"""
Python-Markdown extension: converts [[Wikilinks]] to standard Markdown links.

Mirrors the behavior of mkdocs-ezlinks-plugin's WikiLinkScanner, but as a
pure Markdown preprocessor (no MkDocs plugin API needed). Zensical handles
the resulting .md links natively.

Syntax:
    [[Page Name]]              → [Page Name](page-name.md)
    [[Page Name|Display Text]] → [Display Text](page-name.md)
    [[Page Name#anchor]]       → [Page Name](page-name.md#anchor)
    [[Page Name#anchor|Text]]  → [Text](page-name.md#anchor)
    ![[image.png]]             → ![image.png](image.png)
    [[folder/Page Name]]       → [Page Name](folder/page-name.md)

Code blocks (fenced and inline) are skipped — wiki links inside them pass
through unchanged.
"""

from __future__ import annotations

import re
from markdown.preprocessors import Preprocessor
from markdown.extensions import Extension


# Regex for a wiki link. Borrowed from mkdocs-ezlinks-plugin's
# WikiLinkScanner with minor adjustments.
_WIKILINK_RE = re.compile(
    r"""
    (?P<image>\!?)                    # optional ! for image embeds
    \[\[                              # opening [[
        (?P<link>[^#\|\]]*?)          # target (everything before #, |, or ]])
        (?:\#(?P<anchor>[^\|\]]+)?)?  # optional #anchor
        (?:\|(?P<text>[^\]]+)?)?      # optional |display text
    \]\]                              # closing ]]
    """,
    re.VERBOSE,
)

# Match fenced code blocks or inline code spans (single capture group).
_CODE_RE = re.compile(
    r"(```.*?```|`[^`\n]+`)",
    re.DOTALL,
)


def _slugify(text: str) -> str:
    """Convert a human page name into a filename slug.

    Mirrors ezlinks: lowercase, spaces → hyphens, strip unsupported chars.
    Keeps forward slashes for subdirectory paths, dots for extensions, and CJK.
    """
    slug = text.strip().lower()
    slug = re.sub(r"\s+", "-", slug)
    # Keep: word chars, hyphens, dots, forward slashes, CJK
    slug = re.sub(r"[^\w./\u4e00-\u9fff\-]", "", slug)
    return slug


class WikilinksPreprocessor(Preprocessor):
    """Preprocessor that converts [[wikilinks]] to [text](slug.md)."""

    def run(self, lines: list[str]) -> list[str]:
        text = "\n".join(lines)

        # Walk through the text, skipping code spans. Use finditer to
        # extract code regions, then transform wiki links in the gaps.
        result: list[str] = []
        cursor = 0
        for m in _CODE_RE.finditer(text):
            # Transform the non-code region before this match
            before = text[cursor : m.start()]
            if before:
                result.append(_WIKILINK_RE.sub(self._replace, before))
            # Pass through the code region unchanged
            result.append(m.group(0))
            cursor = m.end()

        # Transform any remaining text after the last code region
        tail = text[cursor:]
        if tail:
            result.append(_WIKILINK_RE.sub(self._replace, tail))

        return "\n".join(result).split("\n")

    def _replace(self, match: re.Match) -> str:
        groups = match.groupdict()
        is_image = groups.get("image") or ""
        link = groups.get("link") or ""
        anchor = groups.get("anchor") or ""
        text = groups.get("text") or link or anchor

        if not (link or text or anchor):
            return match.group(0)

        slug = _slugify(link) if link else ""
        href = slug
        if anchor:
            anchor_slug = _slugify(anchor)
            if anchor_slug:
                href = f"{slug}#{anchor_slug}" if slug else f"#{anchor_slug}"

        if not href:
            return match.group(0)

        # Build standard markdown link / image
        if is_image:
            return f"![{text}]({href})"
        else:
            return f"[{text}]({href})"


class WikilinksExtension(Extension):
    """Register the WikilinksPreprocessor."""

    def extendMarkdown(self, md):
        # Priority 35: after normalize_whitespace (30), before html_block (20)
        md.preprocessors.register(WikilinksPreprocessor(md), "wikilinks", 35)


def makeExtension(**kwargs):
    return WikilinksExtension(**kwargs)