"""Tests for harness/diff.py — field-level structured diff.

The diff checks, for each (field, expected_value) in a canonical record,
whether the candidate formatted string contains that value as a case-sensitive
substring. This is intentionally simpler than parsing — the linter catches
structural issues; the diff catches "did the right facts survive?"
"""

from harness.diff import field_diff


def test_all_fields_present_in_candidate_match():
    canonical = {
        "author": "Smith, Jane",
        "title": "The History of Nothing",
        "publisher": "University of Chicago Press",
        "year": 2023,
    }
    candidate = "Smith, Jane. *The History of Nothing*. University of Chicago Press, 2023."
    result = field_diff(candidate, canonical)
    assert result.matched == ["author", "title", "publisher", "year"]
    assert result.missing == []
    assert result.rate == 1.0


def test_missing_publisher_is_reported():
    canonical = {
        "author": "Smith, Jane",
        "title": "The History of Nothing",
        "publisher": "University of Chicago Press",
        "year": 2023,
    }
    # Publisher dropped.
    candidate = "Smith, Jane. *The History of Nothing*. 2023."
    result = field_diff(candidate, canonical)
    assert "publisher" in result.missing
    assert "author" in result.matched
    assert result.rate == 0.75


def test_title_case_mismatch_counts_as_missing():
    # CMOS 18 requires headline-style caps. If the formatter emits sentence
    # case, the title should not match its canonical headline-case form.
    canonical = {"title": "The History of Nothing"}
    candidate = "Smith, Jane. *The history of nothing*. 2023."
    result = field_diff(candidate, canonical)
    assert result.missing == ["title"]
    assert result.rate == 0.0


def test_empty_canonical_is_rate_one():
    # Degenerate case — no fields to check means nothing is wrong.
    assert field_diff("whatever", {}).rate == 1.0