// Copyright 2018 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Transactions

use std::cmp::max;
use std::cmp::Ordering;
use std::collections::HashSet;
use std::sync::Arc;
use std::{error, fmt};
use util::RwLock;

use byteorder::{BigEndian, ByteOrder};

use consensus::{self, VerifySortOrder};
use core::hash::Hashed;
use core::verifier_cache::VerifierCache;
use core::{committed, Committed};
use keychain::{self, BlindingFactor};
use ser::{self, read_multi, FixedLength, PMMRable, Readable, Reader, Writeable, Writer};
use util;
use util::secp;
use util::secp::pedersen::{Commitment, RangeProof};
use util::static_secp_instance;

bitflags! {
	/// Options for a kernel's structure or use
	#[derive(Serialize, Deserialize)]
	pub struct KernelFeatures: u8 {
		/// No flags
		const DEFAULT_KERNEL = 0b00000000;
		/// Kernel matching a coinbase output
		const COINBASE_KERNEL = 0b00000001;
	}
}

/// Errors thrown by Transaction validation
#[derive(Clone, Eq, Debug, PartialEq)]
pub enum Error {
	/// Underlying Secp256k1 error (signature validation or invalid public key
	/// typically)
	Secp(secp::Error),
	/// Underlying keychain related error
	Keychain(keychain::Error),
	/// The sum of output minus input commitments does not
	/// match the sum of kernel commitments
	KernelSumMismatch,
	/// Restrict tx total weight.
	TooHeavy,
	/// Underlying consensus error (currently for sort order)
	ConsensusError(consensus::Error),
	/// Error originating from an invalid lock-height
	LockHeight(u64),
	/// Range proof validation error
	RangeProof,
	/// Error originating from an invalid Merkle proof
	MerkleProof,
	/// Returns if the value hidden within the a RangeProof message isn't
	/// repeated 3 times, indicating it's incorrect
	InvalidProofMessage,
	/// Error when verifying kernel sums via committed trait.
	Committed(committed::Error),
	/// Error when sums do not verify correctly during tx aggregation.
	/// Likely a "double spend" across two unconfirmed txs.
	AggregationError,
	/// Validation error relating to cut-through (tx is spending its own
	/// output).
	CutThrough,
	/// Validation error relating to output features.
	/// It is invalid for a transaction to contain a coinbase output, for example.
	InvalidOutputFeatures,
	/// Validation error relating to kernel features.
	/// It is invalid for a transaction to contain a coinbase kernel, for example.
	InvalidKernelFeatures,
	/// Signature verification error.
	IncorrectSignature,
}

impl error::Error for Error {
	fn description(&self) -> &str {
		match *self {
			_ => "some kind of keychain error",
		}
	}
}

impl fmt::Display for Error {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match *self {
			_ => write!(f, "some kind of keychain error"),
		}
	}
}

impl From<secp::Error> for Error {
	fn from(e: secp::Error) -> Error {
		Error::Secp(e)
	}
}

impl From<consensus::Error> for Error {
	fn from(e: consensus::Error) -> Error {
		Error::ConsensusError(e)
	}
}

impl From<keychain::Error> for Error {
	fn from(e: keychain::Error) -> Error {
		Error::Keychain(e)
	}
}

impl From<committed::Error> for Error {
	fn from(e: committed::Error) -> Error {
		Error::Committed(e)
	}
}

/// A proof that a transaction sums to zero. Includes both the transaction's
/// Pedersen commitment and the signature, that guarantees that the commitments
/// amount to zero.
/// The signature signs the fee and the lock_height, which are retained for
/// signature validation.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct TxKernel {
	/// Options for a kernel's structure or use
	pub features: KernelFeatures,
	/// Fee originally included in the transaction this proof is for.
	pub fee: u64,
	/// This kernel is not valid earlier than lock_height blocks
	/// The max lock_height of all *inputs* to this transaction
	pub lock_height: u64,
	/// Remainder of the sum of all transaction commitments. If the transaction
	/// is well formed, amounts components should sum to zero and the excess
	/// is hence a valid public key.
	pub excess: Commitment,
	/// The signature proving the excess is a valid public key, which signs
	/// the transaction fee.
	pub excess_sig: secp::Signature,
}

hashable_ord!(TxKernel);

impl ::std::hash::Hash for TxKernel {
	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
		let mut vec = Vec::new();
		ser::serialize(&mut vec, &self).expect("serialization failed");
		::std::hash::Hash::hash(&vec, state);
	}
}

impl Writeable for TxKernel {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		ser_multiwrite!(
			writer,
			[write_u8, self.features.bits()],
			[write_u64, self.fee],
			[write_u64, self.lock_height],
			[write_fixed_bytes, &self.excess]
		);
		self.excess_sig.write(writer)?;
		Ok(())
	}
}

impl Readable for TxKernel {
	fn read(reader: &mut Reader) -> Result<TxKernel, ser::Error> {
		let features =
			KernelFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?;
		Ok(TxKernel {
			features,
			fee: reader.read_u64()?,
			lock_height: reader.read_u64()?,
			excess: Commitment::read(reader)?,
			excess_sig: secp::Signature::read(reader)?,
		})
	}
}

