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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity is distributed in the hope that it will be useful,
    // but WITHOUT ANY WARRANTY; without even the implied warranty of
    // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    // GNU General Public License for more details.

    // You should have received a copy of the GNU General Public License
    // along with Parity.  If not, see <http://www.gnu.org/licenses/>.

    use util::*;
    use rlp::*;
    use network::NetworkError;
    use ethcore::header::Header as BlockHeader;

    known_heap_size!(0, HeaderId);

    /// Block data with optional body.
    struct SyncBlock {
    	header: Bytes,
    	body: Option<Bytes>,
    	receipts: Option<Bytes>,
    }

    /// Block with optional receipt
    pub struct BlockAndReceipts {
    	/// Block data.
    	pub block: Bytes,
    	/// Block receipts RLP list.
    	pub receipts: Option<Bytes>,
    }

    impl HeapSizeOf for SyncBlock {
    	fn heap_size_of_children(&self) -> usize {
    		self.header.heap_size_of_children() + self.body.heap_size_of_children()
    	}
    }

    /// Used to identify header by transactions and uncles hashes
    #[derive(Eq, PartialEq, Hash)]
    struct HeaderId {
    	transactions_root: H256,
    	uncles: H256
    }

    /// A collection of blocks and subchain pointers being downloaded. This keeps track of
    /// which headers/bodies need to be downloaded, which are being downloaded and also holds
    /// the downloaded blocks.
    #[derive(Default)]
    pub struct BlockCollection {
    	/// Does this collection need block receipts.
    	need_receipts: bool,
    	/// Heads of subchains to download
    	heads: Vec<H256>,
    	/// Downloaded blocks.
    	blocks: HashMap<H256, SyncBlock>,
    	/// Downloaded blocks by parent.
    	parents: HashMap<H256, H256>,
    	/// Used to map body to header.
    	header_ids: HashMap<HeaderId, H256>,
    	/// Used to map receipts root to header.
    	receipt_ids: HashMap<H256, H256>,
    	/// First block in `blocks`.
    	head: Option<H256>,
    	/// Set of block header hashes being downloaded
    	downloading_headers: HashSet<H256>,
    	/// Set of block bodies being downloaded identified by block hash.
    	downloading_bodies: HashSet<H256>,
    	/// Set of block receipts being downloaded identified by block hash.
    	downloading_receipts: HashSet<H256>,
    }

    impl BlockCollection {
    	/// Create a new instance.
    	pub fn new(download_receipts: bool) -> BlockCollection {
    		BlockCollection {
    			need_receipts: download_receipts,
    			blocks: HashMap::new(),
    			header_ids: HashMap::new(),
    			receipt_ids: HashMap::new(),
    			heads: Vec::new(),
    			parents: HashMap::new(),
    			head: None,
    			downloading_headers: HashSet::new(),
    			downloading_bodies: HashSet::new(),
    			downloading_receipts: HashSet::new(),
    		}
    	}

    	/// Clear everything.
    	pub fn clear(&mut self) {
    		self.blocks.clear();
    		self.parents.clear();
    		self.header_ids.clear();
    		self.receipt_ids.clear();
    		self.heads.clear();
    		self.head = None;
    		self.downloading_headers.clear();
    		self.downloading_bodies.clear();
    		self.downloading_receipts.clear();
    	}

    	/// Reset collection for a new sync round with given subchain block hashes.
    	pub fn reset_to(&mut self, hashes: Vec<H256>) {
    		self.clear();
    		self.heads = hashes;
    	}

    	/// Insert a set of headers into collection and advance subchain head pointers.
    	pub fn insert_headers(&mut self, headers: Vec<Bytes>) {
    		for h in headers {
    			if let Err(e) =  self.insert_header(h) {
    				trace!(target: "sync", "Ignored invalid header: {:?}", e);
    			}
    		}
    		self.update_heads();
    	}

