import random

from datasets import Dataset

from src.rewards import safe_eval_expression


def random_expression(numbers, rng):
    parts = [str(number) for number in numbers]
    while len(parts) > 1:
        i, j = sorted(rng.sample(range(len(parts)), 2), reverse=True)
        left, right = parts.pop(i), parts.pop(j)
        parts.append(f"({left} {rng.choice(['+', '-', '*'])} {right})")
    return parts[0]


def build_countdown_dataset(size, seed, num_numbers=4, disable_thinking=False):
    rng = random.Random(seed)
    rows, seen = [], set()
    while len(rows) < size:
        numbers = [rng.randint(1, 10) for _ in range(num_numbers)]
        solution = random_expression(numbers, rng)
        target, _ = safe_eval_expression(solution)
        if not target.is_integer() or abs(target) > 500:
            continue
        key = (tuple(numbers), int(target))
        if key in seen:
            continue
        seen.add(key)
        prompt = (
            f"Use each number exactly once to make {int(target)}. Numbers: {numbers}. "
            "Allowed operations: +, -, *, /. Return only the computed arithmetic expression "
            "wrapped between the XML tags <answer> and </answer>. Do not output placeholder "
            "words such as EXPRESSION."
        )
        rows.append({
            "prompt": [
                {
                    "role": "system",
                    "content": (
                        "Solve the arithmetic task. Follow the requested answer format exactly."
                        + (" /no_think" if disable_thinking else "")
                    ),
                },
                {"role": "user", "content": prompt},
            ],
            "numbers": numbers,
            "target": int(target),
            "solution": solution,
        })
    return Dataset.from_list(rows)