/*
    * Copyright (C) 2007 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 com.google.common.annotations.GwtCompatible;
  
  import javax.annotation.Nullable;
  
  /**
   * Static convenience methods that help a method or constructor check whether it was invoked
   * correctly (whether its <i>preconditions</i> have been met). These methods generally accept a
   * {@code boolean} expression which is expected to be {@code true} (or in the case of {@code
   * checkNotNull}, an object reference which is expected to be non-null). When {@code false} (or
   * {@code null}) is passed instead, the {@code Preconditions} method throws an unchecked exception,
   * which helps the calling method communicate to <i>its</i> caller that <i>that</i> caller has made
   * a mistake. Example: <pre>   {@code
   *
   *   /**
   *    * Returns the positive square root of the given value.
   *    *
   *    * @throws IllegalArgumentException if the value is negative
   *    *}{@code /
   *   public static double sqrt(double value) {
   *     Preconditions.checkArgument(value >= 0.0, "negative value: %s", value);
   *     // calculate the square root
   *   }
   *
   *   void exampleBadCaller() {
   *     double d = sqrt(-1.0);
   *   }}</pre>
   *
   * In this example, {@code checkArgument} throws an {@code IllegalArgumentException} to indicate
   * that {@code exampleBadCaller} made an error in <i>its</i> call to {@code sqrt}.
   *
   * <h3>Warning about performance</h3>
   *
   * <p>The goal of this class is to improve readability of code, but in some circumstances this may
   * come at a significant performance cost. 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 precondition check then succeeds (as it should almost always do in production). In some
   * circumstances these wasted CPU cycles and allocations can add up to a real problem.
   * Performance-sensitive precondition checks can always be converted to the customary form:
   * <pre>   {@code
   *
   *   if (value < 0.0) {
   *     throw new IllegalArgumentException("negative value: " + value);
   *   }}</pre>
   *
   * <h3>Other types of preconditions</h3>
   *
   * <p>Not every type of precondition failure is supported by these methods. Continue to throw
   * standard JDK exceptions such as {@link java.util.NoSuchElementException} or {@link
   * UnsupportedOperationException} in the situations they are intended for.
   *
   * <h3>Non-preconditions</h3>
   *
   * <p>It is of course possible to use the methods of this class to check for invalid conditions
   * which are <i>not the caller's fault</i>. Doing so is <b>not recommended</b> because it is
   * misleading to future readers of the code and of stack traces. See
   * <a href="http://code.google.com/p/guava-libraries/wiki/ConditionalFailuresExplained">Conditional
   * failures explained</a> in the Guava User Guide for more advice.
   *
   * <h3>{@code java.util.Objects.requireNonNull()}</h3>
   *
   * <p>Projects which use {@code com.google.common} should generally avoid the use of {@link
   * java.util.Objects#requireNonNull(Object)}. Instead, use whichever of {@link
   * #checkNotNull(Object)} or {@link Verify#verifyNotNull(Object)} is appropriate to the situation.
   * (The same goes for the message-accepting overloads.)
   *
   * <h3>Only {@code %s} is supported</h3>
   *
   * <p>In {@code Preconditions} error message template strings, only the {@code "%s"} specifier is
   * supported, not the full range of {@link java.util.Formatter} specifiers.
   *
   * <h3>More information</h3>
   *
   * <p>See the Guava User Guide on
   * <a href="http://code.google.com/p/guava-libraries/wiki/PreconditionsExplained">using {@code
   * Preconditions}</a>.
   *
   * @author Kevin Bourrillion
   * @since 2.0 (imported from Google Collections Library)
   */
  @GwtCompatible
  public final class Preconditions {
    private Preconditions() {}
  
   /**
    * Ensures the truth of an expression involving one or more parameters to the calling method.
    *
    * @param expression a boolean expression
    * @throws IllegalArgumentException if {@code expression} is false
    */
   public static void checkArgument(boolean expression) {
     if (!expression) {
       throw new IllegalArgumentException();
     }
   }
 
   /**
    * Ensures the truth of an expression involving one or more parameters to the calling method.
    *
    * @param expression a boolean expression
    * @param errorMessage the exception message to use if the check fails; will be converted to a
    *     string using {@link String#valueOf(Object)}
    * @throws IllegalArgumentException if {@code expression} is false
    */
   public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
     if (!expression) {
       throw new IllegalArgumentException(String.valueOf(errorMessage));
     }
   }
 
