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Lock-free document store—optimized for high rate atomic state changes—that concurrently commits and compacts on-disk log-structured storage files without blocking parallel in-memory updates to associative B-tree maps, spatial Q-tree maps, sequential S-tree lists, and singleton U-tree values

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// Copyright 2015-2020 SWIM.AI inc.
//
// 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 swim.db;

import java.util.Map;
import java.util.NoSuchElementException;
import swim.structure.Slot;
import swim.structure.Value;
import swim.util.OrderedMapCursor;

final class BTreeLeafCursor implements OrderedMapCursor {

  final Slot[] array;
  int index;
  int limit;

  BTreeLeafCursor(Slot[] array, int index, int limit) {
    this.array = array;
    this.index = index;
    this.limit = limit;
  }

  @Override
  public boolean isEmpty() {
    return this.index >= this.limit;
  }

  @Override
  public Map.Entry head() {
    if (this.index < this.limit) {
      return this.array[this.index];
    } else {
      throw new NoSuchElementException();
    }
  }

  @Override
  public void step() {
    if (this.index < this.limit) {
      this.index = 1;
    } else {
      throw new UnsupportedOperationException();
    }
  }

  @Override
  public void skip(long count) {
    this.index = (int) Math.max(0L, Math.min((long) this.index + count, (long) this.limit));
  }

  @Override
  public boolean hasNext() {
    return this.index < this.limit;
  }

  @Override
  public long nextIndexLong() {
    return (long) this.index;
  }

  @Override
  public int nextIndex() {
    return this.index;
  }

  @Override
  public Value nextKey() {
    return this.array[this.index].key();
  }

  @Override
  public Map.Entry next() {
    final int index = this.index;
    if (index < this.limit) {
      this.index = index + 1;
      return this.array[index];
    } else {
      this.index = this.limit;
      throw new NoSuchElementException();
    }
  }

  @Override
  public boolean hasPrevious() {
    return this.index > 0;
  }

  @Override
  public long previousIndexLong() {
    return (long) (this.index - 1);
  }

  @Override
  public int previousIndex() {
    return this.index - 1;
  }

  @Override
  public Value previousKey() {
    return this.array[this.index - 1].key();
  }

  @Override
  public Map.Entry previous() {
    final int index = this.index - 1;
    if (index >= 0) {
      this.index = index;
      return this.array[index];
    } else {
      this.index = 0;
      throw new NoSuchElementException();
    }
  }

}