// 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/>.

//! Definition of valid items for the verification queue.

use engines::Engine;
use error::Error;

use heapsize::HeapSizeOf;
use bigint::prelude::U256;
use bigint::hash::H256;

pub use self::blocks::Blocks;
pub use self::headers::Headers;

/// Something which can produce a hash and a parent hash.
pub trait BlockLike {
	/// Get the hash of this item.
	fn hash(&self) -> H256;

	/// Get the hash of this item's parent.
	fn parent_hash(&self) -> H256;

	/// Get the difficulty of this item.
	fn difficulty(&self) -> U256;
}

/// Defines transitions between stages of verification.
///
/// It starts with a fallible transformation from an "input" into the unverified item.
/// This consists of quick, simply done checks as well as extracting particular data.
///
/// Then, there is a `verify` function which performs more expensive checks and
/// produces the verified output.
///
/// For correctness, the hashes produced by each stage of the pipeline should be
/// consistent.
pub trait Kind: 'static + Sized + Send + Sync {
	/// The first stage: completely unverified.
	type Input: Sized + Send + BlockLike + HeapSizeOf;

	/// The second stage: partially verified.
	type Unverified: Sized + Send + BlockLike + HeapSizeOf;

	/// The third stage: completely verified.
	type Verified: Sized + Send + BlockLike + HeapSizeOf;

	/// Attempt to create the `Unverified` item from the input.
	fn create(input: Self::Input, engine: &Engine) -> Result<Self::Unverified, Error>;

	/// Attempt to verify the `Unverified` item using the given engine.
	fn verify(unverified: Self::Unverified, engine: &Engine, check_seal: bool) -> Result<Self::Verified, Error>;
}

/// The blocks verification module.
pub mod blocks {
	use super::{Kind, BlockLike};

	use engines::Engine;
	use error::Error;
	use header::Header;
	use verification::{PreverifiedBlock, verify_block_basic, verify_block_unordered};

	use heapsize::HeapSizeOf;
	use bigint::prelude::U256;
	use bigint::hash::H256;
	use util::Bytes;

	/// A mode for verifying blocks.
	pub struct Blocks;

	impl Kind for Blocks {
		type Input = Unverified;
		type Unverified = Unverified;
		type Verified = PreverifiedBlock;

		fn create(input: Self::Input, engine: &Engine) -> Result<Self::Unverified, Error> {
			match verify_block_basic(&input.header, &input.bytes, engine) {
				Ok(()) => Ok(input),
				Err(e) => {
					warn!(target: "client", "Stage 1 block verification failed for {}: {:?}", input.hash(), e);
					Err(e)
				}
			}
		}

		fn verify(un: Self::Unverified, engine: &Engine, check_seal: bool) -> Result<Self::Verified, Error> {
			let hash = un.hash();
			match verify_block_unordered(un.header, un.bytes, engine, check_seal) {
				Ok(verified) => Ok(verified),
				Err(e) => {
					warn!(target: "client", "Stage 2 block verification failed for {}: {:?}", hash, e);
					Err(e)
				}
			}
		}
	}

	/// An unverified block.
	pub struct Unverified {
		header: Header,
		bytes: Bytes,
	}

	impl Unverified {
		/// Create an `Unverified` from raw bytes.
		pub fn new(bytes: Bytes) -> Self {
			use views::BlockView;

			let header = BlockView::new(&bytes).header();
			Unverified {
				header: header,
				bytes: bytes,
			}
		}
	}

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

	impl BlockLike for Unverified {
		fn hash(&self) -> H256 {
			self.header.hash()
		}

		fn parent_hash(&self) -> H256 {
			self.header.parent_hash().clone()
		}

		fn difficulty(&self) -> U256 {
			self.header.difficulty().clone()
		}
	}

	impl BlockLike for PreverifiedBlock {
		fn hash(&self) -> H256 {
			self.header.hash()
		}

		fn parent_hash(&self) -> H256 {
			self.header.parent_hash().clone()
		}

		fn difficulty(&self) -> U256 {
			self.header.difficulty().clone()
		}
	}
}

/// Verification for headers.
pub mod headers {
	use super::{Kind, BlockLike};

	use engines::Engine;
	use error::Error;
	use header::Header;
	use verification::verify_header_params;

	use bigint::prelude::U256;
	use bigint::hash::H256;

	impl BlockLike for Header {
		fn hash(&self) -> H256 { self.hash() }
		fn parent_hash(&self) -> H256 { self.parent_hash().clone() }
		fn difficulty(&self) -> U256 { self.difficulty().clone() }
	}

	/// A mode for verifying headers.
	pub struct Headers;

	impl Kind for Headers {
		type Input = Header;
		type Unverified = Header;
		type Verified = Header;

		fn create(input: Self::Input, engine: &Engine) -> Result<Self::Unverified, Error> {
			verify_header_params(&input, engine, true).map(|_| input)
		}

		fn verify(unverified: Self::Unverified, engine: &Engine, check_seal: bool) -> Result<Self::Verified, Error> {
			match check_seal {
				true => engine.verify_block_unordered(&unverified, None).map(|_| unverified),
				false => Ok(unverified),
			}
		}
	}
}