
use crate::clarity::util::bitcoin::blockdata::transaction::Transaction;
use crate::clarity::util::bitcoin::network::constants::Network;
use crate::clarity::util::bitcoin::network::encodable::VarInt;
use crate::clarity::util::bitcoin::network::serialize::BitcoinHash;
use crate::clarity::util::bitcoin::util;
use crate::clarity::util::bitcoin::util::hash::Sha256dHash;
use crate::clarity::util::bitcoin::util::Error::{SpvBadProofOfWork, SpvBadTarget};

/// A block header, which contains all the block's information except
/// the actual transactions
#[derive(Copy, 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,
}

/// 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,
}

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) << (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<(), crate::clarity::util::bitcoin::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 crate::clarity::util::bitcoin::network::serialize::serialize;
        Sha256dHash::from_data(&serialize(self).unwrap())
    }
}

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
);
impl_consensus_encoding!(Block, header, txdata);
impl_consensus_encoding!(LoneBlockHeader, header, tx_count);

#[cfg(test)]
mod tests {
    use crate::clarity::util::hash::hex_bytes as hex_decode;

    use crate::clarity::util::bitcoin::blockdata::block::{Block, BlockHeader};
    use crate::clarity::util::bitcoin::network::serialize::{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("4ddccd549d28f385ab457e98d1b11ce80bfea2c5ab93015ade4973e400000000").unwrap();
        let merkle =
            hex_decode("bf4473e53794beae34e64fccc471dace6ae544180816f89591894e0f417a914c").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, 1);
        assert_eq!(
            serialize(&real_decode.header.prev_blockhash).ok(),
            Some(prevhash)
        );
        // [test] TODO: actually compute the merkle root
        assert_eq!(
            serialize(&real_decode.header.merkle_root).ok(),
            Some(merkle)
        );
        assert_eq!(real_decode.header.time, 1231965655);
        assert_eq!(real_decode.header.bits, 486604799);
        assert_eq!(real_decode.header.nonce, 2067413810);
        // [test] TODO: check the transaction data

        assert_eq!(serialize(&real_decode).ok(), Some(some_block));
    }

    // Check testnet block 000000000000045e0b1660b6445b5e5c5ab63c9a4f956be7e1e69be04fa4497b
    #[test]
    fn segwit_block_test() {
        let segwit_block = hex_decode("[encoded data, 8638 characters]").unwrap();

        let decode: Result<Block, _> = deserialize(&segwit_block);

        let prevhash =
            hex_decode("2aa2f2ca794ccbd40c16e2f3333f6b8b683f9e7179b2c4d74906000000000000").unwrap();
        let merkle =
            hex_decode("10bc26e70a2f672ad420a6153dd0c28b40a6002c55531bfc99bf8994a8e8f67e").unwrap();

        assert!(decode.is_ok());
        let real_decode = decode.unwrap();
        assert_eq!(real_decode.header.version, 0x20000000); // VERSIONBITS but no bits set
        assert_eq!(
            serialize(&real_decode.header.prev_blockhash).ok(),
            Some(prevhash)
        );
        assert_eq!(
            serialize(&real_decode.header.merkle_root).ok(),
            Some(merkle)
        );
        assert_eq!(real_decode.header.time, 1472004949);
        assert_eq!(real_decode.header.bits, 0x1a06d450);
        assert_eq!(real_decode.header.nonce, 1879759182);
        // [test] TODO: check the transaction data

        assert_eq!(serialize(&real_decode).ok(), Some(segwit_block));
    }

    #[test]
    fn compact_roundrtip_test() {
        let some_header = hex_decode("010000004ddccd549d28f385ab457e98d1b11ce80bfea2c5ab93015ade4973e400000000bf4473e53794beae34e64fccc471dace6ae544180816f89591894e0f417a914cd74d6e49ffff001d323b3a7b").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())
        );
    }
}
