"""Ephemeral workspace dirs and dataset staging for agent runs.

Each runner allocates `runs/<agent>/<task>/<timestamp>/` so concurrent runs
don't collide and post-mortems are always recoverable from disk.
"""

from __future__ import annotations

import datetime as dt
from pathlib import Path


def make_workspace(agent: str, task: str, root: Path | None = None) -> Path:
    root = Path(root) if root else Path.cwd() / "runs"
    ts = dt.datetime.now().strftime("%Y%m%d-%H%M%S")
    ws = root / agent / task / ts
    ws.mkdir(parents=True, exist_ok=False)
    return ws


def stage_dataset(src_dir: Path, dst_dir: Path, files: list[str]) -> None:
    """Symlink each `files[i]` from src_dir into dst_dir.

    Symlinks (vs copies) keep large CSVs on the cache disk; the agent reads
    from src via the link transparently.
    """
    dst_dir.mkdir(parents=True, exist_ok=True)
    for f in files:
        s = src_dir / f
        if not s.exists():
            raise SystemExit(f"Missing dataset file: {s}")
        d = dst_dir / f
        if d.is_symlink() or d.exists():
            d.unlink()
        d.symlink_to(s.resolve())