"""层 1 / T3：数据管线单测（docs/02 §5.1 规定的验证项）。

用字符级玩具 tokenizer 在 CPU 上对拍 collator 行为，不依赖网络下载真模型。
玩具模板刻意模仿 Qwen3 的关键结构：生成引导符 + no-think 时注入空思考块。
"""

import json

import pytest
from datasets import Dataset

from ars_opd.data import (
    IGNORE_INDEX,
    SFTCollator,
    attach_teacher_completions,
    prompt_key,
    to_messages,
)


class ToyTokenizer:
    """字符级 tokenizer：一个字符一个 token（id = 码点）。

    模板契约与真 chat 模板同构：
    - 每轮渲染成 "[role]content"；
    - assistant 轮（或生成引导符后）在 no-think 模式下注入 "<T></T>"（模仿
      Qwen3 的空 <think>\\n\\n</think>）；
    - 完整渲染 == prompt 渲染 + 解答文本，保证边界可精确断言。
    """

    def __init__(self, pad_token_id=0, eos_token_id=1):
        self.pad_token_id = pad_token_id
        self.eos_token_id = eos_token_id

    def apply_chat_template(
        self,
        messages,
        tokenize=False,
        add_generation_prompt=False,
        enable_thinking=False,
    ):
        think = "" if enable_thinking else "<T></T>"
        parts = []
        for m in messages:
            prefix = think if m["role"] == "assistant" else ""
            parts.append(f"[{m['role']}]{prefix}{m['content']}")
        text = "".join(parts)
        if add_generation_prompt:
            text += f"[assistant]{think}"
        return text

    def __call__(
        self,
        text,
        truncation=False,
        max_length=None,
        padding=False,
        add_special_tokens=False,
    ):
        ids = [ord(c) for c in text]
        if truncation and max_length is not None:
            ids = ids[:max_length]
        return {"input_ids": ids}


def ids_of(text):
    return [ord(c) for c in text]


def row(question, answer=None):
    msgs = [{"role": "user", "content": question}]
    if answer is not None:
        msgs.append({"role": "assistant", "content": answer})
    return {"messages": msgs}


# ---------------------------------------------------------------------------
# to_messages
# ---------------------------------------------------------------------------


def test_dapo_prompt列直接归一():
    ex = {"prompt": [{"role": "user", "content": "1+1=?"}], "data_source": "dapo"}
    assert to_messages(ex) == {"messages": [{"role": "user", "content": "1+1=?"}]}


def test_字符串化的列表被还原():
    ex = {"prompt": "[{'role': 'user', 'content': 'hi'}]"}
    assert to_messages(ex)["messages"] == [{"role": "user", "content": "hi"}]


def test_坏字符串显式报错而非静默放行():
    # 参考实现 except:pass 会让这行以字符串形态流进 collator
    with pytest.raises(ValueError, match="无法解析"):
        to_messages({"prompt": "[{'role': broken"})


def test_question列包成单user轮():
    assert to_messages({"question": "2+2=?"}) == {
        "messages": [{"role": "user", "content": "2+2=?"}]
    }


def test_无法识别的行报错():
    with pytest.raises(ValueError, match="无法识别"):
        to_messages({"foo": 1})


# ---------------------------------------------------------------------------
# prompt_key（与 teacher.py 的缓存契约）
# ---------------------------------------------------------------------------


def test_同题同键_不同题不同键():
    m1 = [{"role": "user", "content": "q"}]
    m2 = [{"role": "user", "content": "q'"}]
    assert prompt_key(m1) == prompt_key(m1)
    assert prompt_key(m1) != prompt_key(m2)


def test_额外元数据字段不影响键():
    plain = [{"role": "user", "content": "q"}]
    noisy = [{"role": "user", "content": "q", "source": "dapo"}]
    assert prompt_key(plain) == prompt_key(noisy)


# ---------------------------------------------------------------------------
# attach_teacher_completions
# ---------------------------------------------------------------------------


def write_cache(path, entries):
    with open(path, "w", encoding="utf-8") as f:
        for msgs, completion in entries:
            f.write(
                json.dumps({"key": prompt_key(msgs), "completion": completion}) + "\n"
            )


def test_挂接teacher解答(tmp_path):
    q = [{"role": "user", "content": "1+1=?"}]
    cache = tmp_path / "cache.jsonl"
    write_cache(cache, [(q, "答案是 2")])
    ds = Dataset.from_list([{"messages": q}])
    out = attach_teacher_completions(ds, str(cache))
    assert out[0]["messages"][-1] == {"role": "assistant", "content": "答案是 2"}


