"""Bounded runtime reconciliation of fixed host-agent result evidence."""

import json
import os
from pathlib import Path
import stat

from host_agent_state import MAX_STATE_BYTES
from runtime_security import reject_reparse_components


HOST_RESULT_DIRECTORY = Path('/data/host-agent-results')
HOST_ROOT_UID = 0
HOST_RUNTIME_GID = 10001


class HostResultError(RuntimeError):
    pass


def fixed_result_directory_is_safe():
    try:
        reject_reparse_components(HOST_RESULT_DIRECTORY)
        details = os.stat(HOST_RESULT_DIRECTORY, follow_symlinks=False)
        return (
            stat.S_ISDIR(details.st_mode)
            and details.st_uid == HOST_ROOT_UID
            and details.st_gid == HOST_RUNTIME_GID
            and stat.S_IMODE(details.st_mode) == 0o750
        )
    except Exception:
        return False


def _read_result(operation_id):
    path = HOST_RESULT_DIRECTORY / f'{operation_id}.json'
    descriptor = None
    try:
        flags = os.O_RDONLY | getattr(os, 'O_CLOEXEC', 0) | getattr(os, 'O_NOFOLLOW', 0)
        descriptor = os.open(path, flags)
        before = os.fstat(descriptor)
        if (
            not stat.S_ISREG(before.st_mode)
            or before.st_nlink != 1
            or before.st_uid != HOST_ROOT_UID
            or before.st_gid != HOST_RUNTIME_GID
            or stat.S_IMODE(before.st_mode) != 0o640
        ):
            raise HostResultError('host result metadata is invalid')
        with os.fdopen(descriptor, 'rb') as handle:
            descriptor = None
            payload = handle.read(MAX_STATE_BYTES + 1)
            after = os.fstat(handle.fileno())
        current = os.stat(path, follow_symlinks=False)
        identity = lambda item: (
            item.st_dev, item.st_ino, item.st_size,
            getattr(item, 'st_mtime_ns', None), getattr(item, 'st_ctime_ns', None),
        )
        if (
            len(payload) > MAX_STATE_BYTES
            or identity(before) != identity(after)
            or identity(after) != identity(current)
        ):
            raise HostResultError('host result changed during read')
        value = json.loads(payload.decode('ascii'))
        canonical = json.dumps(
            value, sort_keys=True, separators=(',', ':'), ensure_ascii=True,
            allow_nan=False,
        ).encode('ascii')
        if canonical != payload:
            raise HostResultError('host result is not canonical')
        return payload
    except FileNotFoundError:
        return None
    except HostResultError:
        raise
    except Exception:
        raise HostResultError('host result is invalid') from None
    finally:
        if descriptor is not None:
            os.close(descriptor)


def reconcile_pending_host_results(database, *, limit=32):
    if not fixed_result_directory_is_safe():
        return 0
    reconciled = 0
    for operation in database.pending_runtime_agent_operations(limit=limit):
        envelope = _read_result(operation['operation_id'])
        if envelope is None:
            continue
        if database.reconcile_runtime_operation_result(envelope) is not None:
            reconciled += 1
    return reconciled