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    use std::collections::HashMap;
    use std::collections::hash_map::Entry;
    use parking_lot::Mutex;
    use network::{ConsensusParams, Deployment};
    use hash::H256;
    use storage::{BlockHeaderProvider, BlockRef, BlockAncestors, BlockIterator};
    use timestamp::median_timestamp;

    #[derive(Debug, PartialEq, Clone, Copy)]
    enum ThresholdState {
    	Defined,
    	Started,
    	LockedIn,
    	Active,
    	Failed,
    }

    impl Default for ThresholdState {
    	fn default() -> Self {
    		ThresholdState::Defined
    	}
    }

    impl ThresholdState {
    	fn is_final(&self) -> bool {
    		match *self {
    			ThresholdState::Active | ThresholdState::Failed => true,
    			ThresholdState::Defined | ThresholdState::Started | ThresholdState::LockedIn => false,
    		}
    	}

    	fn is_active(&self) -> bool {
    		match *self {
    			ThresholdState::Active => true,
    			_ => false,
    		}
    	}
    }

    /// Threshold state at given point of time
    #[derive(Debug, Clone, Default)]
    struct DeploymentState {
    	/// Block number
    	block_number: u32,
    	/// Block hash
    	block_hash: H256,
    	/// Threshold state for given block
    	state: ThresholdState,
    }

    /// Last known deployment states
    type DeploymentStateCache = HashMap<&'static str, DeploymentState>;

    #[derive(Default, Debug)]
    pub struct Deployments {
    	cache: Mutex<DeploymentStateCache>,
    }

    pub struct BlockDeployments<'a> {
    	deployments: &'a Deployments,
    	number: u32,
    	headers: &'a BlockHeaderProvider,
    	consensus: &'a ConsensusParams,
    }

    impl Deployments {
    	pub fn new() -> Self {
    		Deployments::default()
    	}

    	/// Returns true if csv deployment is active
    	pub fn csv(&self, number: u32, headers: &BlockHeaderProvider, consensus: &ConsensusParams) -> bool {
    		match consensus.csv_deployment {
    			Some(csv) => {
    				let mut cache = self.cache.lock();
    				threshold_state(&mut cache, csv, number, headers, consensus.miner_confirmation_window, consensus.rule_change_activation_threshold).is_active()
    			},
    			None => false
    		}
    	}

    	/// Returns true if SegWit deployment is active
    	pub fn segwit(&self, number: u32, headers: &BlockHeaderProvider, consensus: &ConsensusParams) -> bool {
    		match consensus.segwit_deployment {
    			Some(segwit) => {
    				let mut cache = self.cache.lock();
    				threshold_state(&mut cache, segwit, number, headers, consensus.miner_confirmation_window, consensus.rule_change_activation_threshold).is_active()
    			},
    			None => false
    		}
    	}
    }

    impl<'a> BlockDeployments<'a> {
    	pub fn new(deployments: &'a Deployments, number: u32, headers: &'a BlockHeaderProvider, consensus: &'a ConsensusParams) -> Self {
    		BlockDeployments {
    			deployments: deployments,
    			number: number,
    			headers: headers,
    			consensus: consensus,
    		}
    	}

    	pub fn csv(&self) -> bool {
    		self.deployments.csv(self.number, self.headers, self.consensus)
    	}

    	pub fn segwit(&self) -> bool {
    		self.deployments.segwit(self.number, self.headers, self.consensus)
    	}
    }

    impl AsRef<Deployments> for Deployments {
    	fn as_ref(&self) -> &Deployments {
    		&self
    	}
    }

    impl<'a> AsRef<Deployments> for BlockDeployments<'a> {
    	fn as_ref(&self) -> &Deployments {
    		self.deployments
    	}
    }

    /// Calculates threshold state of given deployment
    fn threshold_state(cache: &mut DeploymentStateCache, deployment: Deployment, number: u32, headers: &BlockHeaderProvider, miner_confirmation_window: u32, rule_change_activation_threshold: u32) -> ThresholdState {
    	// deployments are checked using previous block index
    	if let Some(activation) = deployment.activation {
    		if activation <= number {
    			return ThresholdState::Active;
    		} else {
    			return ThresholdState::Defined;
    		}
    	}

