#include "emulator.h"

void add_eb_gb() {
    uint32_t addr = physical_addr(CS, IP);
    uint8_t modrm_byte = ram[addr];
    IP++;

    ModRM modrm = parse_modrm(modrm_byte);
    uint8_t gb_value = get_reg_byte(modrm.reg);
    uint8_t eb_value;
    uint32_t eb_addr;
    bool eb_is_mem = false;

    if (modrm.mod == 3) {
        // eb is a reg
        eb_value = get_reg_byte(modrm.rm);
    } else {
        // eb is an addr
        uint32_t eff_addr = calc_effective_addr(modrm);
        uint16_t segment = (modrm.rm == 2 || modrm.rm == 3 || modrm.rm == 6) ? SS : DS;
        uint32_t phys_addr = physical_addr(segment, eff_addr);
        eb_value = ram[phys_addr];
        eb_is_mem = true;
    }

    uint8_t result = eb_value + gb_value;

    if (eb_is_mem) {
        ram[eb_addr] = result;
    } else {
        set_reg_byte(modrm.rm, result);
    }

    update_flags_add(eb_value, gb_value, result);
}

void add_ev_gv() {
    uint32_t addr = physical_addr(CS, IP);
    uint8_t modrm_byte = ram[addr];
    IP ++;

    ModRM modrm = parse_modrm(modrm_byte);
    uint16_t gv_value = get_reg_word(modrm.reg);
    uint16_t ev_value;
    uint32_t ev_addr;
    bool ev_is_mem = false;

    if (modrm.mod == 3) {
        ev_value = get_reg_word(modrm.rm);
    } else {
        uint16_t seg = (modrm.rm == 4 || modrm.rm == 5 || modrm.rm == 6) ? SS : DS;
        uint16_t eff_addr = calc_effective_addr(modrm);
        ev_addr = physical_addr(seg, eff_addr);
        
        ev_value = ram[ev_addr] | (ram[ev_addr + 1] << 8);
        ev_is_mem = true;
    }

    uint16_t result = ev_value + gv_value;

    if (ev_is_mem) {
        ram[ev_addr] = result & 0xFF;
        ram[ev_addr + 1] = result >> 8;
    } else {
        set_reg_word(modrm.rm, result);
    }

    update_flags_add16(ev_value, gv_value, result);
    std::cout << "AX = " << std::hex << AX.value 
              << " (AL=" << (int)AX.low << ")\n";
}

void hlt() {
    std::cout << "HLT\n";
    exit(0);
}

using instrHandler = void(*)();
instrHandler instr_table[256] = { nullptr };

void init_instr_table() {
    instr_table[0x00] = add_eb_gb;
    instr_table[0x01] = add_ev_gv;
    instr_table[0xf4] = hlt;
}