/// We store TxKernelEntry in the kernel MMR.
impl PMMRable for TxKernel {
	type E = TxKernelEntry;

	fn as_elmt(self) -> Self::E {
		self.into()
	}
}

impl TxKernel {
	/// Return the excess commitment for this tx_kernel.
	pub fn excess(&self) -> Commitment {
		self.excess
	}

	/// The msg signed as part of the tx kernel.
	/// Consists of the fee and the lock_height.
	pub fn msg_to_sign(&self) -> Result<secp::Message, Error> {
		let msg = kernel_sig_msg(self.fee, self.lock_height)?;
		Ok(msg)
	}

	/// Verify the transaction proof validity. Entails handling the commitment
	/// as a public key and checking the signature verifies with the fee as
	/// message.
	pub fn verify(&self) -> Result<(), Error> {
		let secp = static_secp_instance();
		let secp = secp.lock();
		let sig = &self.excess_sig;
		// Verify aggsig directly in libsecp
		let pubkey = &self.excess.to_pubkey(&secp)?;
		if !secp::aggsig::verify_single(
			&secp,
			&sig,
			&self.msg_to_sign()?,
			None,
			&pubkey,
			Some(&pubkey),
			None,
			false,
		) {
			return Err(Error::IncorrectSignature);
		}
		Ok(())
	}

	/// Build an empty tx kernel with zero values.
	pub fn empty() -> TxKernel {
		TxKernel {
			features: KernelFeatures::DEFAULT_KERNEL,
			fee: 0,
			lock_height: 0,
			excess: Commitment::from_vec(vec![0; 33]),
			excess_sig: secp::Signature::from_raw_data(&[0; 64]).unwrap(),
		}
	}

	/// Builds a new tx kernel with the provided fee.
	pub fn with_fee(self, fee: u64) -> TxKernel {
		TxKernel { fee, ..self }
	}

	/// Builds a new tx kernel with the provided lock_height.
	pub fn with_lock_height(self, lock_height: u64) -> TxKernel {
		TxKernel {
			lock_height,
			..self
		}
	}
}

/// Wrapper around a tx kernel used when maintaining them in the MMR.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct TxKernelEntry {
	/// The underlying tx kernel.
	pub kernel: TxKernel,
}

impl Writeable for TxKernelEntry {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		ser_multiwrite!(
			writer,
			[write_u8, self.kernel.features.bits()],
			[write_u64, self.kernel.fee],
			[write_u64, self.kernel.lock_height],
			[write_fixed_bytes, &self.kernel.excess]
		);
		self.kernel.excess_sig.write(writer)?;
		Ok(())
	}
}

impl Readable for TxKernelEntry {
	fn read(reader: &mut Reader) -> Result<TxKernelEntry, ser::Error> {
		let features =
			KernelFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?;
		let kernel = TxKernel {
			features: features,
			fee: reader.read_u64()?,
			lock_height: reader.read_u64()?,
			excess: Commitment::read(reader)?,
			excess_sig: secp::Signature::read(reader)?,
		};
		Ok(TxKernelEntry { kernel })
	}
}

impl TxKernelEntry {
	/// The excess on the underlying tx kernel.
	pub fn excess(&self) -> Commitment {
		self.kernel.excess
	}

	/// Verify the underlying tx kernel.
	pub fn verify(&self) -> Result<(), Error> {
		self.kernel.verify()
	}
}

impl From<TxKernel> for TxKernelEntry {
	fn from(kernel: TxKernel) -> Self {
		TxKernelEntry { kernel }
	}
}

impl FixedLength for TxKernelEntry {
	const LEN: usize = 17 // features plus fee and lock_height
		+ secp::constants::PEDERSEN_COMMITMENT_SIZE
		+ secp::constants::AGG_SIGNATURE_SIZE;
}

/// TransactionBody is a common abstraction for transaction and block
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct TransactionBody {
	/// List of inputs spent by the transaction.
	pub inputs: Vec<Input>,
	/// List of outputs the transaction produces.
	pub outputs: Vec<Output>,
	/// List of kernels that make up this transaction (usually a single kernel).
	pub kernels: Vec<TxKernel>,
}

/// PartialEq
impl PartialEq for TransactionBody {
	fn eq(&self, l: &TransactionBody) -> bool {
		self.inputs == l.inputs && self.outputs == l.outputs && self.kernels == l.kernels
	}
}

/// Implementation of Writeable for a body, defines how to
/// write the body as binary.
impl Writeable for TransactionBody {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		ser_multiwrite!(
			writer,
			[write_u64, self.inputs.len() as u64],
			[write_u64, self.outputs.len() as u64],
			[write_u64, self.kernels.len() as u64]
		);

		self.inputs.write(writer)?;
		self.outputs.write(writer)?;
		self.kernels.write(writer)?;

		Ok(())
	}
}

/// Implementation of Readable for a body, defines how to read a
/// body from a binary stream.
impl Readable for TransactionBody {
	fn read(reader: &mut Reader) -> Result<TransactionBody, ser::Error> {
		let (input_len, output_len, kernel_len) =
			ser_multiread!(reader, read_u64, read_u64, read_u64);

		// quick block weight check before proceeding
		let tx_block_weight =
			TransactionBody::weight(input_len as usize, output_len as usize, kernel_len as usize)
				as usize;

		if tx_block_weight > consensus::MAX_BLOCK_WEIGHT {
			return Err(ser::Error::TooLargeReadErr);
		}

		let inputs = read_multi(reader, input_len)?;
		let outputs = read_multi(reader, output_len)?;
		let kernels = read_multi(reader, kernel_len)?;

