//! Traits and utility impls which allow other parts of rust-lightning to interact with the
//! blockchain - receiving notifications of new blocks and block disconnections and allowing
//! rust-lightning to request that you monitor the chain for certain outpoints/transactions.

use bitcoin::blockdata::block::{Block, BlockHeader};
use bitcoin::blockdata::transaction::Transaction;
use bitcoin::blockdata::script::Script;
use bitcoin::blockdata::constants::genesis_block;
use bitcoin::util::hash::Sha256dHash;
use bitcoin::network::constants::Network;
use bitcoin::network::serialize::BitcoinHash;

use util::logger::Logger;

use std::sync::{Mutex,Weak,MutexGuard,Arc};
use std::sync::atomic::{AtomicUsize, Ordering};
use std::collections::HashSet;

/// Used to give chain error details upstream
pub enum ChainError {
	/// Client doesn't support UTXO lookup (but the chain hash matches our genesis block hash)
	NotSupported,
	/// Chain isn't the one watched
	NotWatched,
	/// Tx doesn't exist or is unconfirmed
	UnknownTx,
}

/// An interface to request notification of certain scripts as they appear the
/// chain.
/// Note that all of the functions implemented here *must* be reentrant-safe (obviously - they're
/// called from inside the library in response to ChainListener events, P2P events, or timer
/// events).
pub trait ChainWatchInterface: Sync + Send {
	/// Provides a txid/random-scriptPubKey-in-the-tx which much be watched for.
	fn install_watch_tx(&self, txid: &Sha256dHash, script_pub_key: &Script);

	/// Provides an outpoint which must be watched for, providing any transactions which spend the
	/// given outpoint.
	fn install_watch_outpoint(&self, outpoint: (Sha256dHash, u32), out_script: &Script);

	/// Indicates that a listener needs to see all transactions.
	fn watch_all_txn(&self);

	/// Register the given listener to receive events. Only a weak pointer is provided and the
	/// registration should be freed once that pointer expires.
	fn register_listener(&self, listener: Weak<ChainListener>);
	//TODO: unregister

	/// Gets the script and value in satoshis for a given unspent transaction output given a
	/// short_channel_id (aka unspent_tx_output_identier). For BTC/tBTC channels the top three
	/// bytes are the block height, the next 3 the transaction index within the block, and the
	/// final two the output within the transaction.
	fn get_chain_utxo(&self, genesis_hash: Sha256dHash, unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError>;
}

/// An interface to send a transaction to the Bitcoin network.
pub trait BroadcasterInterface: Sync + Send {
	/// Sends a transaction out to (hopefully) be mined.
	fn broadcast_transaction(&self, tx: &Transaction);
}

/// A trait indicating a desire to listen for events from the chain
pub trait ChainListener: Sync + Send {
	/// Notifies a listener that a block was connected.
	/// Note that if a new transaction/outpoint is watched during a block_connected call, the block
	/// *must* be re-scanned with the new transaction/outpoints and block_connected should be
	/// called again with the same header and (at least) the new transactions.
	/// Note that if non-new transaction/outpoints may be registered during a call, a second call
	/// *must not* happen.
	/// This also means those counting confirmations using block_connected callbacks should watch
	/// for duplicate headers and not count them towards confirmations!
	fn block_connected(&self, header: &BlockHeader, height: u32, txn_matched: &[&Transaction], indexes_of_txn_matched: &[u32]);
	/// Notifies a listener that a block was disconnected.
	/// Unlike block_connected, this *must* never be called twice for the same disconnect event.
	fn block_disconnected(&self, header: &BlockHeader);
}

/// An enum that represents the speed at which we want a transaction to confirm used for feerate
/// estimation.
pub enum ConfirmationTarget {
	/// We are happy with this transaction confirming slowly when feerate drops some.
	Background,
	/// We'd like this transaction to confirm without major delay, but 12-18 blocks is fine.
	Normal,
	/// We'd like this transaction to confirm in the next few blocks.
	HighPriority,
}

