"""Moteur N-Up : placer plusieurs pages par feuille."""

from pypdf import PdfReader, PdfWriter, PageObject, Transformation
from .pdf_utils import get_page_size, create_blank_page, mm_to_pt, smart_crop_marks
import io


def nup_pages(input_path, output_path, cols=2, rows=2, sheet_size=(841.89, 595.28),
              margin_top=0, margin_bottom=0, margin_left=0, margin_right=0,
              gutter_h=0, gutter_v=0, scale_mode="fit", crop_marks=False,
              background_path=None):
    """Placer plusieurs pages sur chaque feuille.

    cols, rows: grille
    sheet_size: (largeur, hauteur) en points
    margins: en points
    gutter_h, gutter_v: espacement horizontal/vertical entre pages
    scale_mode: "fit" (ajuster) ou "none" (taille reelle)
    crop_marks: ajouter des reperes de coupe
    background_path: chemin vers un PDF de fond
    """
    reader = PdfReader(input_path)
    pages = reader.pages
    sheet_w, sheet_h = sheet_size

    # Zone utile
    usable_w = sheet_w - margin_left - margin_right - gutter_h * (cols - 1)
    usable_h = sheet_h - margin_top - margin_bottom - gutter_v * (rows - 1)

    cell_w = usable_w / cols
    cell_h = usable_h / rows

    # Fond
    bg_page = None
    if background_path:
        bg_reader = PdfReader(background_path)
        if bg_reader.pages:
            bg_page = bg_reader.pages[0]

    writer = PdfWriter()
    pages_per_sheet = cols * rows

    for sheet_idx in range(0, len(pages), pages_per_sheet):
        sheet = PageObject.create_blank_page(width=sheet_w, height=sheet_h)

        if bg_page:
            sheet.merge_page(bg_page)

        grid_positions = []

        for slot in range(pages_per_sheet):
            page_idx = sheet_idx + slot
            if page_idx >= len(pages):
                break

            page = pages[page_idx]
            page_w, page_h = get_page_size(page)

            col = slot % cols
            row = slot // cols
            grid_positions.append((col, row))

            # Position de la cellule
            x = margin_left + col * (cell_w + gutter_h)
            y = sheet_h - margin_top - (row + 1) * cell_h - row * gutter_v

            # Calcul du scale
            if scale_mode == "fit":
                scale_x = cell_w / page_w
                scale_y = cell_h / page_h
                scale = min(scale_x, scale_y)
            else:
                scale = 1.0

            # Centrage dans la cellule
            scaled_w = page_w * scale
            scaled_h = page_h * scale
            offset_x = x + (cell_w - scaled_w) / 2
            offset_y = y + (cell_h - scaled_h) / 2

            # Placer la page
            overlay = PageObject.create_blank_page(width=sheet_w, height=sheet_h)
            overlay.merge_page(page)
            overlay.add_transformation(
                Transformation().scale(scale, scale).translate(offset_x, offset_y)
            )
            sheet.merge_page(overlay)

        # Reperes de coupe
        if crop_marks and grid_positions:
            marks = smart_crop_marks(
                sheet_w, sheet_h, grid_positions,
                cell_w + gutter_h, cell_h + gutter_v,
                margin_left, margin_top
            )
            sheet.merge_page(marks)

        writer.add_page(sheet)

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