    	/// Insert a collection of block bodies for previously downloaded headers.
    	pub fn insert_bodies(&mut self, bodies: Vec<Bytes>) -> usize {
    		let mut inserted = 0;
    		for b in bodies {
    			if let Err(e) =  self.insert_body(b) {
    				trace!(target: "sync", "Ignored invalid body: {:?}", e);
    			} else {
    				inserted += 1;
    			}
    		}
    		inserted
    	}

    	/// Insert a collection of block receipts for previously downloaded headers.
    	pub fn insert_receipts(&mut self, receipts: Vec<Bytes>) -> usize {
    		if !self.need_receipts {
    			return 0;
    		}
    		let mut inserted = 0;
    		for r in receipts {
    			if let Err(e) =  self.insert_receipt(r) {
    				trace!(target: "sync", "Ignored invalid receipt: {:?}", e);
    			} else {
    				inserted += 1;
    			}
    		}
    		inserted
    	}

    	/// Returns a set of block hashes that require a body download. The returned set is marked as being downloaded.
    	pub fn needed_bodies(&mut self, count: usize, _ignore_downloading: bool) -> Vec<H256> {
    		if self.head.is_none() {
    			return Vec::new();
    		}
    		let mut needed_bodies: Vec<H256> = Vec::new();
    		let mut head = self.head;
    		while head.is_some() && needed_bodies.len() < count {
    			head = self.parents.get(&head.unwrap()).cloned();
    			if let Some(head) = head {
    				match self.blocks.get(&head) {
    					Some(block) if block.body.is_none() && !self.downloading_bodies.contains(&head) => {
    						self.downloading_bodies.insert(head.clone());
    						needed_bodies.push(head.clone());
    					}
    					_ => (),
    				}
    			}
    		}
    		for h in self.header_ids.values() {
    			if needed_bodies.len() >= count {
    				break;
    			}
    			if !self.downloading_bodies.contains(h) {
    				needed_bodies.push(h.clone());
    				self.downloading_bodies.insert(h.clone());
    			}
    		}
    		needed_bodies
    	}

    	/// Returns a set of block hashes that require a receipt download. The returned set is marked as being downloaded.
    	pub fn needed_receipts(&mut self, count: usize, _ignore_downloading: bool) -> Vec<H256> {
    		if self.head.is_none() || !self.need_receipts {
    			return Vec::new();
    		}
    		let mut needed_receipts: Vec<H256> = Vec::new();
    		let mut head = self.head;
    		while head.is_some() && needed_receipts.len() < count {
    			head = self.parents.get(&head.unwrap()).cloned();
    			if let Some(head) = head {
    				match self.blocks.get(&head) {
    					Some(block) if block.receipts.is_none() && !self.downloading_receipts.contains(&head) => {
    						self.downloading_receipts.insert(head.clone());
    						needed_receipts.push(head.clone());
    					}
    					_ => (),
    				}
    			}
    		}
    		for h in self.receipt_ids.values() {
    			if needed_receipts.len() >= count {
    				break;
    			}
    			if !self.downloading_receipts.contains(h) {
    				needed_receipts.push(h.clone());
    				self.downloading_receipts.insert(h.clone());
    			}
    		}
    		needed_receipts
    	}

    	/// Returns a set of block hashes that require a header download. The returned set is marked as being downloaded.
    	pub fn needed_headers(&mut self, count: usize, ignore_downloading: bool) -> Option<(H256, usize)> {
    		// find subchain to download
    		let mut download = None;
    		{
    			for h in &self.heads {
    				if ignore_downloading || !self.downloading_headers.contains(h) {
    					self.downloading_headers.insert(h.clone());
    					download = Some(h.clone());
    					break;
    				}
    			}
    		}
    		download.map(|h| (h, count))
    	}

    	/// Unmark header as being downloaded.
    	pub fn clear_header_download(&mut self, hash: &H256) {
    		self.downloading_headers.remove(hash);
    	}

