// STATE

const CPU = {
  running: false,
  IP: 0,
  CF: 0,
  Acc: 0,
  memory: null,
  loadMemory: (data) => { // data: Uint8Array
    // TODO: check length of data
    CPU.memory = data;
  },
}


// FUNCTIONS THAT MODIFY STATE

const Instructions = {
  end: () => {
    console.log('END');
    CPU.running = false;
  },

  store_lit: (lit) => {
    console.log('STO lit#');
    CPU.memory[lit] = CPU.acc;
    logTableTitled(CPU.memory, 'Current memory');
    CPU.IP = CPU.IP += 2;
  },

  store_addr: (addr) => {
    console.log('STO addr');
    CPU.memory[CPU.memory[addr]] = CPU.acc;
    logTableTitled(CPU.memory, 'Memory');
    CPU.IP = CPU.IP += 2;
  },

  load_lit: (lit) => {
    console.log('LDA lit#');
    CPU.acc = lit;
    CPU.IP = CPU.IP += 2;
  },

  load_addr: (addr) => {
    console.log('LDA addr');
    console.log('mem at addr: ', CPU.memory[addr]);
    CPU.acc = CPU.memory[addr];
    CPU.IP = CPU.IP += 2;
  },
}

const instructionLookupTable = {
  0: (arg) => Instructions.end(arg),
  1: (arg) => Instructions.store_lit(arg),
  2: (arg) => Instructions.store_addr(arg),
  3: (arg) => Instructions.load_lit(arg),
  4: (arg) => Instructions.load_addr(arg),
};

function stepCPU() {
  console.group("Step CPU");
  let opcode = CPU.memory[CPU.IP];
  let argument = CPU.memory[CPU.IP+1];

  console.log(`OP: ${opcode}   ARG: ${argument}`);

  let instruction = instructionLookupTable[opcode];
  instruction(argument);

  logCPUState();
  console.groupEnd("Step CPU");
}

function runCPU() {
  const initialMemory = JSON.parse(JSON.stringify(CPU.memory)); // Hack to make a copy-by-value -- https://stackoverflow.com/questions/18829099/copy-a-variables-value-into-another
  console.log();
  console.log("————————————————————————————————————————");
  let time = new Date();
  console.log( `Running at ${time.toLocaleTimeString('en-US')}` );
  console.log("————————————————————————————————————————");
  logCPUState();

  CPU.running = true;
  for (let i = 0; i < 255; i++) { // FIXME: temporary limit as a lazy way to halt infinite loops
    if (!CPU.running) break;
    if (CPU.IP >= CPU.memory.length) break;
    stepCPU();
  };
}


// FUNCTIONS THAT PULL INFO FROM STATE TO DISPLAY

function logCPUState() {
  console.log();
  console.group('CPU state');
  console.log( `Acc: ${CPU.acc}   IP: ${CPU.IP}   CF: ${CPU.CF}   ${CPU.running ? "running" : "halted" }` );
  console.log();
  console.groupEnd('CPU state');
};


// FUNCTIONS FOR DISPLAYING DATA

function num2hex(num) { num.toString(16) };
function hex2num(hex) { parseInt(hex, 16) };

logTableTitled = (memory, tableTitle) => {
  console.log();
  console.group(tableTitle);
  console.table(memory);
  console.groupEnd(tableTitle);
};


// RUN IT !

const test_lda_sto = new Uint8Array([
  3, 17, // LDA lit  ... acc = 17
  1, 14, // STO lit  ... @14 = acc = 17
  3, 16, // LDA lit  ... acc = 16
  1, 15, // STO lit  ... @15 = acc = 16
  2, 15, // STO addr ... @[@15] = acc = 16 ... mem[mem[addr]] <- Acc
  4, 0, // LDA addr ... acc = @00 = 03
  0, 0, // END
  0, 0, // DATA
]);

CPU.loadMemory(test_lda_sto);
runCPU();