"""Split a PDF along its cumulative visible page height, in reading order."""

import math
from pathlib import Path

import pymupdf

from copienator.commands.splitting_int import _prepare_split_pages

# Percentages emitted by the GUI have six decimal places. Recover exact page
# boundaries despite rounding, without turning nearby in-page cuts into breaks.
BOUNDARY_TOLERANCE_PERCENT = 0.000001


def cut_position(heights: list[float], percent: float) -> tuple[int, float]:
    """Return (page index, offset); offset zero denotes an exact page break."""
    if not heights or any(height <= 0 for height in heights):
        raise ValueError("Le PDF doit contenir des pages non vides.")
    if not math.isfinite(percent) or not 0 < percent < 100:
        raise ValueError("Le pourcentage de coupe doit être strictement entre 0 et 100.")
    total = sum(heights)
    position = total * percent / 100
    start = 0.0
    for index, height in enumerate(heights):
        if index and abs(percent - start / total * 100) <= BOUNDARY_TOLERANCE_PERCENT:
            return index, 0.0
        end = start + height
        if index + 1 < len(heights) and abs(percent - end / total * 100) <= BOUNDARY_TOLERANCE_PERCENT:
            return index + 1, 0.0
        if position < end:
            return index, position - start
        start = end
    raise ValueError("Coupe hors du document.")


def split_pdf(source: Path, percent: float, first_path: Path, second_path: Path) -> None:
    """Preserve whole pages; clip only the page actually crossed by the cut."""
    with pymupdf.open(source) as document, pymupdf.open() as first, pymupdf.open() as second:
        index, offset = cut_position([page.rect.height for page in document], percent)
        if index:
            first.insert_pdf(document, from_page=0, to_page=index - 1)
        if offset == 0:
            second.insert_pdf(document, from_page=index)
        else:
            with pymupdf.open() as page_document:
                page_document.insert_pdf(document, from_page=index, to_page=index)
                visible = _prepare_split_pages(page_document)[0]
                for target, clip in (
                    (first, pymupdf.Rect(visible.x0, visible.y0, visible.x1, visible.y0 + offset)),
                    (second, pymupdf.Rect(visible.x0, visible.y0 + offset, visible.x1, visible.y1)),
                ):
                    page = target.new_page(width=clip.width, height=clip.height)
                    page.show_pdf_page(page.rect, page_document, 0, clip=clip)
            if index + 1 < len(document):
                second.insert_pdf(document, from_page=index + 1)
        first.save(first_path)
        second.save(second_path)