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

namespace WhiteMagicTest;

/// <summary>
/// Tests for <see cref="MemoryBase"/> abstract contract and <see cref="ExternalReader"/>
/// round-trip (Read&lt;T&gt;/Write&lt;T&gt;, arrays) using the current process as target.
/// </summary>
public class MemoryBaseTests
{
    private static ExternalReader OpenSelf()
    {
        return new ExternalReader(
            Process.GetCurrentProcess(),
            ProcessAccess.VmRead | ProcessAccess.VmWrite | ProcessAccess.VmOperation | ProcessAccess.QueryInformation);
    }

    [Fact]
    public void ImageBase_is_nonzero_for_self()
    {
        using var reader = OpenSelf();
        Assert.NotEqual(IntPtr.Zero, reader.ImageBase);
    }

    [Fact]
    public void Read_int_writes_and_reads_back()
    {
        using var reader = OpenSelf();

        int slot = 0;
        GCHandle pin = GCHandle.Alloc(slot, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            Assert.True(reader.Write(addr, 0x1BADB002));
            Assert.Equal(0x1BADB002, reader.Read<int>(addr));
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Read_byte_writes_and_reads_back()
    {
        using var reader = OpenSelf();
        byte slot = 0;
        GCHandle pin = GCHandle.Alloc(slot, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            Assert.True(reader.Write(addr, (byte)0xAB));
            Assert.Equal(0xAB, reader.Read<byte>(addr));
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Read_long_writes_and_reads_back()
    {
        using var reader = OpenSelf();
        long slot = 0;
        GCHandle pin = GCHandle.Alloc(slot, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            Assert.True(reader.Write(addr, unchecked((long)0xDEADBEEF_CAFEBABE)));
            Assert.Equal(unchecked((long)0xDEADBEEF_CAFEBABE), reader.Read<long>(addr));
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Read_blittable_struct_writes_and_reads_back()
    {
        using var reader = OpenSelf();
        var slot = new TestStruct { X = 42, Y = 99 };
        GCHandle pin = GCHandle.Alloc(slot, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            Assert.True(reader.Write(addr, new TestStruct { X = 100, Y = 200 }));
            var result = reader.Read<TestStruct>(addr);
            Assert.Equal(100, result.X);
            Assert.Equal(200, result.Y);
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Read_bytes_writes_and_reads_back()
    {
        using var reader = OpenSelf();
        byte[] buffer = new byte[16];
        GCHandle pin = GCHandle.Alloc(buffer, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            byte[] expected = [0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07];

            int written = reader.WriteBytes(addr, expected);
            Assert.Equal(expected.Length, written);

            byte[] actual = reader.ReadBytes(addr, expected.Length);
            Assert.Equal(expected, actual);
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Read_int_array_writes_and_reads_back()
    {
        using var reader = OpenSelf();
        int[] buffer = new int[4];
        GCHandle pin = GCHandle.Alloc(buffer, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            int[] expected = [10, 20, 30, 40];

            Assert.True(reader.Write(addr, expected));
            int[] actual = reader.Read<int>(addr, 4);
            Assert.Equal(expected, actual);
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Read_struct_array_writes_and_reads_back()
    {
        using var reader = OpenSelf();
        var buffer = new TestStruct[4];
        GCHandle pin = GCHandle.Alloc(buffer, GCHandleType.Pinned);
        try
        {
            IntPtr addr = pin.AddrOfPinnedObject();
            var expected = new[]
            {
                new TestStruct { X = 1, Y = 2 },
                new TestStruct { X = 3, Y = 4 },
                new TestStruct { X = 5, Y = 6 },
                new TestStruct { X = 7, Y = 8 },
            };

            Assert.True(reader.Write(addr, expected));
            var actual = reader.Read<TestStruct>(addr, 4);
            Assert.Equal(expected, actual);
        }
        finally
        {
            pin.Free();
        }
    }

    [Fact]
    public void Write_returns_false_for_invalid_address()
    {
        using var reader = OpenSelf();
        Assert.False(reader.Write(IntPtr.Zero, 42));
    }

