/* Copyright (c) 2019 Rick (rick 'at' gibbed 'dot' us)
 * 
 * This software is provided 'as-is', without any express or implied
 * warranty. In no event will the authors be held liable for any damages
 * arising from the use of this software.
 * 
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 * 
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would
 *    be appreciated but is not required.
 * 
 * 2. Altered source versions must be plainly marked as such, and must not
 *    be misrepresented as being the original software.
 * 
 * 3. This notice may not be removed or altered from any source
 *    distribution.
 */

using System;
using System.IO;
using System.Runtime.InteropServices;
using Microsoft.Win32;

namespace SAM.API
{
    public static class Steam
    {
        private struct Native
        {
            [DllImport("kernel32.dll", SetLastError = true, BestFitMapping = false, ThrowOnUnmappableChar = true)]
            internal static extern IntPtr GetProcAddress(IntPtr module, string name);

            [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
            internal static extern IntPtr LoadLibraryEx(string path, IntPtr file, uint flags);

            [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
            [return: MarshalAs(UnmanagedType.Bool)]
            internal static extern bool SetDllDirectory(string path);

            internal const uint LoadWithAlteredSearchPath = 8;
        }

        private static Delegate GetExportDelegate<TDelegate>(IntPtr module, string name)
        {
            IntPtr address = Native.GetProcAddress(module, name);
            return address == IntPtr.Zero ? null : Marshal.GetDelegateForFunctionPointer(address, typeof(TDelegate));
        }

        private static TDelegate GetExportFunction<TDelegate>(IntPtr module, string name)
            where TDelegate : class
        {
            return (TDelegate)((object)GetExportDelegate<TDelegate>(module, name));
        }

        private static IntPtr _Handle = IntPtr.Zero;

        public static string GetInstallPath()
        {
            return (string)Registry.GetValue(@"HKEY_LOCAL_MACHINE\Software\Valve\Steam", "InstallPath", null);
        }

        [UnmanagedFunctionPointer(CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
        private delegate IntPtr NativeCreateInterface(string version, IntPtr returnCode);

        private static NativeCreateInterface _CallCreateInterface;

        public static TClass CreateInterface<TClass>(string version)
            where TClass : INativeWrapper, new()
        {
            IntPtr address = _CallCreateInterface(version, IntPtr.Zero);

            if (address == IntPtr.Zero)
            {
                return default(TClass);
            }

            var rez = new TClass();
            rez.SetupFunctions(address);
            return rez;
        }

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        [return: MarshalAs(UnmanagedType.I1)]
        private delegate bool NativeSteamGetCallback(int pipe, out Types.CallbackMessage message, out int call);

        private static NativeSteamGetCallback _CallSteamBGetCallback;

        public static bool GetCallback(int pipe, out Types.CallbackMessage message, out int call)
        {
            return _CallSteamBGetCallback(pipe, out message, out call);
        }

        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
        [return: MarshalAs(UnmanagedType.I1)]
        private delegate bool NativeSteamFreeLastCallback(int pipe);

        private static NativeSteamFreeLastCallback _CallSteamFreeLastCallback;

        public static bool FreeLastCallback(int pipe)
        {
            return _CallSteamFreeLastCallback(pipe);
        }

        public static bool Load()
        {
            if (_Handle != IntPtr.Zero)
            {
                return true;
            }

            string path = GetInstallPath();
            if (path == null)
            {
                return false;
            }

            Native.SetDllDirectory(path + ";" + Path.Combine(path, "bin"));

            path = Path.Combine(path, "steamclient.dll");
            IntPtr module = Native.LoadLibraryEx(path, IntPtr.Zero, Native.LoadWithAlteredSearchPath);
            if (module == IntPtr.Zero)
            {
                return false;
            }

            _CallCreateInterface = GetExportFunction<NativeCreateInterface>(module, "CreateInterface");
            if (_CallCreateInterface == null)
            {
                return false;
            }

            _CallSteamBGetCallback = GetExportFunction<NativeSteamGetCallback>(module, "Steam_BGetCallback");
            if (_CallSteamBGetCallback == null)
            {
                return false;
            }

            _CallSteamFreeLastCallback = GetExportFunction<NativeSteamFreeLastCallback>(module, "Steam_FreeLastCallback");
            if (_CallSteamFreeLastCallback == null)
            {
                return false;
            }

            _Handle = module;
            return true;
        }
    }
}