		// Initialize tx body and verify everything is sorted.
		let body = TransactionBody::init(inputs, outputs, kernels, true)
			.map_err(|_| ser::Error::CorruptedData)?;

		Ok(body)
	}
}

impl Committed for TransactionBody {
	fn inputs_committed(&self) -> Vec<Commitment> {
		self.inputs.iter().map(|x| x.commitment()).collect()
	}

	fn outputs_committed(&self) -> Vec<Commitment> {
		self.outputs.iter().map(|x| x.commitment()).collect()
	}

	fn kernels_committed(&self) -> Vec<Commitment> {
		self.kernels.iter().map(|x| x.excess()).collect()
	}
}

impl Default for TransactionBody {
	fn default() -> TransactionBody {
		TransactionBody::empty()
	}
}

impl TransactionBody {
	/// Creates a new empty transaction (no inputs or outputs, zero fee).
	pub fn empty() -> TransactionBody {
		TransactionBody {
			inputs: vec![],
			outputs: vec![],
			kernels: vec![],
		}
	}

	/// Sort the inputs|outputs|kernels.
	pub fn sort(&mut self) {
		self.inputs.sort();
		self.outputs.sort();
		self.kernels.sort();
	}

	/// Creates a new transaction body initialized with
	/// the provided inputs, outputs and kernels.
	/// Guarantees inputs, outputs, kernels are sorted lexicographically.
	pub fn init(
		inputs: Vec<Input>,
		outputs: Vec<Output>,
		kernels: Vec<TxKernel>,
		verify_sorted: bool,
	) -> Result<TransactionBody, Error> {
		let body = TransactionBody {
			inputs,
			outputs,
			kernels,
		};

		if verify_sorted {
			// If we are verifying sort order then verify and
			// return an error if not sorted lexicographically.
			body.verify_sorted()?;
			Ok(body)
		} else {
			// If we are not verifying sort order then sort in place and return.
			let mut body = body;
			body.sort();
			Ok(body)
		}
	}

	/// Builds a new body with the provided inputs added. Existing
	/// inputs, if any, are kept intact.
	/// Sort order is maintained.
	pub fn with_input(self, input: Input) -> TransactionBody {
		let mut new_ins = self.inputs;
		new_ins.push(input);
		new_ins.sort();
		TransactionBody {
			inputs: new_ins,
			..self
		}
	}

	/// Builds a new TransactionBody with the provided output added. Existing
	/// outputs, if any, are kept intact.
	/// Sort order is maintained.
	pub fn with_output(self, output: Output) -> TransactionBody {
		let mut new_outs = self.outputs;
		new_outs.push(output);
		new_outs.sort();
		TransactionBody {
			outputs: new_outs,
			..self
		}
	}

	/// Builds a new TransactionBody with the provided kernel added. Existing
	/// kernels, if any, are kept intact.
	/// Sort order is maintained.
	pub fn with_kernel(self, kernel: TxKernel) -> TransactionBody {
		let mut new_kerns = self.kernels;
		new_kerns.push(kernel);
		new_kerns.sort();
		TransactionBody {
			kernels: new_kerns,
			..self
		}
	}

	/// Total fee for a TransactionBody is the sum of fees of all kernels.
	fn fee(&self) -> u64 {
		self.kernels
			.iter()
			.fold(0, |acc, ref x| acc.saturating_add(x.fee))
	}

	fn overage(&self) -> i64 {
		self.fee() as i64
	}

	/// Calculate transaction weight
	pub fn body_weight(&self) -> u32 {
		TransactionBody::weight(self.inputs.len(), self.outputs.len(), self.kernels.len())
	}

	/// Calculate weight of transaction using block weighing
	pub fn body_weight_as_block(&self) -> u32 {
		TransactionBody::weight_as_block(self.inputs.len(), self.outputs.len(), self.kernels.len())
	}

	/// Calculate transaction weight from transaction details. This is non
	/// consensus critical and compared to block weight, incentivizes spending
	/// more outputs (to lower the fee).
	pub fn weight(input_len: usize, output_len: usize, kernel_len: usize) -> u32 {
		let body_weight = -(input_len as i32) + (4 * output_len as i32) + kernel_len as i32;
		max(body_weight, 1) as u32
	}

	/// Calculate transaction weight using block weighing from transaction
	/// details. Consensus critical and uses consensus weight values.
	pub fn weight_as_block(input_len: usize, output_len: usize, kernel_len: usize) -> u32 {
		(input_len * consensus::BLOCK_INPUT_WEIGHT
			+ output_len * consensus::BLOCK_OUTPUT_WEIGHT
			+ kernel_len * consensus::BLOCK_KERNEL_WEIGHT) as u32
	}

	/// Lock height of a body is the max lock height of the kernels.
	pub fn lock_height(&self) -> u64 {
		self.kernels
			.iter()
			.map(|x| x.lock_height)
			.max()
			.unwrap_or(0)
	}

