using System;
using System.IO;
using System.Runtime.InteropServices;
using AOT;
using UnityEngine;

public class SystemModule: CallbackHandler<SystemModule>
{
    private const int MaxFileHandles = 50;
    
    private readonly UniQuake uq;

    private readonly FileStream[] fileHandles = new FileStream[MaxFileHandles];

    public SystemModule(UniQuake uniQuake)
    {
        uq = uniQuake;
        
        var callbacks = new Callbacks
        {
            target = SelfPtr,
            
            SysPrint = CreateCallback<SysPrintCallback>(Callback_SysPrint),
            SysError = CreateCallback<SysErrorCallback>(Callback_SysError),
            SysQuit = CreateCallback<SysQuitCallback>(Callback_SysQuit),
            SysFloatTime = CreateCallback<SysFloatTimeCallback>(Callback_SysFloatTime),
            
            SysFileOpenRead = CreateCallback<SysFileOpenReadCallback>(Callback_SysFileOpenRead),
            SysFileOpenWrite = CreateCallback<SysFileOpenWriteCallback>(Callback_SysFileOpenWrite),
            SysFileClose = CreateCallback<SysFileCloseCallback>(Callback_SysFileClose),
            SysFileSeek = CreateCallback<SysFileSeekCallback>(Callback_SysFileSeek),
            SysFileRead = CreateCallback<SysFileReadCallback>(Callback_SysFileRead),
            SysFileWrite = CreateCallback<SysFileWriteCallback>(Callback_SysFileWrite),
            SysFileTime = CreateCallback<SysFileTimeCallback>(Callback_SysFileTime),
            SysMkDir = CreateCallback<SysMkDirCallback>(Callback_SysMkDir),
        };
        
        RegisterCallbacks(callbacks);
    }

    public override void Destroy()
    {
        for (int i = 0; i < MaxFileHandles; ++i)
        {
            if (fileHandles[i] != null)
                fileHandles[i].Dispose();
        }
        
        base.Destroy();
    }

    /// <summary>
    /// This matches struct unity_syscalls_s from uniquake.h in native code.
    /// </summary>
    [StructLayout(LayoutKind.Sequential, Pack = 0)]
    private class Callbacks
    {
        public IntPtr target;
        
        public IntPtr SysPrint;
        public IntPtr SysError;
        public IntPtr SysQuit;
        public IntPtr SysFloatTime;

        public IntPtr SysFileOpenRead;
        public IntPtr SysFileOpenWrite;
        public IntPtr SysFileClose;
        public IntPtr SysFileSeek;
        public IntPtr SysFileRead;
        public IntPtr SysFileWrite;
        public IntPtr SysFileTime;
        public IntPtr SysMkDir;
    }
    
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void SysPrintCallback(IntPtr target, [MarshalAs(UnmanagedType.LPStr)] string message);
    
    [MonoPInvokeCallback(typeof(SysPrintCallback))]
    private static void Callback_SysPrint(IntPtr target, string message)
    {
        GetSelf(target).Print(message);
    }
    
    private void Print(string message)
    {
        // Debug.Log(message);  // TODO: collect logs per frame and print after each Update loop
    }
    
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void SysErrorCallback(IntPtr target, [MarshalAs(UnmanagedType.LPStr)] string message);

    [MonoPInvokeCallback(typeof(SysErrorCallback))]
    private static void Callback_SysError(IntPtr target, string message)
    {
        GetSelf(target).Error(message);
    }
    
    private void Error(string message)
    {
        // Use an exception to emulate Quake's behavior of immediately terminating the game's code execution on error
        throw new QuakeException(message, 1);
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void SysQuitCallback(IntPtr target);
    
    [MonoPInvokeCallback(typeof(SysQuitCallback))]
    private static void Callback_SysQuit(IntPtr target)
    {
        GetSelf(target).Quit();
    }
    
    private void Quit()
    {
        // This exception will be caught by the UniQuake update loop where the game will be shut down
        throw new QuakeException("Quitting application normally");
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate double SysFloatTimeCallback(IntPtr target);
    
    [MonoPInvokeCallback(typeof(SysFloatTimeCallback))]
    private static double Callback_SysFloatTime(IntPtr target)
    {
        return GetSelf(target).FloatTime();
    }
    
    private double FloatTime()
    {
        return uq.CurrentTime;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int SysFileOpenReadCallback(IntPtr target, [MarshalAs(UnmanagedType.LPStr)] string path, out int handle);

    [MonoPInvokeCallback(typeof(SysFileOpenReadCallback))]
    private static int Callback_SysFileOpenRead(IntPtr target, string path, out int handle)
    {
        return GetSelf(target).FileOpenRead(path, out handle);
    }

    private int FileOpenRead(string path, out int handle)
    {
        int i = FindFileHandle();
        try
        {
            Debug.Log($"Opening file for reading: {path}");
            FileStream fileStream = File.OpenRead(path);
            fileHandles[i] = fileStream;
            handle = i;
            return (int)fileStream.Length;
        }
        catch
        {
            handle = -1;
            return -1;
        }
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int SysFileOpenWriteCallback(IntPtr target, [MarshalAs(UnmanagedType.LPStr)] string path);

