"""Atomic content-addressed JSON and source artifact storage."""
import hashlib
import json
import os
from pathlib import Path
import tempfile


def canonical(value):
    return json.dumps(value, sort_keys=True, separators=(',', ':'), ensure_ascii=False,
                      allow_nan=False).encode('utf-8')


def atomic(path, data, immutable=False):
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    fd, name = tempfile.mkstemp(dir=path.parent, prefix='.write-')
    try:
        with os.fdopen(fd, 'wb') as stream:
            stream.write(data)
            stream.flush()
            os.fsync(stream.fileno())
        if immutable:
            try:
                os.link(name, path)
            except FileExistsError:
                if path.read_bytes() != data:
                    raise ValueError(f'immutable content mismatch: {path}') from None
        else:
            os.replace(name, path)
    finally:
        Path(name).unlink(missing_ok=True)


def put(root, kind, value):
    content = canonical(value)
    ident = hashlib.sha256(content).hexdigest()
    atomic(Path(root) / 'data' / kind / f'{ident}.json', content + b'\n', immutable=True)
    return ident


def get(root, kind, ident):
    if len(ident) != 64 or any(c not in '0123456789abcdef' for c in ident):
        raise ValueError('invalid content ID')
    value = json.loads((Path(root) / 'data' / kind / f'{ident}.json').read_text())
    if hashlib.sha256(canonical(value)).hexdigest() != ident:
        raise ValueError(f'integrity mismatch: {kind}/{ident}')
    return value


def all_records(root, kind):
    return [(p.stem, get(root, kind, p.stem))
            for p in sorted((Path(root) / 'data' / kind).glob('*.json'))]