// This file is part of Substrate.

// Copyright (C) 2021-2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// 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.

//! Compact proof support.
//!
//! This uses compact proof from trie crate and extends
//! it to substrate specific layout and child trie system.

use crate::{
	EMPTY_PREFIX, HashDBT, TrieHash, TrieError, TrieConfiguration,
	CompactProof, StorageProof,
};
use sp_std::boxed::Box;
use sp_std::vec::Vec;
use trie_db::Trie;
#[cfg(feature="std")]
use std::fmt;
#[cfg(feature="std")]
use std::error::Error as StdError;


/// Error for trie node decoding.
pub enum Error<L: TrieConfiguration> {
	/// Verification failed due to root mismatch.
	RootMismatch(TrieHash<L>, TrieHash<L>),
	/// Missing nodes in proof.
	IncompleteProof,
	/// Compact node is not needed.
	ExtraneousChildNode,
	/// Child content with root not in proof.
	ExtraneousChildProof(TrieHash<L>),
	/// Bad child trie root.
	InvalidChildRoot(Vec<u8>, Vec<u8>),
	/// Errors from trie crate.
	TrieError(Box<TrieError<L>>),
}

impl<L: TrieConfiguration> From<Box<TrieError<L>>> for Error<L> {
	fn from(error: Box<TrieError<L>>) -> Self {
		Error::TrieError(error)
	}
}

#[cfg(feature="std")]
impl<L: TrieConfiguration> StdError for Error<L> {
	fn description(&self) -> &str {
		match self {
			Error::InvalidChildRoot(..) => "Invalid child root error",
			Error::TrieError(..) => "Trie db error",
			Error::RootMismatch(..) => "Trie db error",
			Error::IncompleteProof => "Incomplete proof",
			Error::ExtraneousChildNode => "Extraneous child node",
			Error::ExtraneousChildProof(..) => "Extraneous child proof",
		}
	}
}

#[cfg(feature="std")]
impl<L: TrieConfiguration> fmt::Debug for Error<L> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		<Self as fmt::Display>::fmt(&self, f)
	}
}

#[cfg(feature="std")]
impl<L: TrieConfiguration> fmt::Display for Error<L> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			Error::InvalidChildRoot(k, v) => write!(f, "InvalidChildRoot at {:x?}: {:x?}", k, v),
			Error::TrieError(e) => write!(f, "Trie error: {}", e),
			Error::IncompleteProof => write!(f, "Incomplete proof"),
			Error::ExtraneousChildNode => write!(f, "Child node content with no root in proof"),
			Error::ExtraneousChildProof(root) => write!(f, "Proof of child trie {:x?} not in parent proof", root.as_ref()),
			Error::RootMismatch(root, expected) => write!(
				f,
				"Verification error, root is {:x?}, expected: {:x?}",
				root.as_ref(),
				expected.as_ref(),
			),
		}
	}
}

/// Decode a compact proof.
///
/// Takes as input a destination `db` for decoded node and `encoded`
/// an iterator of compact encoded nodes.
///
/// Child trie are decoded in order of child trie root present
/// in the top trie.
pub fn decode_compact<'a, L, DB, I>(
	db: &mut DB,
	encoded: I,
	expected_root: Option<&TrieHash<L>>,
) -> Result<TrieHash<L>, Error<L>>
	where
		L: TrieConfiguration,
		DB: HashDBT<L::Hash, trie_db::DBValue> + hash_db::HashDBRef<L::Hash, trie_db::DBValue>,
		I: IntoIterator<Item = &'a [u8]>,
{
	let mut nodes_iter = encoded.into_iter();
	let (top_root, _nb_used) = trie_db::decode_compact_from_iter::<L, _, _, _>(
		db,
		&mut nodes_iter,
	)?;