    	/// Unmark block body as being downloaded.
    	pub fn clear_body_download(&mut self, hashes: &[H256]) {
    		for h in hashes {
    			self.downloading_bodies.remove(h);
    		}
    	}

    	/// Unmark block receipt as being downloaded.
    	pub fn clear_receipt_download(&mut self, hashes: &[H256]) {
    		for h in hashes {
    			self.downloading_receipts.remove(h);
    		}
    	}

    	/// Get a valid chain of blocks ordered in descending order and ready for importing into blockchain.
    	pub fn drain(&mut self) -> Vec<BlockAndReceipts> {
    		if self.blocks.is_empty() || self.head.is_none() {
    			return Vec::new();
    		}

    		let mut drained = Vec::new();
    		let mut hashes = Vec::new();
    		{
    			let mut blocks = Vec::new();
    			let mut head = self.head;
    			while let Some(h) = head {
    				head = self.parents.get(&h).cloned();
    				if let Some(head) = head {
    					match self.blocks.get(&head) {
    						Some(block) if block.body.is_some() && (!self.need_receipts || block.receipts.is_some()) => {
    							blocks.push(block);
    							hashes.push(head);
    							self.head = Some(head);
    						}
    						_ => break,
    					}
    				}
    			}

    			for block in blocks {
    				let mut block_rlp = RlpStream::new_list(3);
    				block_rlp.append_raw(&block.header, 1);
    				{
    					let body = Rlp::new(block.body.as_ref().expect("blocks contains only full blocks; qed"));
    					block_rlp.append_raw(body.at(0).as_raw(), 1);
    					block_rlp.append_raw(body.at(1).as_raw(), 1);
    				}
    				drained.push(BlockAndReceipts {
    					block: block_rlp.out(),
    					receipts: block.receipts.clone(),
    				});
    			}
    		}
    		for h in hashes {
    			self.blocks.remove(&h);
    		}
    		trace!(target: "sync", "Drained {} blocks, new head :{:?}", drained.len(), self.head);
    		drained
    	}

    	/// Check if the collection is empty. We consider the syncing round complete once
    	/// there is no block data left and only a single or none head pointer remains.
    	pub fn is_empty(&self) -> bool {
    		self.heads.len() == 0 || (self.heads.len() == 1 && self.head.map_or(false, |h| h == self.heads[0]))
    	}

    	/// Check if collection contains a block header.
    	pub fn contains(&self, hash: &H256) -> bool {
    		self.blocks.contains_key(hash)
    	}

    	/// Check if collection contains a block header.
    	pub fn contains_head(&self, hash: &H256) -> bool {
    		self.heads.contains(hash)
    	}

    	/// Return used heap size.
    	pub fn heap_size(&self) -> usize {
    		self.heads.heap_size_of_children()
    			+ self.blocks.heap_size_of_children()
    			+ self.parents.heap_size_of_children()
    			+ self.header_ids.heap_size_of_children()
    			+ self.downloading_headers.heap_size_of_children()
    			+ self.downloading_bodies.heap_size_of_children()
    	}

    	/// Check if given block hash is marked as being downloaded.
    	pub fn is_downloading(&self, hash: &H256) -> bool {
    		self.downloading_headers.contains(hash) || self.downloading_bodies.contains(hash)
    	}

    	fn insert_body(&mut self, b: Bytes) -> Result<(), NetworkError> {
    		let header_id = {
    			let body = UntrustedRlp::new(&b);
    			let tx = body.at(0)?;
    			let tx_root = ordered_trie_root(tx.iter().map(|r| r.as_raw().to_vec())); //TODO: get rid of vectors here
    			let uncles = body.at(1)?.as_raw().sha3();
    			HeaderId {
    				transactions_root: tx_root,
    				uncles: uncles
    			}
    		};

