"""Bind template-declared slide-number placeholders to native Office fields."""
from __future__ import annotations

from copy import deepcopy
from pathlib import Path
import posixpath
import uuid
import zipfile

from lxml import etree as OXML


NS = {"p": "http://schemas.openxmlformats.org/presentationml/2006/main",
      "a": "http://schemas.openxmlformats.org/drawingml/2006/main",
      "r": "http://schemas.openxmlformats.org/officeDocument/2006/relationships"}


def prepare_slide_number(root, definition, number):
    """Use the Layout's fixed carrier, including for older authored page sources.

    The runtime converts a marked number only when its cache equals its actual
    initial slide position. The cache seeds the field; it is never its identity.
    """
    if type(number) is not int or number < 1:
        raise ValueError("Initial slide number must be a positive integer")
    find = lambda tree: [node for node in tree.iter()
                         if node.get("data-pptx-placeholder") == "slide-number"]
    declared, current = find(definition), find(root)
    if len(declared) > 1 or len(current) > 1:
        raise ValueError("Each Layout/page supports one slide-number placeholder")
    if not declared:
        if current:
            raise ValueError("Page declares a slide number absent from its Layout")
        return 0
    replacement = deepcopy(declared[0])
    carriers = [node for node in replacement.iter()
                if node.tag.rsplit("}", 1)[-1] == "text"
                and node.get("data-pptx-carrier") == "true"]
    if len(carriers) != 1:
        raise ValueError("Slide-number placeholder requires one explicit text carrier")
    carrier = carriers[0]
    for child in list(carrier):
        carrier.remove(child)
    carrier.text = str(number)
    if current:
        parent = next((node for node in root.iter() if current[0] in list(node)), None)
        if parent is None:
            raise ValueError("Slide-number placeholder must be a child of the page root")
        index = list(parent).index(current[0])
        parent.remove(current[0])
        parent.insert(index, replacement)
    else:
        root.append(replacement)
    return 1


def finalize_slide_numbers(path: Path, expected: list[int]):
    """Check Slide-local fields and give every page-number field a unique ID."""
    with zipfile.ZipFile(path) as archive:
        parts = {item.filename: archive.read(item) for item in archive.infolist()}
    trees = {name: OXML.fromstring(value) for name, value in parts.items()
             if name.startswith("ppt/") and name.endswith(".xml")}
    presentation = trees["ppt/presentation.xml"]
    if int(presentation.get("firstSlideNum", "1")) != 1:
        raise ValueError("Native export expected the declared initial numbering origin 1")
    rels = OXML.fromstring(parts["ppt/_rels/presentation.xml.rels"])
    targets = {node.get("Id"): node.get("Target") for node in rels}
    slides = [posixpath.normpath(posixpath.join("ppt", targets[node.get("{" + NS["r"] + "}id")])).lstrip("/")
              for node in presentation.findall("p:sldIdLst/p:sldId", NS)]
    if len(slides) != len(expected):
        raise ValueError("Slide-number validation requires the actual presentation order")
    fields = 0
    for index, (name, count) in enumerate(zip(slides, expected), 1):
        root = trees[name]
        shapes = [shape for shape in root.findall(".//p:sp", NS)
                  if shape.find("p:nvSpPr/p:nvPr/p:ph[@type='sldNum']", NS) is not None]
        if len(shapes) != count:
            raise ValueError(f"Slide {index}: slide-number placeholder count differs from its Layout")
        for shape in shapes:
            actual = shape.findall("p:txBody/a:p/a:fld", NS)
            if len(actual) != 1 or actual[0].get("type") != "slidenum":
                raise ValueError(f"Slide {index}: page number must be a native slidenum field")
            if [node.text for node in shape.findall(".//a:t", NS)] != [str(index)]:
                raise ValueError(f"Slide {index}: field cache differs from its actual initial position")
            fields += 1
    # The frozen runtime reuses a GUID for slide-local numbers. Office requires
    # distinct field identities; fix only these fields, leaving other fields alone.
    changed = {}
    for name, root in trees.items():
        numbers = root.findall(".//a:fld[@type='slidenum']", NS)
        if numbers:
            for field in numbers:
                field.set("id", "{" + str(uuid.uuid4()).upper() + "}")
            changed[name] = OXML.tostring(root, encoding="utf-8", xml_declaration=True)
    if changed:
        temporary = path.with_suffix(".numbering.pptx")
        try:
            with zipfile.ZipFile(temporary, "x", zipfile.ZIP_DEFLATED) as archive:
                for name, value in parts.items():
                    archive.writestr(name, changed.get(name, value))
            temporary.replace(path)
        finally:
            temporary.unlink(missing_ok=True)
    return {"slide_number_fields": fields, "slide_numbers_dynamic": bool(fields)}