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    use network::{ConsensusParams, ConsensusFork, TransactionOrdering};
    use crypto::dhash256;
    use storage::{TransactionOutputProvider, BlockHeaderProvider};
    use script;
    use ser::Stream;
    use sigops::{transaction_sigops, transaction_sigops_cost}	;
    use work::block_reward_satoshi;
    use duplex_store::{transaction_index_for_output_check, DuplexTransactionOutputProvider};
    use deployments::BlockDeployments;
    use canon::CanonBlock;
    use error::{Error, TransactionError};
    use timestamp::median_timestamp;

    /// Flexible verification of ordered block
    pub struct BlockAcceptor<'a> {
    	pub finality: BlockFinality<'a>,
    	pub serialized_size: BlockSerializedSize<'a>,
    	pub sigops: BlockSigops<'a>,
    	pub coinbase_claim: BlockCoinbaseClaim<'a>,
    	pub coinbase_script: BlockCoinbaseScript<'a>,
    	pub witness: BlockWitness<'a>,
    	pub ordering: BlockTransactionOrdering<'a>,
    }

    impl<'a> BlockAcceptor<'a> {
    	pub fn new(
    		store: &'a TransactionOutputProvider,
    		consensus: &'a ConsensusParams,
    		block: CanonBlock<'a>,
    		height: u32,
    		median_time_past: u32,
    		deployments: &'a BlockDeployments<'a>,
    		headers: &'a BlockHeaderProvider,
    	) -> Self {
    		BlockAcceptor {
    			finality: BlockFinality::new(block, height, deployments, headers),
    			serialized_size: BlockSerializedSize::new(block, consensus, deployments, height, median_time_past),
    			coinbase_script: BlockCoinbaseScript::new(block, consensus, height),
    			coinbase_claim: BlockCoinbaseClaim::new(block, consensus, store, height, median_time_past),
    			sigops: BlockSigops::new(block, store, consensus, height, median_time_past),
    			witness: BlockWitness::new(block, deployments),
    			ordering: BlockTransactionOrdering::new(block, consensus, median_time_past),
    		}
    	}

    	pub fn check(&self) -> Result<(), Error> {
    		self.finality.check()?;
    		self.sigops.check()?;
    		self.serialized_size.check()?;
    		self.coinbase_claim.check()?;
    		self.coinbase_script.check()?;
    		self.witness.check()?;
    		self.ordering.check()?;
    		Ok(())
    	}
    }

    pub struct BlockFinality<'a> {
    	block: CanonBlock<'a>,
    	height: u32,
    	csv_active: bool,
    	headers: &'a BlockHeaderProvider,
    }

    impl<'a> BlockFinality<'a> {
    	fn new(block: CanonBlock<'a>, height: u32, deployments: &'a BlockDeployments<'a>, headers: &'a BlockHeaderProvider) -> Self {
    		let csv_active = deployments.csv();

    		BlockFinality {
    			block: block,
    			height: height,
    			csv_active: csv_active,
    			headers: headers,
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		let time_cutoff = if self.csv_active {
    			median_timestamp(&self.block.header.raw, self.headers)
    		} else {
    			self.block.header.raw.time
    		};

    		if self.block.transactions.iter().all(|tx| tx.raw.is_final_in_block(self.height, time_cutoff)) {
    			Ok(())
    		} else {
    			Err(Error::NonFinalBlock)
    		}
    	}
    }

    pub struct BlockSerializedSize<'a> {
    	block: CanonBlock<'a>,
    	consensus: &'a ConsensusParams,
    	height: u32,
    	median_time_past: u32,
    	segwit_active: bool,
    }

    impl<'a> BlockSerializedSize<'a> {
    	fn new(block: CanonBlock<'a>, consensus: &'a ConsensusParams, deployments: &'a BlockDeployments<'a>, height: u32, median_time_past: u32) -> Self {
    		let segwit_active = deployments.segwit();

    		BlockSerializedSize {
    			block: block,
    			consensus: consensus,
    			height: height,
    			median_time_past: median_time_past,
    			segwit_active: segwit_active,
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		let size = self.block.size();