	// Verify the body is not too big in terms of number of inputs|outputs|kernels.
	fn verify_weight(&self, with_reward: bool) -> Result<(), Error> {
		// if as_block check the body as if it was a block, with an additional output and
		// kernel for reward
		let reserve = if with_reward { 0 } else { 1 };
		let tx_block_weight = TransactionBody::weight_as_block(
			self.inputs.len(),
			self.outputs.len() + reserve,
			self.kernels.len() + reserve,
		) as usize;

		if tx_block_weight > consensus::MAX_BLOCK_WEIGHT {
			return Err(Error::TooHeavy);
		}
		Ok(())
	}

	// Verify that inputs|outputs|kernels are all sorted in lexicographical order.
	fn verify_sorted(&self) -> Result<(), Error> {
		self.inputs.verify_sort_order()?;
		self.outputs.verify_sort_order()?;
		self.kernels.verify_sort_order()?;
		Ok(())
	}

	// Verify that no input is spending an output from the same block.
	fn verify_cut_through(&self) -> Result<(), Error> {
		let mut out_set = HashSet::new();
		for out in &self.outputs {
			out_set.insert(out.commitment());
		}
		for inp in &self.inputs {
			if out_set.contains(&inp.commitment()) {
				return Err(Error::CutThrough);
			}
		}
		Ok(())
	}

	/// Verify we have no invalid outputs or kernels in the transaction
	/// due to invalid features.
	/// Specifically, a transaction cannot contain a coinbase output or a coinbase kernel.
	pub fn verify_features(&self) -> Result<(), Error> {
		self.verify_output_features()?;
		self.verify_kernel_features()?;
		Ok(())
	}

	// Verify we have no outputs tagged as COINBASE_OUTPUT.
	fn verify_output_features(&self) -> Result<(), Error> {
		if self
			.outputs
			.iter()
			.any(|x| x.features.contains(OutputFeatures::COINBASE_OUTPUT))
		{
			return Err(Error::InvalidOutputFeatures);
		}
		Ok(())
	}

	// Verify we have no kernels tagged as COINBASE_KERNEL.
	fn verify_kernel_features(&self) -> Result<(), Error> {
		if self
			.kernels
			.iter()
			.any(|x| x.features.contains(KernelFeatures::COINBASE_KERNEL))
		{
			return Err(Error::InvalidKernelFeatures);
		}
		Ok(())
	}

	/// "Lightweight" validation that we can perform quickly during read/deserialization.
	/// Subset of full validation that skips expensive verification steps, specifically -
	/// * rangeproof verification
	/// * kernel signature verification
	pub fn validate_read(&self, with_reward: bool) -> Result<(), Error> {
		self.verify_weight(with_reward)?;
		self.verify_sorted()?;
		self.verify_cut_through()?;
		Ok(())
	}

	/// Validates all relevant parts of a transaction body. Checks the
	/// excess value against the signature as well as range proofs for each
	/// output.
	pub fn validate(
		&self,
		with_reward: bool,
		verifier: Arc<RwLock<VerifierCache>>,
	) -> Result<(), Error> {
		self.validate_read(with_reward)?;

		// Find all the outputs that have not had their rangeproofs verified.
		let outputs = {
			let mut verifier = verifier.write();
			verifier.filter_rangeproof_unverified(&self.outputs)
		};

		// Now batch verify all those unverified rangeproofs
		if !outputs.is_empty() {
			let mut commits = vec![];
			let mut proofs = vec![];
			for x in &outputs {
				commits.push(x.commit);
				proofs.push(x.proof);
			}
			Output::batch_verify_proofs(&commits, &proofs)?;
		}

		// Find all the kernels that have not yet been verified.
		let kernels = {
			let mut verifier = verifier.write();
			verifier.filter_kernel_sig_unverified(&self.kernels)
		};

		// Verify the unverified tx kernels.
		// No ability to batch verify these right now
		// so just do them individually.
		for x in &kernels {
			x.verify()?;
		}

		// Cache the successful verification results for the new outputs and kernels.
		{
			let mut verifier = verifier.write();
			verifier.add_rangeproof_verified(outputs);
			verifier.add_kernel_sig_verified(kernels);
		}
		Ok(())
	}
}

/// A transaction
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct Transaction {
	/// The kernel "offset" k2
	/// excess is k1G after splitting the key k = k1 + k2
	pub offset: BlindingFactor,
	/// The transaction body - inputs/outputs/kernels
	body: TransactionBody,
}

/// PartialEq
impl PartialEq for Transaction {
	fn eq(&self, tx: &Transaction) -> bool {
		self.body == tx.body && self.offset == tx.offset
	}
}

impl Into<TransactionBody> for Transaction {
	fn into(self) -> TransactionBody {
		self.body
	}
}

/// Implementation of Writeable for a fully blinded transaction, defines how to
/// write the transaction as binary.
impl Writeable for Transaction {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		self.offset.write(writer)?;
		self.body.write(writer)?;
		Ok(())
	}
}

/// Implementation of Readable for a transaction, defines how to read a full
/// transaction from a binary stream.
impl Readable for Transaction {
	fn read(reader: &mut Reader) -> Result<Transaction, ser::Error> {
		let offset = BlindingFactor::read(reader)?;
		let body = TransactionBody::read(reader)?;
		let tx = Transaction { offset, body };

