// Copyright 2016 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.

//! Facade and handler for the rest of the blockchain implementation
//! and mostly the chain pipeline.

use std::collections::HashMap;
use std::fs::File;
use std::sync::{Arc, Mutex, RwLock};
use std::time::{Duration, Instant};

use core::core::{Block, BlockHeader, Input, OutputFeatures, OutputIdentifier, OutputStoreable, TxKernel};
use core::core::hash::{Hash, Hashed};
use core::core::pmmr::MerkleProof;
use core::core::target::Difficulty;
use core::global;
use grin_store::Error::NotFoundErr;
use pipe;
use store;
use sumtree;
use types::*;
use util::secp::pedersen::RangeProof;
use util::LOGGER;


const MAX_ORPHAN_AGE_SECS: u64 = 30;

#[derive(Debug, Clone)]
struct Orphan {
	block: Block,
	opts: Options,
	added: Instant,
}

struct OrphanBlockPool {
	// blocks indexed by their hash
	orphans: RwLock<HashMap<Hash, Orphan>>,
	// additional index of previous -> hash
	// so we can efficiently identify a child block (ex-orphan) after processing a block
	prev_idx: RwLock<HashMap<Hash, Hash>>,
}

impl OrphanBlockPool {
	fn new() -> OrphanBlockPool {
		OrphanBlockPool {
			orphans: RwLock::new(HashMap::new()),
			prev_idx: RwLock::new(HashMap::new()),
		}
	}

	fn len(&self) -> usize {
		let orphans = self.orphans.read().unwrap();
		orphans.len()
	}

	fn add(&self, orphan: Orphan) {
		{
			let mut orphans = self.orphans.write().unwrap();
			let mut prev_idx = self.prev_idx.write().unwrap();
			orphans.insert(orphan.block.hash(), orphan.clone());
			prev_idx.insert(orphan.block.header.previous, orphan.block.hash());
		}

		{
			let mut orphans = self.orphans.write().unwrap();
			let mut prev_idx = self.prev_idx.write().unwrap();
			orphans.retain(|_, ref mut x| x.added.elapsed() < Duration::from_secs(MAX_ORPHAN_AGE_SECS));
			prev_idx.retain(|_, &mut x| orphans.contains_key(&x));
		}
	}

	fn remove(&self, hash: &Hash) -> Option<Orphan> {
		let mut orphans = self.orphans.write().unwrap();
		let mut prev_idx = self.prev_idx.write().unwrap();
		let orphan = orphans.remove(hash);
		if let Some(x) = orphan.clone() {
			prev_idx.remove(&x.block.header.previous);
		}
		orphan
	}

	/// Get an orphan from the pool indexed by the hash of its parent
	fn get_by_previous(&self, hash: &Hash) -> Option<Orphan> {
		let orphans = self.orphans.read().unwrap();
		let prev_idx = self.prev_idx.read().unwrap();
		if let Some(hash) = prev_idx.get(hash) {
			orphans.get(hash).cloned()
		} else {
			None
		}
	}

	fn contains(&self, hash: &Hash) -> bool {
		let orphans = self.orphans.read().unwrap();
		orphans.contains_key(hash)
	}
}

/// Facade to the blockchain block processing pipeline and storage. Provides
/// the current view of the UTXO set according to the chain state. Also
/// maintains locking for the pipeline to avoid conflicting processing.
pub struct Chain {
	db_root: String,
	store: Arc<ChainStore>,
	adapter: Arc<ChainAdapter>,

	head: Arc<Mutex<Tip>>,
	orphans: Arc<OrphanBlockPool>,
	sumtrees: Arc<RwLock<sumtree::SumTrees>>,

	// POW verification function
	pow_verifier: fn(&BlockHeader, u32) -> bool,
}

unsafe impl Sync for Chain {}
unsafe impl Send for Chain {}

impl Chain {
	/// Check whether the chain exists. If not, the call to 'init' will
	/// expect an already mined genesis block. This keeps the chain free
	/// from needing to know about the mining implementation
	pub fn chain_exists(db_root: String) -> bool {
		let chain_store = store::ChainKVStore::new(db_root).unwrap();
		match chain_store.head() {
			Ok(_) => true,
			Err(NotFoundErr) => false,
			Err(_) => false,
		}
	}