    		// block size (without witness) is valid for all forks:
    		// before SegWit: it is main check for size
    		// after SegWit: without witness data, block size should be <= 1_000_000
    		// after BitcoinCash fork: block size is increased to 8_000_000
    		if size < self.consensus.fork.min_block_size(self.height) ||
    			size > self.consensus.fork.max_block_size(self.height, self.median_time_past) {
    			return Err(Error::Size(size));
    		}

    		// there's no need to define weight for pre-SegWit blocks
    		if self.segwit_active {
    			let size_with_witness = self.block.size_with_witness();
    			let weight = size * (ConsensusFork::witness_scale_factor() - 1) + size_with_witness;
    			if weight > self.consensus.fork.max_block_weight(self.height) {
    				return Err(Error::Weight);
    			}
    		}
    		Ok(())
    	}
    }

    pub struct BlockSigops<'a> {
    	block: CanonBlock<'a>,
    	store: &'a TransactionOutputProvider,
    	consensus: &'a ConsensusParams,
    	height: u32,
    	bip16_active: bool,
    	checkdatasig_active: bool,
    }

    impl<'a> BlockSigops<'a> {
    	fn new(
    		block: CanonBlock<'a>,
    		store: &'a TransactionOutputProvider,
    		consensus: &'a ConsensusParams,
    		height: u32,
    		median_time_past: u32,
    	) -> Self {
    		let bip16_active = block.header.raw.time >= consensus.bip16_time;
    		let checkdatasig_active = match consensus.fork {
    			ConsensusFork::BitcoinCash(ref fork) => median_time_past >= fork.magnetic_anomaly_time,
    			_ => false,
    		};

    		BlockSigops {
    			block: block,
    			store: store,
    			consensus: consensus,
    			height: height,
    			bip16_active,
    			checkdatasig_active,
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		let store = DuplexTransactionOutputProvider::new(self.store, &*self.block);
    		let (sigops, sigops_cost) = self.block.transactions.iter()
    			.map(|tx| {
    				let tx_sigops = transaction_sigops(&tx.raw, &store, self.bip16_active, self.checkdatasig_active);
    				let tx_sigops_cost = transaction_sigops_cost(&tx.raw, &store, tx_sigops);
    				(tx_sigops, tx_sigops_cost)
    			})
    			.fold((0, 0), |acc, (tx_sigops, tx_sigops_cost)| (acc.0 + tx_sigops, acc.1 + tx_sigops_cost));

    		// sigops check is valid for all forks:
    		// before SegWit: 20_000
    		// after SegWit: cost of sigops is sigops * 4 and max cost is 80_000 => max sigops is still 20_000
    		// after BitcoinCash fork: 20_000 sigops for each full/partial 1_000_000 bytes of block
    		let size = self.block.size();
    		if sigops > self.consensus.fork.max_block_sigops(self.height, size) {
    			return Err(Error::MaximumSigops);
    		}

    		// sigops check is valid for all forks:
    		// before SegWit: no witnesses => cost is sigops * 4 and max cost is 80_000
    		// after SegWit: it is main check for sigops
    		// after BitcoinCash fork: no witnesses => cost is sigops * 4 and max cost depends on block size
    		if sigops_cost > self.consensus.fork.max_block_sigops_cost(self.height, size) {
    			Err(Error::MaximumSigopsCost)
    		} else {
    			Ok(())
    		}
    	}
    }

    pub struct BlockCoinbaseClaim<'a> {
    	block: CanonBlock<'a>,
    	store: &'a TransactionOutputProvider,
    	height: u32,
    	transaction_ordering: TransactionOrdering,
    }

    impl<'a> BlockCoinbaseClaim<'a> {
    	fn new(
    		block: CanonBlock<'a>,
    		consensus_params: &ConsensusParams,
    		store: &'a TransactionOutputProvider,
    		height: u32,
    		median_time_past: u32
    	) -> Self {
    		BlockCoinbaseClaim {
    			block: block,
    			store: store,
    			height: height,
    			transaction_ordering: consensus_params.fork.transaction_ordering(median_time_past),
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		let store = DuplexTransactionOutputProvider::new(self.store, &*self.block);

    		let mut fees: u64 = 0;

    		for (tx_idx, tx) in self.block.transactions.iter().enumerate().skip(1) {
    			// (1) Total sum of all referenced outputs
    			let mut incoming: u64 = 0;
    			for input in tx.raw.inputs.iter() {
    				let prevout_tx_idx = transaction_index_for_output_check(self.transaction_ordering, tx_idx);
    				let prevout = store.transaction_output(&input.previous_output, prevout_tx_idx);
    				let (sum, overflow) = incoming.overflowing_add(prevout.map(|o| o.value).unwrap_or(0));
    				if overflow {
    					return Err(Error::ReferencedInputsSumOverflow);
    				}
    				incoming = sum;
    			}

