#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
#include <stdbool.h>
#include <string.h>


struct State{
	uint16_t programCounter;
	int8_t accumulator;
	uint8_t input;
	uint8_t programPage;
	uint8_t memoryPage;
	uint8_t X;
        uint8_t memory[65536];

	bool carry;

	uint16_t program[65536];
};


struct State initState(FILE* f){
	struct State state;
	
	memset(state.program, 0, sizeof(uint16_t)*65536);

	int i=0;
	char hexString[5];
	hexString[4] = '\0';
	int c;
	while((c = fgetc(f))!=-1){
		int val;
		hexString[i%4] = c;
		if((i+1)%4==0){
			int status;
			state.program[i/4] = strtoi(hexString,NULL,16,0,65535,&status);
			if(status)
				fprintf(stderr,"Something went wrong converting %s\n", hexString);
			
		}
		i++;
	}

	state.programCounter =0;
	state.accumulator =0;
	state.input =0;
	state.programPage =0;
	state.programPage =0;
	state.memoryPage =0;
	state.X =0;

	state.carry = false;

	return state;
}

void printState(struct State state){
	printf("Program counter: %x, Accumulator: %x, Input: %x, Program Page:"
			"%x, Memory Page: %x, x:"
			"%x\n",state.programCounter,state.accumulator,state.input,state.programPage,state.memoryPage,state.X);
#define MEM state.memory
	printf("Memory from 0x0000 untill 0x0004: %x, %x, %x, %x, %x\n",
		MEM[0], MEM[1], MEM[2], MEM[3], MEM[4]);
}


//It will always return True unless it is at the end of the program. Beause
//there is no halt instruction it is
//at the the end of the program when it enounters an instruction that jumps
//to itself
bool nextState(struct State* state){
	bool ret = true;
	uint16_t instruction = state->program[state->programCounter];

	int operation = instruction >> 13;
	int condition = (instruction & 0x1c00)>>10;
	int busB      = (instruction & 0x1800)>>11;
	int registerB = (instruction & 0x600)>>9;
	int addrBusB  =  (instruction & 0x100)>>8;

	uint8_t op = (uint8_t)(instruction & 0xff);
	uint8_t addrBus;
	switch(addrBusB){
		case(0):
			addrBus = op;
			break;
		case(1):
			addrBus = state->X;
			break;
	}

	uint8_t* reg;
	switch(registerB){
		case(0):
			reg = &(state->programPage);
			break;
		case(1):
			reg = &(state->memoryPage);
			break;
		case(2):
			reg = &(state->accumulator);
			break;
		case(3):
			reg = &(state->X);
			break;
	}

	uint16_t a = ((uint16_t)state->memoryPage)<<8;
	uint16_t b = (uint16_t)addrBus;

	uint16_t address = a+b;

	uint8_t bus;
	switch(busB){
		case(0):
			bus = state->memory[address];
			break;
		case(1):
			bus = op;
			break;
		case(2):
			bus = state->input;
			break;
		case(3):
			bus = state->accumulator;
			break;
	}



	if(operation==7){
		
		bool conditionIsTrue;
		switch(condition){
			case(0):
				conditionIsTrue = true;
				break;
			case(1):
				conditionIsTrue = state->accumulator>0;
				break;
			case(2):
				conditionIsTrue = state->accumulator>=0;
				break;
			case(3):
				conditionIsTrue = state->accumulator==0;
				break;
			case(4):
				conditionIsTrue = state->accumulator<0;
				break;
			case(5):
				conditionIsTrue = state->accumulator<=0;
				break;
			case(6):
				conditionIsTrue = state->carry;
				break;
			case(7):
				conditionIsTrue = state->accumulator!=0;
				break;
		}
		if(conditionIsTrue){
			//change the program counter
			uint16_t newProgramCounter = 
				(((uint16_t)state->programPage)<<8) + ((uint16_t)addrBus);
			ret = ret && (newProgramCounter!=state->programCounter);
			state->programCounter =  newProgramCounter;
		}else{
			state->programCounter++;
		}
	}else{
		switch(operation){
			case(0):
				//Load
				*reg = bus;
				break;
			case(1):
				//And
				*reg = bus & state->accumulator;
				break;
			case(2):
				//Or
				*reg = bus | state->accumulator;
				break;
			case(3):
				//Xor
				*reg = bus ^ state->accumulator;
				break;
			case(4):
				//Add
				*reg = bus + state->accumulator;
				break;
			case(5):
				//Sub
				*reg = state->accumulator-bus;
				break;
			case(6):
				//Store
				state->memory[address]= bus;
				break;
		}
		state->programCounter++;
	}
	return(ret);
}

void main(int argc, char** argv){
	if(argc!=3){
		fprintf(stderr,"You should give exactly two arguments");
		return;
	}
	FILE* f = fopen(argv[2], "r");

	struct State state = initState(f);

	bool debug = !strcmp(argv[1],"debug");

	while(nextState(&state)){
		if(debug){
			printState(state);
			printf("Press enter to go to the next state:\n");
			getchar();
		}
		
	}
	printf("Terminated with the following state:\n");
	printState(state);
	
}