# Source code for canlib.canlib.envvar

    from .enums import EnvVarType
    from .exceptions import EnvvarNameError

    class DataEnvVar:
        """Represent an environment variable declared as ``char*`` in t programs.

        This attribute object behaves like an array of bytes:

            >>> ch.envvar.DataVal[100:141]
            b'ot working? Messages can be sent to and r'

        The size of the array must match what was defined in the t program. One way
        to do this is to left align the data and fill with zeros:

            >>> data = 'My new data'.encode('utf-8')
            >>> size = len(ch.envvar.DataVal)
            >>> ch.envvar.DataVal = data.ljust(size, b'\\0')
            >>> ch.envvar.DataVal[:15]
            b'My new data\\x00\\x00\\x00\\x00'

        Another way is to use slicing:

            >>> ch.envvar.DataVal[3:6] = b'old'
            >>> ch.envvar.DataVal[:15]
            b'My old data\\x00\\x00\\x00\\x00'

        """

        def __init__(self, channel, handle, name, size):
            self._channel = channel
            self._handle = handle
            self._name = name  # for debugging only
            self._size = size

        def __eq__(self, other):
            value = self._channel.script_envvar_get_data(self._handle, len=self._size, start=0)
            return bytes(value) == other

        def __len__(self):
            return self._size

        # required in Python 2
        def __ne__(self, other):
            return not self == other

        def __getitem__(self, key):
            if isinstance(key, slice):

                # fb:25388, BLB-1104
                # size = key.stop - key.start
                # value = self._channel.script_envvar_get_data(self._handle, len=size, start=key.start)
                # Workaround:
                value = self._channel.script_envvar_get_data(self._handle, len=self._size, start=0)
                value = value[key.start: key.stop]

                if key.step is not None:
                    raise NotImplementedError('step is not yet implemented in read')
            else:
                # fb:25388, BLB-1104
                # value = self._channel.script_envvar_get_data(self._handle, len=1, start=key)
                # Workaround:
                value = self._channel.script_envvar_get_data(self._handle, len=self._size, start=0)
                value = value[key]

            return value

        def __setitem__(self, key, value):
            if isinstance(key, slice):

                # fb:25388, BLB-1104
                # size = key.stop - key.start
                # self._channel.script_envvar_set_data(self._handle, value, len=size, start=key.start)
                # Workaround:
                data = self._channel.script_envvar_get_data(self._handle, len=self._size, start=0)
                pre_data = data[: int(key.start or 0)]
                if key.stop is not None:
                    post_data = data[key.stop:]
                else:
                    post_data = b''
                data = pre_data + value + post_data
                self._channel.script_envvar_set_data(self._handle, data, len=self._size, start=0)

                if key.step is not None:
                    raise NotImplementedError('step is not yet implemented in set')
            else:
                # fb:25388, BLB-1104
                # self._channel.script_envvar_set_data(self._handle, value, len=1, start=key)
                data = self._channel.script_envvar_get_data(self._handle, len=self._size, start=0)
                data = data[:key] + value + data[key + 1:]
                self._channel.script_envvar_set_data(self._handle, data, len=self._size, start=0)

        def __str__(self):
            value = self._channel.script_envvar_get_data(self._handle, len=self._size, start=0)
            return value.decode('utf-8')

    class EnvVar:
        """Used to access environment variables in t programs.

        The environment variables are accessed as an attribute with the same name
        as declared in the t program. If we have a running t program, which has
        defined the following environment variables::

            envvar
            {
              int   IntVal;
              float FloatVal;
              char  DataVal[512];
            }

        We access the first two using `EnvVar`:

            >>> ch.envvar.IntVal
            0
            >>> ch.envvar.IntVal = 3
            >>> ch.envvar.IntVal
            3
            >>> ch.envvar.FloatVal
            15.0

        The third environment variable, declared as ``char*``, is accessed using `.DataEnvVar`.

        """

        class Attrib:
            def __init__(self, handle=None, type_=None, size=None):
                self.handle = handle
                self.type_ = type_
                self.size = size

        def __init__(self, channel):
            self.__dict__['_channel'] = channel
            self.__dict__['_attrib'] = {}

        def _ensure_open(self, name):
            if name.startswith('_'):
                raise EnvvarNameError(name)
            # We just check the handle here
            if name not in self.__dict__['_attrib']:
                self._attrib[name] = EnvVar.Attrib(*self._channel.scriptEnvvarOpen(name))

        def __getattr__(self, name):
            self._ensure_open(name)
            handle = self._attrib[name].handle
            if self._attrib[name].type_ == EnvVarType.INT:
                value = self._channel.scriptEnvvarGetInt(handle)
            elif self._attrib[name].type_ == EnvVarType.FLOAT:
                value = self._channel.scriptEnvvarGetFloat(handle)
            elif self._attrib[name].type_ == EnvVarType.STRING:
                size = self._attrib[name].size
                value = DataEnvVar(self._channel, handle, name, size)
            else:
                msg = "getting is not implemented for type {type_}"
                msg = msg.format(type_=self._attrib[name].type_)
                raise TypeError(msg)
            return value

        def __setattr__(self, name, value):
            self._ensure_open(name)
            handle = self._attrib[name].handle
            if self._attrib[name].type_ == EnvVarType.INT:
                value = self._channel.scriptEnvvarSetInt(handle, value)
            elif self._attrib[name].type_ == EnvVarType.FLOAT:
                value = self._channel.scriptEnvvarSetFloat(handle, value)
            elif self._attrib[name].type_ == EnvVarType.STRING:
                size = self._attrib[name].size
                if len(value) != size:
                    raise ValueError("Size of data and envvar is not same")
                self._channel.script_envvar_set_data(handle, value, len=size, start=0)
            else:
                msg = "setting is not implemented for type {type_}"
                msg = msg.format(type_=self._attrib[name].type_)
                raise TypeError(msg)