/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.lucene.misc.util.fst;

import java.io.IOException;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.util.RamUsageEstimator;
import org.apache.lucene.util.SuppressForbidden;
import org.apache.lucene.util.fst.FSTCompiler;
import org.apache.lucene.util.fst.Outputs;

/**
 * An FST {@link Outputs} implementation where each output is one or two non-negative long values.
 * If it's a single output, Long is returned; else, TwoLongs. Order is preserved in the TwoLongs
 * case, ie .first is the first input/output added to Builder, and .second is the second. You cannot
 * store 0 output with this (that's reserved to mean "no output")!
 *
 * <p>NOTE: the only way to create a TwoLongs output is to add the same input to the FST twice in a
 * row. This is how the FST maps a single input to two outputs (e.g. you cannot pass a TwoLongs to
 * {@link FSTCompiler#add}. If you need more than two then use {@link ListOfOutputs}, but if you
 * only have at most 2 then this implementation will require fewer bytes as it steals one bit from
 * each long value.
 *
 * <p>NOTE: the resulting FST is not guaranteed to be minimal! See {@link FSTCompiler}.
 *
 * @lucene.experimental
 */
@SuppressForbidden(reason = "Uses a Long instance as a marker")
public final class UpToTwoPositiveIntOutputs extends Outputs<Object> {

  /** Holds two long outputs. */
  public static final class TwoLongs {
    public final long first;
    public final long second;

    public TwoLongs(long first, long second) {
      this.first = first;
      this.second = second;
      assert first >= 0;
      assert second >= 0;
    }

    @Override
    public String toString() {
      return "TwoLongs:" + first + "," + second;
    }

    @Override
    public boolean equals(Object _other) {
      if (_other instanceof TwoLongs) {
        final TwoLongs other = (TwoLongs) _other;
        return first == other.first && second == other.second;
      } else {
        return false;
      }
    }

    @Override
    public int hashCode() {
      return (int) ((first ^ (first >>> 32)) ^ (second ^ (second >> 32)));
    }
  }

  // Ignore the deprecated constructor. We do want a unique object here.
  @SuppressWarnings({"all"})
  private static final Long NO_OUTPUT = new Long(0);

  private final boolean doShare;

  private static final UpToTwoPositiveIntOutputs singletonShare =
      new UpToTwoPositiveIntOutputs(true);
  private static final UpToTwoPositiveIntOutputs singletonNoShare =
      new UpToTwoPositiveIntOutputs(false);

  private UpToTwoPositiveIntOutputs(boolean doShare) {
    this.doShare = doShare;
  }

  public static UpToTwoPositiveIntOutputs getSingleton(boolean doShare) {
    return doShare ? singletonShare : singletonNoShare;
  }

  public Long get(long v) {
    if (v == 0) {
      return NO_OUTPUT;
    } else {
      return Long.valueOf(v);
    }
  }

  public TwoLongs get(long first, long second) {
    return new TwoLongs(first, second);
  }

  @Override
  public Long common(Object _output1, Object _output2) {
    assert valid(_output1, false);
    assert valid(_output2, false);
    final Long output1 = (Long) _output1;
    final Long output2 = (Long) _output2;
    if (output1 == NO_OUTPUT || output2 == NO_OUTPUT) {
      return NO_OUTPUT;
    } else if (doShare) {
      assert output1 > 0;
      assert output2 > 0;
      return Math.min(output1, output2);
    } else if (output1.equals(output2)) {
      return output1;
    } else {
      return NO_OUTPUT;
    }
  }

  @Override
  public Long subtract(Object _output, Object _inc) {
    assert valid(_output, false);
    assert valid(_inc, false);
    final Long output = (Long) _output;
    final Long inc = (Long) _inc;
    assert output >= inc;

    if (inc == NO_OUTPUT) {
      return output;
    } else if (output.equals(inc)) {
      return NO_OUTPUT;
    } else {
      return output - inc;
    }
  }

  @Override
  public Object add(Object _prefix, Object _output) {
    assert valid(_prefix, false);
    assert valid(_output, true);
    final Long prefix = (Long) _prefix;
    if (_output instanceof Long) {
      final Long output = (Long) _output;
      if (prefix == NO_OUTPUT) {
        return output;
      } else if (output == NO_OUTPUT) {
        return prefix;
      } else {
        return prefix + output;
      }
    } else {
      final TwoLongs output = (TwoLongs) _output;
      final long v = prefix;
      return new TwoLongs(output.first + v, output.second + v);
    }
  }

  @Override
  public void write(Object _output, DataOutput out) throws IOException {
    assert valid(_output, true);
    if (_output instanceof Long) {
      final Long output = (Long) _output;
      out.writeVLong(output << 1);
    } else {
      final TwoLongs output = (TwoLongs) _output;
      out.writeVLong((output.first << 1) | 1);
      out.writeVLong(output.second);
    }
  }

  @Override
  public Object read(DataInput in) throws IOException {
    final long code = in.readVLong();
    if ((code & 1) == 0) {
      // single long
      final long v = code >>> 1;
      if (v == 0) {
        return NO_OUTPUT;
      } else {
        return Long.valueOf(v);
      }
    } else {
      // two longs
      final long first = code >>> 1;
      final long second = in.readVLong();
      return new TwoLongs(first, second);
    }
  }

  private boolean valid(Long o) {
    assert o != null;
    assert o instanceof Long;
    assert o == NO_OUTPUT || o > 0;
    return true;
  }

  // Used only by assert
  private boolean valid(Object _o, boolean allowDouble) {
    if (!allowDouble) {
      assert _o instanceof Long;
      return valid((Long) _o);
    } else if (_o instanceof TwoLongs) {
      return true;
    } else {
      return valid((Long) _o);
    }
  }

  @Override
  public Object getNoOutput() {
    return NO_OUTPUT;
  }

  @Override
  public String outputToString(Object output) {
    return output.toString();
  }

  @Override
  public Object merge(Object first, Object second) {
    assert valid(first, false);
    assert valid(second, false);
    return new TwoLongs((Long) first, (Long) second);
  }

  private static final long TWO_LONGS_NUM_BYTES =
      RamUsageEstimator.shallowSizeOf(new TwoLongs(0, 0));

  @Override
  public long ramBytesUsed(Object o) {
    if (o instanceof Long) {
      return RamUsageEstimator.sizeOf((Long) o);
    } else {
      assert o instanceof TwoLongs;
      return TWO_LONGS_NUM_BYTES;
    }
  }
}
