"""Tests for the BLEU metric."""

import pytest

from veritext.metrics import Bleu, BleuResult


class TestBleu:
    """Tests for the Bleu metric class."""

    @pytest.fixture
    def bleu(self) -> Bleu:
        """Provide a BLEU metric instance."""
        return Bleu()

    def test_name(self, bleu: Bleu) -> None:
        """Test that name returns 'bleu'."""
        assert bleu.name == "bleu"

    def test_requires_reference(self, bleu: Bleu) -> None:
        """Test that BLEU requires reference text."""
        assert bleu.requires_reference is True

    def test_identical_texts(self, bleu: Bleu) -> None:
        """Test that identical texts produce perfect scores."""
        text = "The cat sat on the mat"
        result = bleu.score(text, text)

        assert result.bleu1 == 1.0
        assert result.bleu2 == 1.0
        assert result.bleu3 == 1.0
        assert result.bleu4 == 1.0
        assert result.brevity_penalty == 1.0

    def test_no_overlap(self, bleu: Bleu) -> None:
        """Test that texts with no overlap produce zero scores."""
        candidate = "The cat sat"
        reference = "A dog runs fast"
        result = bleu.score(candidate, reference)

        assert result.bleu1 == 0.0
        assert result.bleu2 == 0.0
        assert result.bleu3 == 0.0
        assert result.bleu4 == 0.0

    def test_partial_overlap(self, bleu: Bleu) -> None:
        """Test partial overlap produces intermediate scores."""
        candidate = "The cat sat on the mat"
        reference = "The cat is on the floor"
        result = bleu.score(candidate, reference)

        # Should have some overlap but not perfect
        assert 0.0 < result.bleu1 < 1.0
        assert 0.0 < result.bleu2 < 1.0

    def test_brevity_penalty_applied(self, bleu: Bleu) -> None:
        """Test that brevity penalty is applied for short candidates."""
        candidate = "cat"
        reference = "The cat sat on the mat"
        result = bleu.score(candidate, reference)

        # Candidate is much shorter, so brevity penalty should be < 1
        assert result.brevity_penalty < 1.0

    def test_no_brevity_penalty_for_long_candidate(self, bleu: Bleu) -> None:
        """Test that no brevity penalty for longer candidates."""
        candidate = "The cat sat on the mat today"
        reference = "The cat sat"
        result = bleu.score(candidate, reference)

        # Candidate is longer, so no brevity penalty
        assert result.brevity_penalty == 1.0

    def test_single_word_texts(self, bleu: Bleu) -> None:
        """Test BLEU with single word texts."""
        result = bleu.score("cat", "cat")

        assert result.bleu1 == 1.0
        # Higher order n-grams can't be computed for single words
        # but with geometric mean, they still produce a score
        assert result.brevity_penalty == 1.0

    def test_empty_candidate(self, bleu: Bleu) -> None:
        """Test that empty candidate returns zero scores."""
        result = bleu.score("", "The cat sat")

        assert result.bleu1 == 0.0
        assert result.bleu2 == 0.0
        assert result.bleu3 == 0.0
        assert result.bleu4 == 0.0
        assert result.brevity_penalty == 0.0

    def test_whitespace_only_candidate(self, bleu: Bleu) -> None:
        """Test that whitespace-only candidate returns zero scores."""
        result = bleu.score("   \t\n  ", "The cat sat")

        assert result.bleu1 == 0.0
        assert result.bleu4 == 0.0

    def test_empty_reference_raises(self, bleu: Bleu) -> None:
        """Test that empty reference raises ValueError."""
        with pytest.raises(ValueError, match="cannot be empty"):
            bleu.score("The cat sat", "")

    def test_none_reference_raises(self, bleu: Bleu) -> None:
        """Test that None reference raises ValueError."""
        with pytest.raises(ValueError, match="requires reference"):
            bleu.score("The cat sat", None)

    def test_multiple_references(self, bleu: Bleu) -> None:
        """Test BLEU with multiple references uses max n-gram matches."""
        candidate = "The cat sat on the mat"
        references = [
            "The cat is on the floor",
            "The cat sat on the mat",  # Exact match
        ]
        result = bleu.score(candidate, references)

