// Copyright 2019-2021 Parity Technologies (UK) Ltd.
// This file is part of Parity Bridges Common.

// Parity Bridges Common 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 Bridges Common 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 Bridges Common.  If not, see <http://www.gnu.org/licenses/>.

//! Logic for checking Substrate storage proofs.

use hash_db::{HashDB, Hasher, EMPTY_PREFIX};
use sp_runtime::RuntimeDebug;
use sp_std::vec::Vec;
use sp_trie::{read_trie_value, Layout, MemoryDB, StorageProof};

/// This struct is used to read storage values from a subset of a Merklized database. The "proof"
/// is a subset of the nodes in the Merkle structure of the database, so that it provides
/// authentication against a known Merkle root as well as the values in the database themselves.
pub struct StorageProofChecker<H>
where
	H: Hasher,
{
	root: H::Out,
	db: MemoryDB<H>,
}

impl<H> StorageProofChecker<H>
where
	H: Hasher,
{
	/// Constructs a new storage proof checker.
	///
	/// This returns an error if the given proof is invalid with respect to the given root.
	pub fn new(root: H::Out, proof: StorageProof) -> Result<Self, Error> {
		let db = proof.into_memory_db();
		if !db.contains(&root, EMPTY_PREFIX) {
			return Err(Error::StorageRootMismatch);
		}

		let checker = StorageProofChecker { root, db };
		Ok(checker)
	}

	/// Reads a value from the available subset of storage. If the value cannot be read due to an
	/// incomplete or otherwise invalid proof, this returns an error.
	pub fn read_value(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Error> {
		read_trie_value::<Layout<H>, _>(&self.db, &self.root, key).map_err(|_| Error::StorageValueUnavailable)
	}
}

#[derive(RuntimeDebug, PartialEq)]
pub enum Error {
	StorageRootMismatch,
	StorageValueUnavailable,
}

/// Return valid storage proof and state root.
///
/// NOTE: This should only be used for **testing**.
#[cfg(feature = "std")]
pub fn craft_valid_storage_proof() -> (sp_core::H256, StorageProof) {
	use sp_state_machine::{backend::Backend, prove_read, InMemoryBackend};

	// construct storage proof
	let backend = <InMemoryBackend<sp_core::Blake2Hasher>>::from(vec![
		(None, vec![(b"key1".to_vec(), Some(b"value1".to_vec()))]),
		(None, vec![(b"key2".to_vec(), Some(b"value2".to_vec()))]),
		(None, vec![(b"key3".to_vec(), Some(b"value3".to_vec()))]),
		// Value is too big to fit in a branch node
		(None, vec![(b"key11".to_vec(), Some(vec![0u8; 32]))]),
	]);
	let root = backend.storage_root(std::iter::empty()).0;
	let proof = StorageProof::new(
		prove_read(backend, &[&b"key1"[..], &b"key2"[..], &b"key22"[..]])
			.unwrap()
			.iter_nodes()
			.collect(),
	);

	(root, proof)
}

#[cfg(test)]
pub mod tests {
	use super::*;

	#[test]
	fn storage_proof_check() {
		let (root, proof) = craft_valid_storage_proof();

		// check proof in runtime
		let checker = <StorageProofChecker<sp_core::Blake2Hasher>>::new(root, proof.clone()).unwrap();
		assert_eq!(checker.read_value(b"key1"), Ok(Some(b"value1".to_vec())));
		assert_eq!(checker.read_value(b"key2"), Ok(Some(b"value2".to_vec())));
		assert_eq!(checker.read_value(b"key11111"), Err(Error::StorageValueUnavailable));
		assert_eq!(checker.read_value(b"key22"), Ok(None));

		// checking proof against invalid commitment fails
		assert_eq!(
			<StorageProofChecker<sp_core::Blake2Hasher>>::new(sp_core::H256::random(), proof).err(),
			Some(Error::StorageRootMismatch)
		);
	}
}