    	// number is number of block which is currently validating
    	// => it is not in database
    	// we need to make all checks for previous blocks
    	let number = number.saturating_sub(1);

    	// get number of the first block in the period
    	let number = first_of_the_period(number, miner_confirmation_window);

    	let hash = match headers.block_header(BlockRef::Number(number)) {
    		Some(header) => header.hash(),
    		None => return ThresholdState::Defined,
    	};

    	match cache.entry(deployment.name) {
    		// by checking hash, we make sure we are on the same branch
    		Entry::Occupied(ref entry) if entry.get().block_number == number && entry.get().block_hash == hash => {
    			entry.get().state
    		},
    		// otherwise we need to recalculate threshold state
    		Entry::Occupied(mut entry) => {
    			let deployment_state = entry.get().clone();
    			if deployment_state.state.is_final() {
    				return deployment_state.state
    			}
    			let threshold_state = deployment_state.state;
    			let deployment_iter = ThresholdIterator::new(deployment, headers, number, miner_confirmation_window, rule_change_activation_threshold, threshold_state);
    			let state = deployment_iter.last().expect("iter must have at least one item");
    			let result = state.state;
    			entry.insert(state);
    			result
    		},
    		Entry::Vacant(entry) => {
    			let deployment_iter = ThresholdIterator::new(deployment, headers, miner_confirmation_window - 1, miner_confirmation_window, rule_change_activation_threshold, ThresholdState::Defined);
    			let state = deployment_iter.last().unwrap_or_else(|| DeploymentState {
    				block_number: number,
    				block_hash: hash,
    				state: ThresholdState::Defined,
    			});
    			let result = state.state;
    			entry.insert(state);
    			result
    		},
    	}
    }

    fn first_of_the_period(block: u32, miner_confirmation_window: u32) -> u32 {
    	if block < miner_confirmation_window - 1 {
    		0
    	} else {
    		block - ((block + 1) % miner_confirmation_window)
    	}
    }

    fn count_deployment_matches(block_number: u32, blocks: &BlockHeaderProvider, deployment: Deployment, window: u32) -> usize {
    	BlockAncestors::new(BlockRef::Number(block_number), blocks)
    		.take(window as usize)
    		.filter(|header| deployment.matches(header.version))
    		.count()
    }

    struct ThresholdIterator<'a> {
    	deployment: Deployment,
    	block_iterator: BlockIterator<'a>,
    	headers: &'a BlockHeaderProvider,
    	miner_confirmation_window: u32,
    	rule_change_activation_threshold: u32,
    	last_state: ThresholdState,
    }

    impl<'a> ThresholdIterator<'a> {
    	fn new(deployment: Deployment, headers: &'a BlockHeaderProvider, to_check: u32, miner_confirmation_window: u32, rule_change_activation_threshold: u32, state: ThresholdState) -> Self {
    		ThresholdIterator {
    			deployment: deployment,
    			block_iterator: BlockIterator::new(to_check, miner_confirmation_window, headers),
    			headers: headers,
    			miner_confirmation_window: miner_confirmation_window,
    			rule_change_activation_threshold: rule_change_activation_threshold,
    			last_state: state,
    		}
    	}
    }

    impl<'a> Iterator for ThresholdIterator<'a> {
    	type Item = DeploymentState;

    	fn next(&mut self) -> Option<Self::Item> {
    		let (block_number, header) = match self.block_iterator.next() {
    			Some(header) => header,
    			None => return None,
    		};

    		let median = median_timestamp(&header, self.headers);

