"""Local Markdown to PDF rendering."""

from __future__ import annotations

import html
import os
import re
import shutil
import subprocess
import tempfile
from pathlib import Path


_IMAGE_RE = re.compile(r"^!\[([^]]*)\]\((?:<([^>]+)>|([^\s)]+))\)$")
_HEADING_RE = re.compile(r"^(#{1,6})\s+(.+)$")
_ORDERED_RE = re.compile(r"^\d+[.)]\s+(.+)$")
_UNORDERED_RE = re.compile(r"^[-*+]\s+(.+)$")
_MATH_RE = re.compile(r"(\$\$.+?\$\$|(?<!\\)\$(?!\$).+?(?<!\\)\$)", re.DOTALL)
_BOLD_RE = re.compile(r"\*\*(.+?)\*\*", re.DOTALL)
_LINK_RE = re.compile(r"\[([^]]+)]\(([^)]+)\)")


class PdfBuilder:
    """Render the Markdown subset produced by MarkdownBuilder as a styled PDF."""

    def __init__(self, browser: str | None = None) -> None:
        self._browser = browser

    @staticmethod
    def _render_math(source: str, *, display: bool) -> str:
        try:
            from latex2mathml.converter import convert
        except ImportError as error:
            raise RuntimeError(
                "PDF formulas require latex2mathml: pip install latex2mathml"
            ) from error

        try:
            mathml = convert(source.strip())
        except Exception as error:
            raise ValueError(f"Invalid LaTeX formula: {source}") from error
        css_class = "math display" if display else "math inline"
        return f'<span class="{css_class}">{mathml}</span>'

    @classmethod
    def _render_plain_inline(cls, source: str) -> str:
        parts: list[str] = []
        cursor = 0
        for match in _BOLD_RE.finditer(source):
            parts.append(html.escape(source[cursor:match.start()]))
            parts.append(f"<strong>{html.escape(match.group(1))}</strong>")
            cursor = match.end()
        parts.append(html.escape(source[cursor:]))
        rendered = "".join(parts)

        def link(match: re.Match[str]) -> str:
            label = html.escape(match.group(1))
            target = html.escape(match.group(2), quote=True)
            return f'<a href="{target}">{label}</a>'

        return _LINK_RE.sub(link, rendered)

    @classmethod
    def _render_inline(cls, source: str) -> str:
        result: list[str] = []
        cursor = 0
        for match in _MATH_RE.finditer(source):
            result.append(cls._render_plain_inline(source[cursor:match.start()]))
            token = match.group(0)
            display = token.startswith("$$")
            formula = token[2:-2] if display else token[1:-1]
            result.append(cls._render_math(formula, display=display))
            cursor = match.end()
        result.append(cls._render_plain_inline(source[cursor:]))
        return "".join(result)

    @staticmethod
    def _image_uri(markdown_path: Path, image_path: str) -> str:
        path = Path(image_path)
        if not path.is_absolute():
            path = markdown_path.parent / path
        path = path.resolve()
        if not path.is_file():
            raise FileNotFoundError(f"Markdown image not found: {path}")
        return path.as_uri()

    @classmethod
    def _render_blocks(cls, markdown: str, markdown_path: Path) -> str:
        lines = markdown.splitlines()
        blocks: list[str] = []
        index = 0
        first_heading = True

        while index < len(lines):
            line = lines[index].strip()
            if not line:
                index += 1
                continue

            heading = _HEADING_RE.match(line)
            if heading:
                level = min(len(heading.group(1)), 4)
                title_class = ' class="document-title"' if first_heading else ""
                blocks.append(
                    f"<h{level}{title_class}>"
                    f"{cls._render_inline(heading.group(2))}</h{level}>"
                )
                first_heading = False
                index += 1
                continue

            image = _IMAGE_RE.match(line)
            if image:
                alt = image.group(1).strip()
                source = image.group(2) or image.group(3)
                uri = cls._image_uri(markdown_path, source)
                caption = (
                    f"<figcaption>{cls._render_inline(alt)}</figcaption>"
                    if alt else ""
                )
                blocks.append(
                    "<figure>"
                    f'<img src="{html.escape(uri, quote=True)}" alt="{html.escape(alt, quote=True)}">'
                    f"{caption}</figure>"
                )
                index += 1
                continue

            if line.startswith(">"):
                quote: list[str] = []
                while index < len(lines) and lines[index].lstrip().startswith(">"):
                    quote.append(lines[index].lstrip()[1:].strip())
                    index += 1
                blocks.append(
                    f"<blockquote>{cls._render_inline(' '.join(quote))}</blockquote>"
                )
                continue

            ordered = _ORDERED_RE.match(line)
            unordered = _UNORDERED_RE.match(line)
            if ordered or unordered:
                pattern = _ORDERED_RE if ordered else _UNORDERED_RE
                tag = "ol" if ordered else "ul"
                items: list[str] = []
                while index < len(lines):
                    item = pattern.match(lines[index].strip())
                    if not item:
                        break
                    items.append(f"<li>{cls._render_inline(item.group(1))}</li>")
                    index += 1
                blocks.append(f"<{tag}>{''.join(items)}</{tag}>")
                continue

            if line.startswith("$$") and line.endswith("$$") and len(line) > 4:
                blocks.append(cls._render_math(line[2:-2], display=True))
                index += 1
                continue

            paragraph = [line]
            index += 1
            while index < len(lines) and lines[index].strip():
                candidate = lines[index].strip()
                if (
                    _HEADING_RE.match(candidate)
                    or _IMAGE_RE.match(candidate)
                    or candidate.startswith(">")
                    or _ORDERED_RE.match(candidate)
                    or _UNORDERED_RE.match(candidate)
                ):
                    break
                paragraph.append(candidate)
                index += 1
            blocks.append(f"<p>{cls._render_inline(' '.join(paragraph))}</p>")

        return "\n".join(blocks)

