// This file is part of Substrate.

// Copyright (C) 2019-2021 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.

//! Substrate inherent extrinsics
//!
//! Inherent extrinsics are extrinsics that are inherently added to each block. However, it is up to
//! runtime implementation to require an inherent for each block or to make it optional. Inherents
//! are mainly used to pass data from the block producer to the runtime. So, inherents require some
//! part that is running on the client side and some part that is running on the runtime side. Any
//! data that is required by an inherent is passed as [`InherentData`] from the client to the
//! runtime when the inherents are constructed.
//!
//! The process of constructing and applying inherents is the following:
//!
//! 1. The block producer first creates the [`InherentData`] by using the inherent data providers
//! that are created by [`CreateInherentDataProviders`].
//!
//! 2. The [`InherentData`] is passed to the `inherent_extrinsics` function of the `BlockBuilder`
//! runtime api. This will call the runtime which will create all the inherents that should be
//! applied to the block.
//!
//! 3. Apply each inherent to the block like any normal extrinsic.
//!
//! On block import the inherents in the block are checked by calling the `check_inherents` runtime
//! API. This will also pass an instance of [`InherentData`] which the runtime can use to validate
//! all inherents. If some inherent data isn't required for validating an inherent, it can be
//! omitted when providing the inherent data providers for block import.
//!
//! # Providing inherent data
//!
//! To provide inherent data from the client side, [`InherentDataProvider`] should be implemented.
//!
//! ```
//! use codec::Decode;
//! use sp_inherents::{InherentIdentifier, InherentData};
//!
//! // This needs to be unique for the runtime.
//! const INHERENT_IDENTIFIER: InherentIdentifier = *b"testinh0";
//!
//! /// Some custom inherent data provider
//! struct InherentDataProvider;
//!
//! #[async_trait::async_trait]
//! impl sp_inherents::InherentDataProvider for InherentDataProvider {
//! 	fn provide_inherent_data(
//! 		&self,
//! 		inherent_data: &mut InherentData,
//! 	) -> Result<(), sp_inherents::Error> {
//! 		// We can insert any data that implements [`codec::Encode`].
//! 		inherent_data.put_data(INHERENT_IDENTIFIER, &"hello")
//! 	}
//!
//! 	/// When validating the inherents, the runtime implementation can throw errors. We support
//! 	/// two error modes, fatal and non-fatal errors. A fatal error means that the block is invalid
//! 	/// and this function here should return `Err(_)` to not import the block. Non-fatal errors
//! 	/// are allowed to be handled here in this function and the function should return `Ok(())`
//! 	/// if it could be handled. A non-fatal error is for example that a block is in the future
//! 	/// from the point of view of the local node. In such a case the block import for example
//! 	/// should be delayed until the block is valid.
//! 	///
//! 	/// If this functions returns `None`, it means that it is not responsible for this error or
//! 	/// that the error could not be interpreted.
//! 	async fn try_handle_error(
//! 		&self,
//! 		identifier: &InherentIdentifier,
//! 		mut error: &[u8],
//! 	) -> Option<Result<(), sp_inherents::Error>> {
//! 		// Check if this error belongs to us.
//! 		if *identifier != INHERENT_IDENTIFIER {
//! 			return None;
//! 		}
//!
//! 		// For demonstration purposes we are using a `String` as error type. In real
//! 		// implementations it is advised to not use `String`.
//! 		Some(Err(
//! 			sp_inherents::Error::Application(Box::from(String::decode(&mut error).ok()?))
//! 		))
//! 	}
//! }
//! ```
//!
//! In the service the relevant inherent data providers need to be passed the block production and
//! the block import. As already highlighted above, the providers can be different between import
//! and production.
//!
//! ```
//! # use sp_runtime::testing::ExtrinsicWrapper;
//! # use sp_inherents::{InherentIdentifier, InherentData};
//! # use futures::FutureExt;
//! # type Block = sp_runtime::testing::Block<ExtrinsicWrapper<()>>;
//! # const INHERENT_IDENTIFIER: InherentIdentifier = *b"testinh0";
//! # struct InherentDataProvider;
//! # #[async_trait::async_trait]
//! # impl sp_inherents::InherentDataProvider for InherentDataProvider {
//! # 	fn provide_inherent_data(&self, inherent_data: &mut InherentData) -> Result<(), sp_inherents::Error> {
//! # 		inherent_data.put_data(INHERENT_IDENTIFIER, &"hello")
//! # 	}
//! # 	async fn try_handle_error(
//! # 		&self,
//! # 		_: &InherentIdentifier,
//! # 		_: &[u8],
//! # 	) -> Option<Result<(), sp_inherents::Error>> {
//! # 		None
//! # 	}
//! # }
//!
//! async fn cool_consensus_block_production(
//! 	// The second parameter to the trait are parameters that depend on what the caller
//! 	// can provide on extra data.
//! 	_: impl sp_inherents::CreateInherentDataProviders<Block, ()>,
//! ) {
//! 	// do cool stuff
//! }
//!
//! async fn cool_consensus_block_import(
//! 	_: impl sp_inherents::CreateInherentDataProviders<Block, ()>,
//! ) {
//! 	// do cool stuff
//! }
//!
//! async fn build_service(is_validator: bool) {
//! 	// For block import we don't pass any inherent data provider, because our runtime
//! 	// does not need any inherent data to validate the inherents.
//! 	let block_import = cool_consensus_block_import(|_parent, ()| async { Ok(()) });
//!
//! 	let block_production = if is_validator {
//! 		// For block production we want to provide our inherent data provider
//! 		cool_consensus_block_production(|_parent, ()| async {
//! 			Ok(InherentDataProvider)
//! 		}).boxed()
//! 	} else {
//! 		futures::future::pending().boxed()
//! 	};
//!
//! 	futures::pin_mut!(block_import);
//!
//! 	futures::future::select(block_import, block_production).await;
//! }
//! ```
//!
//! # Creating the inherent
//!
//! As the inherents are created by the runtime, it depends on the runtime implementation on how
//! to create the inherents. As already described above the client side passes the [`InherentData`]
//! and expects the runtime to construct the inherents out of it. When validating the inherents,
//! [`CheckInherentsResult`] is used to communicate the result client side.

