// Copyright 2017-2020 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! Proving state machine backend.

use std::sync::Arc;
use parking_lot::RwLock;
use codec::{Decode, Encode, Codec};
use log::debug;
use hash_db::{Hasher, HashDB, EMPTY_PREFIX, Prefix};
use sp_trie::{
	MemoryDB, PrefixedMemoryDB, default_child_trie_root,
	read_trie_value_with, read_child_trie_value_with, record_all_keys
};
pub use sp_trie::Recorder;
pub use sp_trie::trie_types::{Layout, TrieError};
use crate::trie_backend::TrieBackend;
use crate::trie_backend_essence::{Ephemeral, TrieBackendEssence, TrieBackendStorage};
use crate::{Error, ExecutionError, Backend};
use std::collections::{HashMap, HashSet};
use crate::DBValue;
use sp_core::storage::ChildInfo;

/// Patricia trie-based backend specialized in get value proofs.
pub struct ProvingBackendRecorder<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> {
	pub(crate) backend: &'a TrieBackendEssence<S, H>,
	pub(crate) proof_recorder: &'a mut Recorder<H::Out>,
}

/// A proof that some set of key-value pairs are included in the storage trie. The proof contains
/// the storage values so that the partial storage backend can be reconstructed by a verifier that
/// does not already have access to the key-value pairs.
///
/// The proof consists of the set of serialized nodes in the storage trie accessed when looking up
/// the keys covered by the proof. Verifying the proof requires constructing the partial trie from
/// the serialized nodes and performing the key lookups.
#[derive(Debug, PartialEq, Eq, Clone, Encode, Decode)]
pub struct StorageProof {
	trie_nodes: Vec<Vec<u8>>,
}

impl StorageProof {
	/// Constructs a storage proof from a subset of encoded trie nodes in a storage backend.
	pub fn new(trie_nodes: Vec<Vec<u8>>) -> Self {
		StorageProof { trie_nodes }
	}

	/// Returns a new empty proof.
	///
	/// An empty proof is capable of only proving trivial statements (ie. that an empty set of
	/// key-value pairs exist in storage).
	pub fn empty() -> Self {
		StorageProof {
			trie_nodes: Vec::new(),
		}
	}

	/// Returns whether this is an empty proof.
	pub fn is_empty(&self) -> bool {
		self.trie_nodes.is_empty()
	}

	/// Create an iterator over trie nodes constructed from the proof. The nodes are not guaranteed
	/// to be traversed in any particular order.
	pub fn iter_nodes(self) -> StorageProofNodeIterator {
		StorageProofNodeIterator::new(self)
	}
}

/// An iterator over trie nodes constructed from a storage proof. The nodes are not guaranteed to
/// be traversed in any particular order.
pub struct StorageProofNodeIterator {
	inner: <Vec<Vec<u8>> as IntoIterator>::IntoIter,
}

impl StorageProofNodeIterator {
	fn new(proof: StorageProof) -> Self {
		StorageProofNodeIterator {
			inner: proof.trie_nodes.into_iter(),
		}
	}
}

impl Iterator for StorageProofNodeIterator {
	type Item = Vec<u8>;

	fn next(&mut self) -> Option<Self::Item> {
		self.inner.next()
	}
}

/// Merges multiple storage proofs covering potentially different sets of keys into one proof
/// covering all keys. The merged proof output may be smaller than the aggregate size of the input
/// proofs due to deduplication of trie nodes.
pub fn merge_storage_proofs<I>(proofs: I) -> StorageProof
	where I: IntoIterator<Item=StorageProof>
{
	let trie_nodes = proofs.into_iter()
		.flat_map(|proof| proof.iter_nodes())
		.collect::<HashSet<_>>()
		.into_iter()
		.collect();
	StorageProof { trie_nodes }
}

impl<'a, S, H> ProvingBackendRecorder<'a, S, H>
	where
		S: TrieBackendStorage<H>,
		H: Hasher,
		H::Out: Codec,
{
	/// Produce proof for a key query.
	pub fn storage(&mut self, key: &[u8]) -> Result<Option<Vec<u8>>, String> {
		let mut read_overlay = S::Overlay::default();
		let eph = Ephemeral::new(
			self.backend.backend_storage(),
			&mut read_overlay,
		);

		let map_e = |e| format!("Trie lookup error: {}", e);

		read_trie_value_with::<Layout<H>, _, Ephemeral<S, H>>(
			&eph,
			self.backend.root(),
			key,
			&mut *self.proof_recorder
		).map_err(map_e)
	}

