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

namespace WhiteMagic;

/// <summary>
/// Abstract base for all memory-access readers and writers. Provides typed
/// <see cref="Read{T}"/>/<see cref="Write{T}"/>, array IO, string IO, and
/// relative/absolute addressing. Subclasses implement the concrete
/// <see cref="ReadBytes"/> and <see cref="WriteBytes"/> methods.
/// </summary>
public abstract class MemoryBase : IDisposable
{
    /// <summary>The base address of the target process's main module.</summary>
    public abstract IntPtr ImageBase { get; }

    /// <summary>The native handle to the target process.</summary>
    public abstract SafeMemoryHandle Handle { get; }

    // ── Raw byte IO ────────────────────────────────────────────────────────

    /// <summary>Reads a sequence of bytes from the target address.</summary>
    public abstract byte[] ReadBytes(IntPtr address, int count, bool isRelative = false);

    /// <summary>Writes a sequence of bytes to the target address.</summary>
    /// <returns>The number of bytes written.</returns>
    public abstract int WriteBytes(IntPtr address, ReadOnlySpan<byte> bytes, bool isRelative = false);

    // ── Typed IO ───────────────────────────────────────────────────────────

    /// <summary>Reads a value of type <typeparamref name="T"/> from the target address.</summary>
    public T Read<T>(IntPtr address, bool isRelative = false) where T : struct
    {
        if (isRelative)
            address = GetAbsolute(address);

        int size = MarshalCache<T>.Size;
        byte[] raw = ReadBytes(address, size);

        if (MarshalCache<T>.TypeRequiresMarshal)
        {
            return MarshalByteArrayToStructure<T>(raw);
        }

        return MemoryMarshal.Read<T>(raw.AsSpan());
    }

    /// <summary>Writes a value of type <typeparamref name="T"/> to the target address.</summary>
    /// <returns><see langword="true"/> if all bytes were written.</returns>
    public bool Write<T>(IntPtr address, T value, bool isRelative = false) where T : struct
    {
        if (isRelative)
            address = GetAbsolute(address);

        int size = MarshalCache<T>.Size;

        byte[] raw;
        if (MarshalCache<T>.TypeRequiresMarshal)
        {
            raw = StructureToByteArray(value, size);
        }
        else
        {
            raw = new byte[size];
            MemoryMarshal.Write(raw.AsSpan(), in value);
        }

        int written = WriteBytes(address, raw, false);
        return written == size;
    }

    /// <summary>Reads an array of values of type <typeparamref name="T"/> from the target address.</summary>
    public T[] Read<T>(IntPtr address, int count, bool isRelative = false) where T : struct
    {
        if (isRelative)
            address = GetAbsolute(address);

        int elementSize = MarshalCache<T>.Size;
        int totalSize = elementSize * count;
        byte[] raw = ReadBytes(address, totalSize);

        var result = new T[count];

        if (MarshalCache<T>.TypeRequiresMarshal)
        {
            for (int i = 0; i < count; i++)
            {
                var elementBytes = new ReadOnlySpan<byte>(raw, i * elementSize, elementSize);
                result[i] = MarshalByteArrayToStructure<T>(elementBytes.ToArray());
            }
        }
        else
        {
            ReadOnlySpan<byte> span = raw;
            for (int i = 0; i < count; i++)
            {
                result[i] = MemoryMarshal.Read<T>(span.Slice(i * elementSize, elementSize));
            }
        }

        return result;
    }

    /// <summary>Writes an array of values of type <typeparamref name="T"/> to the target address.</summary>
    /// <returns><see langword="true"/> if all bytes were written.</returns>
    public bool Write<T>(IntPtr address, T[] values, bool isRelative = false) where T : struct
    {
        if (isRelative)
            address = GetAbsolute(address);

        if (values is null || values.Length == 0)
            return true;

        int elementSize = MarshalCache<T>.Size;
        int totalSize = elementSize * values.Length;
        byte[] raw = new byte[totalSize];

        Span<byte> span = raw;
        for (int i = 0; i < values.Length; i++)
        {
            Span<byte> slice = span.Slice(i * elementSize, elementSize);
            if (MarshalCache<T>.TypeRequiresMarshal)
            {
                StructureToByteArray(values[i], slice, elementSize);
            }
            else
            {
                MemoryMarshal.Write(slice, in values[i]);
            }
        }

        int written = WriteBytes(address, raw, false);
        return written == totalSize;
    }

    // ── String IO ──────────────────────────────────────────────────────────

    /// <summary>Reads a null-terminated string from the target address.</summary>
    public virtual string ReadString(IntPtr address, Encoding encoding, int maxLength = 512, bool relative = false)
    {
        byte[] buffer = ReadBytes(address, maxLength, relative);
        string decoded = encoding.GetString(buffer);
        int nullIndex = decoded.IndexOf('\0');
        if (nullIndex >= 0)
        {
            return decoded[..nullIndex];
        }
        return decoded;
    }

    /// <summary>Writes a null-terminated string to the target address.</summary>
    public virtual bool WriteString(IntPtr address, string value, Encoding encoding, bool relative = false)
    {
        if (value.Length == 0 || value[^1] != '\0')
            value += '\0';

        byte[] bytes = encoding.GetBytes(value);
        int written = WriteBytes(address, bytes, relative);
        return written == bytes.Length;
    }

    // ── Addressing ─────────────────────────────────────────────────────────

    /// <summary>Converts a relative offset to an absolute address relative to <see cref="ImageBase"/>.</summary>
    public IntPtr GetAbsolute(IntPtr relative)
    {
        return ImageBase + (nint)relative;
    }

    /// <summary>Converts an absolute address to a relative offset from <see cref="ImageBase"/>.</summary>
    public IntPtr GetRelative(IntPtr absolute)
    {
        return (IntPtr)((nint)ImageBase - (nint)absolute);
    }

    // ── Lifecycle ──────────────────────────────────────────────────────────

    /// <inheritdoc />
    public virtual void Dispose()
    {
        Handle?.Dispose();
    }

    // ── Private helpers ────────────────────────────────────────────────────

    private static T MarshalByteArrayToStructure<T>(byte[] bytes) where T : struct
    {
        GCHandle pin = GCHandle.Alloc(bytes, GCHandleType.Pinned);
        try
        {
            return Marshal.PtrToStructure<T>(pin.AddrOfPinnedObject());
        }
        finally
        {
            pin.Free();
        }
    }

    private static byte[] StructureToByteArray<T>(T value, int size) where T : struct
    {
        byte[] bytes = new byte[size];
        GCHandle pin = GCHandle.Alloc(bytes, GCHandleType.Pinned);
        try
        {
            Marshal.StructureToPtr(value, pin.AddrOfPinnedObject(), false);
        }
        finally
        {
            pin.Free();
        }
        return bytes;
    }

    private static void StructureToByteArray<T>(T value, Span<byte> destination, int size) where T : struct
    {
        byte[] temp = destination.ToArray();
        GCHandle pin = GCHandle.Alloc(temp, GCHandleType.Pinned);
        try
        {
            Marshal.StructureToPtr(value, pin.AddrOfPinnedObject(), false);
            temp.CopyTo(destination);
        }
        finally
        {
            pin.Free();
        }
    }
}