#include <stdio.h>
#include <stdlib.h>
#include "lib.h"

#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))

enum Instruction
{
    INST_MOV = 0b10001000
};

enum Mode
{
    MODE_MEM_NOD = 0b00,
    MODE_MEM_08D = 0b01,
    MODE_MEM_16D = 0b10,
    MODE_REGMODE = 0b11,
};

typedef struct Register
{
    char code;
    char *fullname;
    char *bytename;
    union {
        struct {
            char low;
            char high;
        };
        u16 full;
    } value;
} Register;

Register registers[8] = {
    {.code = 0b000, .fullname = "ax", .bytename = "al" },
    {.code = 0b001, .fullname = "cx", .bytename = "cl" },
    {.code = 0b010, .fullname = "dx", .bytename = "dl" },
    {.code = 0b011, .fullname = "bx", .bytename = "bl" },
    {.code = 0b100, .fullname = "sp", .bytename = "ah" },
    {.code = 0b101, .fullname = "bp", .bytename = "ch" },
    {.code = 0b110, .fullname = "si", .bytename = "dh" },
    {.code = 0b111, .fullname = "di", .bytename = "bh" },
};

int main(int argc, char **argv)
{
    if (argc < 2)
    {
        printf("Usage: Please provide assembled instructions as input\n");
        exit(0);
    }
    unsigned char buf[256];
    FILE *f = fopen(argv[1], "r");
    if (!f)
    {
        perror("fopen\n");
        return EXIT_FAILURE;
    }
    size_t bytes_read = fread(buf, sizeof(*buf), ARRAY_SIZE(buf), f);

    printf("; Decoded 8086 Assembly Instructions\n\n");
    printf("bits 16\n\n");
    for (int i = 0; i < (int)bytes_read / 2; i += 2)
    {
        char low_byte = buf[i];
        char high_byte = buf[i+1];
        // char w = byte & 0b00000001;
        char d = low_byte & 0b00000010;
        char mod = (high_byte & 0b11000000) >> 6;
        char reg = (high_byte & 0b00111000) >> 3;
        char r_m = (high_byte & 0b00000111);
        size_t reg_idx = reg;
        size_t r_m_idx = r_m;
        Register src_reg = d == 0 ? registers[reg_idx] : registers[r_m_idx];
        Register dst_reg = d == 0 ? registers[r_m_idx] : registers[reg_idx];
        switch (low_byte & 0b11111100)
        {
        case INST_MOV:
            if (mod == MODE_REGMODE)
            {
                printf("mov %s, %s", dst_reg.fullname, src_reg.fullname);
            }
            break;
        default:
            perror("Unrecognized Instruction\n");
        }
    }
    printf("\n");
}