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1 # Copyright (C) 2013 by Brian Neal.
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2 # This file is part of m209, the M-209 simulation.
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3 # m209 is released under the MIT License (see LICENSE.txt).
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4
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5 """This module contains the key wheel related classes for the M209
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6 simulation.
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7
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8 """
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9 from . import M209Error
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10
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11 class KeyWheelError(M209Error):
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12 """Exception class for all key wheel errors"""
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13 pass
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14
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15
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16 class KeyWheel:
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17 """Simulates a key wheel in a M209 converter"""
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18
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19 def __init__(self, letters, guide_letter, effective_pins=None):
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20 """Initialize a KeyWheel instance:
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21
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22 letters - an iterable of letters which appear on the wheel face
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23
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24 guide_letter - must be a letter that appears within the letters
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25 parameter. It indicates which letter affects the guide arm when the
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26 first letter in letters is displayed to the operator.
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27
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28 effective_pins - see the description of set_pins(), below.
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29
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30 """
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31 self.letters = list(letters)
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32 self.num_pins = len(self.letters)
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33
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34 self.letter_offsets = {letter : n for n, letter in enumerate(self.letters)}
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35
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36 if self.num_pins < 1:
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37 raise KeyWheelError("Too few key wheel letters")
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38
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39 # pin effectivity list:
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40 if effective_pins:
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41 self.set_pins(effective_pins)
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42 else:
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43 self.reset_pins()
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44
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45 try:
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46 self.guide_offset = self.letter_offsets[guide_letter]
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47 except KeyError:
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48 raise KeyWheelError("Invalid guide_letter")
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49
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50 # rotational position; 0 means first letter shown to operator
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51 self.pos = 0
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52
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53 def reset_pins(self):
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54 """Reset all pins to the ineffective state."""
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55 self.pins = [False] * self.num_pins
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56
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57 def set_pins(self, effective_pins):
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58 """Sets which pins are effective.
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59
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60 effective_pins - must be an iterable of letters whose pins are slide to
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61 the "effective" position (to the right). Letters not appearing in this
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62 sequence are considered to be in the "ineffective" position (to the
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63 left). If None or empty, all pins are set to be ineffective.
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64
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65 """
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66 self.reset_pins()
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67 for letter in effective_pins:
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68 try:
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69 n = self.letter_offsets[letter]
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70 except KeyError:
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71 raise KeyWheelError("Invalid pin: {}".format(letter))
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72 self.pins[n] = True
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73
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74 def rotate(self, steps=1):
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75 """Rotate the key wheel the given number of steps."""
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76 self.pos = (self.pos + steps) % self.num_pins
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77
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78 def display(self):
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79 """Returns the letter shown to the operator based on the current key
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80 wheel position.
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81
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82 """
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83 return self.letters[self.pos]
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84
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85 def guide_letter(self):
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86 """Returns the letter of the pin that is in position to effect the guide
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87 arm. To check to see if this pin will effect the guide arm, call
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88 is_effective().
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89
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90 """
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91 n = (self.pos + self.guide_offset) % self.num_pins
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92 return self.letters[n]
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93
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94 def is_effective(self):
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95 """Returns True if the key wheel, in the current position, has a pin in
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96 the effective position, and False otherwise.
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97
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98 """
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99 n = (self.pos + self.guide_offset) % self.num_pins
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100 return self.pins[n]
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101
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102 def set_pos(self, c):
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103 """Sets the position of the key wheel to the letter c."""
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104 try:
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105 self.pos = self.letter_offsets[c]
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106 except KeyError:
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107 raise KeyWheelError("Invalid position {}".format(c))
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