using System;
using System.Linq;
using System.Threading;

namespace Swan {
  /// <summary>
  /// Provides extension methods for <see cref="Exception"/>.
  /// </summary>
  public static class ExceptionExtensions {
    /// <summary>
    /// Returns a value that tells whether an <see cref="Exception"/> is of a type that
    /// we better not catch and ignore.
    /// </summary>
    /// <param name="this">The exception being thrown.</param>
    /// <returns><see langword="true"/> if <paramref name="this"/> is a critical exception;
    /// otherwise, <see langword="false"/>.</returns>
    public static Boolean IsCriticalException(this Exception @this) => @this.IsCriticalExceptionCore() || (@this.InnerException?.IsCriticalException() ?? false) || @this is AggregateException aggregateException && aggregateException.InnerExceptions.Any(e => e.IsCriticalException());

    /// <summary>
    /// Returns a value that tells whether an <see cref="Exception"/> is of a type that
    /// will likely cause application failure.
    /// </summary>
    /// <param name="this">The exception being thrown.</param>
    /// <returns><see langword="true"/> if <paramref name="this"/> is a fatal exception;
    /// otherwise, <see langword="false"/>.</returns>
    public static Boolean IsFatalException(this Exception @this) => @this.IsFatalExceptionCore() || (@this.InnerException?.IsFatalException() ?? false) || @this is AggregateException aggregateException && aggregateException.InnerExceptions.Any(e => e.IsFatalException());

    private static Boolean IsCriticalExceptionCore(this Exception @this) => IsFatalExceptionCore(@this) || @this is AppDomainUnloadedException || @this is BadImageFormatException || @this is CannotUnloadAppDomainException || @this is InvalidProgramException || @this is NullReferenceException;

    private static Boolean IsFatalExceptionCore(this Exception @this) => @this is StackOverflowException || @this is OutOfMemoryException || @this is ThreadAbortException || @this is AccessViolationException;
  }
}