// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum 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.

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

//! Trait for fetching chain data.

use std::sync::Arc;

use common_types::{encoded, header::Header, receipt::Receipt};
use ethcore::{
    engines::{EthEngine, StateDependentProof},
    machine::EthereumMachine,
};
use ethereum_types::H256;
use futures::future::IntoFuture;

/// Provides full chain data.
pub trait ChainDataFetcher: Send + Sync + 'static {
    /// Error type when data unavailable.
    type Error: ::std::fmt::Debug;

    /// Future for fetching block body.
    type Body: IntoFuture<Item = encoded::Block, Error = Self::Error>;
    /// Future for fetching block receipts.
    type Receipts: IntoFuture<Item = Vec<Receipt>, Error = Self::Error>;
    /// Future for fetching epoch transition
    type Transition: IntoFuture<Item = Vec<u8>, Error = Self::Error>;

    /// Fetch a block body.
    fn block_body(&self, header: &Header) -> Self::Body;

    /// Fetch block receipts.
    fn block_receipts(&self, header: &Header) -> Self::Receipts;

    /// Fetch epoch transition proof at given header.
    fn epoch_transition(
        &self,
        _hash: H256,
        _engine: Arc<dyn EthEngine>,
        _checker: Arc<dyn StateDependentProof<EthereumMachine>>,
    ) -> Self::Transition;
}

/// Fetcher implementation which cannot fetch anything.
pub struct Unavailable;

/// Create a fetcher which has all data unavailable.
pub fn unavailable() -> Unavailable {
    Unavailable
}

impl ChainDataFetcher for Unavailable {
    type Error = &'static str;

    type Body = Result<encoded::Block, &'static str>;
    type Receipts = Result<Vec<Receipt>, &'static str>;
    type Transition = Result<Vec<u8>, &'static str>;

    fn block_body(&self, _header: &Header) -> Self::Body {
        Err("fetching block bodies unavailable")
    }

    fn block_receipts(&self, _header: &Header) -> Self::Receipts {
        Err("fetching block receipts unavailable")
    }

    fn epoch_transition(
        &self,
        _hash: H256,
        _engine: Arc<dyn EthEngine>,
        _checker: Arc<dyn StateDependentProof<EthereumMachine>>,
    ) -> Self::Transition {
        Err("fetching epoch transition proofs unavailable")
    }
}