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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/>.

    //! A provider for the LES protocol. This is typically a full node, who can
    //! give as much data as necessary to its peers.

    use ethcore::blockchain_info::BlockChainInfo;
    use ethcore::client::{BlockChainClient, ProvingBlockChainClient};
    use ethcore::transaction::PendingTransaction;
    use ethcore::ids::BlockId;
    use ethcore::encoded;

    use util::{Bytes, H256};

    use request;

    /// Defines the operations that a provider for `LES` must fulfill.
    ///
    /// These are defined at [1], but may be subject to change.
    /// Requests which can't be fulfilled should return either an empty RLP list
    /// or empty vector where appropriate.
    ///
    /// [1]: https://github.com/ethcore/parity/wiki/Light-Ethereum-Subprotocol-(LES)
    #[cfg_attr(feature = "ipc", ipc(client_ident="LightProviderClient"))]
    pub trait Provider: Send + Sync {
    	/// Provide current blockchain info.
    	fn chain_info(&self) -> BlockChainInfo;

    	/// Find the depth of a common ancestor between two blocks.
    	/// If either block is unknown or an ancestor can't be found
    	/// then return `None`.
    	fn reorg_depth(&self, a: &H256, b: &H256) -> Option<u64>;

    	/// Earliest block where state queries are available.
    	/// If `None`, no state queries are servable.
    	fn earliest_state(&self) -> Option<u64>;

    	/// Provide a list of headers starting at the requested block,
    	/// possibly in reverse and skipping `skip` at a time.
    	///
    	/// The returned vector may have any length in the range [0, `max`], but the
    	/// results within must adhere to the `skip` and `reverse` parameters.
    	fn block_headers(&self, req: request::Headers) -> Vec<encoded::Header> {
    		use request::HashOrNumber;

    		if req.max == 0 { return Vec::new() }

    		let best_num = self.chain_info().best_block_number;
    		let start_num = match req.start {
    			HashOrNumber::Number(start_num) => start_num,
    			HashOrNumber::Hash(hash) => match self.block_header(BlockId::Hash(hash)) {
    				None => {
    					trace!(target: "les_provider", "Unknown block hash {} requested", hash);
    					return Vec::new();
    				}
    				Some(header) => {
    					let num = header.number();
    					let canon_hash = self.block_header(BlockId::Number(num))
    						.map(|h| h.hash());

    					if req.max == 1 || canon_hash != Some(hash) {
    						// Non-canonical header or single header requested.
    						return vec![header];
    					}

    					num
    				}
    			}
    		};

    		(0u64..req.max as u64)
    			.map(|x: u64| x.saturating_mul(req.skip + 1))
    			.take_while(|x| if req.reverse { x < &start_num } else { best_num.saturating_sub(start_num) >= *x })
    			.map(|x| if req.reverse { start_num - x } else { start_num + x })
    			.map(|x| self.block_header(BlockId::Number(x)))
    			.take_while(|x| x.is_some())
    			.flat_map(|x| x)
    			.collect()
    	}

    	/// Get a block header by id.
    	fn block_header(&self, id: BlockId) -> Option<encoded::Header>;

    	/// Provide as many as possible of the requested blocks (minus the headers) encoded
    	/// in RLP format.
    	fn block_bodies(&self, req: request::Bodies) -> Vec<Option<encoded::Body>> {
    		req.block_hashes.into_iter()
    			.map(|hash| self.block_body(BlockId::Hash(hash)))
    			.collect()
    	}

    	/// Get a block body by id.
    	fn block_body(&self, id: BlockId) -> Option<encoded::Body>;

    	/// Provide the receipts as many as possible of the requested blocks.
    	/// Returns a vector of RLP-encoded lists of receipts.
    	fn receipts(&self, req: request::Receipts) -> Vec<Bytes> {
    		req.block_hashes.into_iter()
    			.map(|hash| self.block_receipts(&hash))
    			.map(|receipts| receipts.unwrap_or_else(|| ::rlp::EMPTY_LIST_RLP.to_vec()))
    			.collect()
    	}

    	/// Get a block's receipts as an RLP-encoded list by block hash.
    	fn block_receipts(&self, hash: &H256) -> Option<Bytes>;

    	/// Provide a set of merkle proofs, as requested. Each request is a
    	/// block hash and request parameters.
    	///
    	/// Returns a vector of RLP-encoded lists satisfying the requests.
    	fn proofs(&self, req: request::StateProofs) -> Vec<Bytes> {
    		use rlp::{RlpStream, Stream};

    		let mut results = Vec::with_capacity(req.requests.len());

    		for request in req.requests {
    			let proof = self.state_proof(request);

    			let mut stream = RlpStream::new_list(proof.len());
    			for node in proof {
    				stream.append_raw(&node, 1);
    			}

    			results.push(stream.out());
    		}

    		results
    	}

    	/// Get a state proof from a request. Each proof should be a vector
    	/// of rlp-encoded trie nodes, in ascending order by distance from the root.
    	fn state_proof(&self, req: request::StateProof) -> Vec<Bytes>;

    	/// Provide contract code for the specified (block_hash, account_hash) pairs.
    	/// Each item in the resulting vector is either the raw bytecode or empty.
    	fn contract_codes(&self, req: request::ContractCodes) -> Vec<Bytes> {
    		req.code_requests.into_iter()
    			.map(|req| self.contract_code(req))
    			.collect()
    	}

    	/// Get contract code by request. Either the raw bytecode or empty.
    	fn contract_code(&self, req: request::ContractCode) -> Bytes;

