Implementace prevodu HTML na PDF

Sluzba prijme adresu HTML dokumentu nebo HTML v tele requestu a vrati PDF.
Navrzena pro dokumenty o stovkach az tisicich stranek.

Rendering:
- WeasyPrint jako vychozi engine, spravne CSS Paged Media, nizka pametova
  narocnost, bez JavaScriptu
- Chromium pres Playwright pro dokumenty dokreslovane skripty
- rezim auto s detekci skriptu a fallbackem pri selhani WeasyPrintu

Velke dokumenty:
- deleni na casti na strukturalnich hranicich, rez nikdy uvnitr tabulky
  nebo odstavce
- dvoupruchodovy render obsahu se skutecnymi cisly stranek, pozice nadpisu
  se ctou z kotev hlasenych u kazde stranky
- cislovani stranek bud pres CSS countery, nebo pres cislovaci vrstvu
  nastampovanou na hotove PDF, rozmer stranky se cte z vysledneho souboru
- Chromium se restartuje po N jobech, nikdy vsak behem beziciho renderu

API:
- POST /convert synchronne, POST /jobs asynchronne se sledovanim stavu,
  stahovanim vysledku, rusenim a volitelnym callbackem
- GET /health s overenim dostupnosti obou enginu a stavem fronty
- OpenAPI respektuje prefix reverse proxy pres root_path

Bezpecnost a provoz:
- SSRF kontrola po DNS resolvu, na kazdem presmerovani a u vsech pozadavku
  prohlizece
- nedostupne assety render nezastavi, ale hlasi se v odpovedi i v logu
- fronta s omezenym poctem workeru, rozpracovane joby se pri ukonceni
  oznaci jako failed, nezmizi potichu
- strukturovane JSON logovani s job_id
- vsechny limity vypnute ve vychozim stavu

Dockerfile je dvoufazovy, obsahuje zavislosti WeasyPrintu, Chromium
a fonty s ceskou diakritikou.

Autentizace zamerne neni implementovana, zpusob predavani neni domluveny.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test_pagination.py

@@ -0,0 +1,90 @@
+"""Page numbering and table of contents of a merged document.
+
+This is where the chunking approach usually breaks, so the numbers are read back
+out of the produced PDF instead of being trusted.
+"""
+
+from __future__ import annotations
+
+import re
+
+import pytest
+
+pytest.importorskip("weasyprint")
+pytest.importorskip("pypdf")
+
+from app.config import Settings  # noqa: E402
+from app.engines.weasy import WeasyPrintEngine  # noqa: E402
+from app.models import ChunkSettings, ConvertRequest, PageNumbers, Source, TocSettings  # noqa: E402
+from app.services.pipeline import ConversionPipeline  # noqa: E402
+from tests.conftest import build_document  # noqa: E402
+
+pytestmark = pytest.mark.asyncio
+
+
+def page_texts(path) -> list[str]:
+    from pypdf import PdfReader
+
+    with open(path, "rb") as handle:
+        return [page.extract_text() or "" for page in PdfReader(handle).pages]
+
+
+def make_pipeline() -> ConversionPipeline:
+    return ConversionPipeline({"weasyprint": WeasyPrintEngine()}, Settings())
+
+
+async def test_page_numbers_are_continuous_across_chunks(tmp_path) -> None:
+    request = ConvertRequest(
+        source=Source(html=build_document(sections=12, paragraphs_per_section=8)),
+        engine="weasyprint",
+        page_numbers=PageNumbers(enabled=True, format="{page} / {pages}"),
+        chunking=ChunkSettings(enabled=True, pages_per_chunk=2),
+    )
+
+    result = await make_pipeline().run(request, tmp_path)
+    texts = page_texts(result.path)
+
+    assert result.page_count == len(texts)
+    assert result.page_count > 3, "dokument musi mit vic stranek, jinak test nic neoveruje"
+
+    for index, text in enumerate(texts, start=1):
+        assert f"{index} / {result.page_count}" in text.replace("\n", " ")
+
+
+async def test_table_of_contents_points_to_the_real_pages(tmp_path) -> None:
+    request = ConvertRequest(
+        source=Source(html=build_document(sections=10, paragraphs_per_section=8)),
+        engine="weasyprint",
+        toc=TocSettings(enabled=True, depth=1, title="Obsah"),
+        chunking=ChunkSettings(enabled=True, pages_per_chunk=2),
+    )
+
+    result = await make_pipeline().run(request, tmp_path)
+    texts = page_texts(result.path)
+    toc_text = " ".join(texts[:2]).replace("\n", " ")
+
+    for index in range(10):
+        heading = f"Kapitola {index + 1}"
+        match = re.search(re.escape(heading) + r"\s+(\d+)", toc_text)
+        assert match, f"v obsahu chybi polozka {heading}"
+
+        declared_page = int(match.group(1))
+        actual_pages = [
+            number for number, text in enumerate(texts, start=1) if heading in text.replace("\n", " ")
+        ]
+        # The first occurrence after the table of contents is the heading itself.
+        assert declared_page in actual_pages, f"{heading} deklaruje stranku {declared_page}"
+
+
+async def test_unchunked_document_uses_css_counters(tmp_path) -> None:
+    request = ConvertRequest(
+        source=Source(html=build_document(sections=4, paragraphs_per_section=6)),
+        engine="weasyprint",
+        page_numbers=PageNumbers(enabled=True, format="{page} / {pages}"),
+        chunking=ChunkSettings(enabled=False),
+    )
+
+    result = await make_pipeline().run(request, tmp_path)
+    texts = page_texts(result.path)
+
+    assert f"1 / {result.page_count}" in texts[0].replace("\n", " ")