ghost-node/pallets/slow-clap/src/lib.rs

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

use codec::{Decode, Encode, MaxEncodedLen};
use scale_info::TypeInfo;
use serde::{Deserializer, Deserialize};

pub use pallet::*;
use frame_support::{
    pallet_prelude::*,
    traits::{
        tokens::fungible::{Inspect, Mutate},
        EstimateNextSessionRotation, ValidatorSet, ValidatorSetWithIdentification, 
        OneSessionHandler, Get,
    },
    WeakBoundedVec,
    
};
use frame_system::{
    offchain::{SendTransactionTypes, SubmitTransaction},
    pallet_prelude::*,
};

use sp_core::H256;
use sp_runtime::{
    Perbill, RuntimeAppPublic, RuntimeDebug, SaturatedConversion,
    offchain::{
        self as rt_offchain, HttpError,
        storage::{MutateStorageError, StorageRetrievalError, StorageValueRef},
    },
    traits::{BlockNumberProvider, Convert, Saturating},
};
use sp_std::{
    vec::Vec, prelude::*,
    collections::btree_map::BTreeMap, 
};
use sp_staking::{
    offence::{Kind, Offence, ReportOffence},
    SessionIndex,
};

use ghost_networks::{
    NetworkData, NetworkDataBasicHandler, NetworkDataInspectHandler,
    NetworkDataMutateHandler, NetworkType,
};

pub mod weights;
pub use crate::weights::WeightInfo;
mod tests;
mod mock;
mod benchmarking;

pub mod sr25519 {
    mod app_sr25519 {
        use sp_application_crypto::{app_crypto, sr25519, KeyTypeId};
        const SLOW_CLAP: KeyTypeId = KeyTypeId(*b"slow");
        app_crypto!(sr25519, SLOW_CLAP);
    }

    sp_application_crypto::with_pair! {
        pub type AuthorityPair = app_sr25519::Pair;
    }

    pub type AuthoritySignature = app_sr25519::Signature;
    pub type AuthorityId = app_sr25519::Public;
}

const LOG_TARGET: &str = "runtime::ghost-slow-clap";
const DB_PREFIX: &[u8] = b"slow_clap::";

const FETCH_TIMEOUT_PERIOD: u64 = 3_000;
const LOCK_BLOCK_EXPIRATION: u64 = 10;
const NUMBER_OF_TOPICS: usize = 3;

pub type AuthIndex = u32;

#[derive(RuntimeDebug, Clone, PartialEq, Deserialize, Encode, Decode)]
struct EvmResponse {
    #[serde(default)]
    id: Option<u32>,
    #[serde(default, deserialize_with = "de_string_to_bytes")]
    jsonrpc: Option<Vec<u8>>,
    #[serde(default, deserialize_with = "de_string_to_bytes")]
    error: Option<Vec<u8>>,
    #[serde(default)]
    result: Option<EvmResponseType>,
}

#[derive(RuntimeDebug, Clone, PartialEq, Deserialize, Encode, Decode)]
#[serde(untagged)]
enum EvmResponseType {
    #[serde(deserialize_with = "de_string_to_u64_pure")]
    BlockNumber(u64),
    TransactionLogs(Vec<Log>),
}

#[derive(RuntimeDebug, Clone, Eq, PartialEq, Ord, PartialOrd, Deserialize, Encode, Decode)]
#[serde(rename_all = "camelCase")]
struct Log {
    #[serde(default, deserialize_with = "de_string_to_h256")]
    transaction_hash: Option<H256>,
    #[serde(default, deserialize_with = "de_string_to_u64")]
    block_number: Option<u64>,
    #[serde(default, deserialize_with = "de_string_to_vec_of_bytes")]
    topics: Vec<Vec<u8>>,
    #[serde(default, deserialize_with = "de_string_to_bytes")]
    address: Option<Vec<u8>>,
    #[serde(default, deserialize_with = "de_string_to_btree_map")]
    data: BTreeMap<u128, u128>,
    removed: bool,
}

impl Log {
    fn is_sufficient(&self) -> bool {
        self.transaction_hash.is_some() &&
            self.block_number.is_some() &&
            self.topics.len() == NUMBER_OF_TOPICS
    }
}

pub fn de_string_to_bytes<'de, D>(de: D) -> Result<Option<Vec<u8>>, D::Error>
where D: Deserializer<'de> {
    let s: &str = Deserialize::deserialize(de)?;
    Ok(Some(s.as_bytes().to_vec()))
}

pub fn de_string_to_u64<'de, D>(de: D) -> Result<Option<u64>, D::Error>
where D: Deserializer<'de> {
    let s: &str = Deserialize::deserialize(de)?;
    let s = if s.starts_with("0x") { &s[2..] } else { &s };
    Ok(u64::from_str_radix(s, 16).ok())
}

pub fn de_string_to_u64_pure<'de, D>(de: D) -> Result<u64, D::Error>
where D: Deserializer<'de> {
    let s: &str = Deserialize::deserialize(de)?;
    let s = if s.starts_with("0x") { &s[2..] } else { &s };
    Ok(u64::from_str_radix(s, 16).unwrap_or_default())
}