		// Now "lightweight" validation of the tx.
		// Treat any validation issues as data corruption.
		// An example of this would be reading a tx
		// that exceeded the allowed number of inputs.
		tx.validate_read().map_err(|_| ser::Error::CorruptedData)?;

		Ok(tx)
	}
}

impl Committed for Transaction {
	fn inputs_committed(&self) -> Vec<Commitment> {
		self.body.inputs_committed()
	}

	fn outputs_committed(&self) -> Vec<Commitment> {
		self.body.outputs_committed()
	}

	fn kernels_committed(&self) -> Vec<Commitment> {
		self.body.kernels_committed()
	}
}

impl Default for Transaction {
	fn default() -> Transaction {
		Transaction::empty()
	}
}

impl Transaction {
	/// Creates a new empty transaction (no inputs or outputs, zero fee).
	pub fn empty() -> Transaction {
		Transaction {
			offset: BlindingFactor::zero(),
			body: Default::default(),
		}
	}

	/// Creates a new transaction initialized with
	/// the provided inputs, outputs, kernels
	pub fn new(inputs: Vec<Input>, outputs: Vec<Output>, kernels: Vec<TxKernel>) -> Transaction {
		let offset = BlindingFactor::zero();

		// Initialize a new tx body and sort everything.
		let body =
			TransactionBody::init(inputs, outputs, kernels, false).expect("sorting, not verifying");

		Transaction { offset, body }
	}

	/// Creates a new transaction using this transaction as a template
	/// and with the specified offset.
	pub fn with_offset(self, offset: BlindingFactor) -> Transaction {
		Transaction { offset, ..self }
	}

	/// Builds a new transaction with the provided inputs added. Existing
	/// inputs, if any, are kept intact.
	/// Sort order is maintained.
	pub fn with_input(self, input: Input) -> Transaction {
		Transaction {
			body: self.body.with_input(input),
			..self
		}
	}

	/// Builds a new transaction with the provided output added. Existing
	/// outputs, if any, are kept intact.
	/// Sort order is maintained.
	pub fn with_output(self, output: Output) -> Transaction {
		Transaction {
			body: self.body.with_output(output),
			..self
		}
	}

	/// Builds a new transaction with the provided output added. Existing
	/// outputs, if any, are kept intact.
	/// Sort order is maintained.
	pub fn with_kernel(self, kernel: TxKernel) -> Transaction {
		Transaction {
			body: self.body.with_kernel(kernel),
			..self
		}
	}

	/// Get inputs
	pub fn inputs(&self) -> &Vec<Input> {
		&self.body.inputs
	}

	/// Get inputs mutable
	pub fn inputs_mut(&mut self) -> &mut Vec<Input> {
		&mut self.body.inputs
	}

	/// Get outputs
	pub fn outputs(&self) -> &Vec<Output> {
		&self.body.outputs
	}

	/// Get outputs mutable
	pub fn outputs_mut(&mut self) -> &mut Vec<Output> {
		&mut self.body.outputs
	}

	/// Get kernels
	pub fn kernels(&self) -> &Vec<TxKernel> {
		&self.body.kernels
	}

	/// Get kernels mut
	pub fn kernels_mut(&mut self) -> &mut Vec<TxKernel> {
		&mut self.body.kernels
	}

	/// Total fee for a transaction is the sum of fees of all kernels.
	pub fn fee(&self) -> u64 {
		self.body.fee()
	}

	/// Total overage across all kernels.
	pub fn overage(&self) -> i64 {
		self.body.overage()
	}

	/// Lock height of a transaction is the max lock height of the kernels.
	pub fn lock_height(&self) -> u64 {
		self.body.lock_height()
	}

	/// "Lightweight" validation that we can perform quickly during read/deserialization.
	/// Subset of full validation that skips expensive verification steps, specifically -
	/// * rangeproof verification (on the body)
	/// * kernel signature verification (on the body)
	/// * kernel sum verification
	pub fn validate_read(&self) -> Result<(), Error> {
		self.body.validate_read(false)?;
		self.body.verify_features()?;
		Ok(())
	}

	/// Validates all relevant parts of a fully built transaction. Checks the
	/// excess value against the signature as well as range proofs for each
	/// output.
	pub fn validate(&self, verifier: Arc<RwLock<VerifierCache>>) -> Result<(), Error> {
		self.body.validate(false, verifier)?;
		self.body.verify_features()?;
		self.verify_kernel_sums(self.overage(), self.offset)?;
		Ok(())
	}

	/// Calculate transaction weight
	pub fn tx_weight(&self) -> u32 {
		self.body.body_weight()
	}

	/// Calculate transaction weight as a block
	pub fn tx_weight_as_block(&self) -> u32 {
		self.body.body_weight_as_block()
	}

	/// Calculate transaction weight from transaction details
	pub fn weight(input_len: usize, output_len: usize, kernel_len: usize) -> u32 {
		TransactionBody::weight(input_len, output_len, kernel_len)
	}
}

/// Matches any output with a potential spending input, eliminating them
/// from the Vec. Provides a simple way to cut-through a block or aggregated
/// transaction. The elimination is stable with respect to the order of inputs
/// and outputs.
pub fn cut_through(inputs: &mut Vec<Input>, outputs: &mut Vec<Output>) -> Result<(), Error> {
	// assemble output commitments set, checking they're all unique
	let mut out_set = HashSet::new();
	let all_uniq = { outputs.iter().all(|o| out_set.insert(o.commitment())) };
	if !all_uniq {
		return Err(Error::AggregationError);
	}

	let in_set = inputs
		.iter()
		.map(|inp| inp.commitment())
		.collect::<HashSet<_>>();

	let to_cut_through = in_set.intersection(&out_set).collect::<HashSet<_>>();

