from __future__ import annotations

from pathlib import Path

import pytest
from pypdf import PdfReader, PdfWriter

from pdf2md.pdf_splitter import PdfChunkError, count_pdf_pages, plan_pdf_chunks, write_pdf_chunk


def make_blank_pdf(path: Path, page_count: int) -> Path:
    path.parent.mkdir(parents=True, exist_ok=True)
    writer = PdfWriter()
    for _ in range(page_count):
        writer.add_blank_page(width=72, height=72)
    with path.open("wb") as file:
        writer.write(file)
    return path


@pytest.mark.parametrize(
    ("page_count", "expected_ranges"),
    [
        (1, [(1, 1)]),
        (20, [(1, 20)]),
        (21, [(1, 20), (21, 21)]),
        (40, [(1, 20), (21, 40)]),
        (41, [(1, 20), (21, 40), (41, 41)]),
    ],
)
def test_plan_pdf_chunks_uses_one_based_ranges_and_names(
    tmp_path: Path,
    page_count: int,
    expected_ranges: list[tuple[int, int]],
) -> None:
    pdf = make_blank_pdf(tmp_path / "paper.pdf", page_count)

    chunks = plan_pdf_chunks(pdf, chunk_pages=20)

    assert count_pdf_pages(pdf) == page_count
    assert [(chunk.source_page_start, chunk.source_page_end) for chunk in chunks] == expected_ranges
    assert [chunk.output_filename for chunk in chunks] == [
        f"paper.part-{index:03d}.pages-{start:03d}-{end:03d}.pdf"
        for index, (start, end) in enumerate(expected_ranges, start=1)
    ]


def test_write_pdf_chunk_writes_expected_page_count(tmp_path: Path) -> None:
    pdf = make_blank_pdf(tmp_path / "paper.pdf", 41)
    chunk = plan_pdf_chunks(pdf, chunk_pages=20)[1]

    output = write_pdf_chunk(chunk, tmp_path / "chunks" / chunk.output_filename)

    assert output.exists()
    assert len(PdfReader(output).pages) == 20


def test_plan_pdf_chunks_rejects_non_positive_chunk_size(tmp_path: Path) -> None:
    pdf = make_blank_pdf(tmp_path / "paper.pdf", 1)

    with pytest.raises(PdfChunkError, match="positive integer"):
        plan_pdf_chunks(pdf, chunk_pages=0)