"""HTML (1C Help) → Markdown converter (stdlib only)."""

from __future__ import annotations

import re
from html.parser import HTMLParser
from typing import Callable
from urllib.parse import unquote


_SKIP_TAGS = frozenset({"script", "style", "head", "meta", "link"})
_HEADER = {"h1": "#", "h2": "##", "h3": "###", "h4": "####", "h5": "#####", "h6": "######"}


LinkRewriter = Callable[[str, str], str]


class _HelpHTMLParser(HTMLParser):
    def __init__(self, rewrite_link: LinkRewriter | None = None) -> None:
        super().__init__(convert_charrefs=True)
        self.rewrite_link = rewrite_link or (lambda href, text: text)
        self.parts: list[str] = []
        self._skip_depth = 0
        self._bold = 0
        self._italic = 0
        self._code = 0
        self._list_stack: list[str] = []
        self._li_index: list[int] = []
        self._link_href: str | None = None
        self._link_text: list[str] = []
        self._in_anchor_name: str | None = None
        self._pending_header_id: str | None = None
        # single-cell callout tables (1C tip boxes)
        self._table_depth = 0
        self._table_buf: list[str] | None = None
        self._table_cells = 0
        self._outer_parts: list[str] | None = None

    def handle_starttag(self, tag: str, attrs: list[tuple[str, str | None]]) -> None:
        tag = tag.lower()
        ad = {k.lower(): (v or "") for k, v in attrs}

        if tag in _SKIP_TAGS:
            self._skip_depth += 1
            return
        if self._skip_depth:
            return

        if tag == "br":
            self._emit("\n")
            return
        if tag == "hr":
            self._close_inline()
            self._emit("\n\n---\n\n")
            return

        if tag in ("b", "strong"):
            self._bold += 1
            self._emit_inline("**")
            return
        if tag in ("i", "em"):
            self._italic += 1
            self._emit_inline("*")
            return
        if tag in ("code", "tt"):
            self._code += 1
            self._emit_inline("`")
            return

        if tag == "a":
            name = ad.get("name") or ad.get("id")
            href = ad.get("href", "")
            if name and (not href or href.startswith("#")):
                # named destination for TOC / section
                self._in_anchor_name = name
                self._pending_header_id = name
                return
            if href.startswith("v8help://"):
                return
            self._link_href = href
            self._link_text = []
            return

        if tag in _HEADER:
            self._close_inline()
            self._ensure_blank()
            if self._pending_header_id:
                self._emit(f'<a id="{self._pending_header_id}"></a>\n')
                self._pending_header_id = None
            self._emit(f"{_HEADER[tag]} ")
            return

        if tag == "p":
            self._close_inline()
            self._ensure_blank()
            return

        if tag == "ul":
            self._close_inline()
            self._ensure_blank()
            self._list_stack.append("ul")
            self._li_index.append(0)
            return
        if tag == "ol":
            self._close_inline()
            self._ensure_blank()
            self._list_stack.append("ol")
            self._li_index.append(0)
            return
        if tag == "li":
            self._close_inline()
            self._emit("\n")
            depth = max(len(self._list_stack) - 1, 0)
            indent = "  " * depth
            if self._list_stack and self._list_stack[-1] == "ol":
                self._li_index[-1] += 1
                self._emit(f"{indent}{self._li_index[-1]}. ")
            else:
                self._emit(f"{indent}- ")
            return

        if tag == "table":
            self._close_inline()
            self._ensure_blank()
            self._table_depth += 1
            if self._table_depth == 1:
                self._outer_parts = self.parts
                self._table_buf = []
                self.parts = self._table_buf
                self._table_cells = 0
            return
        if tag == "tr":
            return
        if tag in ("td", "th"):
            if self._table_depth:
                self._table_cells += 1
            return

    def handle_endtag(self, tag: str) -> None:
        tag = tag.lower()
        if tag in _SKIP_TAGS:
            if self._skip_depth:
                self._skip_depth -= 1
            return
        if self._skip_depth:
            return

        if tag in ("b", "strong") and self._bold:
            self._emit_inline("**")
            self._bold -= 1
            return
        if tag in ("i", "em") and self._italic:
            self._emit_inline("*")
            self._italic -= 1
            return
        if tag in ("code", "tt") and self._code:
            self._emit_inline("`")
            self._code -= 1
            return

        if tag == "a":
            if self._in_anchor_name is not None:
                self._in_anchor_name = None
                return
            if self._link_href is None:
                return
            text = "".join(self._link_text)
            # tidy bold spaces inside link text
            text = re.sub(r"\*\*\s+", "**", text)
            text = re.sub(r"\s+\*\*", "**", text)
            text = text.strip()
            href = self._link_href
            self._link_href = None
            self._link_text = []
            if not text and not href:
                return
            self._emit(self.rewrite_link(href, text or href))
            return

        if tag in _HEADER:
            self._pending_header_id = None
            self._emit("\n\n")
            return
        if tag in ("p", "div"):
            self._emit("\n\n")
            return
        if tag in ("ul", "ol"):
            if self._list_stack:
                self._list_stack.pop()
            if self._li_index:
                self._li_index.pop()
            self._emit("\n\n")
            return
        if tag == "li":
            return

        if tag == "table":
            if self._table_depth == 1 and self._table_buf is not None and self._outer_parts is not None:
                body = "".join(self._table_buf).strip()
                body = re.sub(r"^`+|`+$", "", body).strip()
                self.parts = self._outer_parts
                self._table_buf = None
                self._outer_parts = None
                self._table_depth = 0
                if body:
                    # 1C tip/note box → blockquote
                    quoted = "\n".join(
                        f"> {line}" if line.strip() else ">"
                        for line in body.splitlines()
                    )
                    self._emit(quoted + "\n\n")
                self._table_cells = 0
                return
            if self._table_depth:
                self._table_depth -= 1
            return

