// 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 ethereum_types::H256;
use elastic_array::ElasticArray36;
use nibbleslice::NibbleSlice;
use nibblevec::NibbleVec;
use bytes::*;
use rlp::{UntrustedRlp, RlpStream, Prototype, DecoderError};
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]) -> Result<Self, DecoderError> {
		let r = UntrustedRlp::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) => Ok(Node::Leaf(slice, r.at(1)?.data()?)),
				(slice, false) => Ok(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();
				}
				Ok(Node::Branch(nodes, if r.at(16)?.is_empty() { None } else { Some(r.at(16)?.data()?) }))
			},
			// an empty branch index.
			Prototype::Data(0) => Ok(Node::Empty),
			// something went wrong.
			_ => Err(DecoderError::Custom("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()
			}
		}
	}

	pub fn try_decode_hash(node_data: &[u8]) -> Option<H256> {
		let r = UntrustedRlp::new(node_data);
		if r.is_data() && r.size() == 32 {
			Some(r.as_val().expect("Hash is the correct size of 32 bytes; qed"))
		} else {
			None
		}
	}
}

/// 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<'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 children = [
					NodeKey::from_slice(c[0]), NodeKey::from_slice(c[1]), NodeKey::from_slice(c[2]), NodeKey::from_slice(c[3]),
					NodeKey::from_slice(c[4]), NodeKey::from_slice(c[5]), NodeKey::from_slice(c[6]), NodeKey::from_slice(c[7]),
					NodeKey::from_slice(c[8]), NodeKey::from_slice(c[9]), NodeKey::from_slice(c[10]), NodeKey::from_slice(c[11]),
					NodeKey::from_slice(c[12]), NodeKey::from_slice(c[13]), NodeKey::from_slice(c[14]), NodeKey::from_slice(c[15]),
				];

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