	/// Produce proof for a child key query.
	pub fn child_storage(
		&mut self,
		storage_key: &[u8],
		child_info: ChildInfo,
		key: &[u8]
	) -> Result<Option<Vec<u8>>, String> {
		let root = self.storage(storage_key)?
			.and_then(|r| Decode::decode(&mut &r[..]).ok())
			.unwrap_or(default_child_trie_root::<Layout<H>>(storage_key));

		let mut read_overlay = S::Overlay::default();
		let eph = Ephemeral::new(
			self.backend.backend_storage(),
			&mut read_overlay,
		);

		let map_e = |e| format!("Trie lookup error: {}", e);

		read_child_trie_value_with::<Layout<H>, _, _>(
			storage_key,
			child_info.keyspace(),
			&eph,
			&root.as_ref(),
			key,
			&mut *self.proof_recorder
		).map_err(map_e)
	}

	/// Produce proof for the whole backend.
	pub fn record_all_keys(&mut self) {
		let mut read_overlay = S::Overlay::default();
		let eph = Ephemeral::new(
			self.backend.backend_storage(),
			&mut read_overlay,
		);

		let mut iter = move || -> Result<(), Box<TrieError<H::Out>>> {
			let root = self.backend.root();
			record_all_keys::<Layout<H>, _>(&eph, root, &mut *self.proof_recorder)
		};

		if let Err(e) = iter() {
			debug!(target: "trie", "Error while recording all keys: {}", e);
		}
	}
}

/// Global proof recorder, act as a layer over a hash db for recording queried
/// data.
pub type ProofRecorder<H> = Arc<RwLock<HashMap<<H as Hasher>::Out, Option<DBValue>>>>;

/// Patricia trie-based backend which also tracks all touched storage trie values.
/// These can be sent to remote node and used as a proof of execution.
pub struct ProvingBackend<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> (
	TrieBackend<ProofRecorderBackend<'a, S, H>, H>,
);

/// Trie backend storage with its proof recorder.
pub struct ProofRecorderBackend<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> {
	backend: &'a S,
	proof_recorder: ProofRecorder<H>,
}

impl<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> ProvingBackend<'a, S, H>
	where H::Out: Codec
{
	/// Create new proving backend.
	pub fn new(backend: &'a TrieBackend<S, H>) -> Self {
		let proof_recorder = Default::default();
		Self::new_with_recorder(backend, proof_recorder)
	}

	/// Create new proving backend with the given recorder.
	pub fn new_with_recorder(
		backend: &'a TrieBackend<S, H>,
		proof_recorder: ProofRecorder<H>,
	) -> Self {
		let essence = backend.essence();
		let root = essence.root().clone();
		let recorder = ProofRecorderBackend {
			backend: essence.backend_storage(),
			proof_recorder: proof_recorder,
		};
		ProvingBackend(TrieBackend::new(recorder, root))
	}

	/// Extracting the gathered unordered proof.
	pub fn extract_proof(&self) -> StorageProof {
		let trie_nodes = self.0.essence().backend_storage().proof_recorder
			.read()
			.iter()
			.filter_map(|(_k, v)| v.as_ref().map(|v| v.to_vec()))
			.collect();
		StorageProof::new(trie_nodes)
	}
}

impl<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> TrieBackendStorage<H> for ProofRecorderBackend<'a, S, H> {
	type Overlay = S::Overlay;

	fn get(&self, key: &H::Out, prefix: Prefix) -> Result<Option<DBValue>, String> {
		if let Some(v) = self.proof_recorder.read().get(key) {
			return Ok(v.clone());
		}
		let backend_value =  self.backend.get(key, prefix)?;
		self.proof_recorder.write().insert(key.clone(), backend_value.clone());
		Ok(backend_value)
	}
}

impl<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> std::fmt::Debug for ProvingBackend<'a, S, H> {
	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
		write!(f, "ProvingBackend")
	}
}

impl<'a, S, H> Backend<H> for ProvingBackend<'a, S, H>
	where
		S: 'a + TrieBackendStorage<H>,
		H: 'a + Hasher,
		H::Out: Ord + Codec,
{
	type Error = String;
	type Transaction = S::Overlay;
	type TrieBackendStorage = PrefixedMemoryDB<H>;

	fn storage(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
		self.0.storage(key)
	}

	fn child_storage(
		&self,
		storage_key: &[u8],
		child_info: ChildInfo,
		key: &[u8],
	) -> Result<Option<Vec<u8>>, Self::Error> {
		self.0.child_storage(storage_key, child_info, key)
	}

	fn for_keys_in_child_storage<F: FnMut(&[u8])>(
		&self,
		storage_key: &[u8],
		child_info: ChildInfo,
		f: F,
	) {
		self.0.for_keys_in_child_storage(storage_key, child_info, f)
	}

	fn next_storage_key(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
		self.0.next_storage_key(key)
	}

