import etcd3
import json

from functools import wraps

from uncloud import UncloudException
from uncloud.common import logger


class EtcdEntry:
    def __init__(self, meta_or_key, value, value_in_json=False):
        if hasattr(meta_or_key, 'key'):
            # if meta has attr 'key' then get it
            self.key = meta_or_key.key.decode('utf-8')
        else:
            # otherwise meta is the 'key'
            self.key = meta_or_key
        self.value = value.decode('utf-8')

        if value_in_json:
            self.value = json.loads(self.value)


def readable_errors(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        try:
            return func(*args, **kwargs)
        except etcd3.exceptions.ConnectionFailedError:
            raise UncloudException('Cannot connect to etcd: is etcd running as configured in uncloud.conf?')
        except etcd3.exceptions.ConnectionTimeoutError as err:
            raise etcd3.exceptions.ConnectionTimeoutError('etcd connection timeout.') from err
        except Exception:
            logger.exception('Some etcd error occured. See syslog for details.')

    return wrapper


class Etcd3Wrapper:
    @readable_errors
    def __init__(self, *args, **kwargs):
        self.client = etcd3.client(*args, **kwargs)

    @readable_errors
    def get(self, *args, value_in_json=False, **kwargs):
        _value, _key = self.client.get(*args, **kwargs)
        if _key is None or _value is None:
            return None
        return EtcdEntry(_key, _value, value_in_json=value_in_json)

    @readable_errors
    def put(self, *args, value_in_json=False, **kwargs):
        _key, _value = args
        if value_in_json:
            _value = json.dumps(_value)

        if not isinstance(_key, str):
            _key = _key.decode('utf-8')

        return self.client.put(_key, _value, **kwargs)

    @readable_errors
    def get_prefix(self, *args, value_in_json=False, raise_exception=True, **kwargs):
        try:
            event_iterator = self.client.get_prefix(*args, **kwargs)
            for e in event_iterator:
                yield EtcdEntry(*e[::-1], value_in_json=value_in_json)
        except Exception as err:
            if raise_exception:
                raise Exception('Exception in etcd_wrapper.get_prefix') from err
            else:
                logger.exception('Error in etcd_wrapper')
                return iter([])

    @readable_errors
    def watch_prefix(self, key, raise_exception=True, value_in_json=False):
        try:
            event_iterator, cancel = self.client.watch_prefix(key)
            for e in event_iterator:
                if hasattr(e, '_event'):
                    e = e._event
                    if e.type == e.PUT:
                        yield EtcdEntry(e.kv.key, e.kv.value, value_in_json=value_in_json)
        except Exception as err:
            if raise_exception:
                raise Exception('Exception in etcd_wrapper.get_prefix') from err
            else:
                logger.exception('Error in etcd_wrapper.watch_prefix')
                try:
                    cancel()
                except Exception:
                    pass
                return iter([])