pub fn de_string_to_h256<'de, D>(de: D) -> Result<Option<H256>, D::Error>
where D: Deserializer<'de> {
    let s: &str = Deserialize::deserialize(de)?;
    let start_index = if s.starts_with("0x") { 2 } else { 0 };
    let h256: Vec<_> = (start_index..s.len())
        .step_by(2)
        .map(|i| u8::from_str_radix(&s[i..i+2], 16).expect("valid u8 symbol; qed"))
        .collect();
    Ok(Some(H256::from_slice(&h256)))
}

pub fn de_string_to_vec_of_bytes<'de, D>(de: D) -> Result<Vec<Vec<u8>>, D::Error>
where D: Deserializer<'de> {
    let strings: Vec<&str> = Deserialize::deserialize(de)?;
    Ok(strings
        .iter()
        .map(|s| {
            let start_index = if s.starts_with("0x") { 2 } else { 0 };
            (start_index..s.len())
                .step_by(2)
                .map(|i| u8::from_str_radix(&s[i..i+2], 16).expect("valid u8 symbol; qed"))
                .collect::<Vec<u8>>()
        })
        .collect::<Vec<Vec<u8>>>())
}

pub fn de_string_to_btree_map<'de, D>(de: D) -> Result<BTreeMap<u128, u128>, D::Error>
where D: Deserializer<'de> {
    let s: &str = Deserialize::deserialize(de)?;
    let start_index = if s.starts_with("0x") { 2 } else { 0 };
    Ok(BTreeMap::from_iter((start_index..s.len())
            .step_by(64)
            .map(|i| (
                    u128::from_str_radix(&s[i..i+32], 16).expect("valid u8 symbol; qed"),
                    u128::from_str_radix(&s[i+32..i+64], 16).expect("valid u8 symbol; qed"),
            ))))
}

#[derive(RuntimeDebug, Clone, Eq, PartialEq, Ord, PartialOrd, Encode, Decode, TypeInfo, MaxEncodedLen)]
pub struct Clap<AccountId, NetworkId, Balance> {
    pub session_index: SessionIndex,
    pub authority_index: AuthIndex,
    pub transaction_hash: H256,
    pub block_number: u64,
    pub removed: bool,
    pub network_id: NetworkId,
    pub receiver: AccountId,
    pub amount: Balance,
}

#[derive(Default, PartialEq, Encode, Decode, RuntimeDebug, TypeInfo)]
pub struct SessionAuthorityInfo {
    pub claps: u32,
    pub disabled: bool,
}

#[cfg_attr(test, derive(PartialEq))]
enum OffchainErr<NetworkId> {
    FailedSigning,
    SubmitTransaction,
    HttpJsonParsingError,
    HttpBytesParsingError,
    HttpRequestError(HttpError),
    RequestUncompleted,
    HttpResponseNotOk(u16),
    ErrorInEvmResponse,
    StorageRetrievalError(NetworkId),
    ConcurrentModificationError(NetworkId),
    UtxoNotImplemented(NetworkId),
    UnknownNetworkType(NetworkId),
}

impl<NetworkId: core::fmt::Debug> core::fmt::Debug for OffchainErr<NetworkId> {
    fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::fmt::Result {
        match *self {
            OffchainErr::FailedSigning => write!(fmt, "Failed to sign clap."),
            OffchainErr::SubmitTransaction => write!(fmt, "Failed to submit transaction."),
            OffchainErr::HttpJsonParsingError => write!(fmt, "Failed to parse evm response as JSON."),
            OffchainErr::HttpBytesParsingError => write!(fmt, "Failed to parse evm response as bytes."),
            OffchainErr::HttpRequestError(http_error) => match http_error {
                HttpError::DeadlineReached => write!(fmt, "Requested action couldn't been completed within a deadline."),
                HttpError::IoError => write!(fmt, "There was an IO error while processing the request."),
                HttpError::Invalid => write!(fmt, "The ID of the request is invalid in this context"),
            },
            OffchainErr::ConcurrentModificationError(ref network_id) => write!(fmt, "The underlying DB failed to update due to a concurrent modification for network #{:?}", network_id),
            OffchainErr::StorageRetrievalError(ref network_id) => write!(fmt, "Storage value found for network #{:?} but it's undecodable", network_id),
            OffchainErr::RequestUncompleted => write!(fmt, "Failed to complete request."),
            OffchainErr::HttpResponseNotOk(code) => write!(fmt, "Http response returned code {:?}", code),
            OffchainErr::ErrorInEvmResponse => write!(fmt, "Error in evm reponse."),
            OffchainErr::UtxoNotImplemented(ref network_id) => write!(fmt, "Network #{:?} is marked as UTXO, which is not implemented yet.", network_id),
            OffchainErr::UnknownNetworkType(ref network_id) => write!(fmt, "Unknown type for network #{:?}.", network_id),
        }
    }
}

pub type NetworkIdOf<T> = 
    <<T as Config>::NetworkDataHandler as NetworkDataBasicHandler>::NetworkId;

pub type BalanceOf<T> = <<T as Config>::Currency as Inspect<
    <T as frame_system::Config>::AccountId,
>>::Balance;

pub type ValidatorId<T> = <<T as Config>::ValidatorSet as ValidatorSet<
    <T as frame_system::Config>::AccountId,
>>::ValidatorId;

pub type IdentificationTuple<T> = (
    ValidatorId<T>,
    <<T as Config>::ValidatorSet as ValidatorSetWithIdentification<
        <T as frame_system::Config>::AccountId,
    >>::Identification,
);

type OffchainResult<T, A> = Result<A, OffchainErr<NetworkIdOf<T>>>;