	fn next_child_storage_key(
		&self,
		storage_key: &[u8],
		child_info: ChildInfo,
		key: &[u8],
	) -> Result<Option<Vec<u8>>, Self::Error> {
		self.0.next_child_storage_key(storage_key, child_info, key)
	}

	fn for_keys_with_prefix<F: FnMut(&[u8])>(&self, prefix: &[u8], f: F) {
		self.0.for_keys_with_prefix(prefix, f)
	}

	fn for_key_values_with_prefix<F: FnMut(&[u8], &[u8])>(&self, prefix: &[u8], f: F) {
		self.0.for_key_values_with_prefix(prefix, f)
	}

	fn for_child_keys_with_prefix<F: FnMut(&[u8])>(
		&self,
		storage_key: &[u8],
		child_info: ChildInfo,
		prefix: &[u8],
		f: F,
	) {
		self.0.for_child_keys_with_prefix(storage_key, child_info, prefix, f)
	}

	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)> {
		self.0.pairs()
	}

	fn keys(&self, prefix: &[u8]) -> Vec<Vec<u8>> {
		self.0.keys(prefix)
	}

	fn child_keys(
		&self,
		storage_key: &[u8],
		child_info: ChildInfo,
		prefix: &[u8],
	) -> Vec<Vec<u8>> {
		self.0.child_keys(storage_key, child_info, prefix)
	}

	fn storage_root<I>(&self, delta: I) -> (H::Out, Self::Transaction)
		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
	{
		self.0.storage_root(delta)
	}

	fn child_storage_root<I>(
		&self,
		storage_key: &[u8],
		child_info: ChildInfo,
		delta: I,
	) -> (H::Out, bool, Self::Transaction)
	where
		I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
		H::Out: Ord
	{
		self.0.child_storage_root(storage_key, child_info, delta)
	}
}

/// Create proof check backend.
pub fn create_proof_check_backend<H>(
	root: H::Out,
	proof: StorageProof,
) -> Result<TrieBackend<MemoryDB<H>, H>, Box<dyn Error>>
where
	H: Hasher,
	H::Out: Codec,
{
	let db = create_proof_check_backend_storage(proof);

	if db.contains(&root, EMPTY_PREFIX) {
		Ok(TrieBackend::new(db, root))
	} else {
		Err(Box::new(ExecutionError::InvalidProof))
	}
}

/// Create in-memory storage of proof check backend.
pub fn create_proof_check_backend_storage<H>(
	proof: StorageProof,
) -> MemoryDB<H>
where
	H: Hasher,
{
	let mut db = MemoryDB::default();
	for item in proof.iter_nodes() {
		db.insert(EMPTY_PREFIX, &item);
	}
	db
}

#[cfg(test)]
mod tests {
	use crate::backend::{InMemory};
	use crate::trie_backend::tests::test_trie;
	use super::*;
	use sp_core::{Blake2Hasher, storage::ChildStorageKey};
	use crate::proving_backend::create_proof_check_backend;

	const CHILD_INFO_1: ChildInfo<'static> = ChildInfo::new_default(b"unique_id_1");
	const CHILD_INFO_2: ChildInfo<'static> = ChildInfo::new_default(b"unique_id_2");

	fn test_proving<'a>(
		trie_backend: &'a TrieBackend<PrefixedMemoryDB<Blake2Hasher>,Blake2Hasher>,
	) -> ProvingBackend<'a, PrefixedMemoryDB<Blake2Hasher>, Blake2Hasher> {
		ProvingBackend::new(trie_backend)
	}

	#[test]
	fn proof_is_empty_until_value_is_read() {
		let trie_backend = test_trie();
		assert!(test_proving(&trie_backend).extract_proof().is_empty());
	}

	#[test]
	fn proof_is_non_empty_after_value_is_read() {
		let trie_backend = test_trie();
		let backend = test_proving(&trie_backend);
		assert_eq!(backend.storage(b"key").unwrap(), Some(b"value".to_vec()));
		assert!(!backend.extract_proof().is_empty());
	}

	#[test]
	fn proof_is_invalid_when_does_not_contains_root() {
		use sp_core::H256;
		let result = create_proof_check_backend::<Blake2Hasher>(
			H256::from_low_u64_be(1),
			StorageProof::empty()
		);
		assert!(result.is_err());
	}

	#[test]
	fn passes_throgh_backend_calls() {
		let trie_backend = test_trie();
		let proving_backend = test_proving(&trie_backend);
		assert_eq!(trie_backend.storage(b"key").unwrap(), proving_backend.storage(b"key").unwrap());
		assert_eq!(trie_backend.pairs(), proving_backend.pairs());

		let (trie_root, mut trie_mdb) = trie_backend.storage_root(::std::iter::empty());
		let (proving_root, mut proving_mdb) = proving_backend.storage_root(::std::iter::empty());
		assert_eq!(trie_root, proving_root);
		assert_eq!(trie_mdb.drain(), proving_mdb.drain());
	}