	/// Initializes the blockchain and returns a new Chain instance. Does a check
	/// on the current chain head to make sure it exists and creates one based
	/// on the genesis block if necessary.
	pub fn init(
		db_root: String,
		adapter: Arc<ChainAdapter>,
		genesis: Block,
		pow_verifier: fn(&BlockHeader, u32) -> bool,
	) -> Result<Chain, Error> {
		let chain_store = store::ChainKVStore::new(db_root.clone())?;

		let store = Arc::new(chain_store);

		// check if we have a head in store, otherwise the genesis block is it
		let head = store.head();
		let sumtree_md = match head {
			Ok(h) => {
				Some(store.get_block_pmmr_file_metadata(&h.last_block_h)?)
			},
			Err(NotFoundErr) => None,
			Err(e) => return Err(Error::StoreErr(e, "chain init load head".to_owned())),
		};

		let mut sumtrees = sumtree::SumTrees::open(db_root.clone(), store.clone(), sumtree_md)?;

		let head = store.head();
		let head = match head {
			Ok(h) => h,
			Err(NotFoundErr) => {
				let tip = Tip::new(genesis.hash());
				store.save_block(&genesis)?;
				store.setup_height(&genesis.header, &tip)?;
				if genesis.kernels.len() > 0 {
					sumtree::extending(&mut sumtrees, |extension| {
						extension.apply_block(&genesis)
					})?;
				}

				// saving a new tip based on genesis
				store.save_head(&tip)?;
				info!(
					LOGGER,
					"Saved genesis block: {:?}, nonce: {:?}, pow: {:?}",
					genesis.hash(),
					genesis.header.nonce,
					genesis.header.pow,
				);
				pipe::save_pmmr_metadata(&tip, &sumtrees, store.clone())?;
				tip
			}
			Err(e) => return Err(Error::StoreErr(e, "chain init load head".to_owned())),
		};

		// Reset sync_head and header_head to head of current chain.
		// Make sure sync_head is available for later use when needed.
		store.reset_head()?;

		debug!(LOGGER, "Chain init: {:?}", head);

		Ok(Chain {
			db_root: db_root,
			store: store,
			adapter: adapter,
			head: Arc::new(Mutex::new(head)),
			orphans: Arc::new(OrphanBlockPool::new()),
			sumtrees: Arc::new(RwLock::new(sumtrees)),
			pow_verifier: pow_verifier,
		})
	}

	/// Processes a single block, then checks for orphans, processing
	/// those as well if they're found
	pub fn process_block(&self, b: Block, opts: Options)
		-> Result<(Option<Tip>, Option<Block>), Error>
		{
			let res = self.process_block_no_orphans(b, opts);
			match res {
				Ok((t, b)) => {
					// We accepted a block, so see if we can accept any orphans
					if let Some(ref b) = b {
						self.check_orphans(b.hash());
					}
					Ok((t, b))
				},
				Err(e) => {
					Err(e)
				}
			}
		}

	/// Attempt to add a new block to the chain. Returns the new chain tip if it
	/// has been added to the longest chain, None if it's added to an (as of
	/// now) orphan chain.
	pub fn process_block_no_orphans(&self, b: Block, opts: Options)
		-> Result<(Option<Tip>, Option<Block>), Error>
	{
		let head = self.store
			.head()
			.map_err(|e| Error::StoreErr(e, "chain load head".to_owned()))?;
		let ctx = self.ctx_from_head(head, opts);

		let res = pipe::process_block(&b, ctx);

		match res {
			Ok(Some(ref tip)) => {
				// block got accepted and extended the head, updating our head
				let chain_head = self.head.clone();
				{
					let mut head = chain_head.lock().unwrap();
					*head = tip.clone();
				}

				// notifying other parts of the system of the update
				if !opts.contains(Options::SYNC) {
					// broadcast the block
					let adapter = self.adapter.clone();
					adapter.block_accepted(&b, opts);
				}
				Ok((Some(tip.clone()), Some(b.clone())))
			},
			Ok(None) => {
				// block got accepted but we did not extend the head
				// so its on a fork (or is the start of a new fork)
				// broadcast the block out so everyone knows about the fork
				//
				// TODO - This opens us to an amplification attack on blocks
				// mined at a low difficulty. We should suppress really old blocks
				// or less relevant blocks somehow.
				// We should also probably consider banning nodes that send us really old blocks.
				//
				if !opts.contains(Options::SYNC) {
					// broadcast the block
					let adapter = self.adapter.clone();
					adapter.block_accepted(&b, opts);
				}
				Ok((None, Some(b.clone())))
			},
			Err(Error::Orphan) => {
				let block_hash = b.hash();
				let orphan = Orphan {
					block: b.clone(),
					opts: opts,
					added: Instant::now(),
				};

