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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/>.

    use elastic_array::ElasticArray36;
    use nibbleslice::*;
    use nibblevec::NibbleVec;
    use bytes::*;
    use rlp::*;
    use hashdb::DBValue;

    /// Partial node key type.
    pub type NodeKey = ElasticArray36<u8>;

    /// Type of node in the trie and essential information thereof.
    #[derive(Eq, PartialEq, Debug, Clone)]
    pub enum Node<'a> {
    	/// Null trie node; could be an empty root or an empty branch entry.
    	Empty,
    	/// Leaf node; has key slice and value. Value may not be empty.
    	Leaf(NibbleSlice<'a>, &'a [u8]),
    	/// Extension node; has key slice and node data. Data may not be null.
    	Extension(NibbleSlice<'a>, &'a [u8]),
    	/// Branch node; has array of 16 child nodes (each possibly null) and an optional immediate node data.
    	Branch([&'a [u8]; 16], Option<&'a [u8]>)
    }

    impl<'a> Node<'a> {
    	/// Decode the `node_rlp` and return the Node.
    	pub fn decoded(node_rlp: &'a [u8]) -> Self {
    		let r = Rlp::new(node_rlp);
    		match r.prototype() {
    			// either leaf or extension - decode first item with NibbleSlice::???
    			// and use is_leaf return to figure out which.
    			// if leaf, second item is a value (is_data())
    			// if extension, second item is a node (either SHA3 to be looked up and
    			// fed back into this function or inline RLP which can be fed back into this function).
    			Prototype::List(2) => match NibbleSlice::from_encoded(r.at(0).data()) {
    				(slice, true) => Node::Leaf(slice, r.at(1).data()),
    				(slice, false) => Node::Extension(slice, r.at(1).as_raw()),
    			},
    			// branch - first 16 are nodes, 17th is a value (or empty).
    			Prototype::List(17) => {
    				let mut nodes = [&[] as &[u8]; 16];
    				for i in 0..16 {
    					nodes[i] = r.at(i).as_raw();
    				}
    				Node::Branch(nodes, if r.at(16).is_empty() { None } else { Some(r.at(16).data()) })
    			},
    			// an empty branch index.
    			Prototype::Data(0) => Node::Empty,
    			// something went wrong.
    			_ => panic!("Rlp is not valid.")
    		}
    	}

    	/// Encode the node into RLP.
    	///
    	/// Will always return the direct node RLP even if it's 32 or more bytes. To get the
    	/// RLP which would be valid for using in another node, use `encoded_and_added()`.
    	pub fn encoded(&self) -> Bytes {
    		match *self {
    			Node::Leaf(ref slice, ref value) => {
    				let mut stream = RlpStream::new_list(2);
    				stream.append(&&*slice.encoded(true));
    				stream.append(value);
    				stream.out()
    			},
    			Node::Extension(ref slice, ref raw_rlp) => {
    				let mut stream = RlpStream::new_list(2);
    				stream.append(&&*slice.encoded(false));
    				stream.append_raw(raw_rlp, 1);
    				stream.out()
    			},
    			Node::Branch(ref nodes, ref value) => {
    				let mut stream = RlpStream::new_list(17);
    				for i in 0..16 {
    					stream.append_raw(nodes[i], 1);
    				}
    				match *value {
    					Some(ref n) => { stream.append(n); },
    					None => { stream.append_empty_data(); },
    				}
    				stream.out()
    			},
    			Node::Empty => {
    				let mut stream = RlpStream::new();
    				stream.append_empty_data();
    				stream.out()
    			}
    		}
    	}
    }

    /// An owning node type. Useful for trie iterators.
    #[derive(Debug, PartialEq, Eq)]
    pub enum OwnedNode {
    	/// Empty trie node.
    	Empty,
    	/// Leaf node: partial key and value.
    	Leaf(NibbleVec, DBValue),
    	/// Extension node: partial key and child node.
    	Extension(NibbleVec, DBValue),
    	/// Branch node: 16 children and an optional value.
    	Branch([NodeKey; 16], Option<DBValue>),
    }

    impl Clone for OwnedNode {
    	fn clone(&self) -> Self {
    		match *self {
    			OwnedNode::Empty => OwnedNode::Empty,
    			OwnedNode::Leaf(ref k, ref v) => OwnedNode::Leaf(k.clone(), v.clone()),
    			OwnedNode::Extension(ref k, ref c) => OwnedNode::Extension(k.clone(), c.clone()),
    			OwnedNode::Branch(ref c, ref v) => {
    				let mut children = [
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    				];

    				for (owned, borrowed) in children.iter_mut().zip(c.iter()) {
    					*owned = borrowed.clone()
    				}

    				OwnedNode::Branch(children, v.as_ref().cloned())
    			}
    		}
    	}
    }

    impl<'a> From<Node<'a>> for OwnedNode {
    	fn from(node: Node<'a>) -> Self {
    		match node {
    			Node::Empty => OwnedNode::Empty,
    			Node::Leaf(k, v) => OwnedNode::Leaf(k.into(), DBValue::from_slice(v)),
    			Node::Extension(k, child) => OwnedNode::Extension(k.into(), DBValue::from_slice(child)),
    			Node::Branch(c, val) => {
    				let mut children = [
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    					NodeKey::new(), NodeKey::new(), NodeKey::new(), NodeKey::new(),
    				];

    				for (owned, borrowed) in children.iter_mut().zip(c.iter()) {
    					*owned = NodeKey::from_slice(borrowed)
    				}

    				OwnedNode::Branch(children, val.map(DBValue::from_slice))
    			}
    		}
    	}
    }

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