// Copyright (c) Ben A Adams. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

global using System;
global using System.Text;
global using System.Collections;
global using System.Collections.Generic;
global using System.Diagnostics;
global using System.Reflection;
global using System.Linq;
using System.Diagnostics.Contracts;
using DTLib.Demystifier.Enumerable;

namespace DTLib.Demystifier;

public static class ExceptionExtensions
{
    private static readonly FieldInfo? StackTraceString =
        typeof(Exception).GetField("_stackTraceString", BindingFlags.Instance | BindingFlags.NonPublic);

    private static void SetStackTracesString(this Exception exception, string value)
    {
        StackTraceString?.SetValue(exception, value);
    }

    /// <summary>
    ///     Demystifies the given <paramref name="exception" /> and tracks the original stack traces for the whole exception
    ///     tree.
    /// </summary>
    public static T Demystify<T>(this T exception) where T : Exception
    {
        try
        {
            var stackTrace = new EnhancedStackTrace(exception);

            if (stackTrace.FrameCount > 0) exception.SetStackTracesString(stackTrace.ToString());

            if (exception is AggregateException aggEx)
                foreach (var ex in EnumerableIList.Create(aggEx.InnerExceptions))
                    ex.Demystify();

            exception.InnerException?.Demystify();
        }
        catch
        {
            // Processing exceptions shouldn't throw exceptions; if it fails
        }

        return exception;
    }

    /// <summary>
    ///     Gets demystified string representation of the <paramref name="exception" />.
    /// </summary>
    /// <remarks>
    ///     <see cref="Demystify{T}" /> method mutates the exception instance that can cause
    ///     issues if a system relies on the stack trace be in the specific form.
    ///     Unlike <see cref="Demystify{T}" /> this method is pure. It calls <see cref="Demystify{T}" /> first,
    ///     computes a demystified string representation and then restores the original state of the exception back.
    /// </remarks>
    [Pure]
    public static string ToStringDemystified(this Exception exception)
    {
        return new StringBuilder().AppendDemystified(exception).ToString();
    }
}