	#[test]
	fn proof_recorded_and_checked() {
		let contents = (0..64).map(|i| (vec![i], Some(vec![i]))).collect::<Vec<_>>();
		let in_memory = InMemory::<Blake2Hasher>::default();
		let mut in_memory = in_memory.update(vec![(None, contents)]);
		let in_memory_root = in_memory.storage_root(::std::iter::empty()).0;
		(0..64).for_each(|i| assert_eq!(in_memory.storage(&[i]).unwrap().unwrap(), vec![i]));

		let trie = in_memory.as_trie_backend().unwrap();
		let trie_root = trie.storage_root(::std::iter::empty()).0;
		assert_eq!(in_memory_root, trie_root);
		(0..64).for_each(|i| assert_eq!(trie.storage(&[i]).unwrap().unwrap(), vec![i]));

		let proving = ProvingBackend::new(trie);
		assert_eq!(proving.storage(&[42]).unwrap().unwrap(), vec![42]);

		let proof = proving.extract_proof();

		let proof_check = create_proof_check_backend::<Blake2Hasher>(in_memory_root.into(), proof).unwrap();
		assert_eq!(proof_check.storage(&[42]).unwrap().unwrap(), vec![42]);
	}

	#[test]
	fn proof_recorded_and_checked_with_child() {
		let subtrie1 = ChildStorageKey::from_slice(b":child_storage:default:sub1").unwrap();
		let subtrie2 = ChildStorageKey::from_slice(b":child_storage:default:sub2").unwrap();
		let own1 = subtrie1.into_owned();
		let own2 = subtrie2.into_owned();
		let contents = vec![
			(None, (0..64).map(|i| (vec![i], Some(vec![i]))).collect()),
			(Some((own1.clone(), CHILD_INFO_1.to_owned())),
				(28..65).map(|i| (vec![i], Some(vec![i]))).collect()),
			(Some((own2.clone(), CHILD_INFO_2.to_owned())),
				(10..15).map(|i| (vec![i], Some(vec![i]))).collect()),
		];
		let in_memory = InMemory::<Blake2Hasher>::default();
		let mut in_memory = in_memory.update(contents);
		let in_memory_root = in_memory.full_storage_root::<_, Vec<_>, _>(
			::std::iter::empty(),
			in_memory.child_storage_keys().map(|k|(k.0.to_vec(), Vec::new(), k.1.to_owned()))
		).0;
		(0..64).for_each(|i| assert_eq!(
			in_memory.storage(&[i]).unwrap().unwrap(),
			vec![i]
		));
		(28..65).for_each(|i| assert_eq!(
			in_memory.child_storage(&own1[..], CHILD_INFO_1, &[i]).unwrap().unwrap(),
			vec![i]
		));
		(10..15).for_each(|i| assert_eq!(
			in_memory.child_storage(&own2[..], CHILD_INFO_2, &[i]).unwrap().unwrap(),
			vec![i]
		));

		let trie = in_memory.as_trie_backend().unwrap();
		let trie_root = trie.storage_root(::std::iter::empty()).0;
		assert_eq!(in_memory_root, trie_root);
		(0..64).for_each(|i| assert_eq!(
			trie.storage(&[i]).unwrap().unwrap(),
			vec![i]
		));

		let proving = ProvingBackend::new(trie);
		assert_eq!(proving.storage(&[42]).unwrap().unwrap(), vec![42]);

		let proof = proving.extract_proof();

		let proof_check = create_proof_check_backend::<Blake2Hasher>(
			in_memory_root.into(),
			proof
		).unwrap();
		assert!(proof_check.storage(&[0]).is_err());
		assert_eq!(proof_check.storage(&[42]).unwrap().unwrap(), vec![42]);
		// note that it is include in root because proof close
		assert_eq!(proof_check.storage(&[41]).unwrap().unwrap(), vec![41]);
		assert_eq!(proof_check.storage(&[64]).unwrap(), None);

		let proving = ProvingBackend::new(trie);
		assert_eq!(proving.child_storage(&own1[..], CHILD_INFO_1, &[64]), Ok(Some(vec![64])));

		let proof = proving.extract_proof();
		let proof_check = create_proof_check_backend::<Blake2Hasher>(
			in_memory_root.into(),
			proof
		).unwrap();
		assert_eq!(
			proof_check.child_storage(&own1[..], CHILD_INFO_1, &[64]).unwrap().unwrap(),
			vec![64]
		);
	}

}
