// NOTES:
//
// - instructions are two bytes long:
//   one byte for the opcode, one for the argument

const INITIAL_IP_ADDRESS = 32;
const CYCLE_LIMIT = 128; // max number of times to step the CPU, to stop endless loops

const display = require('./display.js');

// STATE
const CPU = {
  running: false,
  IP: INITIAL_IP_ADDRESS,
  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;
  },

  add_lit: (lit) => {
    console.log("ADD lit");
    let sum = CPU.Acc + lit;
    if (sum > 15) {
      CPU.CF = 1;
      CPU.Acc = (sum % 15) - 1;
    } else {
      CPU.CF = 0;
      CPU.Acc = sum;
    }
    CPU.IP = CPU.IP += 2;
  },

  add_addr: (addr) => {
    console.log("ADD addr");
    let sum = CPU.Acc + CPU.memory[addr];
    if (sum > 15) {
      CPU.CF = 1;
      CPU.Acc = (sum % 15) - 1;
    } else {
      CPU.CF = 0;
      CPU.Acc = sum;
    }
    CPU.IP = CPU.IP += 2;
  },

  sub_lit: (lit) => { // TODO: carry flag
    console.log("SUB lit");
    CPU.Acc = CPU.Acc - lit;
    CPU.IP = CPU.IP += 2;
  },

  sub_addr: (addr) => { // TODO: carry flag
    console.log("SUB addr");
    CPU.Acc = CPU.Acc - CPU.memory[addr];
    CPU.IP = CPU.IP += 2;
  },

  hop_lit: (lit) => {
    console.log("HOP lit");
    console.log(` ↳ Memory at IP+2 and +3: ${CPU.memory[CPU.IP+2]}, ${CPU.memory[CPU.IP+3]}`);
    if (CPU.Acc === lit) {
      CPU.IP += 4;
    } else {
      CPU.IP += 2;
    }
  },

  hop_addr: (addr) => {
    console.log("HOP addr");
    if (CPU.Acc === CPU.memory[addr]) {
      CPU.IP += 4;
    } else {
      CPU.IP += 2;
    }
  },

  jump_lit: (lit) => {
    console.log("JMP lit");
    CPU.IP = lit;
  },

  jump_addr: (addr) => {
    console.log("JMP addr");
    CPU.IP = CPU.memory[addr];
  },

  carry_clear: () => {
    console.log("CFC");
    CPU.CF = 0;
    CPU.IP += 2;
  },

  carry_hop: () => {
    console.log("CHP");
    console.log(` ↳ Memory at IP+2 and +3: ${CPU.memory[CPU.IP+2]}, ${CPU.memory[CPU.IP+3]}`);
    // console.table(CPU.memory);
    if (CPU.CF != 0) {
      CPU.IP += 4;
    } else {
      CPU.IP += 2;
    }
  },
}

const opcodes2mnemonics = {
  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),
  5: (arg) => Instructions.add_lit(arg),
  6: (arg) => Instructions.add_addr(arg),
  7: (arg) => Instructions.sub_lit(arg),
  8: (arg) => Instructions.sub_addr(arg),
  9: (arg) => Instructions.hop_lit(arg),
  10: (arg) => Instructions.hop_addr(arg),
  11: (arg) => Instructions.jump_lit(arg),
  12: (arg) => Instructions.jump_addr(arg),
  13: (arg) => Instructions.carry_clear(arg),
  14: (arg) => Instructions.carry_hop(arg),
};

function stepCPU() {
  // console.group("Step CPU");
  console.group(`IP: ${CPU.IP}`);
  let opcode = CPU.memory[CPU.IP];
  let argument = CPU.memory[CPU.IP+1];
  console.log(`OP: ${opcode}   ARG: ${argument}`);

  let instruction = opcodes2mnemonics[opcode];
  instruction(argument);

  logCPUState();
  console.groupEnd(`IP:`);
  // console.groupEnd("Step CPU");
}

exports.runProgram = (code) => {
  CPU.loadMemory(code);
  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();
  let time = new Date();
  console.log( `┌─────────────────────┐`);
              // Running at 11:48:15 AM
  console.log( `│ Running at ${time.toLocaleTimeString('en-GB')} │` );
  console.log( `└─────────────────────┘`);
  logCPUState();

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


// FUNCTIONS THAT PULL INFO FROM STATE TO DISPLAY

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


// FUNCTIONS FOR DISPLAYING DATA

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

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