				// In the case of a fork - it is possible to have multiple blocks
				// that are children of a given block.
				// We do not handle this currently for orphans (future enhancement?).
				// We just assume "last one wins" for now.
				&self.orphans.add(orphan);

				debug!(
					LOGGER,
					"process_block: orphan: {:?}, # orphans {}",
					block_hash,
					self.orphans.len(),
				);
				Err(Error::Orphan)
			},
			Err(Error::Unfit(ref msg)) => {
				debug!(
					LOGGER,
					"Block {} at {} is unfit at this time: {}",
					b.hash(),
					b.header.height,
					msg
				);
				Err(Error::Unfit(msg.clone()))
			}
			Err(e) => {
				info!(
					LOGGER,
					"Rejected block {} at {}: {:?}",
					b.hash(),
					b.header.height,
					e
				);
				Err(e)
			}
		}
	}

	/// Process a block header received during "header first" propagation.
	pub fn process_block_header(
		&self,
		bh: &BlockHeader,
		opts: Options,
	) -> Result<Option<Tip>, Error> {
		let header_head = self.get_header_head()?;
		let ctx = self.ctx_from_head(header_head, opts);
		pipe::process_block_header(bh, ctx)
	}

	/// Attempt to add a new header to the header chain.
	/// This is only ever used during sync and uses sync_head.
	pub fn sync_block_header(
		&self,
		bh: &BlockHeader,
		opts: Options,
	) -> Result<Option<Tip>, Error> {
		let sync_head = self.get_sync_head()?;
		let header_head = self.get_header_head()?;
		let sync_ctx = self.ctx_from_head(sync_head, opts);
		let header_ctx = self.ctx_from_head(header_head, opts);
		pipe::sync_block_header(bh, sync_ctx, header_ctx)
	}

	fn ctx_from_head(&self, head: Tip, opts: Options) -> pipe::BlockContext {
		pipe::BlockContext {
			opts: opts,
			store: self.store.clone(),
			head: head,
			pow_verifier: self.pow_verifier,
			sumtrees: self.sumtrees.clone(),
		}
	}

	/// Check if hash is for a known orphan.
	pub fn is_orphan(&self, hash: &Hash) -> bool {
		self.orphans.contains(hash)
	}


	/// Check for orphans, once a block is successfully added
	pub fn check_orphans(&self, mut last_block_hash: Hash) {
		debug!(
			LOGGER,
			"chain: check_orphans: # orphans {}",
			self.orphans.len(),
		);
		// Is there an orphan in our orphans that we can now process?
		// We just processed the given block, are there any orphans that have this block
		// as their "previous" block?
		loop {
			if let Some(orphan) = self.orphans.get_by_previous(&last_block_hash) {
				self.orphans.remove(&orphan.block.hash());
				let res = self.process_block_no_orphans(orphan.block, orphan.opts);
				match res {
					Ok((_, b)) => {
						// We accepted a block, so see if we can accept any orphans
						if b.is_some() {
							last_block_hash = b.unwrap().hash();
						} else {
							break;
						}
					},
					Err(_) => {
						break;
					},
				};
			} else {
				break;
			}
		}
	}

	/// For the given commitment find the unspent output and return the associated
	/// Return an error if the output does not exist or has been spent.
	/// This querying is done in a way that is consistent with the current chain state,
	/// specifically the current winning (valid, most work) fork.
	pub fn is_unspent(&self, output_ref: &OutputIdentifier) -> Result<Hash, Error> {
		let mut sumtrees = self.sumtrees.write().unwrap();
		sumtrees.is_unspent(output_ref)
	}

	/// Validate the current chain state.
	pub fn validate(&self) -> Result<(), Error> {
		let header = self.store.head_header()?;
		let mut sumtrees = self.sumtrees.write().unwrap();
		sumtree::extending(&mut sumtrees, |extension| {
			extension.validate(&header)
		})
	}

	/// Check if the input has matured sufficiently for the given block height.
	/// This only applies to inputs spending coinbase outputs.
	/// An input spending a non-coinbase output will always pass this check.
	pub fn is_matured(&self, input: &Input, height: u64) -> Result<(), Error> {
		if input.features.contains(OutputFeatures::COINBASE_OUTPUT) {
			let mut sumtrees = self.sumtrees.write().unwrap();
			let output = OutputIdentifier::from_input(&input);
			let hash = sumtrees.is_unspent(&output)?;
			let header = self.get_block_header(&input.block_hash())?;
			input.verify_maturity(hash, &header, height)?;
		}
		Ok(())
	}

