"""Unit tests for :mod:`physix.training.dataset`."""

from __future__ import annotations

import pytest

from physix.systems import SUPPORTED_SYSTEMS
from physix.training.dataset import (
    DatasetSpec,
    EvalDatasetSpec,
    build_eval_dataset,
    build_training_dataset,
)


_EXPECTED_COLUMNS = {
    "prompt",
    "system_id",
    "state_variables",
    "parameters",
    "initial_conditions",
    "timestamps",
    "observed",
    "previous_r_match",
}


def test_training_dataset_has_expected_schema() -> None:
    ds = build_training_dataset(DatasetSpec(instances_per_system=2))

    assert _EXPECTED_COLUMNS.issubset(set(ds.column_names))
    # Default curriculum is the 3 demo systems × 2 instances = 6 rows.
    assert len(ds) == len(SUPPORTED_SYSTEMS) * 2


def test_training_dataset_default_curriculum_is_demo_systems() -> None:
    """Default DatasetSpec must train on exactly the same systems the
    live demo exposes. Mismatches would mean GRPO improves systems we
    never benchmark — the failure mode that produced flat headline
    metrics in the v1 training run.
    """
    ds = build_training_dataset(DatasetSpec(instances_per_system=1))
    assert set(ds["system_id"]) == set(SUPPORTED_SYSTEMS)


def test_training_dataset_explicit_system_ids_override_default() -> None:
    ds = build_training_dataset(
        DatasetSpec(system_ids=("free_fall", "simple_pendulum"), instances_per_system=1)
    )
    assert set(ds["system_id"]) == {"free_fall", "simple_pendulum"}


def test_training_dataset_rejects_unknown_system_ids() -> None:
    with pytest.raises(ValueError, match="Unknown system_ids"):
        build_training_dataset(DatasetSpec(system_ids=("not_a_real_system",)))


def test_training_dataset_rejects_empty_system_ids() -> None:
    with pytest.raises(ValueError, match="non-empty"):
        build_training_dataset(DatasetSpec(system_ids=()))


def test_training_dataset_prompts_are_chat_lists() -> None:
    ds = build_training_dataset(DatasetSpec(instances_per_system=1))
    prompt = ds[0]["prompt"]

    assert isinstance(prompt, list)
    assert prompt[0]["role"] == "system"
    assert prompt[1]["role"] == "user"
    assert "TRAJECTORY" in prompt[1]["content"]


def test_eval_dataset_marks_held_out_rows() -> None:
    ds = build_eval_dataset(EvalDatasetSpec(instances_per_system=1))

    held_out_rows = [r for r in ds if r["is_held_out"]]
    train_rows = [r for r in ds if not r["is_held_out"]]

    assert len(held_out_rows) >= 2  # 2 Tier 3 systems
    assert len(train_rows) >= 6  # 6 Tier 1+2 systems
    held_out_ids = {row["system_id"] for row in held_out_rows}
    assert held_out_ids == {"projectile_drag", "charged_b_field"}


def test_dataset_observed_arrays_match_state_variables() -> None:
    ds = build_training_dataset(DatasetSpec(instances_per_system=1))

    for row in ds:
        observed = row["observed"]
        for var in row["state_variables"]:
            assert var in observed
            assert len(observed[var]) > 0