/// A trait which should be implemented to provide feerate information on a number of time
/// horizons.
/// Note that all of the functions implemented here *must* be reentrant-safe (obviously - they're
/// called from inside the library in response to ChainListener events, P2P events, or timer
/// events).
pub trait FeeEstimator: Sync + Send {
	/// Gets estimated satoshis of fee required per 1000 Weight-Units. This translates to:
	///  * satoshis-per-byte * 250
	///  * ceil(satoshis-per-kbyte / 4)
	/// Must be no smaller than 253 (ie 1 satoshi-per-byte rounded up to ensure later round-downs
	/// don't put us below 1 satoshi-per-byte).
	fn get_est_sat_per_1000_weight(&self, confirmation_target: ConfirmationTarget) -> u64;
}

/// Utility for tracking registered txn/outpoints and checking for matches
pub struct ChainWatchedUtil {
	watch_all: bool,

	// We are more conservative in matching during testing to ensure everything matches *exactly*,
	// even though during normal runtime we take more optimized match approaches...
	#[cfg(test)]
	watched_txn: HashSet<(Sha256dHash, Script)>,
	#[cfg(not(test))]
	watched_txn: HashSet<Script>,

	watched_outpoints: HashSet<(Sha256dHash, u32)>,
}

impl ChainWatchedUtil {
	/// Constructs an empty (watches nothing) ChainWatchedUtil
	pub fn new() -> Self {
		Self {
			watch_all: false,
			watched_txn: HashSet::new(),
			watched_outpoints: HashSet::new(),
		}
	}

	/// Registers a tx for monitoring, returning true if it was a new tx and false if we'd already
	/// been watching for it.
	pub fn register_tx(&mut self, txid: &Sha256dHash, script_pub_key: &Script) -> bool {
		if self.watch_all { return false; }
		#[cfg(test)]
		{
			self.watched_txn.insert((txid.clone(), script_pub_key.clone()))
		}
		#[cfg(not(test))]
		{
			let _tx_unused = txid; // Its used in cfg(test), though
			self.watched_txn.insert(script_pub_key.clone())
		}
	}

	/// Registers an outpoint for monitoring, returning true if it was a new outpoint and false if
	/// we'd already been watching for it
	pub fn register_outpoint(&mut self, outpoint: (Sha256dHash, u32), _script_pub_key: &Script) -> bool {
		if self.watch_all { return false; }
		self.watched_outpoints.insert(outpoint)
	}

	/// Sets us to match all transactions, returning true if this is a new setting anf false if
	/// we'd already been set to match everything.
	pub fn watch_all(&mut self) -> bool {
		if self.watch_all { return false; }
		self.watch_all = true;
		true
	}

	/// Checks if a given transaction matches the current filter.
	pub fn does_match_tx(&self, tx: &Transaction) -> bool {
		if self.watch_all {
			return true;
		}
		for out in tx.output.iter() {
			#[cfg(test)]
			for &(ref txid, ref script) in self.watched_txn.iter() {
				if *script == out.script_pubkey {
					if tx.txid() == *txid {
						return true;
					}
				}
			}
			#[cfg(not(test))]
			for script in self.watched_txn.iter() {
				if *script == out.script_pubkey {
					return true;
				}
			}
		}
		for input in tx.input.iter() {
			for outpoint in self.watched_outpoints.iter() {
				let &(outpoint_hash, outpoint_index) = outpoint;
				if outpoint_hash == input.previous_output.txid && outpoint_index == input.previous_output.vout {
					return true;
				}
			}
		}
		false
	}
}

/// Utility to capture some common parts of ChainWatchInterface implementors.
/// Keeping a local copy of this in a ChainWatchInterface implementor is likely useful.
pub struct ChainWatchInterfaceUtil {
	network: Network,
	watched: Mutex<ChainWatchedUtil>,
	listeners: Mutex<Vec<Weak<ChainListener>>>,
	reentered: AtomicUsize,
	logger: Arc<Logger>,
}

