"""
Run-folder naming + content hashing for doocus.

Reuses meetus's `YYYYMMDD-NNN-<stem>` run-folder convention (see
meetus/output_manager.py) so both trees look the same. Kept here to keep doocus
self-contained; meetus could adopt this helper later.
"""
from pathlib import Path
from datetime import datetime
import hashlib


def sha256_file(path: Path, chunk: int = 1 << 20) -> str:
    """Streaming sha256 of a file — never loads the whole file into memory."""
    h = hashlib.sha256()
    with open(path, "rb") as f:
        for block in iter(lambda: f.read(chunk), b""):
            h.update(block)
    return h.hexdigest()


def resolve_run_dir(base_output_dir: Path, stem: str, use_cache: bool = True) -> Path:
    """Return (creating if needed) the run folder for `stem` under `base_output_dir`.

    Mirrors meetus/output_manager.py:37-84 — reuse the most recent
    `*-<stem>` folder when caching, else create `YYYYMMDD-NNN-<stem>` with the
    next run number for today.
    """
    base = Path(base_output_dir)

    if use_cache and base.exists():
        existing = sorted(
            [d for d in base.iterdir() if d.is_dir() and d.name.endswith(f"-{stem}")],
            reverse=True,
        )
        if existing:
            return existing[0]

    date_str = datetime.now().strftime("%Y%m%d")
    next_run = 1
    if base.exists():
        nums = []
        for d in base.iterdir():
            if d.is_dir() and d.name.startswith(date_str) and d.name.endswith(f"-{stem}"):
                parts = d.name.split("-")
                if len(parts) >= 2 and parts[1].isdigit():
                    nums.append(int(parts[1]))
        next_run = max(nums) + 1 if nums else 1

    run_dir = base / f"{date_str}-{next_run:03d}-{stem}"
    run_dir.mkdir(parents=True, exist_ok=True)
    return run_dir