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    use primitives::compact::Compact;
    use chain::IndexedBlockHeader;
    use network::Network;
    use work::is_valid_proof_of_work;
    use error::Error;
    use constants::BLOCK_MAX_FUTURE;

    pub struct HeaderVerifier<'a> {
    	pub proof_of_work: HeaderProofOfWork<'a>,
    	pub timestamp: HeaderTimestamp<'a>,
    }

    impl<'a> HeaderVerifier<'a> {
    	pub fn new(header: &'a IndexedBlockHeader, network: Network, current_time: u32) -> Self {
    		HeaderVerifier {
    			proof_of_work: HeaderProofOfWork::new(header, network),
    			timestamp: HeaderTimestamp::new(header, current_time, BLOCK_MAX_FUTURE as u32),
    		}
    	}

    	pub fn check(&self) -> Result<(), Error> {
    		try!(self.proof_of_work.check());
    		try!(self.timestamp.check());
    		Ok(())
    	}
    }

    pub struct HeaderProofOfWork<'a> {
    	header: &'a IndexedBlockHeader,
    	max_work_bits: Compact,
    }

    impl<'a> HeaderProofOfWork<'a> {
    	fn new(header: &'a IndexedBlockHeader, network: Network) -> Self {
    		HeaderProofOfWork {
    			header: header,
    			max_work_bits: network.max_bits().into(),
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		if is_valid_proof_of_work(self.max_work_bits, self.header.raw.bits, &self.header.hash) {
    			Ok(())
    		} else {
    			Err(Error::Pow)
    		}
    	}
    }

    pub struct HeaderTimestamp<'a> {
    	header: &'a IndexedBlockHeader,
    	current_time: u32,
    	max_future: u32,
    }

    impl<'a> HeaderTimestamp<'a> {
    	fn new(header: &'a IndexedBlockHeader, current_time: u32, max_future: u32) -> Self {
    		HeaderTimestamp {
    			header: header,
    			current_time: current_time,
    			max_future: max_future,
    		}
    	}

    	fn check(&self) -> Result<(), Error> {
    		if self.header.raw.time > self.current_time + self.max_future {
    			Err(Error::FuturisticTimestamp)
    		} else {
    			Ok(())
    		}
    	}
    }

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