using System.Diagnostics;
using System.Runtime.InteropServices;
using WhiteMagic.Native;

namespace WhiteMagic;

/// <summary>
/// In-process memory reader that accesses the owning process's memory through
/// direct pointer dereference (<c>unsafe</c>). Use this reader from within a
/// managed DLL injected into the target process.
/// </summary>
public sealed class InProcessReader : MemoryBase
{
    private readonly SafeMemoryHandle _handle;
    private readonly IntPtr _imageBase;
    private bool _disposed;

    /// <summary>
    /// Creates an in-process reader for the current process.
    /// </summary>
    public InProcessReader()
    {
        Process current = Process.GetCurrentProcess();
        _handle = NativeMethods.OpenProcess(
            ProcessAccess.VmRead | ProcessAccess.VmWrite | ProcessAccess.VmOperation | ProcessAccess.QueryInformation,
            false,
            current.Id);

        _imageBase = current.MainModule?.BaseAddress ?? IntPtr.Zero;
    }

    /// <inheritdoc />
    public override IntPtr ImageBase => _imageBase;

    /// <inheritdoc />
    public override SafeMemoryHandle Handle => _handle;

    /// <inheritdoc />
    public override unsafe byte[] ReadBytes(IntPtr address, int count, bool isRelative = false)
    {
        if (isRelative)
            address = GetAbsolute(address);

        byte[] buffer = new byte[count];
        fixed (byte* ptr = buffer)
        {
            Buffer.MemoryCopy((void*)address, ptr, count, count);
        }
        return buffer;
    }

    /// <inheritdoc />
    public override unsafe int WriteBytes(IntPtr address, ReadOnlySpan<byte> bytes, bool isRelative = false)
    {
        if (isRelative)
            address = GetAbsolute(address);

        fixed (byte* ptr = bytes)
        {
            Buffer.MemoryCopy(ptr, (void*)address, bytes.Length, bytes.Length);
        }
        return bytes.Length;
    }

    /// <inheritdoc />
    public override void Dispose()
    {
        if (!_disposed)
        {
            _disposed = true;
            _handle.Dispose();
        }
    }
}