using System;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;

namespace Ryujinx.Cpu.Signal
{
    static partial class UnixSignalHandlerRegistration
    {
        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public unsafe struct SigSet
        {
            fixed long sa_mask[16];
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct SigAction
        {
            public IntPtr sa_handler;
            public SigSet sa_mask;
            public int sa_flags;
            public IntPtr sa_restorer;
        }

        [SupportedOSPlatform("android")]
        [StructLayout(LayoutKind.Sequential, Pack = 8)]
        public struct SigActionBionic
        {
            public int sa_flags;
            public IntPtr sa_handler;
            public SigSet sa_mask;
            public IntPtr sa_restorer;
        }

        private const int SIGSEGV = 11;
        private const int SIGBUS = 10;
        private const int SA_SIGINFO = 0x00000004;

        [LibraryImport("libc", SetLastError = true)]
        private static partial int sigaction(int signum, ref SigAction sigAction, out SigAction oldAction);

        [SupportedOSPlatform("android")]
        [LibraryImport("libc", SetLastError = true)]
        private static partial int sigaction(int signum, ref SigActionBionic sigAction, out SigActionBionic oldAction);

        [LibraryImport("libc", SetLastError = true)]
        private static partial int sigaction(int signum, IntPtr sigAction, out SigAction oldAction);

        [SupportedOSPlatform("android")]
        [LibraryImport("libc", SetLastError = true)]
        private static partial int sigaction(int signum, IntPtr sigAction, out SigActionBionic oldAction);

        [LibraryImport("libc", SetLastError = true)]
        private static partial int sigemptyset(ref SigSet set);

        public static SigAction GetSegfaultExceptionHandler()
        {
            int result;
            SigAction old;

            if (Ryujinx.Common.SystemInfo.SystemInfo.IsAndroid())
            {
                result = sigaction(SIGSEGV, IntPtr.Zero, out SigActionBionic tmp);

                old = new SigAction
                {
                    sa_handler = tmp.sa_handler,
                    sa_mask = tmp.sa_mask,
                    sa_flags = tmp.sa_flags,
                    sa_restorer = tmp.sa_restorer
                };
            }
            else
            {
                result = sigaction(SIGSEGV, IntPtr.Zero, out old);
            }

            if (result != 0)
            {
                throw new InvalidOperationException($"Could not get SIGSEGV sigaction. Error: {result}");
            }

            return old;
        }

        public static SigAction RegisterExceptionHandler(IntPtr action)
        {
            int result;
            SigAction old;

            if (Ryujinx.Common.SystemInfo.SystemInfo.IsAndroid())
            {
                SigActionBionic sig = new()
                {
                    sa_handler = action,
                    sa_flags = SA_SIGINFO
                };

                sigemptyset(ref sig.sa_mask);

                result = sigaction(SIGSEGV, ref sig, out SigActionBionic tmp);

                old = new SigAction
                {
                    sa_handler = tmp.sa_handler,
                    sa_mask = tmp.sa_mask,
                    sa_flags = tmp.sa_flags,
                    sa_restorer = tmp.sa_restorer
                };

                if (userSignal != -1)
                {
                    result = sigaction(userSignal, ref sig, out SigActionBionic oldu);

                    if (oldu.sa_handler != IntPtr.Zero)
                    {
                        throw new InvalidOperationException($"SIG{userSignal} is already in use.");
                    }

                    if (result != 0)
                    {
                        throw new InvalidOperationException($"Could not register SIG{userSignal} sigaction. Error: {result}");
                    }
                }
            }
            else
            {
                SigAction sig = new SigAction
                {
                    sa_handler = action,
                    sa_flags = SA_SIGINFO
                };

                sigemptyset(ref sig.sa_mask);

                result = sigaction(SIGSEGV, ref sig, out old);

                if (result != 0)
                {
                    throw new InvalidOperationException($"Could not register SIGSEGV sigaction. Error: {result}");
                }

                if (OperatingSystem.IsMacOS())
                {
                    result = sigaction(SIGBUS, ref sig, out _);

                    if (result != 0)
                    {
                        throw new InvalidOperationException($"Could not register SIGBUS sigaction. Error: {result}");
                    }
                }
            }

            return old;
        }

        public static bool RestoreExceptionHandler(SigAction oldAction)
        {
            if (Ryujinx.Common.SystemInfo.SystemInfo.IsAndroid())
            {
                SigActionBionic tmp = new SigActionBionic
                {
                    sa_handler = oldAction.sa_handler,
                    sa_mask = oldAction.sa_mask,
                    sa_flags = oldAction.sa_flags,
                    sa_restorer = oldAction.sa_restorer
                };

                return sigaction(SIGSEGV, ref tmp, out SigActionBionic _) == 0;
            }
            else
            {
                bool success = sigaction(SIGSEGV, ref oldAction, out SigAction _) == 0;

                if (success && OperatingSystem.IsMacOS())
                {
                    success = sigaction(SIGBUS, ref oldAction, out SigAction _) == 0;
                }

                return success;
            }
        }
    }
}