// 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.

//! Utility structs to handle the 3 sumtrees (utxo, range proof, kernel) more
//! conveniently and transactionally.

use std::fs;
use std::collections::HashMap;
use std::path::Path;
use std::sync::Arc;

use secp;
use secp::pedersen::{RangeProof, Commitment};

use core::core::{Block, TxKernel, Output, SumCommit};
use core::core::pmmr::{Summable, NoSum, PMMR, HashSum, Backend};
use grin_store;
use grin_store::sumtree::PMMRBackend;
use types::ChainStore;
use types::Error;

const SUMTREES_SUBDIR: &'static str = "sumtrees";
const UTXO_SUBDIR: &'static str = "utxo";
const RANGE_PROOF_SUBDIR: &'static str = "rangeproof";
const KERNEL_SUBDIR: &'static str = "kernel";

struct PMMRHandle<T>
	where T: Summable + Clone
{
	backend: PMMRBackend<T>,
	last_pos: u64,
}

impl<T> PMMRHandle<T>
    where T: Summable + Clone
{
	fn new(root_dir: String, file_name: &str) -> Result<PMMRHandle<T>, Error> {
		let path = Path::new(&root_dir).join(SUMTREES_SUBDIR).join(file_name);
		fs::create_dir_all(path.clone())?;
		let be = PMMRBackend::new(path.to_str().unwrap().to_string())?;
		let sz = be.unpruned_size()?;
		Ok(PMMRHandle {
			backend: be,
			last_pos: sz,
		})
	}
}

/// An easy to manipulate structure holding the 3 sum trees necessary to
/// validate blocks and capturing the UTXO set, the range proofs and the
/// kernels. Also handles the index of Commitments to positions in the
/// output and range proof sum trees.
///
/// Note that the index is never authoritative, only the trees are
/// guaranteed to indicate whether an output is spent or not. The index
/// may have commitments that have already been spent, even with
/// pruning enabled.
pub struct SumTrees {
	output_pmmr_h: PMMRHandle<SumCommit>,
	rproof_pmmr_h: PMMRHandle<NoSum<RangeProof>>,
	kernel_pmmr_h: PMMRHandle<NoSum<TxKernel>>,

	// chain store used as index of commitments to MMR positions
	commit_index: Arc<ChainStore>,
}

impl SumTrees {
	/// Open an existing or new set of backends for the SumTrees
	pub fn open(root_dir: String, commit_index: Arc<ChainStore>) -> Result<SumTrees, Error> {
		Ok(SumTrees {
			output_pmmr_h: PMMRHandle::new(root_dir.clone(), UTXO_SUBDIR)?,
			rproof_pmmr_h: PMMRHandle::new(root_dir.clone(), RANGE_PROOF_SUBDIR)?,
			kernel_pmmr_h: PMMRHandle::new(root_dir.clone(), KERNEL_SUBDIR)?,
			commit_index: commit_index,
		})
	}

	/// Wether a given commitment exists in the Output MMR and it's unspent
	pub fn is_unspent(&self, commit: &Commitment) -> Result<bool, Error> {
		let rpos = self.commit_index.get_output_pos(commit);
		match rpos {
			Ok(pos) => Ok(self.output_pmmr_h.backend.get(pos).is_some()),
			Err(grin_store::Error::NotFoundErr) => Ok(false),
			Err(e) => Err(Error::StoreErr(e)),
		}
	}
}

/// Starts a new unit of work to extend the chain with additional blocks,
/// accepting a closure that will work within that unit of work. The closure
/// has access to an Extension object that allows the addition of blocks to
/// the sumtrees and the checking of the current tree roots.
///
/// If the closure returns an error, modifications are canceled and the unit
/// of work is abandoned. Otherwise, the unit of work is permanently applied.
pub fn extending<'a, F, T>(trees: &'a mut SumTrees, inner: F) -> Result<T, Error>
	where F: FnOnce(&mut Extension) -> Result<T, Error>
{

	let sizes: (u64, u64, u64);
	let res: Result<T, Error>;
	let rollback: bool;
	{
		let commit_index = trees.commit_index.clone();
		let mut extension = Extension::new(trees, commit_index);
		res = inner(&mut extension);
		rollback = extension.rollback;
		if res.is_ok() && !rollback {
			extension.save_pos_index()?;
		}
		sizes = extension.sizes();
	}
	match res {
		Err(e) => {
			trees.output_pmmr_h.backend.discard();
			trees.rproof_pmmr_h.backend.discard();
			trees.kernel_pmmr_h.backend.discard();
			Err(e)
		}
		Ok(r) => {
			if rollback {
				trees.output_pmmr_h.backend.discard();
				trees.rproof_pmmr_h.backend.discard();
				trees.kernel_pmmr_h.backend.discard();
			} else {
				trees.output_pmmr_h.backend.sync()?;
				trees.rproof_pmmr_h.backend.sync()?;
				trees.kernel_pmmr_h.backend.sync()?;
				trees.output_pmmr_h.last_pos = sizes.0;
				trees.rproof_pmmr_h.last_pos = sizes.1;
				trees.kernel_pmmr_h.last_pos = sizes.2;
			}

