"""
# Summary

Wiki navigation derivation.

This module provides ``build_wiki_nav``, which derives an MkDocs-ready
navigation block from the file structure of a hand-written wiki directory
(typically ``docs/wiki``). wiki content is authored by hand and is never
modified by doc-forge; only the navigation layout is inferred.

# Notes

- ``index.md`` at the wiki root becomes the ``Home`` entry.
- Page labels are derived from filenames: numeric order prefixes such as
  ``01_`` or ``02-`` are stripped, separators are replaced with spaces, and
  names are title-cased (``01_overview.md`` becomes ``Overview``).
- Subdirectories become nested navigation groups. A nested ``index.md`` is
  rendered as the section root placed first inside the group.
- Only ``.md`` files are considered; hidden entries are ignored.
"""

import re
from collections.abc import Callable
from pathlib import Path
from typing import Any


def build_wiki_nav(wiki_dir: Path) -> list[dict[str, Any]]:
    """
    Derive an MkDocs navigation block from a wiki directory.

    Returned paths are relative to the parent of ``wiki_dir`` and carry the
    wiki directory name as their leading component (for example
    ``wiki/01_overview.md`` when the wiki lives at ``docs/wiki``). This makes
    the result directly usable in an MkDocs ``nav`` block with

    - ``index.md`` at the wiki root becomes the ``Home`` entry.
    - Page labels are derived from filenames: numeric order prefixes such as
      ``01_`` or ``02-`` are stripped, separators are replaced with spaces, and
      names are title-cased (``01_overview.md`` becomes ``Overview``).
    - Subdirectories become nested navigation groups. A nested ``index.md`` is
      rendered as the section root placed first inside the group.
    - Only ``.md`` files are considered; hidden entries are ignored.

    Args:
        wiki_dir (Path):
            Path to the hand-written wiki directory, for example ``docs/wiki``.

    Returns:
        list[dict[str, Any]]:
            Navigation entries compatible with the MkDocs ``nav`` configuration.
            The list is empty if the wiki contains no Markdown files.

    Raises:
        FileNotFoundError:
            If the wiki directory does not exist.
    """
    if not wiki_dir.exists():
        raise FileNotFoundError(wiki_dir)

    root = wiki_dir.parent

    def rel(path: Path) -> str:
        try:
            return path.relative_to(root).as_posix()
        except ValueError:
            return path.as_posix()

    nav: list[dict[str, Any]] = []

    if (wiki_dir / "index.md").exists():
        nav.append({"Home": rel(wiki_dir / "index.md")})

    nav.extend(_render_entries(wiki_dir, rel))

    return nav


def _render_entries(
    base_dir: Path,
    rel: Callable[[Path], str],
) -> list[dict[str, Any]]:
    """
    Render navigation entries for the children of a wiki directory.

    Markdown pages become labeled entries, subdirectories containing
    Markdown become nested groups, and a nested ``index.md`` is emitted
    first as the section root.

    Args:
        base_dir (Path):
            Directory whose children are rendered.

        rel (Callable[[Path], str]):
            Callable converting a wiki file path into a docs-relative path.

    Returns:
        list[dict[str, Any]]:
            Navigation entries for ``base_dir`` in natural sort order.
    """
    children = sorted(
        (child for child in base_dir.iterdir() if not child.name.startswith(".")),
        key=lambda child: _natural_key(child.name),
    )

    entries: list[dict[str, Any]] = []

    for child in children:
        if child.is_dir():
            if not any(child.rglob("*.md")):
                continue

            group: list[dict[str, Any]] = []
            nested_index = child / "index.md"
            if nested_index.exists():
                group.append({_prettify(child.name): rel(nested_index)})
            group.extend(_render_entries(child, rel))
            entries.append({_prettify(child.name): group})
        elif child.suffix == ".md":
            if child.name == "index.md":
                continue
            entries.append({_prettify(child.stem): rel(child)})

    return entries


def _prettify(name: str) -> str:
    """
    Convert a filename or directory name into a navigation label.

    Numeric order prefixes (``01_``, ``02-``, ``03.``) are stripped,
    separators are replaced with spaces, and the result is title-cased.

    Args:
        name (str):
            Filename stem or directory name to prettify.

    Returns:
        str:
            Title-cased navigation label.
    """
    name = re.sub(r"^\d+[_\-. ]?", "", name)
    name = re.sub(r"[_-]+", " ", name).strip()
    return name.title()


def _natural_key(name: str) -> list[object]:
    """
    Build a natural sort key from a filename.

    The key splits ``name`` into alternating non-digit and digit parts so
    that numeric prefixes sort numerically (``02`` before ``10``).

    Args:
        name (str):
            Filename or directory name to key.

    Returns:
        list[object]:
            Mixed list of lowercased strings and integers used for sorting.
    """
    return [
        int(part) if part.isdigit() else part.lower()
        for part in re.split(r"(\d+)", name)
    ]