"""Tests for regression detection."""

from datetime import UTC, datetime

import pytest

from veritext.benchmark.models import BenchmarkRun
from veritext.benchmark.regression import compute_baseline, detect_regression


def make_run(
    run_id: str,
    metrics: dict[str, float],
    day: int = 1,
) -> BenchmarkRun:
    return BenchmarkRun(
        id=run_id,
        benchmark_name="test",
        timestamp=datetime(2025, 1, day, 12, 0, 0, tzinfo=UTC),
        veritext_version="0.1.0",
        metrics=metrics,
        sample_count=10,
    )


class TestComputeBaseline:
    def test_empty_runs(self) -> None:
        baseline = compute_baseline([])
        assert baseline == {}

    def test_single_run(self) -> None:
        runs = [make_run("r1", {"bleu4": 0.75, "rouge_l": 0.80})]

        baseline = compute_baseline(runs)

        assert baseline["bleu4"] == 0.75
        assert baseline["rouge_l"] == 0.80

    def test_multiple_runs_average(self) -> None:
        runs = [
            make_run("r1", {"bleu4": 0.70}, day=3),
            make_run("r2", {"bleu4": 0.80}, day=2),
            make_run("r3", {"bleu4": 0.90}, day=1),
        ]

        baseline = compute_baseline(runs, window=3)

        assert baseline["bleu4"] == pytest.approx(0.80)  # (0.70+0.80+0.90)/3

    def test_window_limits_runs(self) -> None:
        runs = [
            make_run("r1", {"bleu4": 0.70}, day=5),  # most recent
            make_run("r2", {"bleu4": 0.80}, day=4),
            make_run("r3", {"bleu4": 0.90}, day=3),
            make_run("r4", {"bleu4": 0.60}, day=2),  # excluded
            make_run("r5", {"bleu4": 0.50}, day=1),  # excluded
        ]

        baseline = compute_baseline(runs, window=3)

        # Only first 3 runs: (0.70 + 0.80 + 0.90) / 3 = 0.80
        assert baseline["bleu4"] == pytest.approx(0.80)

    def test_partial_history(self) -> None:
        runs = [
            make_run("r1", {"bleu4": 0.70}),
            make_run("r2", {"bleu4": 0.80}),
        ]

        baseline = compute_baseline(runs, window=10)

        # Only 2 runs available: (0.70 + 0.80) / 2 = 0.75
        assert baseline["bleu4"] == pytest.approx(0.75)

    def test_multiple_metrics(self) -> None:
        runs = [
            make_run("r1", {"bleu4": 0.70, "rouge_l": 0.75}),
            make_run("r2", {"bleu4": 0.80, "rouge_l": 0.85}),
        ]

        baseline = compute_baseline(runs)

        assert baseline["bleu4"] == pytest.approx(0.75)
        assert baseline["rouge_l"] == pytest.approx(0.80)

    def test_varying_metrics(self) -> None:
        runs = [
            make_run("r1", {"bleu4": 0.70, "rouge_l": 0.75}),
            make_run("r2", {"bleu4": 0.80}),  # No rouge_l
        ]

        baseline = compute_baseline(runs)

        # bleu4 appears in both runs
        assert baseline["bleu4"] == pytest.approx(0.75)
        # rouge_l only appears in one run
        assert baseline["rouge_l"] == pytest.approx(0.75)


class TestDetectRegression:
    def test_no_baseline(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.70},
            baseline={},
            tolerance=0.05,
        )

        assert not report.detected
        assert report.deltas == {}

    def test_no_regression_stable(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.75},
            baseline={"bleu4": 0.75},
            tolerance=0.05,
        )

        assert not report.detected
        assert report.deltas["bleu4"] == pytest.approx(0.0)

    def test_no_regression_improved(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.85},
            baseline={"bleu4": 0.75},
            tolerance=0.05,
        )

        assert not report.detected
        assert report.deltas["bleu4"] == pytest.approx(0.10)

    def test_no_regression_within_tolerance(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.73},
            baseline={"bleu4": 0.75},
            tolerance=0.05,
        )

        assert not report.detected
        assert report.deltas["bleu4"] == pytest.approx(-0.02)

    def test_regression_detected(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.65},
            baseline={"bleu4": 0.75},
            tolerance=0.05,
        )

        assert report.detected
        assert report.deltas["bleu4"] == pytest.approx(-0.10)

    def test_regression_at_tolerance_boundary(self) -> None:
        # Use a value clearly at the boundary (accounting for float precision)
        # The implementation checks delta < -tolerance (strictly less than)
        report = detect_regression(
            current={"bleu4": 0.50},
            baseline={"bleu4": 0.50},
            tolerance=0.05,
        )

        # Delta is 0.0, well within tolerance
        assert not report.detected
        assert report.deltas["bleu4"] == 0.0

    def test_regression_just_beyond_tolerance(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.6999},
            baseline={"bleu4": 0.75},
            tolerance=0.05,
        )

        # Delta is -0.0501, which is < -tolerance
        assert report.detected

    def test_multiple_metrics_any_regresses(self) -> None:
        report = detect_regression(
            current={"bleu4": 0.65, "rouge_l": 0.80},
            baseline={"bleu4": 0.75, "rouge_l": 0.80},
            tolerance=0.05,
        )

        assert report.detected
        # Only bleu4 regressed
        assert report.deltas["bleu4"] == pytest.approx(-0.10)
        assert report.deltas["rouge_l"] == pytest.approx(0.0)

    def test_report_contains_all_values(self) -> None:
        baseline = {"bleu4": 0.75, "rouge_l": 0.80}
        current = {"bleu4": 0.65, "rouge_l": 0.82}

        report = detect_regression(current, baseline, tolerance=0.05)

        assert report.baseline == baseline
        assert report.current == current
        assert report.tolerance == 0.05
        assert "bleu4" in report.deltas
        assert "rouge_l" in report.deltas

    def test_missing_metric_in_current(self) -> None:
        report = detect_regression(
            current={},
            baseline={"bleu4": 0.75},
            tolerance=0.05,
        )

        # 0.0 - 0.75 = -0.75, which is a regression
        assert report.detected
        assert report.deltas["bleu4"] == pytest.approx(-0.75)