// Copyright 2017 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.

//! The primary module containing the implementations of the transaction pool
//! and its top-level members.

use std::vec::Vec;
use std::collections::HashMap;
use std::iter::Iterator;
use std::fmt;

use secp::pedersen::Commitment;

pub use graph;

use core::core::block;
use core::core::transaction;
use core::core::hash;

/// Tranasction pool configuration
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct PoolConfig {
	/// Base fee for a transaction to be accepted by the pool. The transaction
	/// weight is computed from its number of inputs, outputs and kernels and
	/// multipled by the base fee to compare to the actual transaction fee.
	#[serde="default_accept_fee_base"]
	pub accept_fee_base: u64,

	/// Maximum capacity of the pool in number of transactions
	#[serde="default_max_pool_size"]
	pub max_pool_size: usize,
}

impl Default for PoolConfig {
	fn default() -> PoolConfig {
		PoolConfig {
			accept_fee_base: default_accept_fee_base(),
			max_pool_size: default_max_pool_size(),
		}
	}
}

fn default_accept_fee_base() -> u64 { 10 }
fn default_max_pool_size() -> usize { 50_000 }

/// Placeholder: the data representing where we heard about a tx from.
///
/// Used to make decisions based on transaction acceptance priority from
/// various sources. For example, a node may want to bypass pool size
/// restrictions when accepting a transaction from a local wallet.
///
/// Most likely this will evolve to contain some sort of network identifier,
/// once we get a better sense of what transaction building might look like.
pub struct TxSource {
	/// Human-readable name used for logging and errors.
	pub debug_name: String,
	/// Unique identifier used to distinguish this peer from others.
	pub identifier: String,
}

/// This enum describes the parent for a given input of a transaction.
#[derive(Clone)]
pub enum Parent {
	Unknown,
	BlockTransaction { output: transaction::Output },
	PoolTransaction { tx_ref: hash::Hash },
	AlreadySpent { other_tx: hash::Hash },
}

impl fmt::Debug for Parent {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			&Parent::Unknown => write!(f, "Parent: Unknown"),
			&Parent::BlockTransaction { output: _ } => write!(f, "Parent: Block Transaction"),
			&Parent::PoolTransaction { tx_ref: x } => {
				write!(f, "Parent: Pool Transaction ({:?})", x)
			}
			&Parent::AlreadySpent { other_tx: x } => write!(f, "Parent: Already Spent By {:?}", x),
		}
	}
}

// TODO document this enum more accurately
/// Enum of errors
#[derive(Debug)]
pub enum PoolError {
	/// An invalid pool entry
	Invalid,
	/// An entry already in the pool
	AlreadyInPool,
	/// A duplicate output
	DuplicateOutput {
		/// The other transaction
		other_tx: Option<hash::Hash>,
		/// Is in chain?
		in_chain: bool,
		/// The output
		output: Commitment,
	},
	/// A double spend
	DoubleSpend {
		/// The other transaction
		other_tx: hash::Hash,
		/// The spent output
		spent_output: Commitment,
	},
	/// Attempt to spend an output before it matures
	/// lock_height must not exceed current block height
	ImmatureCoinbase {
		/// The block header of the block containing the output
		header: block::BlockHeader,
		/// The unspent output
		output: Commitment,
	},
	/// Attempt to add a transaction to the pool with lock_height
	/// greater than height of current block
	ImmatureTransaction {
		/// The lock height of the invalid transaction
		lock_height: u64,
	},
	/// An orphan successfully added to the orphans set
	OrphanTransaction,
	/// TODO - wip, just getting imports working, remove this and use more
	/// specific errors
	GenericPoolError,
	/// TODO - is this the right level of abstraction for pool errors?
	OutputNotFound,
	/// TODO - is this the right level of abstraction for pool errors?
	OutputSpent,
	/// Transaction pool is over capacity, can't accept more transactions
	OverCapacity,
	/// Transaction fee is too low given its weight
	LowFeeTransaction(u64),
}