    		match self.last_state {
    			ThresholdState::Defined => {
    				if median >= self.deployment.timeout {
    					self.last_state = ThresholdState::Failed;
    				} else if median >= self.deployment.start_time {
    					self.last_state = ThresholdState::Started;
    				}
    			},
    			ThresholdState::Started => {
    				if median >= self.deployment.timeout {
    					self.last_state = ThresholdState::Failed;
    				} else {
    					let count = count_deployment_matches(block_number, self.headers, self.deployment, self.miner_confirmation_window);
    					if count >= self.rule_change_activation_threshold as usize {
    						self.last_state = ThresholdState::LockedIn;
    					}
    				}
    			},
    			ThresholdState::LockedIn => {
    				self.last_state = ThresholdState::Active;
    			},
    			ThresholdState::Failed | ThresholdState::Active => {
    				return None
    			}
    		}

    		let result = DeploymentState {
    			block_number: block_number,
    			block_hash: header.hash(),
    			state: self.last_state,
    		};

    		Some(result)
    	}
    }

    #[cfg(test)]
    mod tests {
    	use std::sync::atomic::{AtomicUsize, Ordering};
    	use std::collections::HashMap;
    	use chain::BlockHeader;
    	use storage::{BlockHeaderProvider, BlockRef};
    	use network::Deployment;
    	use hash::H256;
    	use primitives::bytes::Bytes;
    	use super::{DeploymentStateCache, ThresholdState, first_of_the_period, threshold_state};

    	const MINER_CONFIRMATION_WINDOW: u32 = 1000;
    	const RULE_CHANGE_ACTIVATION_THRESHOLD: u32 = 900;

    	#[derive(Default)]
    	struct DeploymentHeaderProvider {
    		pub request_count: AtomicUsize,
    		pub by_height: Vec<BlockHeader>,
    		pub by_hash: HashMap<H256, usize>,
    	}

    	impl DeploymentHeaderProvider {
    		pub fn mine(&mut self, height: u32, time: u32, version: u32) {
    			let mut previous_header_hash = self.by_height.last().map(|h| h.previous_header_hash.clone()).unwrap_or(H256::default());
    			while self.by_height.len() < height as usize {
    				let header = BlockHeader {
    					version: version,
    					previous_header_hash: previous_header_hash,
    					merkle_root_hash: Default::default(),
    					time: time,
    					bits: 0.into(),
    					nonce: height,
    				};
    				previous_header_hash = header.hash();

    				self.by_height.push(header);
    				self.by_hash.insert(previous_header_hash.clone(), self.by_height.len() - 1);
    			}
    		}
    	}

    	impl BlockHeaderProvider for DeploymentHeaderProvider {
    		fn block_header_bytes(&self, _block_ref: BlockRef) -> Option<Bytes> {
    			unimplemented!()
    		}

    		fn block_header(&self, block_ref: BlockRef) -> Option<BlockHeader> {
    			self.request_count.fetch_add(1, Ordering::Relaxed);
    			match block_ref {
    				BlockRef::Number(height) => self.by_height.get(height as usize).cloned(),
    				BlockRef::Hash(hash) => self.by_hash.get(&hash).and_then(|height| self.by_height.get(*height)).cloned(),
    			}
    		}
    	}

    	fn make_test_time(height: u32) -> u32 {
    		1415926536 + 600 * height
    	}

    	fn prepare_deployments() -> (DeploymentStateCache, DeploymentHeaderProvider, Deployment) {
    		let (mut cache, headers, deployment) = (
    			DeploymentStateCache::default(),
    			DeploymentHeaderProvider::default(),
    			Deployment {
    				name: "test",
    				bit: 0,
    				start_time: make_test_time(10000),
    				timeout: make_test_time(20000),
    				activation: None,
    			},
    		);

    		assert_eq!(threshold_state(&mut cache, deployment, 0, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), ThresholdState::Defined);
    		assert_eq!(threshold_state(&mut DeploymentStateCache::default(), deployment, 0, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), ThresholdState::Defined);

    		(cache, headers, deployment)
    	}

    	#[test]
    	fn test_first_of_the_period() {
    		let window = 2016;
    		assert_eq!(0, first_of_the_period(0, window));
    		assert_eq!(0, first_of_the_period(1, window));
    		assert_eq!(0, first_of_the_period(2014, window));
    		assert_eq!(2015, first_of_the_period(2015, window));
    		assert_eq!(2015, first_of_the_period(2016, window));
    		assert_eq!(8063, first_of_the_period(8063, window));
    		assert_eq!(8063, first_of_the_period(10000, window));
    		assert_eq!(8063, first_of_the_period(10001, window));
    	}