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

    const STORAGE_VERSION: StorageVersion = StorageVersion::new(1);

    #[pallet::pallet]
    #[pallet::storage_version(STORAGE_VERSION)]
    #[pallet::without_storage_info]
    pub struct Pallet<T>(_);

    #[pallet::config]
    pub trait Config: SendTransactionTypes<Call<Self>> + frame_system::Config {
        type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
        type AuthorityId: Member 
            + Parameter
            + RuntimeAppPublic
            + Ord
            + MaybeSerializeDeserialize
            + MaxEncodedLen;

        type NextSessionRotation: EstimateNextSessionRotation<BlockNumberFor<Self>>;
        type ValidatorSet: ValidatorSetWithIdentification<Self::AccountId>;
        type Currency: Inspect<Self::AccountId> + Mutate<Self::AccountId>;
        type NetworkDataHandler: NetworkDataBasicHandler + 
            NetworkDataInspectHandler<NetworkData> + 
            NetworkDataMutateHandler<NetworkData, BalanceOf<Self>>;
        type BlockNumberProvider: BlockNumberProvider<BlockNumber = BlockNumberFor<Self>>;
        type ReportUnresponsiveness: ReportOffence<
            Self::AccountId,
            IdentificationTuple<Self>,
            ThrottlingOffence<IdentificationTuple<Self>>,
        >;

        #[pallet::constant]
        type MaxAuthorities: Get<u32>;
        
        #[pallet::constant]
        type ApplauseThreshold: Get<u32>;

        #[pallet::constant]
        type OffenceThreshold: Get<u32>;

        #[pallet::constant]
        type UnsignedPriority: Get<TransactionPriority>;

        #[pallet::constant]
        type HistoryDepth: Get<SessionIndex>;

        type WeightInfo: WeightInfo;
    }

    #[pallet::event]
    #[pallet::generate_deposit(pub(super) fn deposit_event)]
    pub enum Event<T: Config> {
        AuthoritiesEquilibrium,
        SomeAuthoritiesTrottling { throttling: Vec<IdentificationTuple<T>> },
        Clapped {
            authority_id: AuthIndex,
            network_id: NetworkIdOf<T>,
            transaction_hash: H256,
            receiver: T::AccountId,
            amount: BalanceOf<T>,
        },
        Applaused {
            network_id: NetworkIdOf<T>,
            receiver: T::AccountId,
            received_amount: BalanceOf<T>,
        },
    }

    #[pallet::error]
    pub enum Error<T> {
        NotEnoughClaps,
        NotAnAuthority,
        CurrentValidatorIsDisabled,
        AlreadyClapped,
        UnregisteredClapRemove,
        TooMuchAuthorities,
        CouldNotAccumulateCommission,
        CouldNotAccumulateIncomingImbalance,
        CouldNotIncreaseGatekeeperAmount,
    }

    #[pallet::storage]
    #[pallet::getter(fn received_claps)]
    pub(super) type ReceivedClaps<T: Config> = StorageNMap<
        _,
        (
            NMapKey<Twox64Concat, SessionIndex>,
            NMapKey<Twox64Concat, H256>,
            NMapKey<Twox64Concat, H256>,
        ),
        BoundedBTreeSet<AuthIndex, T::MaxAuthorities>,
        ValueQuery
    >;
    
    #[pallet::storage]
    #[pallet::getter(fn applauses_for_transaction)]
    pub(super) type ApplausesForTransaction<T: Config> = StorageNMap<
        _,
        (
            NMapKey<Twox64Concat, SessionIndex>,
            NMapKey<Twox64Concat, H256>,
            NMapKey<Twox64Concat, H256>,
        ),
        bool,
        ValueQuery
    >;

    #[pallet::storage]
    #[pallet::getter(fn claps_in_session)]
    pub(super) type ClapsInSession<T: Config> = StorageMap<
        _,
        Twox64Concat,
        SessionIndex,
        BTreeMap<AuthIndex, SessionAuthorityInfo>,
        ValueQuery,
    >;

    #[pallet::storage]
    #[pallet::getter(fn authorities)]
    pub(super) type Authorities<T: Config> = StorageMap<
        _,
        Twox64Concat,
        SessionIndex,
        WeakBoundedVec<T::AuthorityId, T::MaxAuthorities>,
        ValueQuery,
    >;

    #[pallet::genesis_config]
    #[derive(frame_support::DefaultNoBound)]
    pub struct GenesisConfig<T: Config> {
        pub authorities: Vec<T::AuthorityId>,
    }

    #[pallet::genesis_build]
    impl<T: Config> BuildGenesisConfig for GenesisConfig<T> {
        fn build(&self) {
            if !self.authorities.is_empty() {
                Pallet::<T>::initialize_authorities(self.authorities.clone());
            }
        }
    }

