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

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

enum Instruction
{
    INST_MOV = 0b10001000
};

enum Register
{
    REG_AL_AX = 0b000,
    REG_CL_CX = 0b001,
    REG_DL_DX = 0b010,
    REG_BL_BX = 0b011,
    REG_AH_SP = 0b100,
    REG_CH_BP = 0b101,
    REG_DH_SI = 0b110,
    REG_BH_DI = 0b111,
};

#define REG_AX "ax"
#define REG_CX "cx"
#define REG_BX "bx"

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

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 byte = buf[i];
        switch (byte & 0b11111100)
        {
        case INST_MOV:
            char high_byte = buf[i+1];
            // char w = byte & 0b00000001;
            // char d = byte & 0b00000010;
            char mod = (high_byte & 0b11000000) >> 6;
            char reg = (high_byte & 0b00111000) >> 3;
            char r_m = (high_byte & 0b00000111);
            printf("mov ");
            if (mod == MODE_REGMODE)
            {
                char *dest_reg_name = NULL;
                switch (r_m)
                {
                case REG_CL_CX:
                    dest_reg_name = REG_CX;
                    break;
                case REG_BL_BX:
                    dest_reg_name = REG_BX;
                    break;
                }
                printf("%s, ", dest_reg_name);
                
                char *src_reg_name = NULL;
                switch (reg)
                {
                case REG_CL_CX:
                    src_reg_name = REG_CX;
                    break;
                case REG_BL_BX:
                    src_reg_name = REG_BX;
                    break;
                }
                printf("%s", src_reg_name);
            }
            break;
        default:
            perror("Unrecognized Instruction\n");
        }
    }
    printf("\n");
}