    	// https://github.com/bitcoin/bitcoin/blob/a90e6d2bffc422ddcdb771c53aac0bceb970a2c4/src/test/versionbits_tests.cpp#L149
    	#[test]
    	fn test_threshold_state_defined_to_failed() {
    		let (mut cache, mut headers, deployment) = prepare_deployments();
    		let test_cases = vec![
    			(1,		make_test_time(1),		0x20000001,	ThresholdState::Defined),
    			(11,	make_test_time(11),		0x20000001,	ThresholdState::Defined),
    			(989,	make_test_time(989),	0x20000001,	ThresholdState::Defined),
    			(999,	make_test_time(20000),	0x20000001,	ThresholdState::Defined),
    			(1000,	make_test_time(30000),	0x20000001,	ThresholdState::Failed),
    			(1999,	make_test_time(30001),	0x20000001,	ThresholdState::Failed),
    			(2000,	make_test_time(30002),	0x20000001,	ThresholdState::Failed),
    			(2001,	make_test_time(30003),	0x20000001,	ThresholdState::Failed),
    			(2999,	make_test_time(30004),	0x20000001,	ThresholdState::Failed),
    			(3000,	make_test_time(30005),	0x20000001,	ThresholdState::Failed),
    		];

    		for (height, time, version, state) in test_cases {
    			headers.mine(height, time, version);

    			assert_eq!(threshold_state(&mut cache, deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    			assert_eq!(threshold_state(&mut DeploymentStateCache::default(), deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    		}
    	}

    	// https://github.com/bitcoin/bitcoin/blob/a90e6d2bffc422ddcdb771c53aac0bceb970a2c4/src/test/versionbits_tests.cpp#L162
    	#[test]
    	fn test_threshold_state_defined_to_started_to_failed() {
    		let (mut cache, mut headers, deployment) = prepare_deployments();
    		let test_cases = vec![
    			(1,		make_test_time(1),			0x20000000,	ThresholdState::Defined),
    			(1000,	make_test_time(10000) - 1,	0x20000001,	ThresholdState::Defined),
    			(2000,	make_test_time(10000),		0x20000001,	ThresholdState::Started),
    			(2051,	make_test_time(10010),		0x20000000,	ThresholdState::Started),
    			(2950,	make_test_time(10020),		0x20000001,	ThresholdState::Started),
    			(3000,	make_test_time(20000),		0x20000000,	ThresholdState::Failed),
    			(4000,	make_test_time(20010),		0x20000001,	ThresholdState::Failed),
    		];

    		for (height, time, version, state) in test_cases {
    			headers.mine(height, time, version);

    			assert_eq!(threshold_state(&mut cache, deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    			assert_eq!(threshold_state(&mut DeploymentStateCache::default(), deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    		}
    	}

    	// https://github.com/bitcoin/bitcoin/blob/a90e6d2bffc422ddcdb771c53aac0bceb970a2c4/src/test/versionbits_tests.cpp#L172
    	#[test]
    	fn test_threshold_state_defined_to_started_to_failed_when_threshold_reached() {
    		let (mut cache, mut headers, deployment) = prepare_deployments();
    		let test_cases = vec![
    			(1,		make_test_time(1),			0x20000000,	ThresholdState::Defined),
    			(1000,	make_test_time(10000) - 1,	0x20000001,	ThresholdState::Defined),
    			(2000,	make_test_time(10000),		0x20000001,	ThresholdState::Started),
    			(2999,	make_test_time(30000),		0x20000001,	ThresholdState::Started),
    			(3000,	make_test_time(30000),		0x20000001,	ThresholdState::Failed),
    			(3999,	make_test_time(30001),		0x20000000,	ThresholdState::Failed),
    			(4000,	make_test_time(30002),		0x20000000,	ThresholdState::Failed),
    			(14333,	make_test_time(30003),		0x20000000,	ThresholdState::Failed),
    			(20000,	make_test_time(40000),		0x20000000,	ThresholdState::Failed),
    		];

    		for (height, time, version, state) in test_cases {
    			headers.mine(height, time, version);

    			assert_eq!(threshold_state(&mut cache, deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    			assert_eq!(threshold_state(&mut DeploymentStateCache::default(), deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    		}
    	}