    #[pallet::call]
    impl<T: Config> Pallet<T> {
        #[pallet::call_index(0)]
        #[pallet::weight((T::WeightInfo::slow_clap(), DispatchClass::Normal, Pays::No))]
        pub fn slow_clap(
            origin: OriginFor<T>,
            clap: Clap<T::AccountId, NetworkIdOf<T>, BalanceOf<T>>,
            // since signature verification is done in `validate_unsigned`
            // we can skip doing it here again.
            _signature: <T::AuthorityId as RuntimeAppPublic>::Signature,
        ) -> DispatchResult {
            ensure_none(origin)?;
            Self::try_slow_clap(&clap)?;
            Ok(())
        }

        #[pallet::call_index(1)]
        #[pallet::weight(T::WeightInfo::self_applause())]
        pub fn self_applause(
            origin: OriginFor<T>,
            network_id: NetworkIdOf<T>,
            session_index: SessionIndex,
            transaction_hash: H256,
            receiver: T::AccountId,
            amount: BalanceOf<T>,
        ) -> DispatchResult {
            let _ = ensure_signed(origin)?;
            Self::applause_if_posible(
                network_id,
                session_index,
                transaction_hash,
                receiver,
                amount,
            )
        }
    }

    #[pallet::hooks]
    impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
        fn offchain_worker(now: BlockNumberFor<T>) {
            // Only send messages of we are a potential validator.
            if sp_io::offchain::is_validator() {
                let networks_len = T::NetworkDataHandler::iter().count();
                if networks_len == 0 { 
                    log::info!(
                        target: LOG_TARGET,
                        "👏 Skipping slow clap at {:?}: no evm networks",
                        now,
                    );
                } else {
                    for result in Self::start_slow_clapping(now, networks_len).into_iter().flatten() {
                        if let Err(e) = result {
                            log::info!(
                                target: LOG_TARGET,
                                "👏 Skipping slow clap at {:?}: {:?}",
                                now, 
                                e,
                            );
                        }
                    }
                }
            } else {
                log::info!(
                    target: LOG_TARGET,
                    "🤥 Not a validator, skipping slow clap at {:?}.",
                    now,
                );
            }
        }
    }

    #[pallet::validate_unsigned]
    impl<T: Config> ValidateUnsigned for Pallet<T> {
        type Call = Call<T>;

        fn validate_unsigned(_source: TransactionSource, call: &Self::Call) -> TransactionValidity {
            if let Call::slow_clap { clap, signature } = call {
                let authorities = Authorities::<T>::get(&clap.session_index);
                let authority = match authorities.get(clap.authority_index as usize) {
                    Some(authority) => authority,
                    None => return InvalidTransaction::BadSigner.into(),
                };

                let signature_valid = clap.using_encoded(|encoded_clap| {
                    authority.verify(&encoded_clap, signature)
                });

                if !signature_valid {
                    return InvalidTransaction::BadProof.into();
                }

                ValidTransaction::with_tag_prefix("SlowClap")
                    .priority(T::UnsignedPriority::get())
                    .and_provides(signature)
                    .longevity(LOCK_BLOCK_EXPIRATION)
                    .propagate(true)
                    .build()
            } else {
                InvalidTransaction::Call.into()
            }
        }
    }
}

impl<T: Config> Pallet<T> {
    fn generate_unique_hash(
        receiver: &T::AccountId,
        amount: &BalanceOf<T>,
        network_id: &NetworkIdOf<T>,
    ) -> H256 {
        let mut clap_args_str = receiver.encode();
        clap_args_str.extend(&amount.encode());
        clap_args_str.extend(&network_id.encode());

        H256::from_slice(&sp_io::hashing::keccak_256(&clap_args_str)[..])
    }

    fn try_slow_clap(clap: &Clap<T::AccountId, NetworkIdOf<T>, BalanceOf<T>>) -> DispatchResult {
        let authorities = Authorities::<T>::get(&clap.session_index);
        ensure!(authorities.get(clap.authority_index as usize).is_some(), Error::<T>::NotAnAuthority);

        let clap_unique_hash = Self::generate_unique_hash(&clap.receiver, &clap.amount, &clap.network_id);
        let received_claps_key = (clap.session_index, &clap.transaction_hash, &clap_unique_hash);

        let number_of_received_claps = ReceivedClaps::<T>::try_mutate(&received_claps_key, |tree_of_claps| {
            let number_of_claps = tree_of_claps.len();
            match (tree_of_claps.contains(&clap.authority_index), clap.removed) {
                (true, true) => tree_of_claps
                    .remove(&clap.authority_index)
                    .then(|| number_of_claps.saturating_sub(1))
                    .ok_or(Error::<T>::UnregisteredClapRemove),
                (true, false) => Err(Error::<T>::AlreadyClapped),
                (false, true) => Err(Error::<T>::UnregisteredClapRemove),
                (false, false) => tree_of_claps
                    .try_insert(clap.authority_index)
                    .map(|_| number_of_claps.saturating_add(1))
                    .map_err(|_| Error::<T>::TooMuchAuthorities),
            }
        })?;

        ClapsInSession::<T>::try_mutate(&clap.session_index, |claps_details| {
            if claps_details.get(&clap.authority_index).map(|x| x.disabled).unwrap_or_default() {
                return Err(Error::<T>::CurrentValidatorIsDisabled);
            }

