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The reactive Postgres client
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/*
 * Copyright (C) 2017 Julien Viet
 *
 * 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.reactiverse.pgclient.impl;

import io.reactiverse.pgclient.*;
import io.reactiverse.pgclient.impl.codec.decoder.RowDescription;
import io.vertx.core.AsyncResult;
import io.vertx.core.Handler;

import java.util.Iterator;
import java.util.UUID;

public class PgCursorStreamImpl implements PgStream {

  private final PgPreparedQueryImpl ps;
  private final int fetch;
  private final Tuple params;

  private Handler endHandler;
  private Handler rowHandler;
  private Handler exceptionHandler;
  private boolean paused;
  private QueryCursor cursor;

  class QueryCursor implements QueryResultHandler, Handler> {

    final String portal = UUID.randomUUID().toString();
    Iterator result;
    boolean suspended;
    boolean closed;

    @Override
    public void handleResult(int updatedCount, int size, RowDescription desc, PgRowSet result) {
      this.result = result.iterator();
    }

    @Override
    public void handle(AsyncResult res) {
      if (res.failed()) {
        cursor = null;
        Handler handler = exceptionHandler;
        if (handler != null) {
          handler.handle(res.cause());
        }
        close();
      } else {
        this.suspended = res.result();
        checkPending();
      }
    }

    private void checkPending() {
      while (!paused && result != null) {
        if (result.hasNext()) {
          Row tuple = result.next();
          Handler handler = rowHandler;
          if (handler != null) {
            handler.handle(tuple);
          }
        } else {
          result = null;
          if (suspended) {
            ps.execute(params, fetch, portal, true, false, PgRowSetImpl.COLLECTOR, this, this);
          } else {
            cursor = null;
            close();
            Handler handler = endHandler;
            if (endHandler != null) {
              handler.handle(null);
            }
          }
        }
      }
    }

    public void close() {
    }

    public void close(Handler> completionHandler) {
      if (!closed) {
        closed = true;
        ps.closePortal(portal, completionHandler);
      }
    }
  }

  PgCursorStreamImpl(PgPreparedQueryImpl ps, int fetch, Tuple params) {
    this.ps = ps;
    this.fetch = fetch;
    this.params = params;
  }

  @Override
  public PgStream exceptionHandler(Handler handler) {
    exceptionHandler = handler;
    return this;
  }

  @Override
  public PgStream handler(Handler handler) {
    if (handler != null) {
      if (cursor == null) {
        rowHandler = handler;
        cursor = new QueryCursor();
        ps.execute(params, fetch, cursor.portal, false, false, PgRowSetImpl.COLLECTOR, cursor, cursor);
      } else {
        throw new UnsupportedOperationException("Handle me gracefully");
      }
    } else {
      if (cursor != null) {
        QueryCursor c = cursor;
        cursor = null;
      } else {
        rowHandler = null;
      }
    }
    return this;
  }

  @Override
  public PgStream pause() {
    paused = true;
    return this;
  }

  @Override
  public PgStream resume() {
    paused = false;
    if (cursor != null) {
      cursor.checkPending();
    }
    return this;
  }

  @Override
  public PgStream endHandler(Handler handler) {
    endHandler = handler;
    return this;
  }
}