/*
 * 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 javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * 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. However, note that if the number of
 * arguments does not match the number of occurrences of {@code "%s"} in the
 * format string, {@code Preconditions} 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>
 *
 * <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();
	}
}