#![cfg_attr(not(feature = "std"), no_std)]
#![warn(missing_docs)]

use codec::{Decode, Encode};

use sp_std::{
	collections::btree_map::{BTreeMap, Entry, IntoIter},
	vec::Vec,
};

#[cfg(feature = "std")]
mod client_side;

#[cfg(feature = "std")]
pub use client_side::*;

/// Errors that occur in context of inherents.
#[derive(Debug)]
#[cfg_attr(feature = "std", derive(thiserror::Error))]
#[allow(missing_docs)]
pub enum Error {
	#[cfg_attr(
		feature = "std",
		error("Inherent data already exists for identifier: {}", "String::from_utf8_lossy(_0)")
	)]
	InherentDataExists(InherentIdentifier),
	#[cfg_attr(
		feature = "std",
		error("Failed to decode inherent data for identifier: {}", "String::from_utf8_lossy(_1)")
	)]
	DecodingFailed(#[cfg_attr(feature = "std", source)] codec::Error, InherentIdentifier),
	#[cfg_attr(
		feature = "std",
		error("There was already a fatal error reported and no other errors are allowed")
	)]
	FatalErrorReported,
	#[cfg(feature = "std")]
	#[error(transparent)]
	Application(#[from] Box<dyn std::error::Error + Send + Sync>),
}

/// An identifier for an inherent.
pub type InherentIdentifier = [u8; 8];

/// Inherent data to include in a block.
#[derive(Clone, Default, Encode, Decode)]
pub struct InherentData {
	/// All inherent data encoded with parity-scale-codec and an identifier.
	data: BTreeMap<InherentIdentifier, Vec<u8>>,
}

impl InherentData {
	/// Create a new instance.
	pub fn new() -> Self {
		Self::default()
	}

	/// Put data for an inherent into the internal storage.
	///
	/// # Return
	///
	/// Returns `Ok(())` if the data could be inserted and no data for an inherent with the same
	/// identifier existed, otherwise an error is returned.
	///
	/// Inherent identifiers need to be unique, otherwise decoding of these values will not work!
	pub fn put_data<I: codec::Encode>(
		&mut self,
		identifier: InherentIdentifier,
		inherent: &I,
	) -> Result<(), Error> {
		match self.data.entry(identifier) {
			Entry::Vacant(entry) => {
				entry.insert(inherent.encode());
				Ok(())
			},
			Entry::Occupied(_) => Err(Error::InherentDataExists(identifier)),
		}
	}

