"""Unit tests for src/chunker.py — the one rule that matters: statements start
chunks, Proof/Solution glue to the statement before them."""
from src.chunker import (
    CHILD_MAX_TOK, CHARS_PER_TOKEN, Chunk, chunk_markdown, est_tokens,
    split_children, _paragraphs,
)


def _mk(md: str):
    return chunk_markdown(md, doc_id="doc", source="test.md")


def test_statement_starts_new_chunk_and_proof_glues():
    md = (
        "# 6.2 Variance of Discrete Random Variables\n\n"
        "Theorem 6.9 The variance is additive for independent variables.\n\n"
        "**Proof.** Expand the square and use linearity.\n\n"
        "Example 6.1 Compute the variance of one die roll.\n"
    )
    chunks = _mk(md)
    assert len(chunks) == 2
    assert chunks[0].type == "theorem"
    assert "Proof." in chunks[0].text          # glued, never its own chunk
    assert chunks[1].type == "example"


def test_chapter_pinned_by_numbering_not_heading_depth():
    md = (
        "# Chapter 6\n\nIntro prose.\n\n"
        "# 6.2 Variance\n\nSection prose.\n\n"
        "# Examples\n\nExample 6.5 Something.\n"
    )
    chunks = _mk(md)
    assert all(c.chapter == "Chapter 6: Expected Value and Variance" for c in chunks)
    # "Examples" is a generic header: it must NOT overwrite the numbered section.
    assert chunks[-1].section == "6.2 Variance"


def test_front_matter_does_not_inherit_chapter():
    md = "# Chapter 1\n\nReal content.\n\n# Index\n\nbinomial, 45\n"
    chunks = _mk(md)
    assert chunks[0].chapter.startswith("Chapter 1")
    assert chunks[-1].chapter == ""            # store.retrieval_units drops these


def test_unnumbered_topic_header_refines_section_only():
    md = "# Chapter 2\n\nA.\n\n## Standard Deviation\n\nB.\n"
    chunks = _mk(md)
    assert chunks[-1].chapter.startswith("Chapter 2")
    assert chunks[-1].section == "Standard Deviation"


def test_statement_marker_inside_display_math_does_not_split():
    md = "Some setup text.\n$$\nExample = 5\n$$\nmore of the same block.\n"
    chunks = _mk(md)
    assert len(chunks) == 1


def test_small_parent_has_no_children():
    p = Chunk(id="d::p1", doc_id="d", source="s", type="text", chapter="", section="",
              text="short", n_tokens=est_tokens("short"))
    assert split_children(p) == []


def test_large_parent_splits_with_parent_id_and_full_coverage():
    paras = [f"Paragraph {i} " + "word " * 60 for i in range(10)]
    text = "\n\n".join(paras)
    p = Chunk(id="d::p1", doc_id="d", source="s", type="text", chapter="C", section="S",
              text=text, n_tokens=est_tokens(text))
    assert p.n_tokens > CHILD_MAX_TOK
    kids = split_children(p)
    assert len(kids) >= 2
    assert all(k.parent_id == "d::p1" and not k.is_parent for k in kids)
    assert all(k.chapter == "C" and k.section == "S" for k in kids)
    joined = "\n".join(k.text for k in kids)
    assert all(f"Paragraph {i}" in joined for i in range(10))  # nothing dropped


def test_paragraphs_keep_display_blocks_intact():
    text = "before\n\n$$\na = 1\n\nb = 2\n$$\n\nafter"
    paras = _paragraphs(text)
    assert len(paras) == 3
    assert "a = 1" in paras[1] and "b = 2" in paras[1]  # blank line inside $$ kept


def test_est_tokens_floor():
    assert est_tokens("") == 1
    assert est_tokens("x" * (CHARS_PER_TOKEN * 10)) == 10