#include <stdint.h>
#include <stdio.h>
#include <limits.h>

enum DT_INSTRUCTIONS
	{
		MOV_RM_TF_R = 0b1000'10,  //d w
		MOV_I_T_RM  = 0b1100'011, // w
		MOV_I_T_R   = 0b1011,     // w reg
		MOV_M_T_A   = 0b1010'000, // w
		MOV_A_T_M   = 0b1010'001, // w
		MOV_RM_T_SR = 0b1000'1110, 
		MOV_SR_T_RM = 0b1000'1100, 
	};

enum MOV_REGISTER_MODE
	{
		MEM_NO_DISP    = 0b00,
		MEM_8BIT_DISP  = 0b01,
		MEM_16BIT_DISP = 0b010,
		REG_NO_DISP    = 0b11
	};


char REG_ENCODING_TXT[0b10000][3] = { "al", "cl", "dl", "bl", "ah", "ch", "dh", "bh",
                                   "ax", "cx", "dx", "bx", "sp", "bp", "si", "di"};
enum REG_ENCODING
	{
		R_AL = 0b000,
		R_CL = 0b001,
		R_DL = 0b010,
		R_BL = 0b011,
		R_AH = 0b100,
		R_CH = 0b101,
		R_DH = 0b110,
		R_BH = 0b111
	};

enum WREG_ENCODING
	{
		WR_AX = 0b000,
		WR_CX = 0b001,
		WR_DX = 0b010,
		WR_BX = 0b011,
		WR_SP = 0b100,
		WR_BP = 0b101,
		WR_SI = 0b110,
		WR_DI = 0b111
	};

typedef struct
{
	FILE *binary;
	uint64_t size;	
} binary_data;

FILE *output;

void MOV_RM_TF_R_parse(uint8_t byte1, uint8_t byte2, uint8_t byte3, uint8_t byte4)
{
	const uint8_t wide_mask = 0b0000'0001;
	const uint8_t dest_mask = 0b0000'0010;
	const uint8_t mod_mask  = 0b1100'0000; 
	const uint8_t regm_mask = 0b0011'1000;
	
    if ((byte2 & mod_mask) != mod_mask) return;
	//Since we're only doing register mode/register to register, both reg and r/m are affected by the W bit
	bool reg_is_dest = (byte1 & dest_mask);
	//if D=1, dest is retrieved from the reg field in byte2 and src from r/m
	uint8_t dest_value = (reg_is_dest) ? ((byte2 & regm_mask) >> 3) + ((byte1 & wide_mask) * 8) : (byte2 & (regm_mask >> 3)) + ((byte1 & wide_mask) * 8);
	uint8_t src_value  = (reg_is_dest) ? (byte2 & (regm_mask >> 3)) + ((byte1 & wide_mask) * 8) : ((byte2 & regm_mask) >> 3) + ((byte1 & wide_mask) * 8);
    printf("%s %s, %s\n", "mov", REG_ENCODING_TXT[dest_value], REG_ENCODING_TXT[src_value]);
	fprintf(output, "%s %s, %s\n", "mov", REG_ENCODING_TXT[dest_value], REG_ENCODING_TXT[src_value]);
	return;
}

int main(int argc, char** argv)
{
	if (argc != 2) return -1;
	if (CHAR_BIT != 8) return -2;

	binary_data bin;
	unsigned char byte[1];
	bin.binary = fopen(argv[1], "rb");
	fseek(bin.binary, 0, SEEK_END);
	bin.size = ftell(bin.binary);
	fseek(bin.binary, 0, SEEK_SET);
	
    output = fopen("output.asm", "w");
	fprintf(output, "%s\n\n", "bits 16");	

	for (int bytes_read = 0; bytes_read < bin.size; bytes_read++)
	{
		fread(byte, sizeof(byte), 1, bin.binary);
		uint8_t manip_inst = (uint8_t)byte[0];
		uint8_t inst = (uint8_t)byte[0];
		//For now we're just checking for RM_TF_R
		manip_inst = (manip_inst >> 2);
		if (manip_inst != MOV_RM_TF_R) break;
		if (bytes_read >= bin.size) break;
    	fread(byte, sizeof(byte), 1, bin.binary);
		bytes_read++;
		uint8_t inst_byte2 = (uint8_t)byte[0];
    	MOV_RM_TF_R_parse(inst, inst_byte2, 0, 0);
	}

	return 0;
}