#include "dos_emu.hpp"

#include <cstdint>
#include <cstdlib>
#include <cstdio>

#include <atomic>

#include <ucontext.h>

static void dos_functions(mcontext_t& mcontext);
static void dpmi_functions(mcontext_t& mcontext,  long unsigned int& flags);

void dos_emu_handler(int, siginfo_t*, void* c) {
    ucontext_t* context = (ucontext_t*) c;

    uint8_t* instruction = (uint8_t*) context->uc_mcontext.gregs[REG_EIP];
    fprintf(stderr, "eip: 0x%lx\n", instruction);
    if (instruction[0] == 0xFB) //mnemonic STI
    {
        //we cant do this in user space so ignore for now.
        context->uc_mcontext.gregs[REG_EIP] += 1;
    }
    else if (instruction[0] == 0xCD) //mnemonic INT
    {
        if(instruction[1] == 0x21) {
            dos_functions(context->uc_mcontext);
        }
        if(instruction[1] == 0x31) {
            dpmi_functions(context->uc_mcontext, context->uc_flags);
        }

        //skip the interrupt and hopefully we handled it owk.
        context->uc_mcontext.gregs[REG_EIP] += 2;
    } else {
        //whoops we fucked up something fierce.
        abort();
    }

    return;
}

static void dos_functions(mcontext_t& mcontext) {
    uint8_t ah = (mcontext.gregs[REG_EAX] & 0x0000FF00) >> 8;
    uint8_t al = mcontext.gregs[REG_EAX] & 0x000000FF;

    uint16_t ax = mcontext.gregs[REG_EAX] & 0x0000FFFF;
    uint16_t dx = mcontext.gregs[REG_EDX] & 0x0000FFFF;

    //Get dos version
    if(ah == 0x30) {
        mcontext.gregs[REG_EAX] &= 0xFFFF0000;
        mcontext.gregs[REG_EAX] |= 6 << 8;
        mcontext.gregs[REG_EAX] |= 22;

        mcontext.gregs[REG_EBX] &= 0xFFFF0000;
        mcontext.gregs[REG_EBX] |= 0x000000DE;
        mcontext.gregs[REG_ECX] =  0xDEADBEAF;

        if(al == 1) {
            mcontext.gregs[REG_EBX] |= 1 << 8;
        } else {
            mcontext.gregs[REG_EBX] |= 2 << 8;
        }
    }

    //Dos4gw install check
    if(ax == 0xFF00 && dx == 0x0078) {
        mcontext.gregs[REG_EAX] &= 0xFFFFFF00;
        mcontext.gregs[REG_EAX] |= 1;
        //should possible set GS... well fuck.
    }
}

static void dpmi_functions(mcontext_t& mcontext, long unsigned int& flags) {
    uint16_t ax = mcontext.gregs[REG_EAX] & 0x0000FFFF;

    //Get Segment base address
    if (ax == 0x0006) {
        mcontext.gregs[REG_ECX] &= 0xFFFF0000;
        mcontext.gregs[REG_EDX] &= 0xFFFF0000;
        flags = 0;
    }
}