/// Interface that the pool requires from a blockchain implementation.
pub trait BlockChain {
	/// Get an unspent output by its commitment. Will return None if the output
	/// is spent or if it doesn't exist. The blockchain is expected to produce
	/// a result with its current view of the most worked chain, ignoring
	/// orphans, etc.
	fn get_unspent(&self, output_ref: &Commitment) -> Result<transaction::Output, PoolError>;

	/// Get the block header by output commitment (needed for spending coinbase
	/// after n blocks)
	fn get_block_header_by_output_commit(
		&self,
		commit: &Commitment,
	) -> Result<block::BlockHeader, PoolError>;

	/// Get the block header at the head
	fn head_header(&self) -> Result<block::BlockHeader, PoolError>;
}

/// Pool contains the elements of the graph that are connected, in full, to
/// the blockchain.
/// Reservations of outputs by orphan transactions (not fully connected) are
/// not respected.
/// Spending references (input -> output) exist in two structures: internal
/// graph references are contained in the pool edge sets, while references
/// sourced from the blockchain's UTXO set are contained in the
/// blockchain_connections set.
/// Spent by references (output-> input) exist in two structures: pool-pool
/// connections are in the pool edge set, while unspent (dangling) references
/// exist in the available_outputs set.
pub struct Pool {
	graph: graph::DirectedGraph,

	// available_outputs are unspent outputs of the current pool set,
	// maintained as edges with empty destinations, keyed by the
	// output's hash.
	available_outputs: HashMap<Commitment, graph::Edge>,

	// Consumed blockchain utxo's are kept in a separate map.
	consumed_blockchain_outputs: HashMap<Commitment, graph::Edge>,
}

impl Pool {
	pub fn empty() -> Pool {
		Pool {
			graph: graph::DirectedGraph::empty(),
			available_outputs: HashMap::new(),
			consumed_blockchain_outputs: HashMap::new(),
		}
	}

	/// Given an output, check if a spending reference (input -> output)
	/// already exists in the pool.
	/// Returns the transaction (kernel) hash corresponding to the conflicting
	/// transaction
	pub fn check_double_spend(&self, o: &transaction::Output) -> Option<hash::Hash> {
		self.graph
			.get_edge_by_commitment(&o.commitment())
			.or(self.consumed_blockchain_outputs.get(&o.commitment()))
			.map(|x| x.destination_hash().unwrap())
	}


	pub fn get_blockchain_spent(&self, c: &Commitment) -> Option<&graph::Edge> {
		self.consumed_blockchain_outputs.get(c)
	}

	pub fn add_pool_transaction(
		&mut self,
		pool_entry: graph::PoolEntry,
		mut blockchain_refs: Vec<graph::Edge>,
		pool_refs: Vec<graph::Edge>,
		mut new_unspents: Vec<graph::Edge>,
	) {

		// Removing consumed available_outputs
		for new_edge in &pool_refs {
			// All of these should correspond to an existing unspent
			assert!(
				self.available_outputs
					.remove(&new_edge.output_commitment())
					.is_some()
			);
		}

		// Accounting for consumed blockchain outputs
		for new_blockchain_edge in blockchain_refs.drain(..) {
			self.consumed_blockchain_outputs.insert(
				new_blockchain_edge
					.output_commitment(),
				new_blockchain_edge,
			);
		}

		// Adding the transaction to the vertices list along with internal
		// pool edges
		self.graph.add_entry(pool_entry, pool_refs);

