/*
 * 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 java.util.NoSuchElementException;

/**
 * Simple static methods to be called at the start of your own methods to verify
 * correct arguments and state. This allows constructs such as
 * <pre>
 *     if (count <= 0) {
 *       throw new IllegalArgumentException("must be positive: " + count);
 *     }</pre>
 *
 * to be replaced with the more compact
 * <pre>
 *     checkArgument(count > 0, "must be positive: %s", count);</pre>
 *
 * Note that the sense of the expression is inverted; with {@code Preconditions}
 * you declare what you expect to be <i>true</i>, just as you do with an
 * <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/assert.html">
 * {@code assert}</a> or a JUnit {@code assertTrue} call.
 *
 * <p><b>Warning:</b> only the {@code "%s"} specifier is recognized as a
 * placeholder in these messages, not the full range of {@link
 * String#format(String, Object[])} specifiers.
 *
 * <p>Take care not to confuse precondition checking with other similar types
 * of checks! Precondition exceptions -- including those provided here, but also
 * {@link IndexOutOfBoundsException}, {@link NoSuchElementException}, {@link
 * UnsupportedOperationException} and others -- are used to signal that the
 * <i>calling method</i> has made an error. This tells the caller that it should
 * not have invoked the method when it did, with the arguments it did, or
 * perhaps ever. Postcondition or other invariant failures should not throw
 * these types of exceptions.
 *
 * <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)
 */
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, 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,
                                     String errorMessageTemplate,
                                     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, 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,
                                  String errorMessageTemplate,
                                  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, 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,
                                     String errorMessageTemplate,
                                     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, 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, 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.
     */
    static String format(String template, 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();
    }
}
