const { INITIAL_IP_ADDRESS, CYCLE_LIMIT } = require('./machine.config');
const { logRunningHeader, num2hex } = require('./logging.js');
const display = require('./display.js');

// STATE
const CPU = {
  running: false,
  IP: INITIAL_IP_ADDRESS,
  CF: 0,
  Acc: 0,
  memory: null,
  loadMemory: (data) => { // data: Uint8Array
    if (data.length > 256) { throw new Error("Out of memory error (program too long)"); }
    CPU.memory = data;
  },
  currentInstruction: {
    opcode: null,
    argument: null,
    mnemonic: null,
  }
}


// FUNCTIONS THAT MODIFY STATE

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

  store_lit: (lit) => {
    CPU.currentInstruction.mnemonic = 'STO lit';
    CPU.memory[lit] = CPU.Acc;
    CPU.IP = CPU.IP += 2;
  },

  store_addr: (addr) => {
    CPU.currentInstruction.mnemonic = 'STO addr';
    CPU.memory[CPU.memory[addr]] = CPU.Acc;
    CPU.IP = CPU.IP += 2;
  },

  load_lit: (lit) => {
    CPU.currentInstruction.mnemonic = 'LDA lit';
    CPU.Acc = lit;
    CPU.IP = CPU.IP += 2;
  },

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

  add_lit: (lit) => {
    CPU.currentInstruction.mnemonic = 'ADD lit';
    let sum = CPU.Acc + lit;
    if (sum > 255) {
      CPU.CF = 1;
      CPU.Acc = (sum % 255) - 1;
    } else {
      CPU.CF = 0;
      CPU.Acc = sum;
    }
    CPU.IP = CPU.IP += 2;
  },

  add_addr: (addr) => {
    CPU.currentInstruction.mnemonic = '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) => {
    CPU.currentInstruction.mnemonic = 'SUB lit';
    let sum = CPU.Acc - lit;
    if (sum < 0) {
      CPU.CF = 1;
      CPU.Acc = (sum % 15) + 1; // FIXME ???
    } else {
      CPU.CF = 0;
      CPU.Acc = sum;
    }
    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) => {
    CPU.currentInstruction.mnemonic = `HOP lit \n  ↳ 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) => {
    CPU.currentInstruction.mnemonic = 'HOP addr';
    if (CPU.Acc === CPU.memory[addr]) {
      CPU.IP += 4;
    } else {
      CPU.IP += 2;
    }
  },

  jump_lit: (lit) => {
    CPU.currentInstruction.mnemonic = 'JMP lit';
    CPU.IP = lit;
  },

  jump_addr: (addr) => {
    CPU.currentInstruction.mnemonic = 'JMP addr';
    CPU.IP = CPU.memory[addr];
  },

  carry_clear: () => {
    CPU.currentInstruction.mnemonic = 'CFC';
    CPU.CF = 0;
    CPU.IP += 2;
  },

  carry_hop: () => {
    CPU.currentInstruction.mnemonic = `CHP \n  ↳ Memory at IP+2 and +3: ${CPU.memory[CPU.IP+2]}, ${CPU.memory[CPU.IP+3]}`;
    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() {
  CPU.currentInstruction.opcode = CPU.memory[CPU.IP];
  CPU.currentInstruction.argument = CPU.memory[CPU.IP+1];
  let executeInstruction = opcodes2mnemonics[CPU.currentInstruction.opcode];
  executeInstruction(CPU.currentInstruction.argument);
}

exports.runProgram = async (code, debug = false) => {
  if (debug) logRunningHeader();

  CPU.loadMemory(code);
  CPU.running = true;
  let step = 0;
  while (true) {
    step = step + 1;
    if (CYCLE_LIMIT && (step > CYCLE_LIMIT)) { break; } // Temporary limit as a lazy way to halt infinite loops:
    if (!CPU.running) break;
    if (CPU.IP >= CPU.memory.length) break;

    stepCPU();

    console.group(`Step`);
    if (!debug) console.clear();
    display.printDisplay(CPU.memory);

    logCPUState();
    if (!debug) await new Promise(resolve => setTimeout(resolve, 75));
    console.groupEnd('Step');
  };
}


// FUNCTIONS THAT PULL INFO FROM STATE TO DISPLAY

function logCPUState() {
  console.log();
  console.log('Mnemonic:', CPU.currentInstruction.mnemonic);
  console.log(`Machine:  $${num2hex(CPU.currentInstruction.opcode)} $${num2hex(CPU.currentInstruction.argument)}`);
  console.log();
  console.log( `IP: $${num2hex(CPU.IP)}  Acc: $${num2hex(CPU.Acc)}  CF: ${CPU.CF}  ${CPU.running ? "running" : "halted" }` );
  console.log();
};