        # Should get perfect score due to exact match reference
        assert result.bleu4 == 1.0

    def test_multiple_references_partial(self, bleu: Bleu) -> None:
        """Test multiple references with partial matches."""
        candidate = "The quick brown fox"
        references = [
            "The fast brown fox",
            "A quick brown dog",
        ]
        result = bleu.score(candidate, references)

        # Should benefit from both references
        assert result.bleu1 > 0.0

    def test_result_score_property(self, bleu: Bleu) -> None:
        """Test that result.score returns bleu4."""
        result = bleu.score("The cat sat", "The cat sat")
        assert result.score == result.bleu4

    def test_case_insensitivity(self, bleu: Bleu) -> None:
        """Test that BLEU is case insensitive by default."""
        result = bleu.score("THE CAT SAT ON THE MAT", "the cat sat on the mat")
        assert result.bleu4 == 1.0

    def test_punctuation_ignored(self, bleu: Bleu) -> None:
        """Test that punctuation is ignored by default."""
        result = bleu.score("The cat sat on the mat.", "The cat sat on the mat!")
        assert result.bleu4 == 1.0


class TestBleuBatch:
    """Tests for BLEU batch scoring."""

    @pytest.fixture
    def bleu(self) -> Bleu:
        """Provide a BLEU metric instance."""
        return Bleu()

    def test_batch_score_basic(self, bleu: Bleu) -> None:
        """Test basic batch scoring."""
        candidates = ["The cat sat on the mat", "A quick brown dog runs fast"]
        references = ["The cat sat on the mat", "A quick brown dog runs fast"]
        result = bleu.batch_score(candidates, references)

        assert result.count == 2
        assert len(result.results) == 2
        assert all(r.bleu4 == 1.0 for r in result.results)

    def test_batch_score_statistics(self, bleu: Bleu) -> None:
        """Test that batch scoring computes statistics."""
        candidates = ["The cat sat", "A different text entirely"]
        references = ["The cat sat", "The cat sat"]
        result = bleu.batch_score(candidates, references)

        # Check statistics are computed
        assert "bleu1" in result.stats
        assert "bleu4" in result.stats
        assert "brevity_penalty" in result.stats

        # Mean should be between min and max
        stats = result.stats["bleu4"]
        assert stats.min <= stats.mean <= stats.max

    def test_batch_score_percentiles(self, bleu: Bleu) -> None:
        """Test that batch scoring computes percentiles."""
        candidates = ["a", "b", "c", "d", "e"]
        references = ["a", "b", "c", "d", "e"]
        result = bleu.batch_score(candidates, references)

        stats = result.stats["bleu1"]
        assert 25 in stats.percentiles
        assert 50 in stats.percentiles
        assert 75 in stats.percentiles
        assert 95 in stats.percentiles

    def test_batch_score_none_references_raises(self, bleu: Bleu) -> None:
        """Test that batch scoring raises for None references."""
        with pytest.raises(ValueError, match="requires reference"):
            bleu.batch_score(["text"], None)

    def test_batch_score_length_mismatch_raises(self, bleu: Bleu) -> None:
        """Test that batch scoring raises for mismatched lengths."""
        with pytest.raises(ValueError, match="must match"):
            bleu.batch_score(["a", "b"], ["a"])

    def test_batch_score_with_multiple_references(self, bleu: Bleu) -> None:
        """Test batch scoring with multiple references per candidate."""
        candidates = [
            "The cat sat on the mat",
            "A quick brown dog runs fast",
        ]
        references = [
            ["The cat sat on the mat", "A cat rests on floor"],
            ["A quick brown dog runs fast", "Dogs run very quickly"],
        ]
        result = bleu.batch_score(candidates, references)

        assert result.count == 2
        assert result.results[0].bleu4 == 1.0
        assert result.results[1].bleu4 == 1.0


class TestBleuResult:
    """Tests for BleuResult type."""

    def test_frozen(self) -> None:
        """Test that BleuResult is frozen."""
        from pydantic import ValidationError

        result = BleuResult(
            bleu1=0.5, bleu2=0.4, bleu3=0.3, bleu4=0.2, brevity_penalty=1.0
        )
        with pytest.raises(ValidationError):
            result.bleu1 = 0.6  # type: ignore[misc]

    def test_score_property(self) -> None:
        """Test that score property returns bleu4."""
        result = BleuResult(
            bleu1=0.9, bleu2=0.8, bleu3=0.7, bleu4=0.6, brevity_penalty=1.0
        )
        assert result.score == 0.6