// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
// Conditional to use more aggressive fail-fast behaviors when debugging.
#define DEV_DEBUG
 
using System.Threading;
 
// This file contains general utilities to aid in development.
// It is distinct from unit test Assert classes.
// Classes here generally shouldn't be exposed publicly since
// they're not particular to any library functionality.
// Because the classes here are internal, it's likely this file
// might be included in multiple assemblies.
 
namespace Standard
{
    /// <summary>A static class for verifying assumptions.</summary>
    internal static class Assert
    {
        private static void _Break()
        {
#if DEV_DEBUG
            Debugger.Break();
#else
            Debug.Assert(false);
#endif
        }
 
        /// <summary>A function signature for Assert.Evaluate.</summary>
        public delegate void EvaluateFunction();
 
        /// <summary>A function signature for Assert.Implies.</summary>
        /// <returns>Returns the truth of a predicate.</returns>
        public delegate bool ImplicationFunction();
 
        /// <summary>
        /// Executes the specified argument.
        /// </summary>
        /// <param name="argument">The function to execute.</param>
        [Conditional("DEBUG")]
        public static void Evaluate(EvaluateFunction argument)
        {
            IsNotNull(argument);
            argument();
        }
 
        /// <summary>Obsolete: Use Standard.Assert.AreEqual instead of Assert.Equals</summary>
        /// <typeparam name="T">The generic type to compare for equality.</typeparam>
        /// <param name="expected">The first generic type data to compare.  This is is the expected value.</param>
        /// <param name="actual">The second generic type data to compare.  This is the actual value.</param>
        [
            Obsolete("Use Assert.AreEqual instead of Assert.Equals", false),
            Conditional("DEBUG")
        ]
        public static void Equals<T>(T expected, T actual)
        {
            AreEqual(expected, actual);
        }
 
        /// <summary>
        /// Verifies that two generic type data are equal.  The assertion fails if they are not.
        /// </summary>
        /// <typeparam name="T">The generic type to compare for equality.</typeparam>
        /// <param name="expected">The first generic type data to compare.  This is is the expected value.</param>
        /// <param name="actual">The second generic type data to compare.  This is the actual value.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void AreEqual<T>(T expected, T actual)
        {
            if (null == expected)
            {
                // Two nulls are considered equal, regardless of type semantics.
                if (null != actual && !actual.Equals(expected))
                {
                    _Break();
                }
            }
            else if (!expected.Equals(actual))
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that two generic type data are not equal.  The assertion fails if they are.
        /// </summary>
        /// <typeparam name="T">The generic type to compare for inequality.</typeparam>
        /// <param name="notExpected">The first generic type data to compare.  This is is the value that's not expected.</param>
        /// <param name="actual">The second generic type data to compare.  This is the actual value.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void AreNotEqual<T>(T notExpected, T actual)
        {
            if (null == notExpected)
            {
                // Two nulls are considered equal, regardless of type semantics.
                if (null == actual || actual.Equals(notExpected))
                {
                    _Break();
                }
            }
            else if (notExpected.Equals(actual))
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that if the specified condition is true, then so is the result.
        /// The assertion fails if the condition is true but the result is false.
        /// </summary>
        /// <param name="condition">if set to <c>true</c> [condition].</param>
        /// <param name="result">
        /// A second Boolean statement.  If the first was true then so must this be.
        /// If the first statement was false then the value of this is ignored.
        /// </param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void Implies(bool condition, bool result)
        {
            if (condition && !result)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Lazy evaluation overload.  Verifies that if a condition is true, then so is a secondary value.
        /// </summary>
        /// <param name="condition">The conditional value.</param>
        /// <param name="result">A function to be evaluated for truth if the condition argument is true.</param>
        /// <remarks>
        /// This overload only evaluates the result if the first condition is true.
        /// </remarks>
        [Conditional("DEBUG")]
        public static void Implies(bool condition, ImplicationFunction result)
        {
            if (condition && !result())
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that a string has content.  I.e. it is not null and it is not empty.
        /// </summary>
        /// <param name="value">The string to verify.</param>
        [Conditional("DEBUG")]
        public static void IsNeitherNullNorEmpty(string value)
        {
            IsFalse(string.IsNullOrEmpty(value));
        }
 
