// 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/>.

use std::sync::{Arc, Weak};

use ethcore::{
    engines::{EthEngine, StateDependentProof},
    machine::EthereumMachine,
};
use sync::{LightNetworkDispatcher, LightSync};
use types::{encoded, header::Header, receipt::Receipt};

use futures::{future, future::Either, Future};

use light::{
    client::fetch::ChainDataFetcher,
    on_demand::{request, OnDemand, OnDemandRequester},
};

use ethereum_types::H256;
use parking_lot::RwLock;

const ALL_VALID_BACKREFS: &str = "no back-references, therefore all back-references valid; qed";

type BoxFuture<T, E> = Box<Future<Item = T, Error = E>>;

/// Allows on-demand fetch of data useful for the light client.
pub struct EpochFetch {
    /// A handle to the sync service.
    pub sync: Arc<RwLock<Weak<LightSync>>>,
    /// The on-demand request service.
    pub on_demand: Arc<OnDemand>,
}

impl EpochFetch {
    fn request<T>(&self, req: T) -> BoxFuture<T::Out, &'static str>
    where
        T: Send + request::RequestAdapter + 'static,
        T::Out: Send + 'static,
    {
        Box::new(match self.sync.read().upgrade() {
            Some(sync) => {
                let on_demand = &self.on_demand;
                let maybe_future = sync.with_context(move |ctx| {
                    on_demand.request(ctx, req).expect(ALL_VALID_BACKREFS)
                });

                match maybe_future {
                    Some(x) => Either::A(x.map_err(|_| "Request canceled")),
                    None => Either::B(future::err("Unable to access network.")),
                }
            }
            None => Either::B(future::err("Unable to access network")),
        })
    }
}

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

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

    fn block_body(&self, header: &Header) -> Self::Body {
        self.request(request::Body(header.encoded().into()))
    }

    /// Fetch block receipts.
    fn block_receipts(&self, header: &Header) -> Self::Receipts {
        self.request(request::BlockReceipts(header.encoded().into()))
    }

    /// Fetch epoch transition proof at given header.
    fn epoch_transition(
        &self,
        hash: H256,
        engine: Arc<EthEngine>,
        checker: Arc<StateDependentProof<EthereumMachine>>,
    ) -> Self::Transition {
        self.request(request::Signal {
            hash: hash,
            engine: engine,
            proof_check: checker,
        })
    }
}