    [Fact]
    public void Dispose_closes_handle()
    {
        var reader = OpenSelf();
        Assert.False(reader.Handle.IsClosed);
        reader.Dispose();
        Assert.True(reader.Handle.IsClosed);
    }

    [Fact]
    public void Double_dispose_does_not_throw()
    {
        var reader = OpenSelf();
        reader.Dispose();
        reader.Dispose();
    }

    // ── Marshal-path round-trip ───────────────────────────────────────────────
    //
    // The marshal path was previously sized using MarshalCache.Size (managed
    // layout width). When a struct carries an inline marshal-expanded field
    // (ByValTStr, ByValArray, etc.) this width is smaller than the actual
    // read/write width — writing overflows the pinned buffer and reading
    // under-fetches the remote bytes, producing silent heap corruption.
    //
    // The marshal path must use MarshalCache.MarshalSize (= Marshal.SizeOf<T>)
    // so the pinned buffer is large enough for PtrToStructure / StructureToPtr.

    [Fact]
    public void Read_struct_via_marshal_path_round_trips_inline_string()
    {
        using var reader = OpenSelf();

        // A marshal-path struct carries a reference, so it cannot be pinned; the
        // target must be an unmanaged buffer of the FULL marshal width. Pre-patch,
        // Write sized its scratch buffer with MarshalCache.Size (managed pointer
        // width, 8) and StructureToPtr overran it, while Read under-fetched the
        // remote bytes — the string came back wrong. Post-patch both use
        // MarshalSize (Marshal.SizeOf<InlineStr>).
        int size = Marshal.SizeOf<InlineStr>();
        IntPtr addr = Marshal.AllocHGlobal(size);
        try
        {
            InlineStr original = new InlineStr { Name = "Hello, World!" };
            Assert.True(reader.Write(addr, original));
            InlineStr read = reader.Read<InlineStr>(addr);
            Assert.Equal("Hello, World!", read.Name);
        }
        finally
        {
            Marshal.FreeHGlobal(addr);
        }
    }

    // ── Graceful failure on invalid addresses ───────────────────────────────

    [Fact]
    public void Read_int_on_invalid_address_returns_default()
    {
        using var reader = OpenSelf();
        Assert.Equal(0, reader.Read<int>(IntPtr.Zero));
    }

    [Fact]
    public void Read_struct_on_invalid_address_returns_default()
    {
        using var reader = OpenSelf();
        var result = reader.Read<TestStruct>(IntPtr.Zero);
        Assert.Equal(0, result.X);
        Assert.Equal(0, result.Y);
    }

    [Fact]
    public void Read_int_array_on_invalid_address_returns_empty()
    {
        using var reader = OpenSelf();
        Assert.Empty(reader.Read<int>(IntPtr.Zero, 10));
    }

    [Fact]
    public void Read_bytes_on_invalid_address_returns_empty()
    {
        using var reader = OpenSelf();
        Assert.Empty(reader.ReadBytes(IntPtr.Zero, 10));
    }
}

/// <summary>
/// A simple blittable struct for use in tests.
/// </summary>
[StructLayout(LayoutKind.Sequential)]
public struct TestStruct : IEquatable<TestStruct>
{
    public int X;
    public int Y;

    public bool Equals(TestStruct other) => X == other.X && Y == other.Y;
    public override bool Equals(object? obj) => obj is TestStruct other && Equals(other);
    public override int GetHashCode() => HashCode.Combine(X, Y);
    public override string ToString() => $"({X}, {Y})";
}

/// <summary>
/// A struct whose managed layout is just a reference pointer (8 bytes) but whose
/// unmanaged marshal layout carries an inline character buffer. Exercised by
/// <see cref="MemoryBaseTests.Read_struct_via_marshal_path_round_trips_inline_string"/>
/// to catch regressions where the marshal path uses the managed width instead
/// of the marshal width.
/// </summary>
[StructLayout(LayoutKind.Sequential)]
public struct InlineStr
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)]
    public string Name;
}