            (*claps_details)
                .entry(clap.authority_index)
                .and_modify(|individual| (*individual).claps.saturating_inc())
                .or_insert(SessionAuthorityInfo { claps: 1u32, disabled: false });

            Ok(())
        })?;

        Self::deposit_event(Event::<T>::Clapped {
            authority_id: clap.authority_index,
            network_id: clap.network_id,
            transaction_hash: clap.transaction_hash,
            receiver: clap.receiver.clone(),
            amount: clap.amount,
        });

        let enough_authorities = Perbill::from_rational(
            number_of_received_claps as u32,
            authorities.len() as u32,
        ) > Perbill::from_percent(T::ApplauseThreshold::get());

        if enough_authorities {
            if let Err(error_msg) = Self::try_applause(&clap, &received_claps_key) {
                log::info!(
                    target: LOG_TARGET,
                    "👏 Could not applause because of: {:?}",
                    error_msg, 
                );
            }
        }

        Ok(())
    }

    fn try_applause(
        clap: &Clap<T::AccountId, NetworkIdOf<T>, BalanceOf<T>>,
        received_claps_key: &(SessionIndex, &H256, &H256),
    ) -> DispatchResult {
        ApplausesForTransaction::<T>::try_mutate(received_claps_key, |is_applaused| {
            if *is_applaused || T::NetworkDataHandler::is_nullification_period() {
                return Ok(())
            }

            let commission = T::NetworkDataHandler::get(&clap.network_id)
                .map(|network_data| Perbill::from_parts(network_data.incoming_fee))
                .unwrap_or_default()
                .mul_ceil(clap.amount);
            let final_amount = clap.amount.saturating_sub(commission);

            let _ = T::NetworkDataHandler::increase_gatekeeper_amount(&clap.network_id, &clap.amount)
                .map_err(|_| Error::<T>::CouldNotIncreaseGatekeeperAmount)?;
            let _ = T::NetworkDataHandler::accumulate_incoming_imbalance(&final_amount)
                .map_err(|_| Error::<T>::CouldNotAccumulateIncomingImbalance)?;
            let _ = T::NetworkDataHandler::accumulate_commission(&commission)
                .map_err(|_| Error::<T>::CouldNotAccumulateCommission)?;

            if final_amount > T::Currency::minimum_balance() {
                T::Currency::mint_into(
                    &clap.receiver,
                    final_amount
                )?;
            }

            *is_applaused = true;

            Self::deposit_event(Event::<T>::Applaused {
                network_id: clap.network_id,
                receiver: clap.receiver.clone(),
                received_amount: final_amount,
            });

            Ok(())
        })
    }

    fn applause_if_posible(
        network_id: NetworkIdOf<T>,
        session_index: SessionIndex,
        transaction_hash: H256,
        receiver: T::AccountId,
        amount: BalanceOf<T>,
    ) -> DispatchResult{
        let clap_unique_hash = Self::generate_unique_hash(&receiver, &amount, &network_id);
        let received_claps_key = (session_index, &transaction_hash, &clap_unique_hash);

        let clap = Clap {
            authority_index: Default::default(),
            block_number: Default::default(),
            removed: false,
            session_index,
            network_id,
            receiver,
            amount,
            transaction_hash,
        };

        let enough_authorities = Perbill::from_rational(
            ReceivedClaps::<T>::get(&received_claps_key).len() as u32,
            Authorities::<T>::get(session_index).len() as u32,
        ) > Perbill::from_percent(T::ApplauseThreshold::get());

        ensure!(enough_authorities, Error::<T>::NotEnoughClaps);
        Self::try_applause(&clap, &received_claps_key)?;

        Ok(())
    }

    fn start_slow_clapping(
        block_number: BlockNumberFor<T>,
        networks_len: usize,
    ) -> OffchainResult<T, impl Iterator<Item = OffchainResult<T, ()>>> {
        let session_index = T::ValidatorSet::session_index();
        let network_in_use = T::NetworkDataHandler::iter()
            .nth(block_number.into().as_usize() % networks_len)
            .expect("network should exist; qed");

        Ok(Self::local_authorities().map(move |(authority_index, authority_key)| {
            Self::do_evm_claps_or_save_block(
                authority_index, 
                authority_key, 
                session_index,
                network_in_use.0,
                &network_in_use.1,
            )
        }))
    }

    fn create_storage_key(first: &[u8], second: &[u8]) -> Vec<u8> {
        let mut key = DB_PREFIX.to_vec();
        key.extend(first);
        key.extend(second);
        key
    }

    fn do_evm_claps_or_save_block(
        authority_index: AuthIndex,
        authority_key: T::AuthorityId,
        session_index: SessionIndex,
        network_id: NetworkIdOf<T>,
        network_data: &NetworkData,
    ) -> OffchainResult<T, ()> {
        let network_id_encoded = network_id.encode();

        let block_number_key = Self::create_storage_key(b"block-", &network_id_encoded);
        let block_distance_key = Self::create_storage_key(b"block-distance-", &network_id_encoded);
        let endpoint_key = Self::create_storage_key(b"endpoint-", &network_id_encoded);

        let rpc_endpoint = StorageValueRef::persistent(&endpoint_key)
            .get()
            .ok()
            .flatten()
            .unwrap_or(network_data.default_endpoint.clone());