	/// Sets the sumtree roots on a brand new block by applying the block on the
	/// current sumtree state.
	pub fn set_sumtree_roots(&self, b: &mut Block, is_fork: bool) -> Result<(), Error> {
		let mut sumtrees = self.sumtrees.write().unwrap();
		let store = self.store.clone();

		let roots = sumtree::extending(&mut sumtrees, |extension| {
			// apply the block on the sumtrees and check the resulting root
			if is_fork {
				pipe::rewind_and_apply_fork(b, store, extension)?;
			}
			extension.apply_block(b)?;
			extension.force_rollback();
			Ok(extension.roots())
		})?;

		b.header.utxo_root = roots.utxo_root;
		b.header.range_proof_root = roots.rproof_root;
		b.header.kernel_root = roots.kernel_root;
		Ok(())
	}

	/// Return a pre-built Merkle proof for the given commitment from the store.
	pub fn get_merkle_proof(
		&self,
		output: &OutputIdentifier,
		block: &Block,
	) -> Result<MerkleProof, Error> {
		let mut sumtrees = self.sumtrees.write().unwrap();

		let merkle_proof = sumtree::extending(&mut sumtrees, |extension| {
			extension.force_rollback();
			extension.merkle_proof_via_rewind(output, block)
		})?;

		Ok(merkle_proof)
	}

	/// Returns current sumtree roots
	pub fn get_sumtree_roots(
		&self,
	) -> (
		Hash,
		Hash,
		Hash,
	) {
		let mut sumtrees = self.sumtrees.write().unwrap();
		sumtrees.roots()
	}

	/// Provides a reading view into the current sumtree state as well as
	/// the required indexes for a consumer to rewind to a consistent state
	/// at the provided block hash.
	pub fn sumtrees_read(&self, h: Hash) -> Result<(u64, u64, File), Error> {
		let b = self.get_block(&h)?;

		// get the indexes for the block
		let out_index: u64;
		let kernel_index: u64;
		{
			let sumtrees = self.sumtrees.read().unwrap();
			let (oi, ki) = sumtrees.indexes_at(&b)?;
			out_index = oi;
			kernel_index = ki;
		}

		// prepares the zip and return the corresponding Read
		let sumtree_reader = sumtree::zip_read(self.db_root.clone())?;
		Ok((out_index, kernel_index, sumtree_reader))
	}

	/// Writes a reading view on a sumtree state that's been provided to us.
	/// If we're willing to accept that new state, the data stream will be
	/// read as a zip file, unzipped and the resulting state files should be
	/// rewound to the provided indexes.
	pub fn sumtrees_write(
		&self,
		h: Hash,
		rewind_to_output: u64,
		rewind_to_kernel: u64,
		sumtree_data: File
	) -> Result<(), Error> {

		let head = self.head().unwrap();
		let header_head = self.get_header_head().unwrap();
		if header_head.height - head.height < global::cut_through_horizon() as u64 {
			return Err(Error::InvalidSumtree("not needed".to_owned()));
		}

		let header = self.store.get_block_header(&h)?;
		sumtree::zip_write(self.db_root.clone(), sumtree_data)?;

		let mut sumtrees = sumtree::SumTrees::open(self.db_root.clone(), self.store.clone(), None)?;
		sumtree::extending(&mut sumtrees, |extension| {
			extension.rewind_pos(header.height, rewind_to_output, rewind_to_kernel)?;
			extension.validate(&header)?;
			// TODO validate kernels and their sums with UTXOs
			extension.rebuild_index()?;
			Ok(())
		})?;

		// replace the chain sumtrees with the newly built one
		{
			let mut sumtrees_ref = self.sumtrees.write().unwrap();
			*sumtrees_ref = sumtrees;
		}

		// setup new head
		{
			let mut head = self.head.lock().unwrap();
			*head = Tip::from_block(&header);
			let _ = self.store.save_body_head(&head);
			self.store.save_header_height(&header)?;
		}

		self.check_orphans(header.hash());