		// Adding the new unspents to the unspent map
		for unspent_output in new_unspents.drain(..) {
			self.available_outputs.insert(
				unspent_output.output_commitment(),
				unspent_output,
			);
		}
	}

	pub fn remove_pool_transaction(
		&mut self,
		tx: &transaction::Transaction,
		marked_txs: &HashMap<hash::Hash, ()>,
	) {

		self.graph.remove_vertex(graph::transaction_identifier(tx));

		for input in tx.inputs.iter().map(|x| x.commitment()) {
			match self.graph.remove_edge_by_commitment(&input) {
				Some(x) => {
					if !marked_txs.contains_key(&x.source_hash().unwrap()) {
						self.available_outputs.insert(
							x.output_commitment(),
							x.with_destination(None),
						);
					}
				}
				None => {
					self.consumed_blockchain_outputs.remove(&input);
				}
			};
		}

		for output in tx.outputs.iter().map(|x| x.commitment()) {
			match self.graph.remove_edge_by_commitment(&output) {
				Some(x) => {
					if !marked_txs.contains_key(&x.destination_hash().unwrap()) {

						self.consumed_blockchain_outputs.insert(
							x.output_commitment(),
							x.with_source(None),
						);
					}
				}
				None => {
					self.available_outputs.remove(&output);
				}
			};
		}
	}

	/// Simplest possible implementation: just return the roots
	pub fn get_mineable_transactions(&self, num_to_fetch: u32) -> Vec<hash::Hash> {
		let mut roots = self.graph.get_roots();
		roots.truncate(num_to_fetch as usize);
		roots
	}
}

impl TransactionGraphContainer for Pool {
	fn get_graph(&self) -> &graph::DirectedGraph {
		&self.graph
	}
	fn get_available_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.available_outputs.get(output)
	}
	fn get_external_spent_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.consumed_blockchain_outputs.get(output)
	}
	fn get_internal_spent_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.graph.get_edge_by_commitment(output)
	}
}

/// Orphans contains the elements of the transaction graph that have not been
/// connected in full to the blockchain.
pub struct Orphans {
	graph: graph::DirectedGraph,

	// available_outputs are unspent outputs of the current orphan set,
	// maintained as edges with empty destinations.
	available_outputs: HashMap<Commitment, graph::Edge>,

	// missing_outputs are spending references (inputs) with missing
	// corresponding outputs, maintained as edges with empty sources.
	missing_outputs: HashMap<Commitment, graph::Edge>,

	// pool_connections are bidirectional edges which connect to the pool
	// graph. They should map one-to-one to pool graph available_outputs.
	// pool_connections should not be viewed authoritatively, they are
	// merely informational until the transaction is officially connected to
	// the pool.
	pool_connections: HashMap<Commitment, graph::Edge>,
}

impl Orphans {
	pub fn empty() -> Orphans {
		Orphans {
			graph: graph::DirectedGraph::empty(),
			available_outputs: HashMap::new(),
			missing_outputs: HashMap::new(),
			pool_connections: HashMap::new(),
		}
	}

	/// Checks for a double spent output, given the hash of the output,
	/// ONLY in the data maintained by the orphans set. This includes links
	/// to the pool as well as links internal to orphan transactions.
	/// Returns the transaction hash corresponding to the conflicting
	/// transaction.
	pub fn check_double_spend(&self, o: transaction::Output) -> Option<hash::Hash> {
		self.graph
			.get_edge_by_commitment(&o.commitment())
			.or(self.pool_connections.get(&o.commitment()))
			.map(|x| x.destination_hash().unwrap())
	}

	pub fn get_unknown_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.missing_outputs.get(output)
	}

	/// Add an orphan transaction to the orphans set.
	///
	/// This method adds a given transaction (represented by the PoolEntry at
	/// orphan_entry) to the orphans set.
	///
	/// This method has no failure modes. All checks should be passed before
	/// entry.
	///
	/// Expects a HashMap at is_missing describing the indices of orphan_refs
	/// which correspond to missing (vs orphan-to-orphan) links.
	pub fn add_orphan_transaction(
		&mut self,
		orphan_entry: graph::PoolEntry,
		mut pool_refs: Vec<graph::Edge>,
		mut orphan_refs: Vec<graph::Edge>,
		is_missing: HashMap<usize, ()>,
		mut new_unspents: Vec<graph::Edge>,
	) {