	// filter and sort
	inputs.retain(|inp| !to_cut_through.contains(&inp.commitment()));
	outputs.retain(|out| !to_cut_through.contains(&out.commitment()));
	inputs.sort();
	outputs.sort();
	Ok(())
}

/// Aggregate a vec of txs into a multi-kernel tx with cut_through.
pub fn aggregate(mut txs: Vec<Transaction>) -> Result<Transaction, Error> {
	// convenience short-circuiting
	if txs.is_empty() {
		return Ok(Transaction::empty());
	} else if txs.len() == 1 {
		return Ok(txs.pop().unwrap());
	}

	let mut inputs: Vec<Input> = vec![];
	let mut outputs: Vec<Output> = vec![];
	let mut kernels: Vec<TxKernel> = vec![];

	// we will sum these together at the end to give us the overall offset for the
	// transaction
	let mut kernel_offsets: Vec<BlindingFactor> = vec![];

	for mut tx in txs {
		// we will sum these later to give a single aggregate offset
		kernel_offsets.push(tx.offset);

		inputs.append(&mut tx.body.inputs);
		outputs.append(&mut tx.body.outputs);
		kernels.append(&mut tx.body.kernels);
	}

	// Sort inputs and outputs during cut_through.
	cut_through(&mut inputs, &mut outputs)?;

	// Now sort kernels.
	kernels.sort();

	// now sum the kernel_offsets up to give us an aggregate offset for the
	// transaction
	let total_kernel_offset = committed::sum_kernel_offsets(kernel_offsets, vec![])?;

	// build a new aggregate tx from the following -
	//   * cut-through inputs
	//   * cut-through outputs
	//   * full set of tx kernels
	//   * sum of all kernel offsets
	let tx = Transaction::new(inputs, outputs, kernels).with_offset(total_kernel_offset);

	Ok(tx)
}

/// Attempt to deaggregate a multi-kernel transaction based on multiple
/// transactions
pub fn deaggregate(mk_tx: Transaction, txs: Vec<Transaction>) -> Result<Transaction, Error> {
	let mut inputs: Vec<Input> = vec![];
	let mut outputs: Vec<Output> = vec![];
	let mut kernels: Vec<TxKernel> = vec![];

	// we will subtract these at the end to give us the overall offset for the
	// transaction
	let mut kernel_offsets = vec![];

	let tx = aggregate(txs)?;

	for mk_input in mk_tx.body.inputs {
		if !tx.body.inputs.contains(&mk_input) && !inputs.contains(&mk_input) {
			inputs.push(mk_input);
		}
	}
	for mk_output in mk_tx.body.outputs {
		if !tx.body.outputs.contains(&mk_output) && !outputs.contains(&mk_output) {
			outputs.push(mk_output);
		}
	}
	for mk_kernel in mk_tx.body.kernels {
		if !tx.body.kernels.contains(&mk_kernel) && !kernels.contains(&mk_kernel) {
			kernels.push(mk_kernel);
		}
	}

	kernel_offsets.push(tx.offset);

	// now compute the total kernel offset
	let total_kernel_offset = {
		let secp = static_secp_instance();
		let secp = secp.lock();
		let mut positive_key = vec![mk_tx.offset]
			.into_iter()
			.filter(|x| *x != BlindingFactor::zero())
			.filter_map(|x| x.secret_key(&secp).ok())
			.collect::<Vec<_>>();
		let mut negative_keys = kernel_offsets
			.into_iter()
			.filter(|x| *x != BlindingFactor::zero())
			.filter_map(|x| x.secret_key(&secp).ok())
			.collect::<Vec<_>>();

		if positive_key.is_empty() && negative_keys.is_empty() {
			BlindingFactor::zero()
		} else {
			let sum = secp.blind_sum(positive_key, negative_keys)?;
			BlindingFactor::from_secret_key(sum)
		}
	};

	// Sorting them lexicographically
	inputs.sort();
	outputs.sort();
	kernels.sort();

	// Build a new tx from the above data.
	let tx = Transaction::new(inputs, outputs, kernels).with_offset(total_kernel_offset);
	Ok(tx)
}

/// A transaction input.
///
/// Primarily a reference to an output being spent by the transaction.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct Input {
	/// The features of the output being spent.
	/// We will check maturity for coinbase output.
	pub features: OutputFeatures,
	/// The commit referencing the output being spent.
	pub commit: Commitment,
}

hashable_ord!(Input);

impl ::std::hash::Hash for Input {
	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
		let mut vec = Vec::new();
		ser::serialize(&mut vec, &self).expect("serialization failed");
		::std::hash::Hash::hash(&vec, state);
	}
}

/// Implementation of Writeable for a transaction Input, defines how to write
/// an Input as binary.
impl Writeable for Input {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		writer.write_u8(self.features.bits())?;
		self.commit.write(writer)?;
		Ok(())
	}
}

