from __future__ import annotations

import re

import markdown as md_lib

from .errors import ValidationIssue


_HEADING_RE = re.compile(r"^(#{1,6})(\s+.*)$")


def extract_title(markdown_text: str, level: int, strict: bool, context: str, issues: list[ValidationIssue]) -> tuple[str, str] | None:
    pattern = re.compile(rf"^{'#' * level}\s+(.*)$", re.MULTILINE)
    matches = list(pattern.finditer(markdown_text))
    if strict and len(matches) != 1:
        issues.append(
            ValidationIssue(
                f"Expected exactly one level-{level} heading, found {len(matches)}",
                context=context,
            )
        )
        return None
    if not matches:
        issues.append(ValidationIssue(f"Missing level-{level} heading", context=context))
        return None

    match = matches[0]
    title = match.group(1).strip()
    if not title:
        issues.append(ValidationIssue("Heading title cannot be empty", context=context))
        return None

    lines = markdown_text.splitlines()
    line_index = markdown_text[: match.start()].count("\n")
    lines.pop(line_index)
    body = "\n".join(lines)
    body = _promote_headings(body)
    return title, body


def _promote_headings(text: str) -> str:
    promoted_lines = []
    for line in text.splitlines():
        match = _HEADING_RE.match(line)
        if not match:
            promoted_lines.append(line)
            continue
        hashes, rest = match.groups()
        level = len(hashes)
        if level > 1:
            level -= 1
        promoted_lines.append("#" * level + rest)
    return "\n".join(promoted_lines)


def convert_markdown(markdown_text: str, context: str, issues: list[ValidationIssue]) -> str | None:
    try:
        return md_lib.markdown(markdown_text, extensions=["extra"], output_format="html5")
    except Exception as exc:  # pragma: no cover - depends on markdown internals
        issues.append(ValidationIssue(f"Markdown conversion failed: {exc}", context=context))
        return None