package de.lmu.ifi.dbs.elki.datasource.bundle;

/*
 This file is part of ELKI:
 Environment for Developing KDD-Applications Supported by Index-Structures

 Copyright (C) 2013
 Ludwig-Maximilians-Universität München
 Lehr- und Forschungseinheit für Datenbanksysteme
 ELKI Development Team

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU Affero General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 This program 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 Affero General Public License for more details.

 You should have received a copy of the GNU Affero General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.util.ArrayList;

import de.lmu.ifi.dbs.elki.data.type.SimpleTypeInformation;
import de.lmu.ifi.dbs.elki.data.type.TypeInformationSerializer;
import de.lmu.ifi.dbs.elki.persistent.ByteArrayUtil;
import de.lmu.ifi.dbs.elki.persistent.ByteBufferSerializer;
import de.lmu.ifi.dbs.elki.utilities.exceptions.AbortException;

/**
 * Read an ELKI bundle file into a data stream.
 * 
 * TODO: resize buffer when necessary?
 * 
 * @author Erich Schubert
 * 
 * @apiviz.uses FileChannel
 */
public class BundleReader implements BundleStreamSource {
  /**
   * Magic number, shared with {@link BundleReader}.
   */
  public static final int MAGIC = BundleWriter.MAGIC;

  /**
   * The stream buffer.
   */
  MappedByteBuffer buffer;

  /**
   * Bundle metadata.
   */
  BundleMeta meta = null;

  /**
   * Input channel.
   */
  FileChannel input;

  /**
   * Serializers to use.
   */
  ArrayList<ByteBufferSerializer<?>> sers;

  /**
   * Current object.
   */
  ArrayList<Object> data;

  /**
   * Constructor.
   * 
   * @param input Input channel
   */
  public BundleReader(FileChannel input) {
    super();
    this.input = input;
  }

  @Override
  public BundleMeta getMeta() {
    if (meta == null) {
      openBuffer();
      readMeta();
    }
    return meta;
  }

  /**
   * Map the input file.
   */
  void openBuffer() {
    try {
      buffer = input.map(MapMode.READ_ONLY, 0, input.size());
    } catch (IOException e) {
      throw new AbortException("Cannot map input bundle.", e);
    }
  }

  /**
   * Read the metadata.
   */
  void readMeta() {
    final int check = buffer.getInt();
    if (check != MAGIC) {
      throw new AbortException("File does not start with expected magic.");
    }
    final int nummeta = buffer.getInt();
    assert (nummeta > 0);
    meta = new BundleMeta(nummeta);
    sers = new ArrayList<>(nummeta);
    data = new ArrayList<>(nummeta);
    for (int i = 0; i < nummeta; i++) {
      try {
        @SuppressWarnings("unchecked")
        SimpleTypeInformation<? extends Object> type = (SimpleTypeInformation<? extends Object>) TypeInformationSerializer.STATIC.fromByteBuffer(buffer);
        meta.add(type);
        sers.add(type.getSerializer());
      } catch (UnsupportedOperationException e) {
        throw new AbortException("Deserialization failed: "+e.getMessage(), e);
      } catch (IOException e) {
        throw new AbortException("IO error", e);
      }
    }
  }

  /**
   * Read an object.
   */
  void readObject() {
    data.clear();
    for (ByteBufferSerializer<?> ser : sers) {
      try {
        data.add(ser.fromByteBuffer(buffer));
      } catch (UnsupportedOperationException e) {
        throw new AbortException("Deserialization failed.", e);
      } catch (IOException e) {
        throw new AbortException("IO error", e);
      }
    }
  }

  @Override
  public Event nextEvent() {
    // Send initial meta
    if (meta == null) {
      return Event.META_CHANGED;
    }
    if (buffer.remaining() == 0) {
      ByteArrayUtil.unmapByteBuffer(buffer);
      return Event.END_OF_STREAM;
    }
    readObject();
    return Event.NEXT_OBJECT;
  }

  @Override
  public Object data(int rnum) {
    return data.get(rnum);
  }
}