/// Implementation of Readable for a transaction Input, defines how to read
/// an Input from a binary stream.
impl Readable for Input {
	fn read(reader: &mut Reader) -> Result<Input, ser::Error> {
		let features =
			OutputFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?;

		let commit = Commitment::read(reader)?;

		Ok(Input::new(features, commit))
	}
}

/// The input for a transaction, which spends a pre-existing unspent output.
/// The input commitment is a reproduction of the commitment of the output
/// being spent. Input must also provide the original output features and the
/// hash of the block the output originated from.
impl Input {
	/// Build a new input from the data required to identify and verify an
	/// output being spent.
	pub fn new(features: OutputFeatures, commit: Commitment) -> Input {
		Input { features, commit }
	}

	/// The input commitment which _partially_ identifies the output being
	/// spent. In the presence of a fork we need additional info to uniquely
	/// identify the output. Specifically the block hash (to correctly
	/// calculate lock_height for coinbase outputs).
	pub fn commitment(&self) -> Commitment {
		self.commit
	}
}

bitflags! {
	/// Options for block validation
	#[derive(Serialize, Deserialize)]
	pub struct OutputFeatures: u8 {
		/// No flags
		const DEFAULT_OUTPUT = 0b00000000;
		/// Output is a coinbase output, must not be spent until maturity
		const COINBASE_OUTPUT = 0b00000001;
	}
}

/// Output for a transaction, defining the new ownership of coins that are being
/// transferred. The commitment is a blinded value for the output while the
/// range proof guarantees the commitment includes a positive value without
/// overflow and the ownership of the private key. The switch commitment hash
/// provides future-proofing against quantum-based attacks, as well as providing
/// wallet implementations with a way to identify their outputs for wallet
/// reconstruction.
#[derive(Debug, Copy, Clone, Serialize, Deserialize)]
pub struct Output {
	/// Options for an output's structure or use
	pub features: OutputFeatures,
	/// The homomorphic commitment representing the output amount
	pub commit: Commitment,
	/// A proof that the commitment is in the right range
	pub proof: RangeProof,
}

hashable_ord!(Output);

impl ::std::hash::Hash for Output {
	fn hash<H: ::std::hash::Hasher>(&self, state: &mut H) {
		let mut vec = Vec::new();
		ser::serialize(&mut vec, &self).expect("serialization failed");
		::std::hash::Hash::hash(&vec, state);
	}
}

/// Implementation of Writeable for a transaction Output, defines how to write
/// an Output as binary.
impl Writeable for Output {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		writer.write_u8(self.features.bits())?;
		self.commit.write(writer)?;
		// The hash of an output doesn't include the range proof, which
		// is committed to separately
		if writer.serialization_mode() != ser::SerializationMode::Hash {
			writer.write_bytes(&self.proof)?
		}
		Ok(())
	}
}

/// Implementation of Readable for a transaction Output, defines how to read
/// an Output from a binary stream.
impl Readable for Output {
	fn read(reader: &mut Reader) -> Result<Output, ser::Error> {
		let features =
			OutputFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?;

		Ok(Output {
			features,
			commit: Commitment::read(reader)?,
			proof: RangeProof::read(reader)?,
		})
	}
}

/// We can build an Output MMR but store instances of OutputIdentifier in the MMR data file.
impl PMMRable for Output {
	type E = OutputIdentifier;

	fn as_elmt(self) -> Self::E {
		self.into()
	}
}

impl Output {
	/// Commitment for the output
	pub fn commitment(&self) -> Commitment {
		self.commit
	}

	/// Range proof for the output
	pub fn proof(&self) -> RangeProof {
		self.proof
	}

	/// Validates the range proof using the commitment
	pub fn verify_proof(&self) -> Result<(), Error> {
		let secp = static_secp_instance();
		secp.lock()
			.verify_bullet_proof(self.commit, self.proof, None)?;
		Ok(())
	}

	/// Batch validates the range proofs using the commitments
	pub fn batch_verify_proofs(
		commits: &Vec<Commitment>,
		proofs: &Vec<RangeProof>,
	) -> Result<(), Error> {
		let secp = static_secp_instance();
		secp.lock()
			.verify_bullet_proof_multi(commits.clone(), proofs.clone(), None)?;
		Ok(())
	}
}

/// An output_identifier can be build from either an input _or_ an output and
/// contains everything we need to uniquely identify an output being spent.
/// Needed because it is not sufficient to pass a commitment around.
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
pub struct OutputIdentifier {
	/// Output features (coinbase vs. regular transaction output)
	/// We need to include this when hashing to ensure coinbase maturity can be
	/// enforced.
	pub features: OutputFeatures,
	/// Output commitment
	pub commit: Commitment,
}

impl OutputIdentifier {
	/// Build a new output_identifier.
	pub fn new(features: OutputFeatures, commit: &Commitment) -> OutputIdentifier {
		OutputIdentifier {
			features,
			commit: *commit,
		}
	}

	/// Our commitment.
	pub fn commitment(&self) -> Commitment {
		self.commit
	}

	/// Build an output_identifier from an existing output.
	pub fn from_output(output: &Output) -> OutputIdentifier {
		OutputIdentifier {
			features: output.features,
			commit: output.commit,
		}
	}