        /// <summary>
        /// Verifies that a string has content.  I.e. it is not null and it is not purely whitespace.
        /// </summary>
        /// <param name="value">The string to verify.</param>
        [Conditional("DEBUG")]
        public static void IsNeitherNullNorWhitespace(string value)
        {
            if (string.IsNullOrEmpty(value))
            {
                _Break();
            }
 
            if (value.Trim().Length == 0)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies the specified value is not null.  The assertion fails if it is.
        /// </summary>
        /// <typeparam name="T">The generic reference type.</typeparam>
        /// <param name="value">The value to check for nullness.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void IsNotNull<T>(T value) where T : class
        {
            if (null == value)
            {
                _Break();
            }
        }
 
        [Conditional("DEBUG")]
        public static void IsDefault<T>(T value) where T : struct
        {
            if (!value.Equals(default(T)))
            {
                Assert.Fail();
            }
        }
 
        [Conditional("DEBUG")]
        public static void IsNotDefault<T>(T value) where T : struct
        {
            if (value.Equals(default(T)))
            {
                Assert.Fail();
            }
        }
 
        /// <summary>
        /// Verifies that the specified condition is false.  The assertion fails if it is true.
        /// </summary>
        /// <param name="condition">The expression that should be <c>false</c>.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void IsFalse(bool condition)
        {
            if (condition)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that the specified condition is false.  The assertion fails if it is true.
        /// </summary>
        /// <param name="condition">The expression that should be <c>false</c>.</param>
        /// <param name="message">The message to display if the condition is <c>true</c>.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void IsFalse(bool condition, string message)
        {
            if (condition)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that the specified condition is true.  The assertion fails if it is not.
        /// </summary>
        /// <param name="condition">A condition that is expected to be <c>true</c>.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void IsTrue(bool condition)
        {
            if (!condition)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that the specified condition is true.  The assertion fails if it is not.
        /// </summary>
        /// <param name="condition">A condition that is expected to be <c>true</c>.</param>
        /// <param name="message">The message to write in case the condition is <c>false</c>.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void IsTrue(bool condition, string message)
        {
            if (!condition)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// This line should never be executed.  The assertion always fails.
        /// </summary>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void Fail()
        {
            _Break();
        }
 
        /// <summary>
        /// This line should never be executed.  The assertion always fails.
        /// </summary>
        /// <param name="message">The message to display if this function is executed.</param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void Fail(string message)
        {
            _Break();
        }
 
        /// <summary>
        /// Verifies that the specified object is null.  The assertion fails if it is not.
        /// </summary>
        /// <param name="item">The item to verify is null.</param>
        [Conditional("DEBUG")]
        public static void IsNull<T>(T item) where T : class
        {
            if (null != item)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that the specified value is within the expected range.  The assertion fails if it isn't.
        /// </summary>
        /// <param name="lowerBoundInclusive">The lower bound inclusive value.</param>
        /// <param name="value">The value to verify.</param>
        /// <param name="upperBoundInclusive">The upper bound inclusive value.</param>
        [Conditional("DEBUG")]
        public static void BoundedDoubleInc(double lowerBoundInclusive, double value, double upperBoundInclusive)
        {
            if (value < lowerBoundInclusive || value > upperBoundInclusive)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verifies that the specified value is within the expected range.  The assertion fails if it isn't.
        /// </summary>
        /// <param name="lowerBoundInclusive">The lower bound inclusive value.</param>
        /// <param name="value">The value to verify.</param>
        /// <param name="upperBoundExclusive">The upper bound exclusive value.</param>
        [Conditional("DEBUG")]
        public static void BoundedInteger(int lowerBoundInclusive, int value, int upperBoundExclusive)
        {
            if (value < lowerBoundInclusive || value >= upperBoundExclusive)
            {
                _Break();
            }
        }
 
        /// <summary>
        /// Verify the current thread's apartment state is what's expected.  The assertion fails if it isn't
        /// </summary>
        /// <param name="expectedState">
        /// The expected apartment state for the current thread.
        /// </param>
        /// <remarks>This breaks into the debugger in the case of a failed assertion.</remarks>
        [Conditional("DEBUG")]
        public static void IsApartmentState(ApartmentState expectedState)
        {
            if (Thread.CurrentThread.GetApartmentState() != expectedState)
            {
                _Break();
            }
        }
 
        [Conditional("DEBUG")]
        public static void NullableIsNotNull<T>(T? value) where T : struct
        {
            if (null == value)
            {
                _Break();
            }
        }
 
        [Conditional("DEBUG")]
        public static void NullableIsNull<T>(T? value) where T : struct
        {
            if (null != value)
            {
                _Break();
            }
        }
 
        [Conditional("DEBUG")]
        public static void IsNotOnMainThread()
        {
            if (System.Windows.Application.Current.Dispatcher.CheckAccess())
            {
                _Break();
            }
        }
    }
}