"""Unit tests for the SFT render canonicalisation and assistant-only mask.

These run anywhere: a fake additive tokenizer stands in for a real chat
template, so no torch/transformers is needed."""
from __future__ import annotations

from typing import Any

import pytest

from tiararodney.sekft import sft


class FakeTok:
    """Additive chat template: each turn renders to ``<role> tokens... </e>``;
    the generation prompt appends ``<assistant>``."""

    def apply_chat_template(self, msgs: list[dict[str, str]], add_generation_prompt: bool = False,
                            return_tensors: Any = None) -> list[str]:
        toks: list[str] = []
        for m in msgs:
            toks.append(f"<{m['role']}>")
            toks += m["content"].split()
            toks.append("</e>")
        if add_generation_prompt:
            toks.append("<assistant>")
        return toks


def test_normalize_folds_system_and_merges_consecutive() -> None:
    raw = [
        {"role": "system", "content": "orient"},
        {"role": "user", "content": "login"},
        {"role": "user", "content": "prompt"},
        {"role": "assistant", "content": "cat f"},
        {"role": "user", "content": "out"},
        {"role": "user", "content": "prompt"},
        {"role": "assistant", "content": "exit"},
    ]
    norm = sft.normalize_for_template(raw)
    assert [m["role"] for m in norm] == ["user", "assistant", "user", "assistant"]
    assert norm[0]["content"] == "orient\nlogin\nprompt"


def test_normalize_leaves_clean_alternation_untouched() -> None:
    raw = [{"role": "user", "content": "a"}, {"role": "assistant", "content": "b"}]
    assert sft.normalize_for_template(raw) == raw


def test_mask_trains_assistant_turns_only() -> None:
    raw = [
        {"role": "system", "content": "orient"},
        {"role": "user", "content": "login"},
        {"role": "assistant", "content": "cat f"},
        {"role": "user", "content": "out"},
        {"role": "assistant", "content": "exit"},
    ]
    ex = sft.build_masked_example(raw, FakeTok())
    trained = [t for t, lab in zip(ex["input_ids"], ex["labels"]) if lab != -100]
    masked = [t for t, lab in zip(ex["input_ids"], ex["labels"]) if lab == -100]
    assert set(trained) <= {"<assistant>", "cat", "f", "exit", "</e>"}
    assert "cat" in trained and "exit" in trained          # both commands present
    assert {"orient", "login", "out"} <= set(masked)       # environment masked


def test_mask_raises_on_non_additive_template() -> None:
    class BadTok:
        def apply_chat_template(self, msgs: list[dict[str, str]], add_generation_prompt: bool = False,
                                return_tensors: Any = None) -> list[int]:
            return list(range(len(msgs), 0, -1))   # reversed: prefixes do not nest

    with pytest.raises(ValueError):
        sft.build_masked_example(
            [{"role": "user", "content": "a"}, {"role": "assistant", "content": "b"}],
            BadTok())