	/// Converts this identifier to a full output, provided a RangeProof
	pub fn into_output(self, proof: RangeProof) -> Output {
		Output {
			proof,
			features: self.features,
			commit: self.commit,
		}
	}

	/// Build an output_identifier from an existing input.
	pub fn from_input(input: &Input) -> OutputIdentifier {
		OutputIdentifier {
			features: input.features,
			commit: input.commit,
		}
	}

	/// convert an output_identifier to hex string format.
	pub fn to_hex(&self) -> String {
		format!(
			"{:b}{}",
			self.features.bits(),
			util::to_hex(self.commit.0.to_vec()),
		)
	}
}

impl FixedLength for OutputIdentifier {
	const LEN: usize = 1 + secp::constants::PEDERSEN_COMMITMENT_SIZE;
}

impl Writeable for OutputIdentifier {
	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ser::Error> {
		writer.write_u8(self.features.bits())?;
		self.commit.write(writer)?;
		Ok(())
	}
}

impl Readable for OutputIdentifier {
	fn read(reader: &mut Reader) -> Result<OutputIdentifier, ser::Error> {
		let features =
			OutputFeatures::from_bits(reader.read_u8()?).ok_or(ser::Error::CorruptedData)?;
		Ok(OutputIdentifier {
			features,
			commit: Commitment::read(reader)?,
		})
	}
}

impl From<Output> for OutputIdentifier {
	fn from(out: Output) -> Self {
		OutputIdentifier {
			features: out.features,
			commit: out.commit,
		}
	}
}

/// Construct msg from tx fee and lock_height.
pub fn kernel_sig_msg(fee: u64, lock_height: u64) -> Result<secp::Message, Error> {
	let mut bytes = [0; 32];
	BigEndian::write_u64(&mut bytes[16..24], fee);
	BigEndian::write_u64(&mut bytes[24..], lock_height);
	let msg = secp::Message::from_slice(&bytes)?;
	Ok(msg)
}

#[cfg(test)]
mod test {
	use super::*;
	use core::hash::Hash;
	use core::id::{ShortId, ShortIdentifiable};
	use keychain::{ExtKeychain, Keychain};
	use util::secp;

	#[test]
	fn test_kernel_ser_deser() {
		let keychain = ExtKeychain::from_random_seed().unwrap();
		let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);
		let commit = keychain.commit(5, &key_id).unwrap();

		// just some bytes for testing ser/deser
		let sig = secp::Signature::from_raw_data(&[0; 64]).unwrap();

		let kernel = TxKernel {
			features: KernelFeatures::DEFAULT_KERNEL,
			lock_height: 0,
			excess: commit,
			excess_sig: sig.clone(),
			fee: 10,
		};

		let mut vec = vec![];
		ser::serialize(&mut vec, &kernel).expect("serialized failed");
		let kernel2: TxKernel = ser::deserialize(&mut &vec[..]).unwrap();
		assert_eq!(kernel2.features, KernelFeatures::DEFAULT_KERNEL);
		assert_eq!(kernel2.lock_height, 0);
		assert_eq!(kernel2.excess, commit);
		assert_eq!(kernel2.excess_sig, sig.clone());
		assert_eq!(kernel2.fee, 10);

		// now check a kernel with lock_height serialize/deserialize correctly
		let kernel = TxKernel {
			features: KernelFeatures::DEFAULT_KERNEL,
			lock_height: 100,
			excess: commit,
			excess_sig: sig.clone(),
			fee: 10,
		};

		let mut vec = vec![];
		ser::serialize(&mut vec, &kernel).expect("serialized failed");
		let kernel2: TxKernel = ser::deserialize(&mut &vec[..]).unwrap();
		assert_eq!(kernel2.features, KernelFeatures::DEFAULT_KERNEL);
		assert_eq!(kernel2.lock_height, 100);
		assert_eq!(kernel2.excess, commit);
		assert_eq!(kernel2.excess_sig, sig.clone());
		assert_eq!(kernel2.fee, 10);
	}

	#[test]
	fn commit_consistency() {
		let keychain = ExtKeychain::from_seed(&[0; 32]).unwrap();
		let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);

		let commit = keychain.commit(1003, &key_id).unwrap();
		let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);

		let commit_2 = keychain.commit(1003, &key_id).unwrap();

		assert!(commit == commit_2);
	}

	#[test]
	fn input_short_id() {
		let keychain = ExtKeychain::from_seed(&[0; 32]).unwrap();
		let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);
		let commit = keychain.commit(5, &key_id).unwrap();

		let input = Input {
			features: OutputFeatures::DEFAULT_OUTPUT,
			commit: commit,
		};

		let block_hash =
			Hash::from_hex("3a42e66e46dd7633b57d1f921780a1ac715e6b93c19ee52ab714178eb3a9f673")
				.unwrap();

		let nonce = 0;

		let short_id = input.short_id(&block_hash, nonce);
		assert_eq!(short_id, ShortId::from_hex("df31d96e3cdb").unwrap());

		// now generate the short_id for a *very* similar output (single feature flag
		// different) and check it generates a different short_id
		let input = Input {
			features: OutputFeatures::COINBASE_OUTPUT,
			commit: commit,
		};

		let short_id = input.short_id(&block_hash, nonce);
		assert_eq!(short_id, ShortId::from_hex("784fc5afd5d9").unwrap());
	}
}
