#!/usr/bin/env python3
"""Check required lesson sections and local Markdown links."""

from __future__ import annotations

import re
import sys
from pathlib import Path


REQUIRED = (
    "本节目标",
    "前置知识",
    "问题动机",
    "核心",
    "实现指南",
    "扩展与联系",
    "精选例题",
    "总结与自检",
    "课后训练建议",
)


def main() -> int:
    root = Path(sys.argv[1] if len(sys.argv) > 1 else "课程")
    errors: list[str] = []
    lessons = [
        path
        for path in sorted(root.rglob("*.md"))
        if path.name != "README.md" and not path.name.startswith("00-")
    ]
    for path in lessons:
        text = path.read_text(encoding="utf-8")
        headings = "\n".join(re.findall(r"^#{1,6}\s+(.+)$", text, flags=re.MULTILINE))
        for required in REQUIRED:
            if required not in headings:
                errors.append(f"{path}: missing section containing {required!r}")
        if "<details>" not in text:
            errors.append(f"{path}: no folded hints/self-check content")
        if re.search(r"```(?:cpp|c\+\+)\n.*?\bint\s+main\s*\(", text, flags=re.DOTALL):
            errors.append(f"{path}: standalone C++ implementation must be an attachment")
        if re.search(r"^\\\[\s*$|^\\\]\s*$", text, flags=re.MULTILINE):
            errors.append(f"{path}: display LaTeX must use $$ delimiters, not \\[ or \\]")

    for path in sorted(root.rglob("*.md")):
        text = path.read_text(encoding="utf-8")
        prose = re.sub(r"```.*?```", "", text, flags=re.DOTALL)
        for target in re.findall(r"\[[^]]*\]\(([^)]+)\)", prose):
            target = target.split("#", 1)[0]
            if not target or re.match(r"(?:https?|mailto):", target):
                continue
            resolved = (path.parent / target).resolve()
            if not resolved.exists():
                errors.append(f"{path}: broken local link {target}")

    for error in errors:
        print(error, file=sys.stderr)
    print(f"lessons={len(lessons)} errors={len(errors)}")
    return 1 if errors else 0


if __name__ == "__main__":
    raise SystemExit(main())