ouroboros/tests/test_reference_book_migration.py

"""The chapter split moved bytes, not meaning: a reversible byte proof.

Each chapter file was written as a two-line prologue plus the old `##` section
body:

    # <the old section title>
    <blank>
    <one authored introductory paragraph>
    <the old section body, byte for byte, starting with its own newline>

So the move is INVERTIBLE, and the inverse is this module's whole method:

    first  = raw.index(b"\\n\\n")               -> the H1 line is raw[:first]
    second = raw.index(b"\\n\\n", first + 2)    -> the introduction is between them
    section = b"## " + raw[2:first] + raw[second:]

Concatenating those sections in membership order must reproduce the old
monolith from its first `## ` heading to EOF, byte for byte.

That is a claim about HISTORY, so it is checked against history: the base
commit's monolith against the migration commit's chapters, both resolved from
Git (`quick-test` and `full-test` check out with `fetch-depth: 0`). The
migration commit is found by content — the commit that added the transfer
table — so a rebase cannot strand the proof on a rewritten SHA, and a later
ordinary edit to a chapter cannot turn a historical fact red. The structural
half below has no such bound and holds on the working tree forever.

The entrypoint preamble is deliberately NOT part of the byte proof: it was
replaced by one merged/authored paragraph plus the `## Chapters` membership
list. The historical `docs/reference-books-migration.md` blob at the split
commit records the former preamble; that file is no longer needed in HEAD.
The H1 line IS pinned here, because it is the release version carrier.
"""

import hashlib
import pathlib
import subprocess

import pytest

from ouroboros.reference_books import BOOK_ENTRYPOINTS, load_reference_book

REPO = pathlib.Path(__file__).resolve().parents[1]

# The integration base this migration was cut from.
MIGRATION_BASE = "5585133db86419c1a28673e498de4fb13c6b2d1e"

# Historical lookup key, not a current-file dependency: the commit that
# ADDED the former operator transfer table is the split commit.
TRANSFER_TABLE = "docs/reference-books-migration.md"

# Recorded at the base commit by the split itself (and mirrored in the transfer
# table): the whole old file, and the part of it that moved -- everything from
# the first `## ` heading to EOF.
OLD_MONOLITHS = {
    "architecture": {
        "old_bytes": 724691,
        "old_sha256": "5db278f8ef5060c4aff5ee1e8743c279661ddd975a311a9bafb5858f32b080de",
        "preamble_bytes": 610,
        "moved_bytes": 724081,
        "moved_sha256": "f1f054c700a15533687e0cf81cf19ac53ffcf022eb179f84c0cbccacbb1d305e",
        "h1": "# Ouroboros v7.0.0 — Architecture & Reference",
    },
    "development": {
        "old_bytes": 275551,
        "old_sha256": "50eb460602f1501915195e3ad1918366312e6292b0dccec6f7ef53f5a5302f3b",
        "preamble_bytes": 60,
        "moved_bytes": 275491,
        "moved_sha256": "bffc00227bc5e91f054b38eaed63acd256c2ddf111e231754bfbe92c7dd122e3",
        "h1": "# DEVELOPMENT.md — Development Principles & Module Guide",
    },
}


def _git(*args: str) -> bytes | None:
    try:
        return subprocess.run(
            ["git", *args], cwd=REPO, check=True, capture_output=True,
        ).stdout
    except (OSError, subprocess.CalledProcessError):
        return None


def _migration_commit() -> str | None:
    out = _git("log", "--diff-filter=A", "--format=%H", "--", TRANSFER_TABLE)
    lines = [line for line in (out or b"").decode().split("\n") if line.strip()]
    return lines[-1] if lines else None


def _restore_section(raw: bytes) -> bytes:
    """Undo one chapter's prologue and return the old `## ` section bytes."""
    first = raw.index(b"\n\n")
    second = raw.index(b"\n\n", first + 2)
    h1 = raw[:first]
    assert h1.startswith(b"# "), h1[:40]
    introduction = raw[first + 2:second]
    assert introduction.strip() and b"\n\n" not in introduction, h1
    return b"## " + h1[2:] + raw[second:]