    		match self.header_ids.get(&header_id).cloned() {
    			Some(h) => {
    				self.header_ids.remove(&header_id);
    				self.downloading_bodies.remove(&h);
    				match self.blocks.get_mut(&h) {
    					Some(ref mut block) => {
    						trace!(target: "sync", "Got body {}", h);
    						block.body = Some(b);
    						Ok(())
    					},
    					None => {
    						warn!("Got body with no header {}", h);
    						Err(NetworkError::BadProtocol)
    					}
    				}
    			}
    			None => {
    				trace!(target: "sync", "Ignored unknown/stale block body. tx_root = {:?}, uncles = {:?}", header_id.transactions_root, header_id.uncles);
    				Err(NetworkError::BadProtocol)
    			}
    		}
    	}

    	fn insert_receipt(&mut self, r: Bytes) -> Result<(), NetworkError> {
    		let receipt_root = {
    			let receipts = UntrustedRlp::new(&r);
    			ordered_trie_root(receipts.iter().map(|r| r.as_raw().to_vec())) //TODO: get rid of vectors here
    		};
    		match self.receipt_ids.get(&receipt_root).cloned() {
    			Some(h) => {
    				self.receipt_ids.remove(&receipt_root);
    				self.downloading_receipts.remove(&h);
    				match self.blocks.get_mut(&h) {
    					Some(ref mut block) => {
    						trace!(target: "sync", "Got receipt {}", h);
    						block.receipts = Some(r);
    						Ok(())
    					},
    					None => {
    						warn!("Got receipt with no header {}", h);
    						Err(NetworkError::BadProtocol)
    					}
    				}
    			}
    			None => {
    				trace!(target: "sync", "Ignored unknown/stale block receipt {:?}", receipt_root);
    				Err(NetworkError::BadProtocol)
    			}
    		}
    	}

    	fn insert_header(&mut self, header: Bytes) -> Result<H256, UtilError> {
    		let info: BlockHeader = UntrustedRlp::new(&header).as_val()?;
    		let hash = info.hash();
    		if self.blocks.contains_key(&hash) {
    			return Ok(hash);
    		}
    		match self.head {
    			None if hash == self.heads[0] => {
    				trace!(target: "sync", "New head {}", hash);
    				self.head = Some(info.parent_hash().clone());
    			},
    			_ => ()
    		}

    		let mut block = SyncBlock {
    			header: header,
    			body: None,
    			receipts: None,
    		};
    		let header_id = HeaderId {
    			transactions_root: info.transactions_root().clone(),
    			uncles: info.uncles_hash().clone(),
    		};
    		if header_id.transactions_root == sha3::SHA3_NULL_RLP && header_id.uncles == sha3::SHA3_EMPTY_LIST_RLP {
    			// empty body, just mark as downloaded
    			let mut body_stream = RlpStream::new_list(2);
    			body_stream.append_raw(&::rlp::EMPTY_LIST_RLP, 1);
    			body_stream.append_raw(&::rlp::EMPTY_LIST_RLP, 1);
    			block.body = Some(body_stream.out());
    		}
    		else {
    			trace!("Queueing body tx_root = {:?}, uncles = {:?}, block = {:?}, number = {}", header_id.transactions_root, header_id.uncles, hash, info.number());
    			self.header_ids.insert(header_id, hash.clone());
    		}
    		if self.need_receipts {
    			let receipt_root = info.receipts_root().clone();
    			if receipt_root == sha3::SHA3_NULL_RLP {
    				let receipts_stream = RlpStream::new_list(0);
    				block.receipts = Some(receipts_stream.out());
    			} else {
    				if self.receipt_ids.contains_key(&receipt_root) {
    					warn!(target: "sync", "Duplicate receipt root {:?}, block: {:?}", receipt_root, hash);
    				}
    				self.receipt_ids.insert(receipt_root, hash.clone());
    			}
    		}

    		self.parents.insert(info.parent_hash().clone(), hash.clone());
    		self.blocks.insert(hash.clone(), block);
    		trace!(target: "sync", "New header: {}", hash.hex());
    		Ok(hash)
    	}