    			// (2) Total sum of all outputs
    			let spends = tx.raw.total_spends();

    			// Difference between (1) and (2)
    			let (difference, overflow) = incoming.overflowing_sub(spends);
    			if overflow {
    				return Err(Error::Transaction(tx_idx, TransactionError::Overspend))
    			}

    			// Adding to total fees (with possible overflow)
    			let (sum, overflow) = fees.overflowing_add(difference);
    			if overflow {
    				return Err(Error::TransactionFeesOverflow)
    			}

    			fees = sum;
    		}

    		let claim = self.block.transactions[0].raw.total_spends();

    		let (reward, overflow) = fees.overflowing_add(block_reward_satoshi(self.height));
    		if overflow {
    			return Err(Error::TransactionFeeAndRewardOverflow);
    		}

    		if claim > reward {
    			Err(Error::CoinbaseOverspend { expected_max: reward, actual: claim })
    		} else {
    			Ok(())
    		}
    	}
    }

    pub struct BlockCoinbaseScript<'a> {
    	block: CanonBlock<'a>,
    	bip34_active: bool,
    	height: u32,
    }

    impl<'a> BlockCoinbaseScript<'a> {
    	fn new(block: CanonBlock<'a>, consensus_params: &ConsensusParams, height: u32) -> Self {
    		BlockCoinbaseScript {
    			block: block,
    			bip34_active: height >= consensus_params.bip34_height,
    			height: height,
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		if !self.bip34_active {
    			return Ok(())
    		}

    		let prefix = script::Builder::default()
    			.push_num(self.height.into())
    			.into_script();

    		let matches = self.block.transactions.first()
    			.and_then(|tx| tx.raw.inputs.first())
    			.map(|input| input.script_sig.starts_with(&prefix))
    			.unwrap_or(false);

    		if matches {
    			Ok(())
    		} else {
    			Err(Error::CoinbaseScript)
    		}
    	}
    }

    pub struct BlockWitness<'a> {
    	block: CanonBlock<'a>,
    	segwit_active: bool,
    }

    impl<'a> BlockWitness<'a> {
    	fn new(block: CanonBlock<'a>, deployments: &'a BlockDeployments<'a>) -> Self {
    		let segwit_active = deployments.segwit();

    		BlockWitness {
    			block: block,
    			segwit_active: segwit_active,
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		if !self.segwit_active {
    			return Ok(());
    		}

    		// check witness from coinbase transaction
    		let mut has_witness = false;
    		if let Some(coinbase) = self.block.transactions.first() {
    			let commitment = coinbase.raw.outputs.iter().rev()
    				.find(|output| script::is_witness_commitment_script(&output.script_pubkey));
    			if let Some(commitment) = commitment {
    				let witness_merkle_root = self.block.raw().witness_merkle_root();
    				if coinbase.raw.inputs.get(0).map(|i| i.script_witness.len()).unwrap_or_default() != 1 ||
    					coinbase.raw.inputs[0].script_witness[0].len() != 32 {
    					return Err(Error::WitnessInvalidNonceSize);
    				}

    				let mut stream = Stream::new();
    				stream.append(&witness_merkle_root);
    				stream.append_slice(&coinbase.raw.inputs[0].script_witness[0]);
    				let hash_witness = dhash256(&stream.out());

    				if hash_witness != commitment.script_pubkey[6..].into() {
    					return Err(Error::WitnessMerkleCommitmentMismatch);
    				}

    				has_witness = true;
    			}
    		}

    		// witness commitment is required when block contains transactions with witness
    		if !has_witness && self.block.transactions.iter().any(|tx| tx.raw.has_witness()) {
    			return Err(Error::UnexpectedWitness);
    		}

