/**
    * 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.hadoop.hbase.hbtop.screen.top;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * Utility class for paging for the metrics.
   */
  @InterfaceAudience.Private
  public class Paging {
    private int currentPosition;
    private int pageStartPosition;
    private int pageEndPosition;
  
    private int pageSize;
    private int recordsSize;
  
    public void init() {
      currentPosition = 0;
      pageStartPosition = 0;
      pageEndPosition = Math.min(pageSize, recordsSize);
    }
  
    public void updatePageSize(int pageSize) {
      this.pageSize = pageSize;
  
      if (pageSize == 0) {
        pageStartPosition = 0;
        pageEndPosition = 0;
      } else {
        pageEndPosition = pageStartPosition + pageSize;
        keepConsistent();
      }
    }
  
    public void updateRecordsSize(int recordsSize) {
      if (this.recordsSize == 0) {
        currentPosition = 0;
        pageStartPosition = 0;
        pageEndPosition = Math.min(pageSize, recordsSize);
        this.recordsSize = recordsSize;
      } else if (recordsSize == 0) {
        currentPosition = 0;
        pageStartPosition = 0;
        pageEndPosition = 0;
        this.recordsSize = recordsSize;
      } else {
        this.recordsSize = recordsSize;
        if (pageSize > 0) {
          pageEndPosition = pageStartPosition + pageSize;
          keepConsistent();
        }
      }
    }
  
    public void arrowUp() {
      if (currentPosition > 0) {
        currentPosition -= 1;
        if (pageSize > 0) {
          keepConsistent();
        }
      }
    }
  
    public void arrowDown() {
      if (currentPosition < recordsSize - 1) {
        currentPosition += 1;
        if (pageSize > 0) {
          keepConsistent();
        }
      }
    }
  
    public void pageUp() {
      if (pageSize > 0 && currentPosition > 0) {
        currentPosition -= pageSize;
        if (currentPosition < 0) {
          currentPosition = 0;
        }
        keepConsistent();
      }
    }
  
   public void pageDown() {
     if (pageSize > 0 && currentPosition < recordsSize - 1) {
 
       currentPosition = currentPosition + pageSize;
       if (currentPosition >= recordsSize) {
         currentPosition = recordsSize - 1;
       }
 
       pageStartPosition = currentPosition;
       pageEndPosition = pageStartPosition + pageSize;
       keepConsistent();
     }
   }
 
   private void keepConsistent() {
     if (currentPosition < pageStartPosition) {
       pageStartPosition = currentPosition;
       pageEndPosition = pageStartPosition + pageSize;
     } else if (currentPosition > recordsSize - 1) {
       currentPosition = recordsSize - 1;
       pageEndPosition = recordsSize;
       pageStartPosition = pageEndPosition - pageSize;
     } else if (currentPosition > pageEndPosition - 1) {
       pageEndPosition = currentPosition + 1;
       pageStartPosition = pageEndPosition - pageSize;
     }
 
     if (pageStartPosition < 0) {
       pageStartPosition = 0;
     }
 
     if (pageEndPosition > recordsSize) {
       pageEndPosition = recordsSize;
       pageStartPosition = pageEndPosition - pageSize;
       if (pageStartPosition < 0) {
         pageStartPosition = 0;
       }
     }
   }
 
   public int getCurrentPosition() {
     return currentPosition;
   }
 
   public int getPageStartPosition() {
     return pageStartPosition;
   }
 
   public int getPageEndPosition() {
     return pageEndPosition;
   }
 }