package rebelsky.text;

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

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

  /** 
   * The stuff on the left
   */
  TextBlock left;

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


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

  /**
   * Surround a simple text block.
   *
   * @pre
   *   The block is not null
   * @exception Exception
   *   If the block is null.
   */
  public HorizontallyCompose(TextBlock _left, TextBlock _right)
    throws Exception
  {
    if ((_left == null) || (_right == null))
      throw new Exception("Cannot compose null text");
    this.left = _left;
    this.right = _right;
  } // HorizontallyCompose(TextBlock)


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

  /**
   * Determine the width of the composed block.
   */
  public int getWidth()
  {
    return this.left.getWidth() + this.right.getWidth();
  } // getWidth()

  /**
   * Determine the number of lines of the composed block.
   */
  public int getLines()
  {
    if (this.left.getLines() > this.right.getLines())
      return this.left.getLines();
    else
      return this.right.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 left and right, because we 
    // use those values repeatedly.
    int leftlines = this.left.getLines();
    int rightlines = this.right.getLines();
    // Compute the width of the left b/c we use it repeatedl.
    int leftwidth = this.left.getWidth();
    // Normal case: Within both blocks
    if ((n < leftlines) && (n < rightlines))
      return new TextLine(this.left.getLine(n).atWidth(leftwidth)
                          + this.right.getLine(n).toString());
    // Special case: No right
    else if ((n < leftlines) && (n >= rightlines))
      return this.left.getLine(n);
    // Special case: No left
    else if ((n >= leftlines) && (n < rightlines)) { // STUB
      return this.right.getLine(n);
    }
    // Default: Crash and burn.
    else
      throw new Exception("Invalid line number.");
  } // getLine()

} // class HorizontallyCompose