    	// update subchain headers
    	fn update_heads(&mut self) {
    		let mut new_heads = Vec::new();
    		let old_subchains: HashSet<_> = { self.heads.iter().cloned().collect() };
    		for s in self.heads.drain(..) {
    			let mut h = s.clone();
    			if !self.blocks.contains_key(&h) {
    				new_heads.push(h);
    				continue;
    			}
    			loop {
    				match self.parents.get(&h) {
    					Some(next) => {
    						h = next.clone();
    						if old_subchains.contains(&h) {
    							trace!(target: "sync", "Completed subchain {:?}", s);
    							break; // reached head of the other subchain, merge by not adding
    						}
    					},
    					_ => {
    						new_heads.push(h);
    						break;
    					}
    				}
    			}
    		}
    		self.heads = new_heads;
    	}
    }

    #[cfg(test)]
    mod test {
    	use super::BlockCollection;
    	use ethcore::client::{TestBlockChainClient, EachBlockWith, BlockId, BlockChainClient};
    	use ethcore::views::HeaderView;
    	use ethcore::header::BlockNumber;
    	use util::*;
    	use rlp::*;

    	fn is_empty(bc: &BlockCollection) -> bool {
    		bc.heads.is_empty() &&
    		bc.blocks.is_empty() &&
    		bc.parents.is_empty() &&
    		bc.header_ids.is_empty() &&
    		bc.head.is_none() &&
    		bc.downloading_headers.is_empty() &&
    		bc.downloading_bodies.is_empty()
    	}

    	#[test]
    	fn create_clear() {
    		let mut bc = BlockCollection::new(false);
    		assert!(is_empty(&bc));
    		let client = TestBlockChainClient::new();
    		client.add_blocks(100, EachBlockWith::Nothing);
    		let hashes = (0 .. 100).map(|i| (&client as &BlockChainClient).block_hash(BlockId::Number(i)).unwrap()).collect();
    		bc.reset_to(hashes);
    		assert!(!is_empty(&bc));
    		bc.clear();
    		assert!(is_empty(&bc));
    	}

    	#[test]
    	fn insert_headers() {
    		let mut bc = BlockCollection::new(false);
    		assert!(is_empty(&bc));
    		let client = TestBlockChainClient::new();
    		let nblocks = 200;
    		client.add_blocks(nblocks, EachBlockWith::Nothing);
    		let blocks: Vec<_> = (0..nblocks)
    			.map(|i| (&client as &BlockChainClient).block(BlockId::Number(i as BlockNumber)).unwrap().into_inner())
    			.collect();
    		let headers: Vec<_> = blocks.iter().map(|b| Rlp::new(b).at(0).as_raw().to_vec()).collect();
    		let hashes: Vec<_> = headers.iter().map(|h| HeaderView::new(h).sha3()).collect();
    		let heads: Vec<_> = hashes.iter().enumerate().filter_map(|(i, h)| if i % 20 == 0 { Some(h.clone()) } else { None }).collect();
    		bc.reset_to(heads);
    		assert!(!bc.is_empty());
    		assert_eq!(hashes[0], bc.heads[0]);
    		assert!(bc.needed_bodies(1, false).is_empty());
    		assert!(!bc.contains(&hashes[0]));
    		assert!(!bc.is_downloading(&hashes[0]));

    		let (h, n) = bc.needed_headers(6, false).unwrap();
    		assert!(bc.is_downloading(&hashes[0]));
    		assert_eq!(hashes[0], h);
    		assert_eq!(n, 6);
    		assert_eq!(bc.downloading_headers.len(), 1);
    		assert!(bc.drain().is_empty());