			Ok(r)
		}
	}
}

/// Allows the application of new blocks on top of the sum trees in a
/// reversible manner within a unit of work provided by the `extending`
/// function.
pub struct Extension<'a> {
	output_pmmr: PMMR<'a, SumCommit, PMMRBackend<SumCommit>>,
	rproof_pmmr: PMMR<'a, NoSum<RangeProof>, PMMRBackend<NoSum<RangeProof>>>,
	kernel_pmmr: PMMR<'a, NoSum<TxKernel>, PMMRBackend<NoSum<TxKernel>>>,

	commit_index: Arc<ChainStore>,
	new_output_commits: HashMap<Commitment, u64>,
	new_kernel_excesses: HashMap<Commitment, u64>,
	rollback: bool,
}

impl<'a> Extension<'a> {
	// constructor
	fn new(trees: &'a mut SumTrees, commit_index: Arc<ChainStore>) -> Extension<'a> {
		Extension {
			output_pmmr: PMMR::at(
				&mut trees.output_pmmr_h.backend,
				trees.output_pmmr_h.last_pos,
			),
			rproof_pmmr: PMMR::at(
				&mut trees.rproof_pmmr_h.backend,
				trees.rproof_pmmr_h.last_pos,
			),
			kernel_pmmr: PMMR::at(
				&mut trees.kernel_pmmr_h.backend,
				trees.kernel_pmmr_h.last_pos,
			),
			commit_index: commit_index,
			new_output_commits: HashMap::new(),
			new_kernel_excesses: HashMap::new(),
			rollback: false,
		}
	}

	/// Apply a new set of blocks on top the existing sum trees. Blocks are
	/// applied in order of the provided Vec. If pruning is enabled, inputs also
	/// prune MMR data.
	pub fn apply_block(&mut self, b: &Block) -> Result<(), Error> {
		let secp = secp::Secp256k1::with_caps(secp::ContextFlag::Commit);

		// doing inputs first guarantees an input can't spend an output in the
		// same block, enforcing block cut-through
		for input in &b.inputs {
			let pos_res = self.commit_index.get_output_pos(&input.commitment());
			if let Ok(pos) = pos_res {
				match self.output_pmmr.prune(pos, b.header.height as u32) {
					Ok(true) => {
						self.rproof_pmmr
							.prune(pos, b.header.height as u32)
							.map_err(|s| Error::SumTreeErr(s))?;
					}
					Ok(false) => return Err(Error::AlreadySpent),
					Err(s) => return Err(Error::SumTreeErr(s)),
				}
			} else {
				return Err(Error::SumTreeErr(
					format!("Missing index for {:?}", input.commitment()),
				));
			}
		}

		for out in &b.outputs {
			if let Ok(_) = self.commit_index.get_output_pos(&out.commitment()) {
				return Err(Error::DuplicateCommitment(out.commitment()));
			}
			// push new outputs commitments in their MMR and save them in the index
			let pos = self.output_pmmr
				.push(SumCommit {
					commit: out.commitment(),
					secp: secp.clone(),
				})
				.map_err(&Error::SumTreeErr)?;

			self.new_output_commits.insert(out.commitment(), pos);

			// push range proofs in their MMR
			self.rproof_pmmr
				.push(NoSum(out.proof))
				.map_err(&Error::SumTreeErr)?;
		}

		for kernel in &b.kernels {
			if let Ok(_) = self.commit_index.get_kernel_pos(&kernel.excess) {
				return Err(Error::DuplicateKernel(kernel.excess.clone()));
			}
			// push kernels in their MMR
			let pos = self.kernel_pmmr
				.push(NoSum(kernel.clone()))
				.map_err(&Error::SumTreeErr)?;
			self.new_kernel_excesses.insert(kernel.excess, pos);
		}
		Ok(())
	}

	fn save_pos_index(&self) -> Result<(), Error> {
		for (commit, pos) in &self.new_output_commits {
			self.commit_index.save_output_pos(commit, *pos)?;
		}
		for (excess, pos) in &self.new_kernel_excesses {
			self.commit_index.save_kernel_pos(excess, *pos)?;
		}
		Ok(())
	}

	/// Rewinds the MMRs to the provided position, given the last output and
	/// last kernel of the block we want to rewind to.
	pub fn rewind(&mut self, height: u64, output: &Output, kernel: &TxKernel) -> Result<(), Error> {
		let out_pos_rew = self.commit_index.get_output_pos(&output.commitment())?;
		let kern_pos_rew = self.commit_index.get_kernel_pos(&kernel.excess)?;

		self.output_pmmr
			.rewind(out_pos_rew, height as u32)
			.map_err(&Error::SumTreeErr)?;
		self.rproof_pmmr
			.rewind(out_pos_rew, height as u32)
			.map_err(&Error::SumTreeErr)?;
		self.kernel_pmmr
			.rewind(kern_pos_rew, height as u32)
			.map_err(&Error::SumTreeErr)?;
		Ok(())
	}

	/// Current root hashes and sums (if applicable) for the UTXO, range proof
	/// and kernel sum trees.
	pub fn roots(&self)
	             -> (HashSum<SumCommit>, HashSum<NoSum<RangeProof>>, HashSum<NoSum<TxKernel>>) {
		(self.output_pmmr.root(), self.rproof_pmmr.root(), self.kernel_pmmr.root())
	}

	/// Force the rollback of this extension, no matter the result
	pub fn force_rollback(&mut self) {
		self.rollback = true;
	}

	// Sizes of the sum trees, used by `extending` on rollback.
	fn sizes(&self) -> (u64, u64, u64) {
		(self.output_pmmr.unpruned_size(),
		 self.rproof_pmmr.unpruned_size(),
		 self.kernel_pmmr.unpruned_size())
	}
}