		Ok(())
	}

	/// returns the last n nodes inserted into the utxo sum tree
	pub fn get_last_n_utxo(&self, distance: u64) -> Vec<(Hash, Option<OutputStoreable>)> {
		let mut sumtrees = self.sumtrees.write().unwrap();
		sumtrees.last_n_utxo(distance)
	}

	/// as above, for rangeproofs
	pub fn get_last_n_rangeproof(&self, distance: u64) -> Vec<(Hash, Option<RangeProof>)> {
		let mut sumtrees = self.sumtrees.write().unwrap();
		sumtrees.last_n_rangeproof(distance)
	}

	/// as above, for kernels
	pub fn get_last_n_kernel(&self, distance: u64) -> Vec<(Hash, Option<TxKernel>)> {
		let mut sumtrees = self.sumtrees.write().unwrap();
		sumtrees.last_n_kernel(distance)
	}

	/// Total difficulty at the head of the chain
	pub fn total_difficulty(&self) -> Difficulty {
		self.head.lock().unwrap().clone().total_difficulty
	}

	/// Total difficulty at the head of the header chain
	pub fn total_header_difficulty(&self) -> Result<Difficulty, Error> {
		Ok(self.store.get_header_head()?.total_difficulty)
	}

	/// Reset header_head and sync_head to head of current body chain
	pub fn reset_head(&self) -> Result<(), Error> {
		self.store
			.reset_head()
			.map_err(|e| Error::StoreErr(e, "chain reset_head".to_owned()))
	}

	/// Get the tip that's also the head of the chain
	pub fn head(&self) -> Result<Tip, Error> {
		Ok(self.head.lock().unwrap().clone())
	}

	/// Block header for the chain head
	pub fn head_header(&self) -> Result<BlockHeader, Error> {
		self.store
			.head_header()
			.map_err(|e| Error::StoreErr(e, "chain head header".to_owned()))
	}

	/// Gets a block header by hash
	pub fn get_block(&self, h: &Hash) -> Result<Block, Error> {
		self.store
			.get_block(h)
			.map_err(|e| Error::StoreErr(e, "chain get block".to_owned()))
	}

	/// Gets a block header by hash
	pub fn get_block_header(&self, h: &Hash) -> Result<BlockHeader, Error> {
		self.store
			.get_block_header(h)
			.map_err(|e| Error::StoreErr(e, "chain get header".to_owned()))
	}

	/// Gets the block header at the provided height
	pub fn get_header_by_height(&self, height: u64) -> Result<BlockHeader, Error> {
		self.store.get_header_by_height(height).map_err(|e| {
			Error::StoreErr(e, "chain get header by height".to_owned())
		})
	}

	/// Verifies the given block header is actually on the current chain.
	/// Checks the header_by_height index to verify the header is where we say it is
	pub fn is_on_current_chain(&self, header: &BlockHeader) -> Result<(), Error> {
		self.store.is_on_current_chain(header).map_err(|e| {
			Error::StoreErr(e, "chain is_on_current_chain".to_owned())
		})
	}

	/// Get the tip of the current "sync" header chain.
	/// This may be significantly different to current header chain.
	pub fn get_sync_head(&self) -> Result<Tip, Error> {
		self.store
			.get_sync_head()
			.map_err(|e| Error::StoreErr(e, "chain get sync head".to_owned()))
	}

	/// Get the tip of the header chain.
	pub fn get_header_head(&self) -> Result<Tip, Error> {
		self.store
			.get_header_head()
			.map_err(|e| Error::StoreErr(e, "chain get header head".to_owned()))
	}

	/// Builds an iterator on blocks starting from the current chain head and
	/// running backward. Specialized to return information pertaining to block
	/// difficulty calculation (timestamp and previous difficulties).
	pub fn difficulty_iter(&self) -> store::DifficultyIter {
		let head = self.head.lock().unwrap();
		store::DifficultyIter::from(head.last_block_h, self.store.clone())
	}

	/// Check whether we have a block without reading it
	pub fn block_exists(&self, h: Hash) -> Result<bool, Error> {
		self.store.block_exists(&h)
			.map_err(|e| Error::StoreErr(e, "chain block exists".to_owned()))
	}

	/// Retrieve the file index metadata for a given block
	pub fn get_block_pmmr_file_metadata(&self, h: &Hash) -> Result<PMMRFileMetadataCollection, Error> {
		self.store.get_block_pmmr_file_metadata(h)
			.map_err(|e| Error::StoreErr(e, "retrieve block pmmr metadata".to_owned()))
	}
}