   /**
    * Ensures the truth of an expression involving one or more parameters to the calling method.
    *
    * @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 IllegalArgumentException if {@code expression} is false
    * @throws NullPointerException if the check fails and either {@code errorMessageTemplate} or
    *     {@code errorMessageArgs} is null (don't let this happen)
    */
   public static void checkArgument(boolean expression,
       @Nullable String errorMessageTemplate,
       @Nullable Object... errorMessageArgs) {
     if (!expression) {
       throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs));
     }
   }
 
   /**
    * Ensures the truth of an expression involving the state of the calling instance, but not
    * involving any parameters to the calling method.
    *
    * @param expression a boolean expression
    * @throws IllegalStateException if {@code expression} is false
    */
   public static void checkState(boolean expression) {
     if (!expression) {
       throw new IllegalStateException();
     }
   }
 
   /**
    * Ensures the truth of an expression involving the state of the calling instance, but not
    * involving any parameters to the calling method.
    *
    * @param expression a boolean expression
    * @param errorMessage the exception message to use if the check fails; will be converted to a
    *     string using {@link String#valueOf(Object)}
    * @throws IllegalStateException if {@code expression} is false
    */
   public static void checkState(boolean expression, @Nullable Object errorMessage) {
     if (!expression) {
       throw new IllegalStateException(String.valueOf(errorMessage));
     }
   }
 
   /**
    * Ensures the truth of an expression involving the state of the calling instance, but not
    * involving any parameters to the calling method.
    *
    * @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 IllegalStateException if {@code expression} is false
    * @throws NullPointerException if the check fails and either {@code errorMessageTemplate} or
    *     {@code errorMessageArgs} is null (don't let this happen)
    */
   public static void checkState(boolean expression,
       @Nullable String errorMessageTemplate,
       @Nullable Object... errorMessageArgs) {
     if (!expression) {
       throw new IllegalStateException(format(errorMessageTemplate, errorMessageArgs));
     }
   }
 
   /**
    * Ensures that an object reference passed as a parameter to the calling method is not null.
    *
    * @param reference an object reference
    * @return the non-null reference that was validated
    * @throws NullPointerException if {@code reference} is null
    */
   public static <T> T checkNotNull(T reference) {
     if (reference == null) {
       throw new NullPointerException();
     }
     return reference;
   }
 
   /**
    * Ensures that an object reference passed as a parameter to the calling method is not null.
    *
    * @param reference an object reference
    * @param errorMessage the exception message to use if the check fails; will be converted to a
    *     string using {@link String#valueOf(Object)}
    * @return the non-null reference that was validated
    * @throws NullPointerException if {@code reference} is null
    */
   public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
     if (reference == null) {
       throw new NullPointerException(String.valueOf(errorMessage));
     }
     return reference;
   }
 
   /**
    * Ensures that an object reference passed as a parameter to the calling method is not null.
    *
    * @param reference an object reference
    * @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 the non-null reference that was validated
    * @throws NullPointerException if {@code reference} is null
    */
   public static <T> T checkNotNull(T reference,
       @Nullable String errorMessageTemplate,
       @Nullable Object... errorMessageArgs) {
     if (reference == null) {
       // If either of these parameters is null, the right thing happens anyway
       throw new NullPointerException(format(errorMessageTemplate, errorMessageArgs));
     }
     return reference;
   }
 
   /*
    * All recent hotspots (as of 2009) *really* like to have the natural code
    *
    * if (guardExpression) {
    *    throw new BadException(messageExpression);
    * }
    *
    * refactored so that messageExpression is moved to a separate String-returning method.
    *
    * if (guardExpression) {
    *    throw new BadException(badMsg(...));
    * }
    *
    * The alternative natural refactorings into void or Exception-returning methods are much slower.
    * This is a big deal - we're talking factors of 2-8 in microbenchmarks, not just 10-20%.  (This
    * is a hotspot optimizer bug, which should be fixed, but that's a separate, big project).
    *
    * The coding pattern above is heavily used in java.util, e.g. in ArrayList.  There is a
    * RangeCheckMicroBenchmark in the JDK that was used to test this.
    *
    * But the methods in this class want to throw different exceptions, depending on the args, so it
    * appears that this pattern is not directly applicable.  But we can use the ridiculous, devious
    * trick of throwing an exception in the middle of the construction of another exception.  Hotspot
    * is fine with that.
    */
 
   /**
    * Ensures that {@code index} specifies a valid <i>element</i> in an array, list or string of size
    * {@code size}. An element index may range from zero, inclusive, to {@code size}, exclusive.
    *
    * @param index a user-supplied index identifying an element of an array, list or string
    * @param size the size of that array, list or string
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is not less than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkElementIndex(int index, int size) {
     return checkElementIndex(index, size, "index");
   }
 