    [MonoPInvokeCallback(typeof(SysFileOpenWriteCallback))]
    private static int Callback_SysFileOpenWrite(IntPtr target, string path)
    {
        return GetSelf(target).FileOpenWrite(path);
    }

    private int FileOpenWrite(string path)
    {
        int i = FindFileHandle();
        try
        {
            Debug.Log($"Opening file for writing: {path}");
            FileStream fileStream = File.OpenWrite(path);
            fileHandles[i] = fileStream;
            return i;
        }
        catch (Exception ex)
        {
            Error($"Error opening {path}: {ex.Message}");
            return -1;
        }
    }

    private int FindFileHandle()
    {
        for (int i = 1; i < MaxFileHandles; ++i)
        {
            if (fileHandles[i] == null)
                return i;
        }
        
        Error("Out of handles!");
        return -1;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void SysFileCloseCallback(IntPtr target, int handle);

    [MonoPInvokeCallback(typeof(SysFileCloseCallback))]
    private static void Callback_SysFileClose(IntPtr target, int handle)
    {
        GetSelf(target).FileClose(handle);
    }

    private void FileClose(int handle)
    {
        if (handle < 0 || handle >= MaxFileHandles)
        {
            Debug.LogWarning($"Invalid file handle! {handle}");
            return;
        }
        
        fileHandles[handle].Dispose();
        fileHandles[handle] = null;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void SysFileSeekCallback(IntPtr target, int handle, int position);

    [MonoPInvokeCallback(typeof(SysFileSeekCallback))]
    private static void Callback_SysFileSeek(IntPtr target, int handle, int position)
    {
        GetSelf(target).FileSeek(handle, position);
    }

    private void FileSeek(int handle, int position)
    {
        if (handle < 0 || handle >= MaxFileHandles)
        {
            Debug.LogWarning($"Invalid file handle! {handle}");
            return;
        }

        fileHandles[handle].Seek(position, SeekOrigin.Begin);
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int SysFileReadCallback(IntPtr target, int handle, IntPtr dest, int count);

    [MonoPInvokeCallback(typeof(SysFileReadCallback))]
    private static int Callback_SysFileRead(IntPtr target, int handle, IntPtr dest, int count)
    {
        return GetSelf(target).FileRead(handle, dest, count);
    }

    private int FileRead(int handle, IntPtr dest, int count)
    {
        if (handle < 0 || handle >= MaxFileHandles)
        {
            Debug.LogWarning($"Invalid file handle! {handle}");
            return 0;
        }

        byte[] buf = new byte[count];   // TODO: reuse buffer
        int numRead = fileHandles[handle].Read(buf, 0, count);
        Marshal.Copy(buf, 0, dest, numRead);
        return numRead;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int SysFileWriteCallback(IntPtr target, int handle, IntPtr data, int count);

    [MonoPInvokeCallback(typeof(SysFileWriteCallback))]
    private static int Callback_SysFileWrite(IntPtr target, int handle, IntPtr data, int count)
    {
        return GetSelf(target).FileWrite(handle, data, count);
    }

    private int FileWrite(int handle, IntPtr data, int count)
    {
        if (handle < 0 || handle >= MaxFileHandles)
        {
            Debug.LogWarning($"Invalid file handle! {handle}");
            return 0;
        }

        byte[] buf = new byte[count];   // TODO: reuse buffer
        Marshal.Copy(data, buf, 0, count);
        fileHandles[handle].Write(buf, 0, count);
        return count;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate int SysFileTimeCallback(IntPtr target, [MarshalAs(UnmanagedType.LPStr)] string path);

    [MonoPInvokeCallback(typeof(SysFileTimeCallback))]
    private static int Callback_SysFileTime(IntPtr target, string path)
    {
        return GetSelf(target).FileTime(path);
    }

    private int FileTime(string path)
    {
        // It would logically make more sense to return an actual file write time here,
        // but a signed 32-bit int is quite limited and we don't want any Year 2038 problems here.
        return File.Exists(path) ? 1 : -1;
    }

    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    private delegate void SysMkDirCallback(IntPtr target, [MarshalAs(UnmanagedType.LPStr)] string path);

    [MonoPInvokeCallback(typeof(SysMkDirCallback))]
    private static void Callback_SysMkDir(IntPtr target, string path)
    {
        GetSelf(target).MkDir(path);
    }

    private void MkDir(string path)
    {
        try
        {
            Directory.CreateDirectory(path);
        }
        catch
        {
            Debug.LogWarning($"Could not create directory: {path}");
        }
    }
}