/// Register listener
impl ChainWatchInterface for ChainWatchInterfaceUtil {
	fn install_watch_tx(&self, txid: &Sha256dHash, script_pub_key: &Script) {
		let mut watched = self.watched.lock().unwrap();
		if watched.register_tx(txid, script_pub_key) {
			self.reentered.fetch_add(1, Ordering::Relaxed);
		}
	}

	fn install_watch_outpoint(&self, outpoint: (Sha256dHash, u32), out_script: &Script) {
		let mut watched = self.watched.lock().unwrap();
		if watched.register_outpoint(outpoint, out_script) {
			self.reentered.fetch_add(1, Ordering::Relaxed);
		}
	}

	fn watch_all_txn(&self) {
		let mut watched = self.watched.lock().unwrap();
		if watched.watch_all() {
			self.reentered.fetch_add(1, Ordering::Relaxed);
		}
	}

	fn register_listener(&self, listener: Weak<ChainListener>) {
		let mut vec = self.listeners.lock().unwrap();
		vec.push(listener);
	}

	fn get_chain_utxo(&self, genesis_hash: Sha256dHash, _unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError> {
		if genesis_hash != genesis_block(self.network).header.bitcoin_hash() {
			return Err(ChainError::NotWatched);
		}
		Err(ChainError::NotSupported)
	}
}

impl ChainWatchInterfaceUtil {
	/// Creates a new ChainWatchInterfaceUtil for the given network
	pub fn new(network: Network, logger: Arc<Logger>) -> ChainWatchInterfaceUtil {
		ChainWatchInterfaceUtil {
			network: network,
			watched: Mutex::new(ChainWatchedUtil::new()),
			listeners: Mutex::new(Vec::new()),
			reentered: AtomicUsize::new(1),
			logger: logger,
		}
	}

	/// Notify listeners that a block was connected given a full, unfiltered block.
	/// Handles re-scanning the block and calling block_connected again if listeners register new
	/// watch data during the callbacks for you (see ChainListener::block_connected for more info).
	pub fn block_connected_with_filtering(&self, block: &Block, height: u32) {
		let mut reentered = true;
		while reentered {
			let mut matched = Vec::new();
			let mut matched_index = Vec::new();
			{
				let watched = self.watched.lock().unwrap();
				for (index, transaction) in block.txdata.iter().enumerate() {
					if self.does_match_tx_unguarded(transaction, &watched) {
						matched.push(transaction);
						matched_index.push(index as u32);
					}
				}
			}
			reentered = self.block_connected_checked(&block.header, height, matched.as_slice(), matched_index.as_slice());
		}
	}

	/// Notify listeners that a block was disconnected.
	pub fn block_disconnected(&self, header: &BlockHeader) {
		let listeners = self.listeners.lock().unwrap().clone();
		for listener in listeners.iter() {
			match listener.upgrade() {
				Some(arc) => arc.block_disconnected(header),
				None => ()
			}
		}
	}

	/// Notify listeners that a block was connected, given pre-filtered list of transactions in the
	/// block which matched the filter (probably using does_match_tx).
	/// Returns true if notified listeners registered additional watch data (implying that the
	/// block must be re-scanned and this function called again prior to further block_connected
	/// calls, see ChainListener::block_connected for more info).
	pub fn block_connected_checked(&self, header: &BlockHeader, height: u32, txn_matched: &[&Transaction], indexes_of_txn_matched: &[u32]) -> bool {
		let last_seen = self.reentered.load(Ordering::Relaxed);

		let listeners = self.listeners.lock().unwrap().clone();
		for listener in listeners.iter() {
			match listener.upgrade() {
				Some(arc) => arc.block_connected(header, height, txn_matched, indexes_of_txn_matched),
				None => ()
			}
		}
		return last_seen != self.reentered.load(Ordering::Relaxed);
	}

	/// Checks if a given transaction matches the current filter.
	pub fn does_match_tx(&self, tx: &Transaction) -> bool {
		let watched = self.watched.lock().unwrap();
		self.does_match_tx_unguarded (tx, &watched)
	}

	fn does_match_tx_unguarded(&self, tx: &Transaction, watched: &MutexGuard<ChainWatchedUtil>) -> bool {
		watched.does_match_tx(tx)
	}
}