        let max_block_distance = StorageValueRef::persistent(&block_distance_key)
            .get()
            .ok()
            .flatten()
            .unwrap_or(network_data.block_distance);

        let mutation_result = StorageValueRef::persistent(&block_number_key).mutate(|result_block_range: Result<Option<(u64, u64)>, StorageRetrievalError>| {
            match result_block_range {
                Ok(maybe_block_range) => {
                    let request_body = match maybe_block_range {
                        Some((from_block, to_block)) if from_block < to_block.saturating_sub(1) =>
                            Self::prepare_request_body_for_latest_transfers(from_block, to_block.saturating_sub(1), network_data),
                        _ => Self::prepare_request_body_for_latest_block(network_data),
                    };

                    let response_bytes = Self::fetch_from_remote(&rpc_endpoint, &request_body)?;

                    match network_data.network_type {
                        NetworkType::Evm => {
                            let maybe_new_evm_block = Self::apply_evm_response(
                                &response_bytes,
                                authority_index,
                                authority_key,
                                session_index,
                                network_id
                            )?;

                            let estimated_block = maybe_new_evm_block
                                .map(|new_evm_block| new_evm_block.saturating_sub(network_data.finality_delay))
                                .unwrap_or_default();

                            Ok(match maybe_block_range {
                                Some((from_block, to_block)) => match maybe_new_evm_block {
                                    Some(_) => match estimated_block.checked_sub(from_block) {
                                        Some(current_distance) if current_distance < max_block_distance =>
                                            (from_block, estimated_block),
                                        _ => (from_block, from_block
                                                .saturating_add(max_block_distance)
                                                .min(estimated_block)),
                                    },
                                    None => (to_block, to_block),
                                },
                                None => (estimated_block, estimated_block),
                            })
                        },
                        NetworkType::Utxo => Err(OffchainErr::UtxoNotImplemented(network_id).into()),
                        _ => Err(OffchainErr::UnknownNetworkType(network_id).into()),
                    }
                }
                Err(_) => Err(OffchainErr::StorageRetrievalError(network_id).into())
            }
        });

        match mutation_result {
            Ok(_) => Ok(()),
            Err(MutateStorageError::ValueFunctionFailed(offchain_error)) => Err(offchain_error),
            Err(MutateStorageError::ConcurrentModification(_)) => Err(OffchainErr::ConcurrentModificationError(network_id).into()),
        }
    }

    fn apply_evm_response(
        response_bytes: &[u8],
        authority_index: AuthIndex,
        authority_key: T::AuthorityId,
        session_index: SessionIndex,
        network_id: NetworkIdOf<T>
    ) -> OffchainResult<T, Option<u64>> {
        match Self::parse_evm_response(&response_bytes)? {
            EvmResponseType::BlockNumber(new_evm_block) => {
                log::info!(
                    target: LOG_TARGET,
                    "🧐 New evm block #{:?} found for network {:?}",
                    new_evm_block,
                    network_id,
                );
                Ok(Some(new_evm_block))
            },
            EvmResponseType::TransactionLogs(evm_logs) => {
                let claps: Vec<_> = evm_logs
                    .iter()
                    .filter_map(|log| log.is_sufficient().then(|| {
                        Clap {
                            authority_index,
                            session_index,
                            network_id,
                            removed: log.removed,
                            receiver: T::AccountId::decode(&mut &log.topics[1][0..32])
                                .expect("32 bytes always construct an AccountId32"),
                            amount: u128::from_be_bytes(log.topics[2][16..32]
                                .try_into()
                                .expect("amount is valid hex; qed"))
                                .saturated_into::<BalanceOf<T>>(),
                            transaction_hash: log.transaction_hash
                                .clone()
                                .expect("tx hash exists; qed"),
                            block_number: log.block_number
                                .expect("block number exists; qed"),
                        }
                    }))
                    .collect();

                log::info!(
                    target: LOG_TARGET,
                    "🧐 {:?} evm logs found for network {:?}",
                    claps.len(),
                    network_id,
                );

                for clap in claps {
                    let signature = authority_key.sign(&clap.encode())
                        .ok_or(OffchainErr::FailedSigning)?;
                    let call = Call::slow_clap { clap, signature };

                    SubmitTransaction::<T, Call<T>>::submit_unsigned_transaction(call.into())
                        .map_err(|_| OffchainErr::SubmitTransaction)?;
                }

                Ok(None)
            }
        }
    }

    fn local_authorities() -> impl Iterator<Item = (u32, T::AuthorityId)> {
        let session_index = T::ValidatorSet::session_index();
        let authorities = Authorities::<T>::get(&session_index);
        let mut local_authorities = T::AuthorityId::all();
        local_authorities.sort();

        authorities.into_iter().enumerate().filter_map(move |(index, authority)| {
            local_authorities
                .binary_search(&authority)
                .ok()
                .map(|location| (index as u32, local_authorities[location].clone()))
        })
    }

    fn fetch_from_remote(
        rpc_endpoint: &[u8],
        request_body: &[u8],
    ) -> OffchainResult<T, Vec<u8>> {
        let rpc_endpoint_str = core::str::from_utf8(rpc_endpoint).expect("rpc endpoint valid str; qed");
        let request_body_str = core::str::from_utf8(request_body).expect("request body valid str: qed");

