// Copyright 2019 The MediaPipe Authors.
//
// 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.

#include "absl/strings/substitute.h"
#include "absl/synchronization/mutex.h"
#include "mediapipe/framework/collection_item_id.h"
#include "mediapipe/framework/input_stream_handler.h"
#include "mediapipe/framework/port/logging.h"

namespace mediapipe {

// Implementation of the input stream handler for the MuxCalculator.
//
// One of the input streams is the control stream; all the other input streams
// are data streams. To make MuxInputStreamHandler work properly, the tag of the
// input streams must obey the following rules:
// Let N be the number of input streams. Data streams must use tag "INPUT" with
// index 0, ..., N - 2; the control stream must use tag "SELECT".
//
// The control stream carries packets of type 'int'. The 'int' value in a
// control stream packet must be a valid index in the range 0, ..., N - 2 and
// select the data stream at that index. The selected data stream must have a
// packet with the same timestamp as the control stream packet.
//
// When the control stream is done, GetNodeReadiness() returns
// NodeReadiness::kReadyForClose.
//
// TODO: pass the input stream tags to the MuxInputStreamHandler
// constructor so that it can refer to input streams by tag. See b/30125118.
class MuxInputStreamHandler : public InputStreamHandler {
public:
    MuxInputStreamHandler() = delete;
    MuxInputStreamHandler(std::shared_ptr<tool::TagMap> tag_map,
                          CalculatorContextManager* cc_manager,
                          const MediaPipeOptions& options,
                          bool calculator_run_in_parallel)
        : InputStreamHandler(std::move(tag_map), cc_manager, options,
                             calculator_run_in_parallel) {}

protected:
    // In MuxInputStreamHandler, a node is "ready" if:
    // - the control stream is done (need to call Close() in this case), or
    // - we have received the packets on the control stream and the selected data
    //   stream at the next timestamp.
    NodeReadiness GetNodeReadiness(Timestamp* min_stream_timestamp) override {
        DCHECK(min_stream_timestamp);
        absl::MutexLock lock(&input_streams_mutex_);

        const auto& control_stream =
            input_stream_managers_.Get(input_stream_managers_.EndId() - 1);
        bool empty;
        *min_stream_timestamp = control_stream->MinTimestampOrBound(&empty);
        if (empty) {
            if (*min_stream_timestamp == Timestamp::Done()) {
                // Calculator is done if the control input stream is done.
                return NodeReadiness::kReadyForClose;
            }
            // Calculator is not ready to run if the control input stream is empty.
            return NodeReadiness::kNotReady;
        }

        Packet control_packet = control_stream->QueueHead();
        CHECK(!control_packet.IsEmpty());
        int control_value = control_packet.Get<int>();
        CHECK_LE(0, control_value);
        CHECK_LT(control_value, input_stream_managers_.NumEntries() - 1);
        const auto& data_stream = input_stream_managers_.Get(
            input_stream_managers_.BeginId() + control_value);

        // Data stream may contain some outdated packets which failed to be popped
        // out during "FillInputSet". (This handler doesn't sync input streams,
        // hence "FillInputSet" can be triggerred before every input stream is
        // filled with packets corresponding to the same timestamp.)
        data_stream->ErasePacketsEarlierThan(*min_stream_timestamp);
        Timestamp stream_timestamp = data_stream->MinTimestampOrBound(&empty);
        if (empty) {
            if (stream_timestamp <= *min_stream_timestamp) {
                // "data_stream" didn't receive a packet corresponding to the current
                // "control_stream" packet yet.
                return NodeReadiness::kNotReady;
            }
            // "data_stream" timestamp bound update detected.
            return NodeReadiness::kReadyForProcess;
        }
        if (stream_timestamp > *min_stream_timestamp) {
            // The earliest packet "data_stream" holds corresponds to a control packet
            // yet to arrive, which means there won't be a "data_stream" packet
            // corresponding to the current "control_stream" packet, which should be
            // indicated as timestamp boun update.
            return NodeReadiness::kReadyForProcess;
        }
        CHECK_EQ(stream_timestamp, *min_stream_timestamp);
        return NodeReadiness::kReadyForProcess;
    }

    // Only invoked when associated GetNodeReadiness() returned kReadyForProcess.
    void FillInputSet(Timestamp input_timestamp,
                      InputStreamShardSet* input_set) override {
        CHECK(input_timestamp.IsAllowedInStream());
        CHECK(input_set);
        absl::MutexLock lock(&input_streams_mutex_);

        const CollectionItemId control_stream_id =
            input_stream_managers_.EndId() - 1;
        auto& control_stream = input_stream_managers_.Get(control_stream_id);
        int num_packets_dropped = 0;
        bool stream_is_done = false;
        Packet control_packet = control_stream->PopPacketAtTimestamp(
            input_timestamp, &num_packets_dropped, &stream_is_done);
        CHECK_EQ(num_packets_dropped, 0)
            << absl::Substitute("Dropped $0 packet(s) on input stream \"$1\".",
                                num_packets_dropped, control_stream->Name());
        CHECK(!control_packet.IsEmpty());
        int control_value = control_packet.Get<int>();
        AddPacketToShard(&input_set->Get(control_stream_id),
                         std::move(control_packet), stream_is_done);

        const CollectionItemId data_stream_id =
            input_stream_managers_.BeginId() + control_value;
        CHECK_LE(input_stream_managers_.BeginId(), data_stream_id);
        CHECK_LT(data_stream_id, control_stream_id);
        auto& data_stream = input_stream_managers_.Get(data_stream_id);
        stream_is_done = false;
        Packet data_packet = data_stream->PopPacketAtTimestamp(
            input_timestamp, &num_packets_dropped, &stream_is_done);
        CHECK_EQ(num_packets_dropped, 0)
            << absl::Substitute("Dropped $0 packet(s) on input stream \"$1\".",
                                num_packets_dropped, data_stream->Name());
        AddPacketToShard(&input_set->Get(data_stream_id), std::move(data_packet),
                         stream_is_done);

        // Discard old packets on other streams.
        // Note that control_stream_id is the last valid id.
        auto next_timestamp = input_timestamp.NextAllowedInStream();
        for (CollectionItemId id = input_stream_managers_.BeginId();
             id < control_stream_id; ++id) {
            if (id == data_stream_id) continue;
            auto& other_stream = input_stream_managers_.Get(id);
            other_stream->ErasePacketsEarlierThan(next_timestamp);
        }
    }

private:
    // Must be acquired when manipulating the control and data streams to ensure
    // we have a consistent view of the two streams.
    absl::Mutex input_streams_mutex_;
};

REGISTER_INPUT_STREAM_HANDLER(MuxInputStreamHandler);

}  // namespace mediapipe