M209 Class
==========

Naturally, the ``m209`` library includes a class that simulates a M-209
converter. The :class:`~m209.converter.M209` class allows you to experiment
with all moving parts of an M-209, including encrypting and decrypting
messages. Keep in mind there is a higher level class,
:class:`~m209.procedure.StdProcedure`, that encapsulates all the steps of the
standard encrypting and decrypting operations, including generating indicators
and placing or removing them from messages. However if you need lower-level
access or you are inventing your own procedures, you would use the M209 class
directly.

.. class:: m209.converter.M209([lugs=None[, pin_list=None]])

   The ``M209`` class takes the following optional arguments.

  :param lugs: either a lug settings list or string as per :meth:`set_drum_lugs`
  :param pin_list: a list of six strings each formatted as per :ref:`pin-settings`

``M209`` objects have the following attributes.

   .. attribute:: letter_count

      This attribute represents the *letter counter* functionality. It is an
      integer that is incremented after every letter is encrypted or decrypted.
      It may be set to any integer value or examined at any time.

``M209`` objects support the following methods.

   .. method:: set_pins(n, effective_pins)

      Sets the pin settings on the specified key wheel ``n``.

      :param n: an integer between 0-5, inclusive. Key wheel 0 is the 
         left-most wheel and wheel 5 is the right-most.

      :param effective_pins: an iterable of letters whose pins are slid to
        the "effective" position (to the right). See :ref:`pin-settings`.

   .. method:: set_all_pins(pin_list)

      Sets all key wheel pins according to the supplied pin list.

      :param pin_list: must either be ``None`` or a 6-element list of strings
         where each string element is as described in :ref:`pin-settings`.
         If ``None``, all pins in all key wheels are moved to the ineffective position.

   .. method:: set_drum_lugs(lug_list)

      Sets the drum lugs according to the given ``lug_list`` parameter.

      If ``lug_list`` is ``None`` or empty, all lugs will be placed in neutral
      positions.

      Otherwise, the ``lug_list`` can either be a list or a string.

      If ``lug_list`` is passed a list, it must be a list of 1 or 2-tuple integers,
      where each integer is between 0-5, inclusive, and represents a 0-based
      key wheel position. The list can not be longer than 27 items. Only lug
      bars with lugs in non-neutral positions need be listed. Lug bars with one
      lug in a non-neutral position are represented by a 1-tuple. Bars with
      2 non-netural lugs are represented as a 2-tuple.

      If ``lug_list`` is passed as a string, it is assumed to be in key list
      format as described in :ref:`lug-settings`.

      Example::

         m = M209()
         m.set_drum_lugs('1-0 2-0*2 0-3 0-5*3 0-6 2-4 3-6')

         # or equivalently
         m.set_drum_lugs([(0, ), (1, ), (1, ), (2, ), (4, ), (4, ), (4, ), (5, ), (1, 3), (2, 5)])


   .. method:: set_key_wheel(n, c)

      Set key wheel ``n`` to the letter ``c``.

      :param n: an integer between 0-5 where key wheel 0 is the leftmost key wheel,
         and 5 is the rightmost
      :param c: a 1-letter string valid for key wheel ``n``
      :raises KeyWheelError: if ``c`` is not valid for wheel ``n``

   .. method:: set_key_wheels(s)

      Set the key wheels from left to right to the six letter string ``s``.

      :raises KeyWheelError: if any letter in ``s`` is not valid for the corresponding key wheel

   .. method:: set_random_key_wheels()

      Sets the six key wheels to random letters.

      :returns: a string of length six representing the new key wheel settings

   .. method:: get_settings()

      Returns the current key settings.

      :returns: a named tuple of ``(lugs, pin_list)`` representing the current
         key settings. ``lugs`` will be in string format.

   .. method:: encrypt(plaintext[, group=True[, spaces=True]])

      Performs an encrypt operation on the given plaintext and returns the
      encrypted ciphertext as a string.

      :param plaintext: the text string to encrypt
      :param group: if ``True``, the ciphertext string will be grouped into 5-letter
         groups, separated by spaces
      :param spaces: if ``True``, space characters in the input plaintext will
         automatically be treated as ``Z`` characters. Otherwise spaces in the
         plaintext will raise an ``M209Error``.
      :returns: the ciphertext as a string

   .. method:: decrypt(ciphertext[, spaces=True[, z_sub=True]])

      Performs a decrypt operation on the given ciphertext and returns the
      decrypted plaintext as a string.

      :param ciphertext: the text string to decyrpt
      :param spaces: if ``True``, spaces will be allowed in the input ciphertext and
         ignored. Otherwise space characters will raise an ``M209Error``.
         This is useful if the input ciphertext is in 5-letter groups, separated
         by spaces.
      :param z_sub: if ``True``, ``Z`` characters in the output plaintext will be
         replaced by space characters, just like an actual M-209.
      :returns: the plaintext as a string

Example:

>>> from m209.converter import M209
>>> m = M209()
>>> m.set_drum_lugs('1-0 2-0*2 0-3 0-5*3 0-6 2-4 3-6')
>>> pin_list = [
...     'FGIKOPRSUVWYZ',
...     'DFGKLMOTUY',
...     'ADEFGIORTUVX',
...     'ACFGHILMRSU',
...     'BCDEFJKLPS',
...     'EFGHIJLMNP'
... ]
>>> m.set_all_pins(pin_list)
>>> m.set_key_wheels('FFEGJP')
>>> ct = m.encrypt('THE PIZZA HAS ARRIVED')
>>> ct
'QBCHU WCCDI YFNCH LOZJY G'
>>> m.set_key_wheels('FFEGJP')
>>> pt = m.decrypt(ct)
>>> pt
'THE PI  A HAS ARRIVED'