"""Moteur Trim & Shift — decaler le contenu des pages."""

from pypdf import PdfReader, PdfWriter, PageObject, Transformation
from .pdf_utils import get_page_size


def trim_and_shift(input_path, output_path, shift_x=0, shift_y=0,
                   shift_x_even=None, shift_y_even=None,
                   creep=0, creep_pages=0):
    """Decaler le contenu des pages.

    shift_x, shift_y: decalage en points (pages impaires si even specifie)
    shift_x_even, shift_y_even: decalage pour pages paires (None = meme que impaires)
    creep: decalage progressif en points (compensation epaisseur papier)
    creep_pages: nombre total de pages pour le calcul du creep
    """
    reader = PdfReader(input_path)
    writer = PdfWriter()
    num_pages = len(reader.pages)

    if shift_x_even is None:
        shift_x_even = shift_x
    if shift_y_even is None:
        shift_y_even = shift_y

    for i, page in enumerate(reader.pages):
        page_num = i + 1
        w, h = get_page_size(page)

        # Decalage de base
        if page_num % 2 == 0:
            dx, dy = shift_x_even, shift_y_even
        else:
            dx, dy = shift_x, shift_y

        # Creep progressif (pour livrets)
        if creep != 0 and creep_pages > 0:
            # Les pages du centre se decalent le plus
            mid = num_pages / 2
            distance_from_center = abs(i - mid) / mid  # 0 au centre, 1 aux bords
            creep_amount = creep * (1 - distance_from_center)
            if page_num % 2 == 0:
                dx -= creep_amount  # pages paires : decaler vers la gauche
            else:
                dx += creep_amount  # pages impaires : decaler vers la droite

        if dx != 0 or dy != 0:
            new_page = PageObject.create_blank_page(width=w, height=h)
            overlay = PageObject.create_blank_page(width=w, height=h)
            overlay.merge_page(page)
            overlay.add_transformation(Transformation().translate(dx, dy))
            new_page.merge_page(overlay)
            writer.add_page(new_page)
        else:
            writer.add_page(page)

    with open(output_path, "wb") as f:
        writer.write(f)
    return output_path