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// SPDX-License-Identifier: Apache-2.0
// This file is part of Frontier.
//
// Copyright (c) 2020-2022 Parity Technologies (UK) Ltd.
//
// 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.

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

extern crate alloc;

#[cfg(test)]
mod mock;

#[cfg(test)]
mod tests;

use alloc::format;
use core::marker::PhantomData;

use scale_codec::{Decode, DecodeLimit};
// Substrate
use frame_support::{
	dispatch::{DispatchClass, GetDispatchInfo, Pays, PostDispatchInfo},
	traits::{ConstU32, Get},
};
use sp_runtime::traits::Dispatchable;
// Frontier
use fp_evm::{
	ExitError, ExitSucceed, Precompile, PrecompileFailure, PrecompileHandle, PrecompileOutput,
	PrecompileResult,
};
use pallet_evm::{AddressMapping, GasWeightMapping};

// `DecodeLimit` specifies the max depth a call can use when decoding, as unbounded depth
// can be used to overflow the stack.
// Default value is 8, which is the same as in XCM call decoding.
pub struct Dispatch<T, DispatchValidator = (), DecodeLimit = ConstU32<8>> {
	_marker: PhantomData<(T, DispatchValidator, DecodeLimit)>,
}

impl<T, DispatchValidator, DecodeLimit> Precompile for Dispatch<T, DispatchValidator, DecodeLimit>
where
	T: pallet_evm::Config,
	T::RuntimeCall: Dispatchable<PostInfo = PostDispatchInfo> + GetDispatchInfo + Decode,
	<T::RuntimeCall as Dispatchable>::RuntimeOrigin: From<Option<T::AccountId>>,
	DispatchValidator: DispatchValidateT<T::AccountId, T::RuntimeCall>,
	DecodeLimit: Get<u32>,
{
	fn execute(handle: &mut impl PrecompileHandle) -> PrecompileResult {
		let input = handle.input();
		let target_gas = handle.gas_limit();
		let context = handle.context();

		let call = T::RuntimeCall::decode_with_depth_limit(DecodeLimit::get(), &mut &*input)
			.map_err(|_| PrecompileFailure::Error {
				exit_status: ExitError::Other("decode failed".into()),
			})?;
		let info = call.get_dispatch_info();

		if let Some(gas) = target_gas {
			let valid_weight =
				info.weight.ref_time() <= T::GasWeightMapping::gas_to_weight(gas, false).ref_time();
			if !valid_weight {
				return Err(PrecompileFailure::Error {
					exit_status: ExitError::OutOfGas,
				});
			}
		}

		let origin = T::AddressMapping::into_account_id(context.caller);

		if let Some(err) = DispatchValidator::validate_before_dispatch(&origin, &call) {
			return Err(err);
		}

		handle.record_external_cost(
			Some(info.weight.ref_time()),
			Some(info.weight.proof_size()),
			None,
		)?;

		match call.dispatch(Some(origin).into()) {
			Ok(post_info) => {
				if post_info.pays_fee(&info) == Pays::Yes {
					let actual_weight = post_info.actual_weight.unwrap_or(info.weight);
					let cost = T::GasWeightMapping::weight_to_gas(actual_weight);
					handle.record_cost(cost)?;

					handle.refund_external_cost(
						Some(
							info.weight
								.ref_time()
								.saturating_sub(actual_weight.ref_time()),
						),
						Some(
							info.weight
								.proof_size()
								.saturating_sub(actual_weight.proof_size()),
						),
					);
				}

				Ok(PrecompileOutput {
					exit_status: ExitSucceed::Stopped,
					output: Default::default(),
				})
			}
			Err(e) => Err(PrecompileFailure::Error {
				exit_status: ExitError::Other(
					format!("dispatch execution failed: {}", <&'static str>::from(e)).into(),
				),
			}),
		}
	}
}

/// Dispatch validation trait.
pub trait DispatchValidateT<AccountId, RuntimeCall> {
	fn validate_before_dispatch(
		origin: &AccountId,
		call: &RuntimeCall,
	) -> Option<PrecompileFailure>;
}

/// The default implementation of `DispatchValidateT`.
impl<AccountId, RuntimeCall> DispatchValidateT<AccountId, RuntimeCall> for ()
where
	RuntimeCall: GetDispatchInfo,
{
	fn validate_before_dispatch(
		_origin: &AccountId,
		call: &RuntimeCall,
	) -> Option<PrecompileFailure> {
		let info = call.get_dispatch_info();
		if !(info.pays_fee == Pays::Yes && info.class == DispatchClass::Normal) {
			return Some(PrecompileFailure::Error {
				exit_status: ExitError::Other("invalid call".into()),
			});
		}
		None
	}
}