"""Small runtime helpers for the isolated M2RL execution directory."""
from __future__ import annotations

import hashlib
import json
import os
import re
import tempfile
from pathlib import Path


def require_allocation():
    job = os.environ.get('SLURM_JOB_ID', '')
    cgroup = Path('/proc/self/cgroup').read_text()
    if not job.isdigit() or not re.search(r'(?:/|^)job_' + job + r'(?:/|$)', cgroup):
        raise RuntimeError('M2RL sustained work requires a real Slurm cgroup')
    if not os.environ.get('SLURM_CPUS_PER_TASK') or not os.environ.get('SLURM_MEM_PER_NODE'):
        raise RuntimeError('Explicit CPU and memory allocation required')
    return {'job_id': job, 'cgroup': cgroup.strip(),
            'cpus': os.environ['SLURM_CPUS_PER_TASK'],
            'memory_mb': os.environ['SLURM_MEM_PER_NODE']}


def sha256(path):
    digest = hashlib.sha256()
    with open(path, 'rb') as stream:
        for chunk in iter(lambda: stream.read(1024 * 1024), b''):
            digest.update(chunk)
    return digest.hexdigest()


def atomic_json(path, value):
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    fd, temporary = tempfile.mkstemp(prefix=path.name + '.', dir=path.parent)
    try:
        with os.fdopen(fd, 'w') as stream:
            json.dump(value, stream, indent=2, ensure_ascii=False, allow_nan=False)
            stream.write('\n')
            stream.flush()
            os.fsync(stream.fileno())
        os.replace(temporary, path)
        directory = os.open(path.parent, os.O_DIRECTORY)
        try:
            os.fsync(directory)
        finally:
            os.close(directory)
    finally:
        if os.path.exists(temporary):
            os.unlink(temporary)