// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Linq;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Diagnostics.CodeAnalysis;
using Microsoft.Diagnostics.DataContractReader.Contracts;

namespace Microsoft.Diagnostics.DataContractReader.Legacy;

internal sealed class StackWalkHandleData
{
    private readonly IStackWalk _stackWalk;
    private readonly ThreadData _threadData;
    private IEnumerator<IStackDataFrameHandle>? _enumerator;

    public StackWalkHandleData(IStackWalk stackWalk, ThreadData threadData)
    {
        _stackWalk = stackWalk;
        _threadData = threadData;
    }

    public IStackDataFrameHandle? Current { get; private set; }

    [MemberNotNullWhen(true, nameof(Current))]
    public bool IsValid => Current is not null;
    public nuint LegacyHandle { get; set; }
    public void Reset(byte[] contextBuffer, bool isFirst)
    {
        _enumerator?.Dispose();
        _enumerator = _stackWalk
            .CreateStackWalk(_threadData, contextBuffer, isFirst)
            .Where(h => h.State is not (StackWalkState.Frame or StackWalkState.SkippedFrame))
            .GetEnumerator();
        Current = _enumerator is not null && _enumerator.MoveNext() ? _enumerator.Current : null;
        if (Current is null)
            throw Marshal.GetExceptionForHR(HResults.E_FAIL)!;
    }

    public void Advance()
    {
        Current = _enumerator is not null && _enumerator.MoveNext() ? _enumerator.Current : null;
    }

    public nuint GetHandle()
    {
        GCHandle gcHandle = GCHandle.Alloc(this);
        return (nuint)GCHandle.ToIntPtr(gcHandle);
    }

    public void Dispose() => _enumerator?.Dispose();
}