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// Copyright 2015-2018 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/>.

//! Generic trait for trie node encoding/decoding. Takes a `hashdb::Hasher` 
//! to parametrize the hashes used in the codec.

use hashdb::Hasher;
use node::Node;
use ChildReference;

use elastic_array::{ElasticArray1024, ElasticArray128};

/// Trait for trie node encoding/decoding
pub trait NodeCodec<H: Hasher>: Sized {
	/// Encoding error type
	type Error: ::std::error::Error;

	/// Null node type
	const HASHED_NULL_NODE: H::Out;
	
	/// Decode bytes to a `Node`. Returns `Self::E` on failure.
	fn decode(data: &[u8]) -> Result<Node, Self::Error>;

	/// Decode bytes to the `Hasher`s output type.  Returns `None` on failure.
	fn try_decode_hash(data: &[u8]) -> Option<H::Out>;

	/// Check if the provided bytes correspond to the codecs "empty" node.
	fn is_empty_node(data: &[u8]) -> bool;

	/// Returns an empty node
	fn empty_node() -> ElasticArray1024<u8>;

	/// Returns an encoded leaft node
	fn leaf_node(partial: &[u8], value: &[u8]) -> ElasticArray1024<u8>;

	/// Returns an encoded extension node
	fn ext_node(partial: &[u8], child_ref: ChildReference<H::Out>) -> ElasticArray1024<u8>;

	/// Returns an encoded branch node. Takes an iterator yielding `ChildReference<H::Out>` and an optional value
	fn branch_node<I>(children: I, value: Option<ElasticArray128<u8>>) -> ElasticArray1024<u8>
	where I: IntoIterator<Item=Option<ChildReference<H::Out>>>;
}