Start.java

/**
 * Copyright [2020] David J. Rusek <dave.rusek@gmail.com>
 * <p>
 * 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.robotninjas.stream;

import java.util.Objects;
import java.util.function.Function;

// wishing I had sealed interfaces here.
public abstract class Start {
  private Start() {}

  public abstract Offset offset();

  public abstract <R> R match(
    Function<Offset, R> fromNewest,
    Function<Offset, R> fromOldest,
    Function<Offset, R> fromOffset
  );

  public final static class FromNewest extends Start {
    private FromNewest() { }

    @Override
    public Offset offset() {
      return Offset.empty();
    }

    @Override
    public <R> R match(
      Function<Offset, R> fromNewest,
      Function<Offset, R> ignore1,
      Function<Offset, R> ignore2) {
      return fromNewest.apply(Offset.empty());
    }
  }

  public final static class FromOldest extends Start {
    private FromOldest() { }

    @Override
    public Offset offset() {
      return Offset.empty();
    }

    @Override
    public <R> R match(
      Function<Offset, R> ignore1,
      Function<Offset, R> fromOldest,
      Function<Offset, R> ignore2) {
      return fromOldest.apply(Offset.empty());
    }
  }

  public final static class FromOffset extends Start {
    private final Offset offset;

    private FromOffset(Offset offset) {
      this.offset = offset;
    }

    @Override
    public Offset offset() {
      return offset;
    }

    @Override
    public <R> R match(
      Function<Offset, R> ignore1,
      Function<Offset, R> ignore2,
      Function<Offset, R> fromOffset) {
      return fromOffset.apply(offset);
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (!(o instanceof FromOffset that)) return false;
      return offset.equals(that.offset);
    }

    @Override
    public int hashCode() {
      return Objects.hash(offset);
    }
  }

  public static FromNewest newest() {
    return new FromNewest();
  }

  public static FromOldest oldest() {
    return new FromOldest();
  }

  public static FromOffset offset(Offset offset) {
    return new FromOffset(offset);
  }
}