    		Ok(())
    	}
    }

    pub struct BlockTransactionOrdering<'a> {
    	block: CanonBlock<'a>,
    	transaction_ordering: TransactionOrdering,
    }

    impl<'a> BlockTransactionOrdering<'a> {
    	fn new(block: CanonBlock<'a>, consensus: &'a ConsensusParams, median_time_past: u32) -> Self {
    		BlockTransactionOrdering {
    			block,
    			transaction_ordering: consensus.fork.transaction_ordering(median_time_past),
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		match self.transaction_ordering {
    			// topological transaction ordering is checked in TransactionMissingInputs
    			TransactionOrdering::Topological => Ok(()),
    			// canonical transaction ordering means that transactions are ordered by
    			// their id (i.e. hash) in ascending order
    			TransactionOrdering::Canonical =>
    				if self.block.transactions.windows(2).skip(1).all(|w| w[0].hash < w[1].hash) {
    					Ok(())
    				} else {
    					Err(Error::NonCanonicalTransactionOrdering)
    				},
    		}
    	}
    }

    #[cfg(test)]
    mod tests {
    	extern crate test_data;

    	use chain::{IndexedBlock, Transaction};
    	use network::{Network, ConsensusFork, ConsensusParams, BitcoinCashConsensusParams};
    	use {Error, CanonBlock};
    	use super::{BlockCoinbaseScript, BlockTransactionOrdering};

    	#[test]
    	fn test_block_coinbase_script() {
    		// transaction from block 461373
    		// https://blockchain.info/rawtx/7cf05175ce9c8dbfff9aafa8263edc613fc08f876e476553009afcf7e3868a0c?format=hex
    		let tx = "01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff3f033d0a070004b663ec58049cba630608733867a0787a02000a425720537570706f727420384d200a666973686572206a696e78696e092f425720506f6f6c2fffffffff01903d9d4e000000001976a914721afdf638d570285d02d3076d8be6a03ee0794d88ac00000000".into();
    		let block_number = 461373;
    		let block = test_data::block_builder()
    			.with_transaction(tx)
    			.header().build()
    			.build()
    			.into();

    		let coinbase_script_validator = BlockCoinbaseScript {
    			block: CanonBlock::new(&block),
    			bip34_active: true,
    			height: block_number,
    		};

    		assert_eq!(coinbase_script_validator.check(), Ok(()));

    		let coinbase_script_validator2 = BlockCoinbaseScript {
    			block: CanonBlock::new(&block),
    			bip34_active: true,
    			height: block_number - 1,
    		};

    		assert_eq!(coinbase_script_validator2.check(), Err(Error::CoinbaseScript));
    	}

    	#[test]
    	fn block_transaction_ordering_works() {
    		let tx1: Transaction = test_data::TransactionBuilder::with_output(1).into();
    		let tx2: Transaction = test_data::TransactionBuilder::with_output(2).into();
    		let tx3: Transaction = test_data::TransactionBuilder::with_output(3).into();
    		let bad_block: IndexedBlock = test_data::block_builder()
    			.with_transaction(tx1.clone())
    			.with_transaction(tx2.clone())
    			.with_transaction(tx3.clone())
    			.header().build()
    			.build()
    			.into();
    		let good_block: IndexedBlock = test_data::block_builder()
    			.with_transaction(tx1)
    			.with_transaction(tx3)
    			.with_transaction(tx2)
    			.header().build()
    			.build()
    			.into();

    		let bad_block = CanonBlock::new(&bad_block);
    		let good_block = CanonBlock::new(&good_block);

    		// when topological ordering is used => we don't care about tx ordering
    		let consensus = ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCore);
    		let checker = BlockTransactionOrdering::new(bad_block, &consensus, 0);
    		assert_eq!(checker.check(), Ok(()));

    		// when topological ordering is used => we care about tx ordering
    		let mut bch = BitcoinCashConsensusParams::new(Network::Unitest);
    		bch.magnetic_anomaly_time = 0;
    		let consensus = ConsensusParams::new(Network::Unitest, ConsensusFork::BitcoinCash(bch));
    		let checker = BlockTransactionOrdering::new(bad_block, &consensus, 0);
    		assert_eq!(checker.check(), Err(Error::NonCanonicalTransactionOrdering));
    		let checker = BlockTransactionOrdering::new(good_block, &consensus, 0);
    		assert_eq!(checker.check(), Ok(()));
    	}
    }

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