@pytest.mark.parametrize("book_id", sorted(BOOK_ENTRYPOINTS))
def test_the_migration_commit_reconstructs_the_base_monolith_byte_for_byte(book_id):
    recorded = OLD_MONOLITHS[book_id]
    rel = BOOK_ENTRYPOINTS[book_id]
    split = _migration_commit()
    old = _git("show", f"{MIGRATION_BASE}:{rel}")
    if split is None or old is None:
        pytest.fail(
            f"the migration proof needs Git history: base {MIGRATION_BASE} "
            f"{'unreachable' if old is None else 'ok'}, the commit that added "
            f"{TRANSFER_TABLE} {'unreachable' if split is None else 'ok'}. "
            "CI checks out with fetch-depth: 0 for exactly this."
        )

    assert len(old) == recorded["old_bytes"]
    assert hashlib.sha256(old).hexdigest() == recorded["old_sha256"]
    assert old[:recorded["preamble_bytes"]].startswith(recorded["h1"].encode("utf-8"))

    book = load_reference_book(
        REPO, book_id,
        read_bytes=lambda path: _git("show", f"{split}:{path}"),
    )
    assert not book.legacy, f"{book_id} was not chaptered by the migration commit"
    moved = b"".join(_restore_section(chapter.raw) for chapter in book.chapters)

    assert len(moved) == recorded["moved_bytes"]
    assert hashlib.sha256(moved).hexdigest() == recorded["moved_sha256"]
    assert moved == old[recorded["preamble_bytes"]:]


@pytest.mark.parametrize("book_id", sorted(BOOK_ENTRYPOINTS))
def test_every_base_section_is_still_exactly_one_chapter(book_id):
    """The structural half, unbounded in time: the base's `##` titles are the
    chapters' H1 titles, in order, one each. A later edit to a chapter body
    cannot make this red, and a lost, merged or re-titled chapter still can."""
    old = _git("show", f"{MIGRATION_BASE}:{BOOK_ENTRYPOINTS[book_id]}")
    if old is None:
        pytest.skip(f"base commit {MIGRATION_BASE} is unreachable in this checkout")
    in_fence = False
    base_titles = []
    for line in old.decode("utf-8").split("\n"):
        if line.lstrip().startswith("```"):
            in_fence = not in_fence
            continue
        if not in_fence and line.startswith("## "):
            base_titles.append(line[3:].strip())

    book = load_reference_book(REPO, book_id)
    chapter_titles = [chapter.headings[0].title for chapter in book.chapters]
    assert chapter_titles == base_titles


@pytest.mark.parametrize("book_id", sorted(BOOK_ENTRYPOINTS))
def test_entrypoint_keeps_its_h1_line_and_carries_only_the_membership(book_id):
    rel = BOOK_ENTRYPOINTS[book_id]
    raw = (REPO / rel).read_bytes()
    lines = raw.decode("utf-8").split("\n")
    assert lines[0] == OLD_MONOLITHS[book_id]["h1"]
    book = load_reference_book(REPO, book_id)
    # One `## Chapters` heading and nothing else: the entrypoint orients, the
    # chapters carry the book.
    assert [h.title for h in book.entrypoint.headings] == [lines[0][2:], "Chapters"]
    members = [chapter.source_path for chapter in book.chapters]
    assert members == sorted(members), "membership order must be the reading order"
    for chapter in book.chapters:
        assert chapter.source_path.startswith(f"docs/{book_id}/")
        assert f"]({chapter.source_path[len('docs/'):]})" in book.entrypoint.text


def test_no_chapter_body_was_reheaded_into_a_duplicate_title():
    """Relocation kept `###`/`####` levels, so a section title still names one
    physical place across the whole book -- what `read_book_section` needs."""
    for book_id in BOOK_ENTRYPOINTS:
        book = load_reference_book(REPO, book_id)
        titles = [h.title for source in (book.entrypoint, *book.chapters) for h in source.headings]
        duplicates = sorted({t for t in titles if titles.count(t) > 1})
        assert not duplicates, f"{book_id}: ambiguous section titles {duplicates}"