    	// https://github.com/bitcoin/bitcoin/blob/a90e6d2bffc422ddcdb771c53aac0bceb970a2c4/src/test/versionbits_tests.cpp#L184
    	#[test]
    	fn test_threshold_state_defined_to_started_to_lockedin() {
    		let (mut cache, mut headers, deployment) = prepare_deployments();
    		let test_cases = vec![
    			(1,		make_test_time(1),			0x20000000,	ThresholdState::Defined, false),
    			(1000,	make_test_time(10000) - 1,	0x20000001,	ThresholdState::Defined, false),
    			(2000,	make_test_time(10000),		0x20000001,	ThresholdState::Started, false),
    			(2050,	make_test_time(10010),		0x20000000,	ThresholdState::Started, true),
    			(2950,	make_test_time(10020),		0x20000001,	ThresholdState::Started, true),
    			(2999,	make_test_time(19999),		0x20000000,	ThresholdState::Started, true),
    			(3000,	make_test_time(29999),		0x20000000,	ThresholdState::LockedIn, false),
    			(3999,	make_test_time(30001),		0x20000000,	ThresholdState::LockedIn, true),
    			(4000,	make_test_time(30002),		0x20000000,	ThresholdState::Active, false),
    			(14333,	make_test_time(30003),		0x20000000,	ThresholdState::Active, false),
    			(24000,	make_test_time(40000),		0x20000000,	ThresholdState::Active, false),
    		];

    		for (height, time, version, state, is_single_request) in test_cases {
    			headers.mine(height, time, version);

    			let req_old = headers.request_count.load(Ordering::Relaxed);
    			assert_eq!(threshold_state(&mut cache, deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    			let req_new = headers.request_count.load(Ordering::Relaxed);

    			// also check that same-period states are read from cache
    			if is_single_request {
    				assert_eq!(req_old + 1, req_new);
    			} else {
    				assert!(req_old < req_new);
    			}

    			assert_eq!(threshold_state(&mut DeploymentStateCache::default(), deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    		}
    	}

    	// https://github.com/bitcoin/bitcoin/blob/a90e6d2bffc422ddcdb771c53aac0bceb970a2c4/src/test/versionbits_tests.cpp#L198
    	#[test]
    	fn test_threshold_state_defined_multiple_to_started_multiple_to_failed() {
    		let (mut cache, mut headers, deployment) = prepare_deployments();
    		let test_cases = vec![
    			(999,	make_test_time(999),		0x20000000,	ThresholdState::Defined),
    			(1000,	make_test_time(1000),		0x20000000,	ThresholdState::Defined),
    			(2000,	make_test_time(2000),		0x20000000,	ThresholdState::Defined),
    			(3000,	make_test_time(10000),		0x20000000,	ThresholdState::Started),
    			(4000,	make_test_time(10000),		0x20000000,	ThresholdState::Started),
    			(5000,	make_test_time(10000),		0x20000000,	ThresholdState::Started),
    			(6000,	make_test_time(20000),		0x20000000,	ThresholdState::Failed),
    			(7000,	make_test_time(20000),		0x20000001,	ThresholdState::Failed),
    		];

    		for (height, time, version, state) in test_cases {
    			headers.mine(height, time, version);

    			assert_eq!(threshold_state(&mut cache, deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    			assert_eq!(threshold_state(&mut DeploymentStateCache::default(), deployment, height, &headers, MINER_CONFIRMATION_WINDOW, RULE_CHANGE_ACTIVATION_THRESHOLD), state);
    		}
    	}
    }

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