using System.Security.Cryptography;

namespace AcDream.App.Credentials;

/// <summary>
/// Campaign LA slice LA1: retains a resolved <c>--session-config</c>
/// credential in erasable memory — the App-side mirror of
/// <c>AcDream.Headless.Credentials.HeadlessCredentialSecret</c> (that type is
/// internal to the Headless project, so this is a minimal, independent port
/// rather than a shared reference). The network boundary still requires one
/// short-lived immutable string; callers must not retain that value beyond
/// constructing the connect request.
/// </summary>
internal sealed class AppCredentialSecret : IDisposable
{
    private char[]? _buffer;

    internal AppCredentialSecret(string referenceId, ReadOnlySpan<char> value)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(referenceId);
        if (value.IsEmpty)
        {
            throw new AppCredentialException(
                $"Credential '{referenceId}' resolved to an empty secret.");
        }

        ReferenceId = referenceId;
        _buffer = value.ToArray();
    }

    internal string ReferenceId { get; }
    internal bool IsDisposed => _buffer is null;

    internal string Reveal()
    {
        ObjectDisposedException.ThrowIf(_buffer is null, this);
        return new string(_buffer);
    }

    public void Dispose()
    {
        char[]? buffer = Interlocked.Exchange(ref _buffer, null);
        if (buffer is null)
            return;
        CryptographicOperations.ZeroMemory(
            System.Runtime.InteropServices.MemoryMarshal.AsBytes(
                buffer.AsSpan()));
    }

    public override string ToString() =>
        $"[redacted:{ReferenceId}]";
}

internal sealed class AppCredentialException : Exception
{
    internal AppCredentialException(string message)
        : base(message)
    {
    }

    internal AppCredentialException(string message, Exception innerException)
        : base(message, innerException)
    {
    }
}