    @staticmethod
    def _document(body: str, title: str) -> str:
        return f"""<!doctype html>
<html lang="ru">
<head>
<meta charset="utf-8">
<title>{html.escape(title)}</title>
<style>
  @page {{
    size: A4;
    margin: 19mm 18mm 20mm;
    @bottom-center {{
      content: "SUMKA  ·  " counter(page);
      color: #718096;
      font: 8.5pt "Ubuntu", "DejaVu Sans", sans-serif;
      letter-spacing: .08em;
    }}
  }}
  * {{ box-sizing: border-box; }}
  html {{ color: #172033; font-family: "Ubuntu", "DejaVu Sans", sans-serif; }}
  body {{ margin: 0; font-size: 10.7pt; line-height: 1.62; }}
  h1, h2, h3, h4 {{ color: #102a43; line-height: 1.22; break-after: avoid; }}
  h1 {{ font-size: 28pt; }}
  h2 {{ font-size: 21pt; margin: 1.2em 0 .55em; }}
  h3 {{ font-size: 15.5pt; margin: 1.45em 0 .5em; padding-bottom: .22em;
        border-bottom: 1px solid #d9e2ec; }}
  h4 {{ font-size: 12.5pt; margin: 1.25em 0 .4em; color: #1f5f8b; }}
  .document-title {{ margin: 0 0 1.15em; padding: .75em .9em .8em;
      border-left: 5px solid #2f80ed;
      background: linear-gradient(120deg, #eef6ff, #f8fbff 70%);
      border-radius: 0 10px 10px 0; }}
  p {{ margin: 0 0 .85em; text-align: justify; hyphens: auto; orphans: 3; widows: 3; }}
  strong {{ color: #0f3557; font-weight: 700; }}
  ul, ol {{ margin: .3em 0 1em; padding-left: 1.55em; }}
  li {{ margin: .24em 0; padding-left: .2em; }}
  li::marker {{ color: #2f80ed; font-weight: 700; }}
  blockquote {{ margin: 1.1em 0; padding: .8em 1em .8em 1.15em;
      border-left: 4px solid #f2b84b; background: #fff8e8; color: #483b22;
      border-radius: 0 8px 8px 0; break-inside: avoid; }}
  figure {{ margin: 1.25em auto 1.45em; text-align: center; break-inside: avoid; }}
  figure img {{ display: block; max-width: 100%; max-height: 188mm; margin: auto;
      object-fit: contain; border: 1px solid #d9e2ec; border-radius: 7px;
      box-shadow: 0 5px 18px rgba(23, 32, 51, .12); }}
  figcaption {{ margin: .55em auto 0; max-width: 88%; color: #637083;
      font-size: 8.7pt; line-height: 1.4; }}
  .math.inline {{ display: inline-block; white-space: nowrap; vertical-align: -.12em; }}
  .math.display {{ display: block; margin: 1.1em auto; padding: .75em 1em;
      overflow: hidden; text-align: center; background: #f6f9fc;
      border: 1px solid #e3eaf2; border-radius: 7px; break-inside: avoid; }}
  math {{ font-family: "STIX Two Math", "STIX Math", "Cambria Math", serif; }}
  a {{ color: #1769aa; text-decoration: none; }}
</style>
</head>
<body>{body}</body>
</html>
"""

    def _find_browser(self) -> str:
        if self._browser:
            browser = shutil.which(self._browser) or self._browser
            if Path(browser).is_file():
                return browser
            raise RuntimeError(f"PDF browser not found: {self._browser}")

        for candidate in (
            "chromium",
            "chromium-browser",
            "google-chrome",
            "google-chrome-stable",
        ):
            browser = shutil.which(candidate)
            if browser:
                return browser
        raise RuntimeError("PDF generation requires Chromium or Google Chrome")

    def build(self, markdown_path: str | Path, output_path: str | Path) -> None:
        source = Path(markdown_path).resolve()
        destination = Path(output_path).resolve()
        if not source.is_file():
            raise FileNotFoundError(f"Markdown file not found: {source}")

        markdown = source.read_text(encoding="utf-8")
        body = self._render_blocks(markdown, source)
        title_match = re.search(r"^#{1,6}\s+(.+)$", markdown, re.MULTILINE)
        title = title_match.group(1).replace("**", "") if title_match else "Конспект"
        document = self._document(body, title)
        browser = self._find_browser()
        destination.parent.mkdir(parents=True, exist_ok=True)

        with tempfile.TemporaryDirectory(prefix=".sumka-pdf-", dir=source.parent) as tmp:
            workdir = Path(tmp)
            html_path = workdir / "document.html"
            html_path.write_text(document, encoding="utf-8")
            command = [
                browser,
                "--headless",
                "--disable-gpu",
                "--disable-dev-shm-usage",
                "--allow-file-access-from-files",
                "--no-pdf-header-footer",
                f"--user-data-dir={workdir / 'profile'}",
                f"--print-to-pdf={destination}",
                html_path.as_uri(),
            ]
            if os.geteuid() == 0:
                command.insert(1, "--no-sandbox")
            try:
                result = subprocess.run(
                    command,
                    capture_output=True,
                    text=True,
                    timeout=120,
                    check=False,
                )
            except subprocess.TimeoutExpired as error:
                raise RuntimeError("Chromium timed out while generating PDF") from error

            if result.returncode != 0 or not destination.is_file():
                details = (result.stderr or result.stdout).strip()
                raise RuntimeError(
                    f"Chromium failed to generate PDF: {details or result.returncode}"
                )