/*
    * Copyright (C) 2013 The Guava Authors
    *
    * 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.common.base;
  
  import static com.google.common.base.Preconditions.format;
  
  import com.google.common.annotations.Beta;
  import com.google.common.annotations.GwtCompatible;
  
  import javax.annotation.Nullable;
  
  /**
   * Static convenience methods that serve the same purpose as Java language
   * <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/language/assert.html">
   * assertions</a>, except that they are always enabled. These methods should be used instead of Java
   * assertions whenever there is a chance the check may fail "in real life". Example: <pre>   {@code
   *
   *   Bill bill = remoteService.getLastUnpaidBill();
   *
   *   // In case bug 12345 happens again we'd rather just die
   *   Verify.verify(bill.status() == Status.UNPAID,
   *       "Unexpected bill status: %s", bill.status());}</pre>
   *
   * <h3>Comparison to alternatives</h3>
   *
   * <p><b>Note:</b> In some cases the differences explained below can be subtle. When it's unclear
   * which approach to use, <b>don't worry</b> too much about it; just pick something that seems
   * reasonable and it will be fine.
   *
   * <ul>
   * <li>If checking whether the <i>caller</i> has violated your method or constructor's contract
   *     (such as by passing an invalid argument), use the utilities of the {@link Preconditions}
   *     class instead.
   *
   * <li>If checking an <i>impossible</i> condition (which <i>cannot</i> happen unless your own class
   *     or its <i>trusted</i> dependencies is badly broken), this is what ordinary Java assertions
   *     are for. Note that assertions are not enabled by default; they are essentially considered
   *     "compiled comments."
   *
   * <li>An explicit {@code if/throw} (as illustrated below) is always acceptable; we still recommend
   *     using our {@link VerifyException} exception type. Throwing a plain {@link RuntimeException}
   *     is frowned upon.
   *
   * <li>Use of {@link java.util.Objects#requireNonNull(Object)} is generally discouraged, since
   *     {@link #verifyNotNull(Object)} and {@link Preconditions#checkNotNull(Object)} perform the
   *     same function with more clarity.
   * </ul>
   *
   * <h3>Warning about performance</h3>
   *
   * <p>Remember that parameter values for message construction must all be computed eagerly, and
   * autoboxing and varargs array creation may happen as well, even when the verification succeeds and
   * the message ends up unneeded. Performance-sensitive verification checks should continue to use
   * usual form: <pre>   {@code
   *
   *   Bill bill = remoteService.getLastUnpaidBill();
   *   if (bill.status() != Status.UNPAID) {
   *     throw new VerifyException("Unexpected bill status: " + bill.status());
   *   }}</pre>
   *
   * <h3>Only {@code %s} is supported</h3>
   *
   * <p>As with {@link Preconditions} error message template strings, only the {@code "%s"} specifier
   * is supported, not the full range of {@link java.util.Formatter} specifiers. However, note that
   * if the number of arguments does not match the number of occurrences of {@code "%s"} in the
   * format string, {@code Verify} will still behave as expected, and will still include all argument
   * values in the error message; the message will simply not be formatted exactly as intended.
   *
   * <h3>More information</h3>
   *
   * See
   * <a href="http://code.google.com/p/guava-libraries/wiki/ConditionalFailuresExplained">Conditional
   * failures explained</a> in the Guava User Guide for advice on when this class should be used.
   *
   * @since 17.0
   */
  @Beta
  @GwtCompatible
  public final class Verify {
    /**
     * Ensures that {@code expression} is {@code true}, throwing a {@code VerifyException} with no
     * message otherwise.
     */
    public static void verify(boolean expression) {
      if (!expression) {
        throw new VerifyException();
      }
   }
 
   /**
    * Ensures that {@code expression} is {@code true}, throwing a {@code VerifyException} with a
    * custom message otherwise.
    *
    * @param expression a boolean expression
    * @param errorMessageTemplate a template for the exception message should the
    *     check fail. The message is formed by replacing each {@code %s}
    *     placeholder in the template with an argument. These are matched by
    *     position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
    *     Unmatched arguments will be appended to the formatted message in square
    *     braces. Unmatched placeholders will be left as-is.
    * @param errorMessageArgs the arguments to be substituted into the message
    *     template. Arguments are converted to strings using
    *     {@link String#valueOf(Object)}.
    * @throws VerifyException if {@code expression} is {@code false}
    */
   public static void verify(
       boolean expression,
       @Nullable String errorMessageTemplate,
       @Nullable Object... errorMessageArgs) {
     if (!expression) {
       throw new VerifyException(format(errorMessageTemplate, errorMessageArgs));
     }
   }
 
   /**
    * Ensures that {@code reference} is non-null, throwing a {@code VerifyException} with a default
    * message otherwise.
    *
    * @return {@code reference}, guaranteed to be non-null, for convenience
    */
   public static <T> T verifyNotNull(@Nullable T reference) {
     return verifyNotNull(reference, "expected a non-null reference");
   }
 
   /**
    * Ensures that {@code reference} is non-null, throwing a {@code VerifyException} with a custom
    * message otherwise.
    *
    * @param errorMessageTemplate a template for the exception message should the
    *     check fail. The message is formed by replacing each {@code %s}
    *     placeholder in the template with an argument. These are matched by
    *     position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
    *     Unmatched arguments will be appended to the formatted message in square
    *     braces. Unmatched placeholders will be left as-is.
    * @param errorMessageArgs the arguments to be substituted into the message
    *     template. Arguments are converted to strings using
    *     {@link String#valueOf(Object)}.
    * @return {@code reference}, guaranteed to be non-null, for convenience
    */
   public static <T> T verifyNotNull(
       @Nullable T reference,
       @Nullable String errorMessageTemplate,
       @Nullable Object... errorMessageArgs) {
     verify(reference != null, errorMessageTemplate, errorMessageArgs);
     return reference;
   }
 
   // TODO(kevinb): consider <T> T verifySingleton(Iterable<T>) to take over for
   // Iterables.getOnlyElement()
 
   private Verify() {}
 }