from __future__ import annotations
from pathlib import Path
import tomlkit

def parse_frontmatter(path: Path) -> tuple[dict, str]:
    """Parse TOML frontmatter delimited by +++. Returns (frontmatter_dict, body_str)."""
    text = path.read_text(encoding="utf-8")
    if not text.startswith("+++"):
        raise ValueError(f"No TOML frontmatter found in {path}")
    parts = text.split("+++", 2)
    if len(parts) < 3:
        raise ValueError(f"Malformed frontmatter in {path}")
    _, toml_block, body = parts
    fm = dict(tomlkit.loads(toml_block))
    return fm, body.lstrip("\n")

def write_frontmatter(path: Path, frontmatter: dict, body: str) -> None:
    """Write frontmatter + body back to file, preserving TOML format."""
    text = path.read_text(encoding="utf-8")
    parts = text.split("+++", 2)
    if len(parts) < 3:
        raise ValueError(f"Malformed frontmatter in {path}")
    _, original_toml, _ = parts
    doc = tomlkit.loads(original_toml)
    for k, v in frontmatter.items():
        doc[k] = v
    new_text = f"+++\n{tomlkit.dumps(doc).strip()}\n+++\n\n{body}"
    path.write_text(new_text, encoding="utf-8")