def test_缓存缺键一次性报全部缺失(tmp_path):
    cache = tmp_path / "cache.jsonl"
    write_cache(cache, [])
    ds = Dataset.from_list([row("q1"), row("q2")])
    with pytest.raises(KeyError, match="2/2"):
        attach_teacher_completions(ds, str(cache))


def test_自带解答的行不被覆盖(tmp_path):
    cache = tmp_path / "cache.jsonl"
    write_cache(cache, [])
    ds = Dataset.from_list([row("q", "人写的答案")])
    out = attach_teacher_completions(ds, str(cache))
    assert out[0]["messages"][-1]["content"] == "人写的答案"


def test_缓存文件不存在报错():
    ds = Dataset.from_list([row("q")])
    with pytest.raises(FileNotFoundError):
        attach_teacher_completions(ds, "/不存在/cache.jsonl")


# ---------------------------------------------------------------------------
# SFTCollator
# ---------------------------------------------------------------------------


def make_collator(**kw):
    defaults = dict(max_length=1000, max_prompt_length=100, enable_thinking=False)
    defaults.update(kw)
    return SFTCollator(ToyTokenizer(), **defaults)


def test_基本形态_掩码与边界():
    collator = make_collator()
    batch = collator([row("ab", "cd")])
    prompt_text = "[user]ab[assistant]<T></T>"

    labels = batch["labels"][0].tolist()
    # prompt 全 -100，completion 位置是解答的 token
    assert labels[: len(prompt_text)] == [IGNORE_INDEX] * len(prompt_text)
    assert labels[len(prompt_text) :] == ids_of("cd")
    assert batch["input_ids"][0].tolist() == ids_of(prompt_text + "cd")
    assert batch["attention_mask"][0].tolist() == [1] * (len(prompt_text) + 2)


def test_超长解答不挤占prompt():
    # 头号正确性卖点：completion 被截，prompt 一个 token 不少
    prompt_text = "[user]ab[assistant]<T></T>"
    collator = make_collator(max_length=len(prompt_text) + 3)
    batch = collator([row("ab", "x" * 50)])

    input_ids = batch["input_ids"][0].tolist()
    assert input_ids[: len(prompt_text)] == ids_of(prompt_text)  # prompt 完整
    assert len(input_ids) == len(prompt_text) + 3  # completion 只剩预算内 3 个


def test_超长题目截断但边界不错位():
    # 坑二场景：prompt 超预算被截断，completion 的 token 必须仍然精确
    # （切分点用未截断长度，而非截断后长度）
    collator = make_collator(max_prompt_length=10)
    batch = collator([row("很长的题目" * 20, "答案")])

    labels = batch["labels"][0].tolist()
    non_masked = [t for t in labels if t != IGNORE_INDEX]
    assert non_masked == ids_of("答案")  # 解答 token 一个不错
    assert sum(t == IGNORE_INDEX for t in labels) == 10  # prompt 恰被截到预算


def test_enable_thinking两种取值边界都正确():
    for thinking in (False, True):
        collator = make_collator(enable_thinking=thinking)
        batch = collator([row("q", "ans")])
        non_masked = [t for t in batch["labels"][0].tolist() if t != IGNORE_INDEX]
        assert non_masked == ids_of("ans"), f"enable_thinking={thinking} 时边界错位"


def test_nothink模板注入空思考块():
    # 参考实现的一次性诊断打印，在这里变成永久契约
    text = ToyTokenizer().apply_chat_template(
        [{"role": "user", "content": "q"}],
        add_generation_prompt=True,
        enable_thinking=False,
    )
    assert text.endswith("<T></T>")


def test_prompt_only行显式报错():
    with pytest.raises(ValueError, match="prompt-only"):
        make_collator()([row("没有答案的题")])


def test_左padding对齐():
    collator = make_collator()
    batch = collator([row("ab", "cd"), row("a", "c")])
    t = batch["input_ids"].shape[1]
    short_mask = batch["attention_mask"][1].tolist()
    n_pad = t - short_mask.count(1)

    assert n_pad > 0
    assert short_mask[:n_pad] == [0] * n_pad  # padding 在左
    assert batch["labels"][1].tolist()[:n_pad] == [IGNORE_INDEX] * n_pad
    assert batch["input_ids"][1].tolist()[:n_pad] == [0] * n_pad  # pad_token_id=0


def test_pad回退到eos():
    collator = SFTCollator(
        ToyTokenizer(pad_token_id=None, eos_token_id=7),
        max_length=100,
        max_prompt_length=50,
    )
    assert collator.pad_token_id == 7