    	/// Provide header proofs from the Canonical Hash Tries as well as the headers
    	/// they correspond to -- each element in the returned vector is a 2-tuple.
    	/// The first element is a block header and the second a merkle proof of
    	/// the header in a requested CHT.
    	fn header_proofs(&self, req: request::HeaderProofs) -> Vec<Bytes> {
    		use rlp::{self, RlpStream, Stream};

    		req.requests.into_iter()
    			.map(|req| self.header_proof(req))
    			.map(|maybe_proof| match maybe_proof {
    				None => rlp::EMPTY_LIST_RLP.to_vec(),
    				Some((header, proof)) => {
    					let mut stream = RlpStream::new_list(2);
    					stream.append_raw(&header.into_inner(), 1).begin_list(proof.len());

    					for node in proof {
    						stream.append_raw(&node, 1);
    					}

    					stream.out()
    				}
    			})
    			.collect()
    	}

    	/// Provide a header proof from a given Canonical Hash Trie as well as the
    	/// corresponding header. The first element is the block header and the
    	/// second is a merkle proof of the CHT.
    	fn header_proof(&self, req: request::HeaderProof) -> Option<(encoded::Header, Vec<Bytes>)>;

    	/// Provide pending transactions.
    	fn ready_transactions(&self) -> Vec<PendingTransaction>;
    }

    // Implementation of a light client data provider for a client.
    impl<T: ProvingBlockChainClient + ?Sized> Provider for T {
    	fn chain_info(&self) -> BlockChainInfo {
    		BlockChainClient::chain_info(self)
    	}

    	fn reorg_depth(&self, a: &H256, b: &H256) -> Option<u64> {
    		self.tree_route(a, b).map(|route| route.index as u64)
    	}

    	fn earliest_state(&self) -> Option<u64> {
    		Some(self.pruning_info().earliest_state)
    	}

    	fn block_header(&self, id: BlockId) -> Option<encoded::Header> {
    		BlockChainClient::block_header(self, id)
    	}

    	fn block_body(&self, id: BlockId) -> Option<encoded::Body> {
    		BlockChainClient::block_body(self, id)
    	}

    	fn block_receipts(&self, hash: &H256) -> Option<Bytes> {
    		BlockChainClient::block_receipts(self, hash)
    	}

    	fn state_proof(&self, req: request::StateProof) -> Vec<Bytes> {
    		match req.key2 {
    			Some(key2) => self.prove_storage(req.key1, key2, req.from_level, BlockId::Hash(req.block)),
    			None => self.prove_account(req.key1, req.from_level, BlockId::Hash(req.block)),
    		}
    	}

    	fn contract_code(&self, req: request::ContractCode) -> Bytes {
    		self.code_by_hash(req.account_key, BlockId::Hash(req.block_hash))
    	}

    	fn header_proof(&self, req: request::HeaderProof) -> Option<(encoded::Header, Vec<Bytes>)> {
    		use util::MemoryDB;
    		use util::trie::{Trie, TrieMut, TrieDB, TrieDBMut, Recorder};

    		if Some(req.cht_number) != ::cht::block_to_cht_number(req.block_number) {
    			debug!(target: "les_provider", "Requested CHT number mismatch with block number.");
    			return None;
    		}

    		let mut memdb = MemoryDB::new();
    		let mut root = H256::default();
    		let mut needed_hdr = None;
    		{
    			let mut t = TrieDBMut::new(&mut memdb, &mut root);
    			let start_num = ::cht::start_number(req.cht_number);
    			for i in (0..::cht::SIZE).map(|x| x + start_num) {
    				match self.block_header(BlockId::Number(i)) {
    					None => return None,
    					Some(hdr) => {
    						t.insert(
    							&*::rlp::encode(&i),
    							&*::rlp::encode(&hdr.hash()),
    						).expect("fresh in-memory database is infallible; qed");

    						if i == req.block_number { needed_hdr = Some(hdr) }
    					}
    				}
    			}
    		}
    		let needed_hdr = needed_hdr.expect("`needed_hdr` always set in loop, number checked before; qed");

    		let mut recorder = Recorder::with_depth(req.from_level);
    		let t = TrieDB::new(&memdb, &root)
    			.expect("Same DB and root as just produced by TrieDBMut; qed");

    		if let Err(e) = t.get_with(&*::rlp::encode(&req.block_number), &mut recorder) {
    			debug!(target: "les_provider", "Error looking up number in freshly-created CHT: {}", e);
    			return None;
    		}

    		// TODO: cache calculated CHT if possible.
    		let proof = recorder.drain().into_iter().map(|x| x.data).collect();
    		Some((needed_hdr, proof))
    	}

    	fn ready_transactions(&self) -> Vec<PendingTransaction> {
    		BlockChainClient::ready_transactions(self)
    	}
    }

    #[cfg(test)]
    mod tests {
    	use ethcore::client::{EachBlockWith, TestBlockChainClient};
    	use super::Provider;

    	#[test]
    	fn cht_proof() {
    		let client = TestBlockChainClient::new();
    		client.add_blocks(2000, EachBlockWith::Nothing);

    		let req = ::request::HeaderProof {
    			cht_number: 0,
    			block_number: 1500,
    			from_level: 0,
    		};

    		assert!(client.header_proof(req.clone()).is_none());

    		client.add_blocks(48, EachBlockWith::Nothing);

    		assert!(client.header_proof(req.clone()).is_some());
    	}
    }

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