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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.

//! Traits and types for replaying captured timely dataflow streams.
//!
//! This is roughly based on [timely::dataflow::operators::capture::Replay], which
//! provides the protocol and semantics of the [MzReplay] operator.

use std::any::Any;
use std::rc::Rc;
use std::time::{Duration, Instant};

use timely::dataflow::channels::pushers::buffer::Buffer as PushBuffer;
use timely::dataflow::channels::pushers::Counter as PushCounter;
use timely::dataflow::operators::capture::event::EventIterator;
use timely::dataflow::operators::capture::Event;
use timely::dataflow::operators::generic::builder_raw::OperatorBuilder;
use timely::dataflow::{Scope, Stream};
use timely::progress::Timestamp;
use timely::scheduling::ActivateOnDrop;
use timely::Data;

use crate::activator::ActivatorTrait;

/// Replay a capture stream into a scope with the same timestamp.
pub trait MzReplay<T: Timestamp, D: Data, A: ActivatorTrait>: Sized {
    /// Replays `self` into the provided scope, as a `Stream<S, D>' and provides a cancelation token.
    ///
    /// The `period` argument allows the specification of a re-activation period, where the operator
    /// will re-activate itself every so often.
    fn mz_replay<S: Scope<Timestamp = T>>(
        self,
        scope: &mut S,
        name: &str,
        period: Duration,
        activator: A,
    ) -> (Stream<S, D>, Rc<dyn Any>);
}

impl<T: Timestamp, D: Data, I, A: ActivatorTrait + 'static> MzReplay<T, D, A> for I
where
    I: IntoIterator,
    <I as IntoIterator>::Item: EventIterator<T, D> + 'static,
{
    /// Replay a collection of [EventIterator]s into a Timely stream.
    ///
    /// * `scope`: The [Scope] to replay into.
    /// * `name`: Human-readable debug name of the Timely operator.
    /// * `period`: Reschedule the operator once the period has elapsed.
    ///    Provide [Duration::MAX] to disable periodic scheduling.
    /// * `activator`: An activator to trigger the operator.
    fn mz_replay<S: Scope<Timestamp = T>>(
        self,
        scope: &mut S,
        name: &str,
        period: Duration,
        activator: A,
    ) -> (Stream<S, D>, Rc<dyn Any>) {
        let name = format!("Replay {}", name);
        let mut builder = OperatorBuilder::new(name, scope.clone());

        let address = builder.operator_info().address;
        let periodic_activator = scope.activator_for(&address[..]);

        let (targets, stream) = builder.new_output();

        let mut output = PushBuffer::new(PushCounter::new(targets));
        let mut event_streams = self.into_iter().collect::<Vec<_>>();
        let mut started = false;

        let mut last_active = Instant::now();

        let mut progress_sofar =
            timely::progress::ChangeBatch::new_from(S::Timestamp::minimum(), 1);
        let token = Rc::new(ActivateOnDrop::new(
            (),
            Rc::new(address.clone()),
            scope.activations(),
        ));
        let weak_token = Rc::downgrade(&token);

        activator.register(scope, &address[..]);

        builder.build(move |progress| {
            activator.ack();
            if last_active
                .checked_add(period)
                .map_or(false, |next_active| next_active <= Instant::now())
                || !started
            {
                last_active = Instant::now();
                if period < Duration::MAX {
                    periodic_activator.activate_after(period);
                }
            }

            if !started {
                // The first thing we do is modify our capabilities to match the number of streams we manage.
                // This should be a simple change of `self.event_streams.len() - 1`. We only do this once, as
                // our very first action.
                let len: i64 = event_streams
                    .len()
                    .try_into()
                    .expect("Implausibly large vector");
                progress.internals[0].update(S::Timestamp::minimum(), len - 1);
                progress_sofar.update(S::Timestamp::minimum(), len);
                started = true;
            }

            if weak_token.upgrade().is_some() {
                let mut buffer = Vec::new();

                for event_stream in event_streams.iter_mut() {
                    while let Some(event) = event_stream.next() {
                        match &event {
                            Event::Progress(vec) => {
                                progress.internals[0].extend(vec.iter().cloned());
                                progress_sofar.extend(vec.iter().cloned());
                            }
                            Event::Messages(time, data) => {
                                buffer.extend_from_slice(data);
                                output.session(time).give_vec(&mut buffer);
                            }
                        }
                    }
                }
            } else {
                // Negate the accumulated progress contents emitted so far.
                progress.internals[0]
                    .extend(progress_sofar.drain().map(|(time, diff)| (time, -diff)));
            }

            output.cease();
            output
                .inner()
                .produced()
                .borrow_mut()
                .drain_into(&mut progress.produceds[0]);

            false
        });

        (stream, token)
    }
}