	/// Replace the data for an inherent.
	///
	/// If it does not exist, the data is just inserted.
	pub fn replace_data<I: codec::Encode>(&mut self, identifier: InherentIdentifier, inherent: &I) {
		self.data.insert(identifier, inherent.encode());
	}

	/// Returns the data for the requested inherent.
	///
	/// # Return
	///
	/// - `Ok(Some(I))` if the data could be found and deserialized.
	/// - `Ok(None)` if the data could not be found.
	/// - `Err(_)` if the data could be found, but deserialization did not work.
	pub fn get_data<I: codec::Decode>(
		&self,
		identifier: &InherentIdentifier,
	) -> Result<Option<I>, Error> {
		match self.data.get(identifier) {
			Some(inherent) => I::decode(&mut &inherent[..])
				.map_err(|e| Error::DecodingFailed(e, *identifier))
				.map(Some),
			None => Ok(None),
		}
	}

	/// Get the number of inherents in this instance
	pub fn len(&self) -> usize {
		self.data.len()
	}
}

/// The result of checking inherents.
///
/// It either returns okay for all checks, stores all occurred errors or just one fatal error.
///
/// When a fatal error occurs, all other errors are removed and the implementation needs to
/// abort checking inherents.
#[derive(Encode, Decode, Clone)]
pub struct CheckInherentsResult {
	/// Did the check succeed?
	okay: bool,
	/// Did we encounter a fatal error?
	fatal_error: bool,
	/// We use the `InherentData` to store our errors.
	errors: InherentData,
}

impl Default for CheckInherentsResult {
	fn default() -> Self {
		Self { okay: true, errors: InherentData::new(), fatal_error: false }
	}
}

impl CheckInherentsResult {
	/// Create a new instance.
	pub fn new() -> Self {
		Self::default()
	}

	/// Put an error into the result.
	///
	/// This makes this result resolve to `ok() == false`.
	///
	/// # Parameters
	///
	/// - identifier - The identifier of the inherent that generated the error.
	/// - error - The error that will be encoded.
	pub fn put_error<E: codec::Encode + IsFatalError>(
		&mut self,
		identifier: InherentIdentifier,
		error: &E,
	) -> Result<(), Error> {
		// Don't accept any other error
		if self.fatal_error {
			return Err(Error::FatalErrorReported)
		}

		if error.is_fatal_error() {
			// remove the other errors.
			self.errors.data.clear();
		}

		self.errors.put_data(identifier, error)?;

		self.okay = false;
		self.fatal_error = error.is_fatal_error();
		Ok(())
	}

	/// Get an error out of the result.
	///
	/// # Return
	///
	/// - `Ok(Some(I))` if the error could be found and deserialized.
	/// - `Ok(None)` if the error could not be found.
	/// - `Err(_)` if the error could be found, but deserialization did not work.
	pub fn get_error<E: codec::Decode>(
		&self,
		identifier: &InherentIdentifier,
	) -> Result<Option<E>, Error> {
		self.errors.get_data(identifier)
	}

	/// Convert into an iterator over all contained errors.
	pub fn into_errors(self) -> IntoIter<InherentIdentifier, Vec<u8>> {
		self.errors.data.into_iter()
	}

	/// Is this result ok?
	pub fn ok(&self) -> bool {
		self.okay
	}

	/// Is this a fatal error?
	pub fn fatal_error(&self) -> bool {
		self.fatal_error
	}
}

#[cfg(feature = "std")]
impl PartialEq for CheckInherentsResult {
	fn eq(&self, other: &Self) -> bool {
		self.fatal_error == other.fatal_error &&
			self.okay == other.okay &&
			self.errors.data == other.errors.data
	}
}

/// Did we encounter a fatal error while checking an inherent?
///
/// A fatal error is everything that fails while checking an inherent error, e.g. the inherent
/// was not found, could not be decoded etc.
/// Then there are cases where you not want the inherent check to fail, but report that there is an
/// action required. For example a timestamp of a block is in the future, the timestamp is still
/// correct, but it is required to verify the block at a later time again and then the inherent
/// check will succeed.
pub trait IsFatalError {
	/// Is this a fatal error?
	fn is_fatal_error(&self) -> bool;
}