    		bc.insert_headers(headers[0..6].to_vec());
    		assert_eq!(hashes[5], bc.heads[0]);
    		for h in &hashes[0..6] {
    			bc.clear_header_download(h)
    		}
    		assert_eq!(bc.downloading_headers.len(), 0);
    		assert!(!bc.is_downloading(&hashes[0]));
    		assert!(bc.contains(&hashes[0]));

    		assert_eq!(&bc.drain().into_iter().map(|b| b.block).collect::<Vec<_>>()[..], &blocks[0..6]);
    		assert!(!bc.contains(&hashes[0]));
    		assert_eq!(hashes[5], bc.head.unwrap());

    		let (h, _) = bc.needed_headers(6, false).unwrap();
    		assert_eq!(hashes[5], h);
    		let (h, _) = bc.needed_headers(6, false).unwrap();
    		assert_eq!(hashes[20], h);
    		bc.insert_headers(headers[10..16].to_vec());
    		assert!(bc.drain().is_empty());
    		bc.insert_headers(headers[5..10].to_vec());
    		assert_eq!(&bc.drain().into_iter().map(|b| b.block).collect::<Vec<_>>()[..], &blocks[6..16]);
    		assert_eq!(hashes[15], bc.heads[0]);

    		bc.insert_headers(headers[15..].to_vec());
    		bc.drain();
    		assert!(bc.is_empty());
    	}

    	#[test]
    	fn insert_headers_with_gap() {
    		let mut bc = BlockCollection::new(false);
    		assert!(is_empty(&bc));
    		let client = TestBlockChainClient::new();
    		let nblocks = 200;
    		client.add_blocks(nblocks, EachBlockWith::Nothing);
    		let blocks: Vec<_> = (0..nblocks)
    			.map(|i| (&client as &BlockChainClient).block(BlockId::Number(i as BlockNumber)).unwrap().into_inner())
    			.collect();
    		let headers: Vec<_> = blocks.iter().map(|b| Rlp::new(b).at(0).as_raw().to_vec()).collect();
    		let hashes: Vec<_> = headers.iter().map(|h| HeaderView::new(h).sha3()).collect();
    		let heads: Vec<_> = hashes.iter().enumerate().filter_map(|(i, h)| if i % 20 == 0 { Some(h.clone()) } else { None }).collect();
    		bc.reset_to(heads);

    		bc.insert_headers(headers[2..22].to_vec());
    		assert_eq!(hashes[0], bc.heads[0]);
    		assert_eq!(hashes[21], bc.heads[1]);
    		assert!(bc.head.is_none());
    		bc.insert_headers(headers[0..2].to_vec());
    		assert!(bc.head.is_some());
    		assert_eq!(hashes[21], bc.heads[0]);
    	}

    	#[test]
    	fn insert_headers_no_gap() {
    		let mut bc = BlockCollection::new(false);
    		assert!(is_empty(&bc));
    		let client = TestBlockChainClient::new();
    		let nblocks = 200;
    		client.add_blocks(nblocks, EachBlockWith::Nothing);
    		let blocks: Vec<_> = (0..nblocks)
    			.map(|i| (&client as &BlockChainClient).block(BlockId::Number(i as BlockNumber)).unwrap().into_inner())
    			.collect();
    		let headers: Vec<_> = blocks.iter().map(|b| Rlp::new(b).at(0).as_raw().to_vec()).collect();
    		let hashes: Vec<_> = headers.iter().map(|h| HeaderView::new(h).sha3()).collect();
    		let heads: Vec<_> = hashes.iter().enumerate().filter_map(|(i, h)| if i % 20 == 0 { Some(h.clone()) } else { None }).collect();
    		bc.reset_to(heads);

    		bc.insert_headers(headers[1..2].to_vec());
    		assert!(bc.drain().is_empty());
    		bc.insert_headers(headers[0..1].to_vec());
    		assert_eq!(bc.drain().len(), 2);
    	}
    }

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