===== ISTEM =====
Solve the following programming task.

TASK: TIK Register Machine

Write a function 'runTik(program)' that runs a program written in TIK, a small made-up language, and returns an array of the numbers it outputs.

Program text:
- Instructions are separated by newlines. Leading and trailing spaces on a line are ignored.
- Lines that are empty (or only spaces) and lines whose first non-space character is '#' are ignored and are not instructions.
- Within an instruction, tokens are separated by one or more spaces.

Machine:
- There are four registers named a, b, c and d. All start at 0.
- Every value stored in a register is reduced to the range 0..999 by taking it modulo 1000, always giving a non-negative result (for example -1 becomes 999 and 1003 becomes 3).
- An integer literal is an optional '-' followed by one or more digits ('+5' and '5.0' are not valid).
- An operand written as X below is either a register name or an integer literal. Its value is the register's value, or the literal reduced to 0..999 in the same way.

Instructions (R must be a register name, N must be an integer literal):
- set R X: R becomes the value of X.
- add R X: R becomes R plus the value of X.
- mul R X: R becomes R times the value of X.
- out X: appends the value of X to the output.
- jmp X N: if the value of X is not 0, the next instruction is the one N instructions away from this one (N may be negative; ignored lines are not counted). Otherwise execution continues with the next instruction.
Instruction names and register names are lowercase; anything else is invalid.

Running:
- Before running anything, check the whole program. If any line that is not ignored is not a valid instruction (unknown name, wrong number of operands, or an invalid register, literal or operand), throw an Error whose message is 'bad instruction at line K', where K is the 1-based line number of the first such line in the original text, counting ignored lines too. In that case nothing is run.
- Execution starts at the first instruction and stops normally when the next instruction position is before the first instruction or after the last one.
- A program may execute at most 10,000 instructions. If it has not stopped after executing 10,000 instructions, throw an Error with the message 'step limit'.

STARTER CODE (javascript):
function runTik(program) {
  // Write your code here
}

module.exports = { runTik };


RULES:
- Keep the function name and signature EXACTLY as given.
- Return working code only. No explanations.
- Put the code in a single ``` block.
- Try to solve it first. If you genuinely cannot, write only this single
  line instead of producing faulty code: CANNOT_SOLVE

===== HAM YANIT =====
```javascript
function runTik(program) {
  const instructions = [];
  const registerPattern = /^[abcd]$/;
  const integerPattern = /^-?\d+$/;

  const isOperand = token =>
    typeof token === "string" &&
    (registerPattern.test(token) || integerPattern.test(token));

  const parseOperand = token => {
    if (registerPattern.test(token)) return token;
    const value = BigInt(token);
    return Number(((value % 1000n) + 1000n) % 1000n);
  };

  const lines = program.split("\n");

  for (let i = 0; i < lines.length; i++) {
    const line = lines[i].trim();
    if (line === "" || line.startsWith("#")) continue;

    const tokens = line.split(/\s+/);
    const [op, first, second] = tokens;
    let valid = false;

    if (op === "set" || op === "add" || op === "mul") {
      valid =
        tokens.length === 3 &&
        registerPattern.test(first) &&
        isOperand(second);
    } else if (op === "out") {
      valid = tokens.length === 2 && isOperand(first);
    } else if (op === "jmp") {
      valid =
        tokens.length === 3 &&
        isOperand(first) &&
        integerPattern.test(second);
    }

    if (!valid) {
      throw new Error(`bad instruction at line ${i + 1}`);
    }

    if (op === "jmp") {
      instructions.push({ op, operand: parseOperand(first), offset: BigInt(second) });
    } else if (op === "out") {
      instructions.push({ op, operand: parseOperand(first) });
    } else {
      instructions.push({ op, register: first, operand: parseOperand(second) });
    }
  }

  const registers = { a: 0, b: 0, c: 0, d: 0 };
  const output = [];
  const instructionCount = BigInt(instructions.length);
  let pc = 0;
  let steps = 0;

  while (pc >= 0 && pc < instructions.length) {
    if (steps === 10000) throw new Error("step limit");
    steps++;

    const instruction = instructions[pc];
    const value =
      typeof instruction.operand === "number"
        ? instruction.operand
        : registers[instruction.operand];

    switch (instruction.op) {
      case "set":
        registers[instruction.register] = value;
        break;
      case "add":
        registers[instruction.register] =
          (registers[instruction.register] + value) % 1000;
        break;
      case "mul":
        registers[instruction.register] =
          (registers[instruction.register] * value) % 1000;
        break;
      case "out":
        output.push(value);
        break;
      case "jmp":
        if (value !== 0) {
          const target = BigInt(pc) + instruction.offset;
          if (target < 0n || target >= instructionCount) return output;
          pc = Number(target);
          continue;
        }
        break;
    }

    pc++;
  }

  return output;
}

module.exports = { runTik };
```