        let deadline = sp_io::offchain::timestamp().add(rt_offchain::Duration::from_millis(FETCH_TIMEOUT_PERIOD));

        let pending = rt_offchain::http::Request::post(&rpc_endpoint_str, vec![request_body_str])
            .add_header("Accept", "application/json")
            .add_header("Content-Type", "application/json")
            .deadline(deadline)
            .send()
            .map_err(|err| OffchainErr::HttpRequestError(err))?;

        let response = pending
            .try_wait(deadline)
            .map_err(|_| OffchainErr::RequestUncompleted)?
            .map_err(|_| OffchainErr::RequestUncompleted)?;

        if response.code != 200 {
            return Err(OffchainErr::HttpResponseNotOk(response.code))
        }

        Ok(response.body().collect::<Vec<u8>>())
    }

    fn u64_to_hexadecimal_bytes(value: u64) -> Vec<u8> {
        let mut hex_str = Vec::new();
        hex_str.push(b'0');
        hex_str.push(b'x');

        if value == 0 {
            hex_str.push(b'0');
            return hex_str;
        }

        for i in (0..16).rev() {
            let nibble = (value >> (i * 4)) & 0xF;
            if nibble != 0 || hex_str.len() > 2 {
                hex_str.push(match nibble {
                    0..=9 => b'0' + nibble as u8,
                    10..=15 => b'a' + (nibble - 10) as u8,
                    _ => unreachable!(),
                });
            }
        }

        hex_str
    }

    fn prepare_request_body_for_latest_block(network_data: &NetworkData) -> Vec<u8> {
        match network_data.network_type {
            NetworkType::Evm => b"{\"id\":0,\"jsonrpc\":\"2.0\",\"method\":\"eth_blockNumber\"}".to_vec(),
            _ => Default::default(),
        }
    }

    fn prepare_request_body_for_latest_transfers(from_block: u64, to_block: u64, network_data: &NetworkData) -> Vec<u8> {
        match network_data.network_type {
            NetworkType::Evm => {
                let mut body = b"{\"id\":0,\"jsonrpc\":\"2.0\",\"method\":\"eth_getLogs\",\"params\":[{".to_vec();
                body.extend(b"\"fromBlock\":\"".to_vec());
                body.extend(Self::u64_to_hexadecimal_bytes(from_block));
                body.extend(b"\",\"toBlock\":\"".to_vec());
                body.extend(Self::u64_to_hexadecimal_bytes(to_block));
                body.extend(b"\",\"address\":\"".to_vec());
                body.extend(network_data.gatekeeper.to_vec());
                body.extend(b"\",\"topics\":[\"".to_vec());
                body.extend(network_data.topic_name.to_vec());
                body.extend(b"\"]}]}".to_vec());
                body
            },
            _ => Default::default(),
        }
    }

    fn parse_evm_response(response_bytes: &[u8]) -> OffchainResult<T, EvmResponseType> {
        let response_str = sp_std::str::from_utf8(&response_bytes)
            .map_err(|_| OffchainErr::HttpBytesParsingError)?;

        let response_result: EvmResponse = serde_json::from_str(&response_str)
            .map_err(|_| OffchainErr::HttpJsonParsingError)?;

        if response_result.error.is_some() {
            return Err(OffchainErr::ErrorInEvmResponse);
        }

        Ok(response_result.result.ok_or(OffchainErr::ErrorInEvmResponse)?)
    }

    fn is_good_actor(
        authority_index: usize, 
        session_index: SessionIndex,
        median_claps: u32,
    ) -> bool {
        if median_claps == 0 {
            return true;
        }

        let number_of_claps = ClapsInSession::<T>::get(session_index)
            .entry(authority_index as AuthIndex)
            .or_default()
            .claps;

        let authority_deviation = if number_of_claps < median_claps {
            Perbill::from_rational(median_claps - number_of_claps, median_claps)
        } else {
            Perbill::from_rational(number_of_claps - median_claps, median_claps)
        };
        authority_deviation < Perbill::from_percent(T::OffenceThreshold::get())
    }

    fn initialize_authorities(authorities: Vec<T::AuthorityId>) {
        let session_index = T::ValidatorSet::session_index();
        assert!(Authorities::<T>::get(&session_index).is_empty(), "Authorities are already initilized!");
        let bounded_authorities = WeakBoundedVec::<_, T::MaxAuthorities>::try_from(authorities)
            .expect("more than the maximum number of authorities");

        if let Some(target_session_index) = session_index.checked_sub(T::HistoryDepth::get()) {
            Self::clear_history(&target_session_index);
        }

