package expressions;

import common.prettyprinter.PrettyStringBuilder;

/**
 * Representation of a <b>(COND)</b> expression for
 * the small step interpreter.
 * 
 * @author bmeurer
 * @version $Id$
 */
public final class Condition extends Expression {
  /**
   * Generates a new condition.
   * @param e0 the condition.
   * @param e1 the true case.
   * @param e2 the false case.
   */
  public Condition(Expression e0, Expression e1, Expression e2) {
    this.e0 = e0;
    this.e1 = e1;
    this.e2 = e2;
  }

  /**
   * Performs the substitution for <b>(COND)</b> expressions.
   * 
   * @param id the identifier for the substitution.
   * @param e the expression to substitute.
   * @return the new expression.
   */
  public Expression substitute(String id, Expression e) {
    Expression e0 = this.e0.substitute(id, e);
    Expression e1 = this.e1.substitute(id, e);
    Expression e2 = this.e2.substitute(id, e);
    return new Condition(e0, e1, e2);
  }

  /**
   * @return Returns the e0.
   */
  public Expression getE0() {
    return this.e0;
  }
  
  /**
   * @return Returns the e1.
   */
  public Expression getE1() {
    return this.e1;
  }
  
  /**
   * @return Returns the e2.
   */
  public Expression getE2() {
    return this.e2;
  }
  
  /**
   * Returns the pretty string builder for conditions.
   * @return the pretty string builder for conditions.
   * @see expressions.Expression#toPrettyStringBuilder()
   */
  @Override
  protected PrettyStringBuilder toPrettyStringBuilder() {
    PrettyStringBuilder builder = new PrettyStringBuilder(this, 0);
    builder.appendKeyword("if");
    builder.appendText(" ");
    builder.appendBuilder(this.e0.toPrettyStringBuilder(), 0);
    builder.appendBreak();
    builder.appendText(" ");
    builder.appendKeyword("then");
    builder.appendText(" ");
    builder.appendBuilder(this.e1.toPrettyStringBuilder(), 0);
    builder.appendBreak();
    builder.appendText(" ");
    builder.appendKeyword("else");
    builder.appendText(" ");
    builder.appendBuilder(this.e2.toPrettyStringBuilder(), 0);
    return builder;
  }
  
  // sub expressions
  private Expression e0;
  private Expression e1;
  private Expression e2;
}