	// Only check root if expected root is passed as argument.
	if let Some(expected_root) = expected_root {
		if expected_root != &top_root {
			return Err(Error::RootMismatch(top_root.clone(), expected_root.clone()));
		}
	}

	let mut child_tries = Vec::new();
	{
		// fetch child trie roots
		let trie = crate::TrieDB::<L>::new(db, &top_root)?;

		let mut iter = trie.iter()?;

		let childtrie_roots = sp_core::storage::well_known_keys::DEFAULT_CHILD_STORAGE_KEY_PREFIX;
		if iter.seek(childtrie_roots).is_ok() {
			loop {
				match iter.next() {
					Some(Ok((key, value))) if key.starts_with(childtrie_roots) => {
						// we expect all default child trie root to be correctly encoded.
						// see other child trie functions.
						let mut root = TrieHash::<L>::default();
						// still in a proof so prevent panic
						if root.as_mut().len() != value.as_slice().len() {
							return Err(Error::InvalidChildRoot(key, value));
						}
						root.as_mut().copy_from_slice(value.as_ref());
						child_tries.push(root);
					},
					// allow incomplete database error: we only
					// require access to data in the proof.
					Some(Err(error)) => match *error {
						trie_db::TrieError::IncompleteDatabase(..) => (),
						e => return Err(Box::new(e).into()),
					},
					_ => break,
				}
			}
		}
	}

	if !HashDBT::<L::Hash, _>::contains(db, &top_root, EMPTY_PREFIX) {
		return Err(Error::IncompleteProof);
	}

	let mut previous_extracted_child_trie = None;
	for child_root in child_tries.into_iter() {
		if previous_extracted_child_trie.is_none() {
			let (top_root, _) = trie_db::decode_compact_from_iter::<L, _, _, _>(
				db,
				&mut nodes_iter,
			)?;
			previous_extracted_child_trie = Some(top_root);
		}

		// we do not early exit on root mismatch but try the
		// other read from proof (some child root may be
		// in proof without actual child content).
		if Some(child_root) == previous_extracted_child_trie {
			previous_extracted_child_trie = None;
		}
	}

	if let Some(child_root) = previous_extracted_child_trie {
		// A child root was read from proof but is not present
		// in top trie.
		return Err(Error::ExtraneousChildProof(child_root));
	}

	if nodes_iter.next().is_some() {
		return Err(Error::ExtraneousChildNode);
	}

	Ok(top_root)
}

/// Encode a compact proof.
///
/// Takes as input all full encoded node from the proof, and
/// the root.
/// Then parse all child trie root and compress main trie content first
/// then all child trie contents.
/// Child trie are ordered by the order of their roots in the top trie.
pub fn encode_compact<L>(
	proof: StorageProof,
	root: TrieHash<L>,
) -> Result<CompactProof, Error<L>>
	where
		L: TrieConfiguration,
{
	let mut child_tries = Vec::new();
	let partial_db = proof.into_memory_db();
	let mut compact_proof = {
		let trie = crate::TrieDB::<L>::new(&partial_db, &root)?;

		let mut iter = trie.iter()?;

		let childtrie_roots = sp_core::storage::well_known_keys::DEFAULT_CHILD_STORAGE_KEY_PREFIX;
		if iter.seek(childtrie_roots).is_ok() {
			loop {
				match iter.next() {
					Some(Ok((key, value))) if key.starts_with(childtrie_roots) => {
						let mut root = TrieHash::<L>::default();
						if root.as_mut().len() != value.as_slice().len() {
							// some child trie root in top trie are not an encoded hash.
							return Err(Error::InvalidChildRoot(key.to_vec(), value.to_vec()));
						}
						root.as_mut().copy_from_slice(value.as_ref());
						child_tries.push(root);
					},
					// allow incomplete database error: we only
					// require access to data in the proof.
					Some(Err(error)) => match *error {
						trie_db::TrieError::IncompleteDatabase(..) => (),
						e => return Err(Box::new(e).into()),
					},
					_ => break,
				}
			}
		}

		trie_db::encode_compact::<L>(&trie)?
	};

	for child_root in child_tries {
		if !HashDBT::<L::Hash, _>::contains(&partial_db, &child_root, EMPTY_PREFIX) {
			// child proof are allowed to be missing (unused root can be included
			// due to trie structure modification).
			continue;
		}

		let trie = crate::TrieDB::<L>::new(&partial_db, &child_root)?;
		let child_proof = trie_db::encode_compact::<L>(&trie)?;

		compact_proof.extend(child_proof);
	}

	Ok(CompactProof { encoded_nodes: compact_proof })
}
