/*
 * Copyright 2011 Google 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 com.google.web.bindery.event.shared;

import java.util.Collections;
import java.util.Set;

/**
 * A {@link RuntimeException} that collects a {@link Set} of child
 * {@link Throwable}s together. Typically thrown after a loop, with all of the
 * exceptions thrown during that loop, but delayed so that the loop finishes
 * executing.
 */
public class UmbrellaException extends RuntimeException {

  // Visible for testing
  static final String MULTIPLE = " exceptions caught: ";

  // Visible for testing
  static final String ONE = "Exception caught: ";

  protected static Throwable makeCause(Set<Throwable> causes) {
    return causes.isEmpty() ? null : causes.iterator().next();
  }

  protected static String makeMessage(Set<Throwable> causes) {
    int count = causes.size();
    if (count == 0) {
      return null;
    }

    StringBuilder b = new StringBuilder(count == 1 ? ONE : count + MULTIPLE);
    boolean first = true;
    for (Throwable t : causes) {
      if (first) {
        first = false;
      } else {
        b.append("; ");
      }
      b.append(t.getMessage());
    }

    return b.toString();
  }

  /**
   * The causes of the exception.
   */
  private Set<Throwable> causes;

  public UmbrellaException(Set<Throwable> causes) {
    super(makeMessage(causes), makeCause(causes));
    this.causes = causes;
    int i = 0;
    for (Throwable cause : causes) {
      if (i++ == 0) {
        // First one already added as cause.
        continue;
      }
      addSuppressed(cause);
    }
  }

  /**
   * Required for GWT RPC serialization.
   */
  protected UmbrellaException() {
    // Can't delegate to the other constructor or GWT RPC gets cranky
    super(MULTIPLE);
    this.causes = Collections.<Throwable> emptySet();
  }

  /**
   * Get the set of exceptions that caused the failure.
   * 
   * @return the set of causes
   */
  public Set<Throwable> getCauses() {
    return causes;
  }
}