/// Auxiliary to make any given error resolve to `is_fatal_error() == true` for [`IsFatalError`].
#[derive(codec::Encode)]
pub struct MakeFatalError<E>(E);

impl<E: codec::Encode> From<E> for MakeFatalError<E> {
	fn from(err: E) -> Self {
		MakeFatalError(err)
	}
}

impl<E: codec::Encode> IsFatalError for MakeFatalError<E> {
	fn is_fatal_error(&self) -> bool {
		true
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use codec::{Decode, Encode};

	const TEST_INHERENT_0: InherentIdentifier = *b"testinh0";
	const TEST_INHERENT_1: InherentIdentifier = *b"testinh1";

	#[derive(Encode)]
	struct NoFatalError<E: codec::Encode>(E);
	impl<E: codec::Encode> IsFatalError for NoFatalError<E> {
		fn is_fatal_error(&self) -> bool {
			false
		}
	}

	#[test]
	fn inherent_data_encodes_and_decodes() {
		let inherent_0 = vec![1, 2, 3];
		let inherent_1: u32 = 7;

		let mut data = InherentData::new();
		data.put_data(TEST_INHERENT_0, &inherent_0).unwrap();
		data.put_data(TEST_INHERENT_1, &inherent_1).unwrap();

		let encoded = data.encode();

		let decoded = InherentData::decode(&mut &encoded[..]).unwrap();

		assert_eq!(decoded.get_data::<Vec<u32>>(&TEST_INHERENT_0).unwrap().unwrap(), inherent_0);
		assert_eq!(decoded.get_data::<u32>(&TEST_INHERENT_1).unwrap().unwrap(), inherent_1);
	}

	#[test]
	fn adding_same_inherent_returns_an_error() {
		let mut data = InherentData::new();
		data.put_data(TEST_INHERENT_0, &8).unwrap();
		assert!(data.put_data(TEST_INHERENT_0, &10).is_err());
	}

	#[derive(Clone)]
	struct TestInherentDataProvider;

	const ERROR_TO_STRING: &str = "Found error!";

	#[async_trait::async_trait]
	impl InherentDataProvider for TestInherentDataProvider {
		fn provide_inherent_data(&self, data: &mut InherentData) -> Result<(), Error> {
			data.put_data(TEST_INHERENT_0, &42)
		}

		async fn try_handle_error(
			&self,
			_: &InherentIdentifier,
			_: &[u8],
		) -> Option<Result<(), Error>> {
			Some(Err(Error::Application(Box::from(ERROR_TO_STRING))))
		}
	}

	#[test]
	fn create_inherent_data() {
		let provider = TestInherentDataProvider;

		let inherent_data = provider.create_inherent_data().unwrap();

		assert_eq!(inherent_data.get_data::<u32>(&TEST_INHERENT_0).unwrap().unwrap(), 42u32);
	}

	#[test]
	fn check_inherents_result_encodes_and_decodes() {
		let mut result = CheckInherentsResult::new();
		assert!(result.ok());

		result.put_error(TEST_INHERENT_0, &NoFatalError(2u32)).unwrap();
		assert!(!result.ok());
		assert!(!result.fatal_error());

		let encoded = result.encode();

		let decoded = CheckInherentsResult::decode(&mut &encoded[..]).unwrap();

		assert_eq!(decoded.get_error::<u32>(&TEST_INHERENT_0).unwrap().unwrap(), 2);
		assert!(!decoded.ok());
		assert!(!decoded.fatal_error());
	}

	#[test]
	fn check_inherents_result_removes_other_errors_on_fatal_error() {
		let mut result = CheckInherentsResult::new();
		assert!(result.ok());

		result.put_error(TEST_INHERENT_0, &NoFatalError(2u32)).unwrap();
		assert!(!result.ok());
		assert!(!result.fatal_error());

		result.put_error(TEST_INHERENT_1, &MakeFatalError(4u32)).unwrap();
		assert!(!result.ok());
		assert!(result.fatal_error());

		assert!(result.put_error(TEST_INHERENT_0, &NoFatalError(5u32)).is_err());

		result.into_errors().for_each(|(i, e)| match i {
			TEST_INHERENT_1 => assert_eq!(u32::decode(&mut &e[..]).unwrap(), 4),
			_ => panic!("There should be no other error!"),
		});
	}
}