        Authorities::<T>::set(&session_index, bounded_authorities);
        ClapsInSession::<T>::set(&session_index, Default::default());
    }

    fn clear_history(target_session_index: &SessionIndex) {
        ClapsInSession::<T>::remove(target_session_index);
        let mut cursor = ReceivedClaps::<T>::clear_prefix((target_session_index,), u32::MAX, None);
        debug_assert!(cursor.maybe_cursor.is_none());
        cursor = ApplausesForTransaction::<T>::clear_prefix((target_session_index,), u32::MAX, None);
        debug_assert!(cursor.maybe_cursor.is_none());
    }

    fn calculate_median_claps(session_index: &SessionIndex) -> u32 {
        let mut claps_in_session = ClapsInSession::<T>::get(session_index)
            .values()
            .filter_map(|value| (!value.disabled).then(|| value.claps))
            .collect::<Vec<_>>();

        if claps_in_session.is_empty() {
            return 0;
        }

        claps_in_session.sort();
        let number_of_claps = claps_in_session.len();

        if number_of_claps % 2 == 0 {
            let mid_left = claps_in_session[number_of_claps / 2 - 1];
            let mid_right = claps_in_session[number_of_claps / 2];
            (mid_left + mid_right) / 2
        } else {
            claps_in_session[number_of_claps / 2]
        }
    }

    #[cfg(test)]
    fn set_test_authorities(session_index: SessionIndex, authorities: Vec<T::AuthorityId>) {
        let bounded_authorities = WeakBoundedVec::<_, T::MaxAuthorities>::try_from(authorities)
            .expect("more than the maximum number of authorities");
        Authorities::<T>::set(session_index, bounded_authorities);
    }

    #[cfg(feature = "runtime-benchmarks")]
    fn trigger_nullification_for_benchmark() {
        T::NetworkDataHandler::trigger_nullification();
    }
}

impl<T: Config> sp_runtime::BoundToRuntimeAppPublic for Pallet<T> {
    type Public = T::AuthorityId;
}

impl<T: Config> BlockNumberProvider for Pallet<T> {
    type BlockNumber = BlockNumberFor<T>;
    fn current_block_number() -> Self::BlockNumber {
        T::BlockNumberProvider::current_block_number()
    }
}

impl<T: Config> OneSessionHandler<T::AccountId> for Pallet<T> {
    type Key = T::AuthorityId;

    fn on_genesis_session<'a, I: 'a>(validators: I)
    where
        I: Iterator<Item = (&'a T::AccountId, T::AuthorityId)>,
    {
        let authorities = validators.map(|x| x.1).collect::<Vec<_>>();
        Self::initialize_authorities(authorities);
    }

    fn on_new_session<'a, I: 'a>(_changed: bool, validators: I, _queued_validators: I)
    where
        I: Iterator<Item = (&'a T::AccountId, T::AuthorityId)>,
    {
        let authorities = validators.map(|x| x.1).collect::<Vec<_>>();
        Self::initialize_authorities(authorities);
    }

    fn on_before_session_ending() {
        let session_index = T::ValidatorSet::session_index();
        let validators = T::ValidatorSet::validators();
        let authorities = Authorities::<T>::get(&session_index);

        let median_claps = Self::calculate_median_claps(&session_index);

        let offenders = validators
            .into_iter()
            .enumerate()
            .filter(|(index, _)| !Self::is_good_actor(*index, session_index, median_claps))
            .filter_map(|(_, id)| {
                <T::ValidatorSet as ValidatorSetWithIdentification<T::AccountId>>::IdentificationOf::convert(
                    id.clone(),
                ).map(|full_id| (id, full_id))
            })
            .collect::<Vec<IdentificationTuple<T>>>();

        if offenders.is_empty() {
            Self::deposit_event(Event::<T>::AuthoritiesEquilibrium);
        } else {
            Self::deposit_event(Event::<T>::SomeAuthoritiesTrottling { throttling: offenders.clone() });

            let validator_set_count = authorities.len() as u32;
            let offence = ThrottlingOffence { session_index, validator_set_count, offenders };
            if let Err(e) = T::ReportUnresponsiveness::report_offence(vec![], offence) {
                sp_runtime::print(e)
            }
        }
    }

    fn on_disabled(validator_index: u32) {
        let session_index = T::ValidatorSet::session_index();
        ClapsInSession::<T>::mutate(&session_index, |claps_details| {
            (*claps_details)
                .entry(validator_index as AuthIndex)
                .and_modify(|individual| (*individual).disabled = true)
                .or_insert(SessionAuthorityInfo { claps: 0u32, disabled: true });
        });
    }
}

#[derive(RuntimeDebug, TypeInfo)]
#[cfg_attr(feature = "std", derive(Clone, PartialEq, Eq))]
pub struct ThrottlingOffence<Offender> {
    pub session_index: SessionIndex,
    pub validator_set_count: u32,
    pub offenders: Vec<Offender>
}

impl<Offender: Clone> Offence<Offender> for ThrottlingOffence<Offender> {
    const ID: Kind = *b"slow-clap:throtl";
    type TimeSlot = SessionIndex;

    fn offenders(&self) -> Vec<Offender> {
        self.offenders.clone()
    }

    fn session_index(&self) -> SessionIndex {
        self.session_index
    }

    fn validator_set_count(&self) -> u32 {
        self.validator_set_count
    }

    fn time_slot(&self) -> Self::TimeSlot {
        self.session_index
    }

    fn slash_fraction(&self, offenders_count: u32) -> Perbill {
        if let Some(threshold) = offenders_count.checked_sub(self.validator_set_count / 10 + 1) {
            let x = Perbill::from_rational(3 * threshold, self.validator_set_count);
            x.saturating_mul(Perbill::from_percent(7))
        } else {
            Perbill::default()
        }
    }
}