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// SPDX-License-Identifier: Apache-2.0
// This file is part of Frontier.
//
// Copyright (c) 2021-2022 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.

// Ensure we're `no_std` when compiling for Wasm.
#![cfg_attr(not(feature = "std"), no_std)]
#![warn(unused_crate_dependencies)]

#[cfg(test)]
mod tests;

use frame_support::{inherent::IsFatalError, traits::Get, weights::Weight};
use sp_core::U256;
use sp_inherents::{InherentData, InherentIdentifier};
use sp_std::cmp::{max, min};

pub use self::pallet::*;
#[cfg(feature = "std")]
pub use fp_dynamic_fee::InherentDataProvider;
pub use fp_dynamic_fee::{InherentType, INHERENT_IDENTIFIER};

#[frame_support::pallet]
pub mod pallet {
    use super::*;
    use frame_support::pallet_prelude::*;
    use frame_system::pallet_prelude::*;

    #[pallet::pallet]
    pub struct Pallet<T>(PhantomData<T>);

    #[pallet::config]
    pub trait Config: frame_system::Config {
        /// Bound divisor for min gas price.
        type MinGasPriceBoundDivisor: Get<U256>;
    }

    #[pallet::hooks]
    impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
        fn on_initialize(_n: BlockNumberFor<T>) -> Weight {
            TargetMinGasPrice::<T>::kill();

            T::DbWeight::get().writes(1)
        }

        fn on_finalize(_n: BlockNumberFor<T>) {
            if let Some(target) = TargetMinGasPrice::<T>::take() {
                let bound =
                    MinGasPrice::<T>::get() / T::MinGasPriceBoundDivisor::get() + U256::one();

                let upper_limit = MinGasPrice::<T>::get().saturating_add(bound);
                let lower_limit = MinGasPrice::<T>::get().saturating_sub(bound);

                MinGasPrice::<T>::set(min(upper_limit, max(lower_limit, target)));
            }
        }
    }

    #[pallet::call]
    impl<T: Config> Pallet<T> {
        #[pallet::call_index(0)]
        #[pallet::weight((T::DbWeight::get().writes(1), DispatchClass::Mandatory))]
        pub fn note_min_gas_price_target(origin: OriginFor<T>, target: U256) -> DispatchResult {
            ensure_none(origin)?;
            assert!(
                TargetMinGasPrice::<T>::get().is_none(),
                "TargetMinGasPrice must be updated only once in the block",
            );

            TargetMinGasPrice::<T>::set(Some(target));
            Ok(())
        }
    }

    #[pallet::genesis_config]
    #[derive(frame_support::DefaultNoBound)]
    pub struct GenesisConfig<T> {
        pub min_gas_price: U256,
        #[serde(skip)]
        pub _marker: PhantomData<T>,
    }

    #[pallet::genesis_build]
    impl<T: Config> BuildGenesisConfig for GenesisConfig<T> {
        fn build(&self) {
            MinGasPrice::<T>::put(self.min_gas_price);
        }
    }

    #[pallet::storage]
    pub type MinGasPrice<T: Config> = StorageValue<_, U256, ValueQuery>;

    #[pallet::storage]
    pub type TargetMinGasPrice<T: Config> = StorageValue<_, U256>;

    #[derive(Encode, Decode, RuntimeDebug)]
    pub enum InherentError {}

    impl IsFatalError for InherentError {
        fn is_fatal_error(&self) -> bool {
            match *self {}
        }
    }

    #[pallet::inherent]
    impl<T: Config> ProvideInherent for Pallet<T> {
        type Call = Call<T>;
        type Error = InherentError;

        const INHERENT_IDENTIFIER: InherentIdentifier = INHERENT_IDENTIFIER;

        fn create_inherent(data: &InherentData) -> Option<Self::Call> {
            let target = data.get_data::<InherentType>(&INHERENT_IDENTIFIER).ok()??;

            Some(Call::note_min_gas_price_target { target })
        }

        fn check_inherent(_call: &Self::Call, _data: &InherentData) -> Result<(), Self::Error> {
            Ok(())
        }

        fn is_inherent(call: &Self::Call) -> bool {
            matches!(call, Call::note_min_gas_price_target { .. })
        }
    }
}

impl<T: Config> fp_evm::FeeCalculator for Pallet<T> {
    fn min_gas_price() -> (U256, Weight) {
        (MinGasPrice::<T>::get(), T::DbWeight::get().reads(1))
    }
}