    def handle_data(self, data: str) -> None:
        if self._skip_depth or not data:
            return
        if self._link_href is not None:
            self._link_text.append(data)
            return
        self._emit(data)

    def _emit_inline(self, s: str) -> None:
        """Bold/italic/code markers: stay inside link buffer when collecting a link."""
        if self._link_href is not None:
            self._link_text.append(s)
        else:
            self.parts.append(s)

    def _emit(self, s: str) -> None:
        self.parts.append(s)

    def _ensure_blank(self) -> None:
        text = "".join(self.parts)
        if not text.endswith("\n\n"):
            if text.endswith("\n"):
                self.parts.append("\n")
            elif text:
                self.parts.append("\n\n")

    def _close_inline(self) -> None:
        while self._bold:
            self._emit_inline("**")
            self._bold -= 1
        while self._italic:
            self._emit_inline("*")
            self._italic -= 1
        while self._code:
            self._emit_inline("`")
            self._code -= 1


def _normalize_md(text: str) -> str:
    text = text.replace("\r\n", "\n").replace("\r", "\n")
    text = re.sub(r"[ \t]+\n", "\n", text)
    text = re.sub(r"\n{3,}", "\n\n", text)
    # empty bold
    text = re.sub(r"\*\*\s*\*\*", "", text)
    # **Товар **– → **Товар** – (trailing spaces move outside bold)
    def _fix_bold(m: re.Match[str]) -> str:
        inner = m.group(1)
        core = inner.rstrip()
        pad = inner[len(core) :]
        return f"**{core}**{pad}"

    text = re.sub(r"\*\*([^*\n]+)\*\*", _fix_bold, text)
    text = text.replace("****", "")
    return text.strip() + "\n"


def extract_h1(html: str) -> str | None:
    m = re.search(r"<h1[^>]*>(.*?)</h1>", html, flags=re.IGNORECASE | re.DOTALL)
    if not m:
        return None
    raw = re.sub(r"<[^>]+>", "", m.group(1))
    raw = re.sub(r"\s+", " ", raw).strip()
    return raw or None


def html_to_markdown(
    html: str,
    *,
    rewrite_link: LinkRewriter | None = None,
    strip_first_h1: str | None = None,
) -> str:
    """Convert 1C help HTML to GitHub/Gitea-flavoured Markdown."""
    parser = _HelpHTMLParser(rewrite_link=rewrite_link)
    parser.feed(html)
    parser.close()
    md = _normalize_md("".join(parser.parts))

    if strip_first_h1:
        esc = re.escape(strip_first_h1.strip())
        md = re.sub(rf"^#\s+{esc}\s*\n+", "", md, count=1, flags=re.IGNORECASE)

    md = re.sub(r"\n\|\s*\n", "\n", md)
    md = _toc_paragraphs_to_list(md)
    return _normalize_md(md)


_TOC_LINK_LINE = re.compile(r"^\[([^\]]+)\]\(#([^)]+)\)$")


def _toc_paragraphs_to_list(md: str) -> str:
    """Turn leading consecutive [text](#id) paragraphs into a bullet TOC."""
    lines = md.split("\n")
    out: list[str] = []
    i = 0
    # skip leading blanks
    while i < len(lines) and not lines[i].strip():
        out.append(lines[i])
        i += 1
    # keep intro paragraphs until we hit TOC-looking run
    # Heuristic: a run of ≥2 lines that are only markdown fragment links
    while i < len(lines):
        # collect potential TOC run starting at i (allow blank lines inside)
        j = i
        toc_items: list[str] = []
        while j < len(lines):
            s = lines[j].strip()
            if not s:
                # peek if next non-empty is still TOC
                k = j + 1
                while k < len(lines) and not lines[k].strip():
                    k += 1
                if k < len(lines) and _TOC_LINK_LINE.match(lines[k].strip()):
                    j = k
                    continue
                break
            if _TOC_LINK_LINE.match(s) and not s.startswith("#"):
                toc_items.append(s)
                j += 1
                continue
            break
        if len(toc_items) >= 2:
            for item in toc_items:
                out.append(f"- {item}")
            out.append("")
            i = j
            continue
        out.append(lines[i])
        i += 1
    return "\n".join(out)


def default_link_rewrite(href: str, text: str, meta_to_title: dict[str, str]) -> str:
    """Rewrite href into markdown / wiki link."""
    href = href.strip()
    text = text.strip() or href

    if href.startswith("#"):
        # in-page TOC → markdown link to <a id="…">
        anchor = href[1:]
        plain = text.replace("**", "").replace("*", "").strip()
        if anchor:
            return f"[{plain}](#{anchor})"
        return plain

    if href.startswith(("http://", "https://", "mailto:")):
        return f"[{text}]({href})"

    m = re.match(
        r"^([A-Za-z]+(?:\.[^/#\s]+)+)/Help(?:#(.*))?$",
        unquote(href),
    )
    if m:
        meta_key = m.group(1)
        title = meta_to_title.get(meta_key)
        if title:
            if text == title or text == meta_key:
                return f"[[{title}]]"
            return f"[[{text}|{title}]]"
        return f"{text} (`{meta_key}`)"

    if re.search(r"\.(png|jpe?g|gif|webp|bmp)$", href, re.I):
        return f"![{text}]({href})"

    return text