		// Removing consumed available_outputs
		for (i, new_edge) in orphan_refs.drain(..).enumerate() {
			if is_missing.contains_key(&i) {
				self.missing_outputs.insert(
					new_edge.output_commitment(),
					new_edge,
				);
			} else {
				assert!(
					self.available_outputs
						.remove(&new_edge.output_commitment())
						.is_some()
				);
				self.graph.add_edge_only(new_edge);
			}
		}

		// Accounting for consumed blockchain and pool outputs
		for external_edge in pool_refs.drain(..) {
			self.pool_connections.insert(
				external_edge.output_commitment(),
				external_edge,
			);
		}

		// if missing_refs is the same length as orphan_refs, we have
		// no orphan-orphan links for this transaction and it is a
		// root transaction of the orphans set
		self.graph.add_vertex_only(
			orphan_entry,
			is_missing.len() == orphan_refs.len(),
		);


		// Adding the new unspents to the unspent map
		for unspent_output in new_unspents.drain(..) {
			self.available_outputs.insert(
				unspent_output.output_commitment(),
				unspent_output,
			);
		}
	}
}

impl TransactionGraphContainer for Orphans {
	fn get_graph(&self) -> &graph::DirectedGraph {
		&self.graph
	}
	fn get_available_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.available_outputs.get(output)
	}
	fn get_external_spent_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.pool_connections.get(output)
	}
	fn get_internal_spent_output(&self, output: &Commitment) -> Option<&graph::Edge> {
		self.graph.get_edge_by_commitment(output)
	}
}

/// Trait for types that embed a graph and connect to external state.
///
/// The types implementing this trait consist of a graph with nodes and edges
/// representing transactions and outputs, respectively. Outputs fall into one
/// of three categories:
/// 1) External spent: An output sourced externally consumed by a transaction
///     in this graph,
/// 2) Internal spent: An output produced by a transaction in this graph and
///     consumed by another transaction in this graph,
/// 3) [External] Unspent: An output produced by a transaction in this graph
///     that is not yet spent.
///
/// There is no concept of an external "spent by" reference (output produced by
/// a transaction in the graph spent by a transaction in another source), as
/// these references are expected to be maintained by descendent graph. Outputs
/// follow a heirarchy (Blockchain -> Pool -> Orphans) where each descendent
/// exists at a lower priority than their parent. An output consumed by a
/// child graph is marked as unspent in the parent graph and an external spent
/// in the child. This ensures that no descendent set must modify state in a
/// set of higher priority.
pub trait TransactionGraphContainer {
	/// Accessor for graph object
	fn get_graph(&self) -> &graph::DirectedGraph;
	/// Accessor for internal spents
	fn get_internal_spent_output(&self, output: &Commitment) -> Option<&graph::Edge>;
	/// Accessor for external unspents
	fn get_available_output(&self, output: &Commitment) -> Option<&graph::Edge>;
	/// Accessor for external spents
	fn get_external_spent_output(&self, output: &Commitment) -> Option<&graph::Edge>;

	/// Checks if the available_output set has the output at the given
	/// commitment
	fn has_available_output(&self, c: &Commitment) -> bool {
		self.get_available_output(c).is_some()
	}

	/// Checks if the pool has anything by this output already, between
	/// available outputs and internal ones.
	fn find_output(&self, c: &Commitment) -> Option<hash::Hash> {
		self.get_available_output(c)
			.or(self.get_internal_spent_output(c))
			.map(|x| x.source_hash().unwrap())
	}

	/// Search for a spent reference internal to the graph
	fn get_internal_spent(&self, c: &Commitment) -> Option<&graph::Edge> {
		self.get_internal_spent_output(c)
	}

	fn num_root_transactions(&self) -> usize {
		self.get_graph().len_roots()
	}

	fn num_transactions(&self) -> usize {
		self.get_graph().len_vertices()
	}

	fn num_output_edges(&self) -> usize {
		self.get_graph().len_edges()
	}
}