/*
 * Copyright 2018 The Vert.x Community.
 *
 * 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.
 */
package io.vertx.cassandra.impl;

import com.datastax.driver.core.Row;
import io.vertx.cassandra.CassandraRowStream;
import io.vertx.cassandra.ResultSet;
import io.vertx.core.Context;
import io.vertx.core.Handler;
import io.vertx.core.Vertx;
import io.vertx.core.streams.impl.InboundBuffer;

Author:
Pavel Drankou, Thomas Segismont/**
 * @author Pavel Drankou
 * @author Thomas Segismont
 */
public class CassandraRowStreamImpl implements CassandraRowStream {

  private enum State {
    IDLE, STARTED, EXHAUSTED, STOPPED
  }

  private final Context context;
  private final ResultSet resultSet;
  private final InboundBuffer<Row> internalQueue;

  private State state;
  private int inFlight;
  private Handler<Row> handler;
  private Handler<Throwable> exceptionHandler;
  private Handler<Void> endHandler;

  public CassandraRowStreamImpl(Context context, ResultSet resultSet) {
    this.context = context;
    this.resultSet = resultSet;
    internalQueue = new InboundBuffer<Row>(context)
      .exceptionHandler(this::handleException)
      .drainHandler(v -> fetchRow());
    state = State.IDLE;
  }

  @Override
  public synchronized CassandraRowStream exceptionHandler(Handler<Throwable> handler) {
    if (state != State.STOPPED) {
      exceptionHandler = handler;
    }
    return this;
  }

  @Override
  public synchronized CassandraRowStream handler(Handler<Row> handler) {
    if (state == State.STOPPED) {
      return this;
    }
    if (handler == null) {
      stop();
      if (context != Vertx.currentContext()) {
        context.runOnContext(v -> handleEnd());
      } else {
        handleEnd();
      }
    } else {
      this.handler = handler;
      internalQueue.handler(this::handleRow);
      if (state == State.IDLE) {
        state = State.STARTED;
        if (context != Vertx.currentContext()) {
          context.runOnContext(v -> fetchRow());
        } else {
          fetchRow();
        }
      }
    }
    return this;
  }

  @Override
  public synchronized CassandraRowStream pause() {
    if (state != State.STOPPED) {
      internalQueue.pause();
    }
    return this;
  }

  @Override
  public synchronized CassandraRowStream resume() {
    if (state != State.STOPPED) {
      internalQueue.resume();
    }
    return this;
  }

  @Override
  public synchronized CassandraRowStream endHandler(Handler<Void> handler) {
    if (state != State.STOPPED) {
      endHandler = handler;
    }
    return this;
  }

  @Override
  public synchronized CassandraRowStream fetch(long l) {
    if (state != State.STOPPED) {
      internalQueue.fetch(l);
    }
    return this;
  }

  private synchronized void fetchRow() {
    if (state == State.STOPPED) {
      return;
    }
    resultSet.one(ar -> {
      if (ar.succeeded()) {
        handleFetched(ar.result());
      } else {
        handleException(ar.cause());
      }
    });
  }

  private synchronized void handleFetched(Row row) {
    if (state == State.STOPPED) {
      return;
    }
    if (row != null) {
      inFlight++;
      if (internalQueue.write(row)) {
        fetchRow();
      }
    } else {
      state = State.EXHAUSTED;
      if (inFlight == 0) {
        stop();
        handleEnd();
      }
    }
  }

  private void handleRow(Row row) {
    synchronized (this) {
      if (state == State.STOPPED) {
        return;
      }
      inFlight--;
    }
    handler.handle(row);
    synchronized (this) {
      if (state == State.EXHAUSTED && inFlight == 0) {
        stop();
        handleEnd();
      }
    }
  }

  private void handleException(Throwable cause) {
    Handler<Throwable> h;
    synchronized (this) {
      if (state != State.STOPPED) {
        stop();
        h = exceptionHandler;
      } else {
        h = null;
      }
    }
    if (h != null) {
      h.handle(cause);
    }
  }

  private synchronized void handleEnd() {
    Handler<Void> h;
    synchronized (this) {
      h = endHandler;
    }
    if (h != null) {
      h.handle(null);
    }
  }

  private synchronized void stop() {
    state = State.STOPPED;
    internalQueue.handler(null).drainHandler(null);
  }
}