   /**
    * Ensures that {@code index} specifies a valid <i>element</i> in an array, list or string of size
    * {@code size}. An element index may range from zero, inclusive, to {@code size}, exclusive.
    *
    * @param index a user-supplied index identifying an element of an array, list or string
    * @param size the size of that array, list or string
    * @param desc the text to use to describe this index in an error message
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is not less than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkElementIndex(
       int index, int size, @Nullable String desc) {
     // Carefully optimized for execution by hotspot (explanatory comment above)
     if (index < 0 || index >= size) {
       throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
     }
     return index;
   }
 
   private static String badElementIndex(int index, int size, String desc) {
     if (index < 0) {
       return format("%s (%s) must not be negative", desc, index);
     } else if (size < 0) {
       throw new IllegalArgumentException("negative size: " + size);
     } else { // index >= size
       return format("%s (%s) must be less than size (%s)", desc, index, size);
     }
   }
 
   /**
    * Ensures that {@code index} specifies a valid <i>position</i> in an array, list or string of
    * size {@code size}. A position index may range from zero to {@code size}, inclusive.
    *
    * @param index a user-supplied index identifying a position in an array, list or string
    * @param size the size of that array, list or string
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is greater than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkPositionIndex(int index, int size) {
     return checkPositionIndex(index, size, "index");
   }
 
   /**
    * Ensures that {@code index} specifies a valid <i>position</i> in an array, list or string of
    * size {@code size}. A position index may range from zero to {@code size}, inclusive.
    *
    * @param index a user-supplied index identifying a position in an array, list or string
    * @param size the size of that array, list or string
    * @param desc the text to use to describe this index in an error message
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is greater than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkPositionIndex(int index, int size, @Nullable String desc) {
     // Carefully optimized for execution by hotspot (explanatory comment above)
     if (index < 0 || index > size) {
       throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
     }
     return index;
   }
 
   private static String badPositionIndex(int index, int size, String desc) {
     if (index < 0) {
       return format("%s (%s) must not be negative", desc, index);
     } else if (size < 0) {
       throw new IllegalArgumentException("negative size: " + size);
     } else { // index > size
       return format("%s (%s) must not be greater than size (%s)", desc, index, size);
     }
   }
 
   /**
    * Ensures that {@code start} and {@code end} specify a valid <i>positions</i> in an array, list
    * or string of size {@code size}, and are in order. A position index may range from zero to
    * {@code size}, inclusive.
    *
    * @param start a user-supplied index identifying a starting position in an array, list or string
    * @param end a user-supplied index identifying a ending position in an array, list or string
    * @param size the size of that array, list or string
    * @throws IndexOutOfBoundsException if either index is negative or is greater than {@code size},
    *     or if {@code end} is less than {@code start}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static void checkPositionIndexes(int start, int end, int size) {
     // Carefully optimized for execution by hotspot (explanatory comment above)
     if (start < 0 || end < start || end > size) {
       throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
     }
   }
 
   private static String badPositionIndexes(int start, int end, int size) {
     if (start < 0 || start > size) {
       return badPositionIndex(start, size, "start index");
     }
     if (end < 0 || end > size) {
       return badPositionIndex(end, size, "end index");
     }
     // end < start
     return format("end index (%s) must not be less than start index (%s)", end, start);
   }
 
   /**
    * Substitutes each {@code %s} in {@code template} with an argument. These are matched by
    * position: the first {@code %s} gets {@code args[0]}, etc.  If there are more arguments than
    * placeholders, the unmatched arguments will be appended to the end of the formatted message in
    * square braces.
    *
    * @param template a non-null string containing 0 or more {@code %s} placeholders.
    * @param args the arguments to be substituted into the message template. Arguments are converted
    *     to strings using {@link String#valueOf(Object)}. Arguments can be null.
    */
   // Note that this is somewhat-improperly used from Verify.java as well.
   static String format(String template, @Nullable Object... args) {
     template = String.valueOf(template); // null -> "null"
 
     // start substituting the arguments into the '%s' placeholders
     StringBuilder builder = new StringBuilder(template.length() + 16 * args.length);
     int templateStart = 0;
     int i = 0;
     while (i < args.length) {
       int placeholderStart = template.indexOf("%s", templateStart);
       if (placeholderStart == -1) {
         break;
       }
       builder.append(template.substring(templateStart, placeholderStart));
       builder.append(args[i++]);
       templateStart = placeholderStart + 2;
     }
     builder.append(template.substring(templateStart));
 
     // if we run out of placeholders, append the extra args in square braces
     if (i < args.length) {
       builder.append(" [");
       builder.append(args[i++]);
       while (i < args.length) {
         builder.append(", ");
         builder.append(args[i++]);
       }
       builder.append(']');
     }
 
     return builder.toString();
   }
 }