package rebelsky.text;

/**
 * A simple representation of the vertical composition of two
 * blocks of text.
 *
 * @author Samuel A. Rebelsky
 * @author Everyone else in CSC152 2005S
 */
public class VerticallyCompose
  implements TextBlock
{

// +--------+--------------------------------------------------
// | Fields |
// +--------+

  /** 
   * The stuff on top.
   */
  TextBlock top;

  /**
   * The stuff on the bottom.
   */
  TextBlock bottom;


// +--------------+--------------------------------------------
// | Constructors |
// +--------------+

  /**
   * Surround a simple text block.
   *
   * @pre
   *   The block is not null
   * @exception Exception
   *   If the block is null.
   */
  public VerticallyCompose(TextBlock _top, TextBlock _bottom)
    throws Exception
  {
    if ((_top == null) || (_bottom == null))
      throw new Exception("Cannot compose null text");
    this.top = _top;
    this.bottom = _bottom;
  } // VerticallyCompose(TextBlock)


// +----------------+------------------------------------------
// | Public Methods |
// +----------------+

  /**
   * Determine the width of the composed block.
   */
  public int getWidth()
  {
    if (this.top.getWidth() > this.bottom.getWidth())
      return this.top.getWidth();
    else
      return this.bottom.getWidth();
  } // getWidth()

  /**
   * Determine the number of lines of the composed block.
   */
  public int getLines()
  {
    return this.top.getLines() + this.bottom.getLines();
  } // getLines()

  /**
   * Determine the nth line of this block.  Lines are numbered
   * starting with 0.  
   *
   * @exception Exception
   *   If an invalid line number is given.
   */
  public TextLine getLine(int n)
    throws Exception
  {
    // Compute the number of lines in the top, because we use
    // it repeatedly.
    int toplines = this.top.getLines();
    // The first toplines lines belong to the top.
    if (n < toplines)
      return this.top.getLine(n);
    // The next this.bottom.getLines() lines belong to this.bottom
    else if (n < toplines + this.bottom.getLines())
      return this.bottom.getLine(n-toplines);
    else
      throw new Exception("Invalid line number.");
  } // getLine()

} // class VerticallyCompose