# HG changeset patch
# User Brian Neal <bgneal@gmail.com>
# Date 1371176705 18000
# Node ID 19364133f86e87d4d256b1b87e3845ff068881e3
# Parent  986876a37f4acefbfa5e6938b69c1a505ad46e57
Started working on functions to generate a key list.

diff -r 986876a37f4a -r 19364133f86e m209/keylist/generate.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/m209/keylist/generate.py	Thu Jun 13 21:25:05 2013 -0500
@@ -0,0 +1,104 @@
+# Copyright (C) 2013 by Brian Neal.
+# This file is part of m209, the M-209 simulation.
+# m209 is released under the MIT License (see LICENSE.txt).
+
+"""This module contains routes to generate key lists."""
+
+import collections
+import random
+
+from .key_list import KeyList
+from ..converter import M209
+from .. import M209Error
+from ..data import KEY_WHEEL_DATA
+
+
+# Maximum number of attempts to generate valid settings before giving up and
+# raising a M209Error:
+MAX_ATTEMPTS = 128
+
+# Total number of pins on all 6 wheels:
+TOTAL_PINS = sum(len(letters) for letters, _ in KEY_WHEEL_DATA)
+
+
+def generate_key_list(indicator):
+    """Create a key list at random with the given indicator.
+
+    The procedure used is based upon manuals for the M-209 as found online:
+
+    [1]: TM-11-380, War Department, Technical Manual, Converter M-209, April 27,
+         1942.
+         http://maritime.org/tech/csp1500inst.htm
+
+    [2]: TM-11-380, War Department, Technical Manual, Converter M-209, M-209-A,
+         M-209-B (cipher) 17 March, 1944.
+         http://www.ilord.com/m209manual.html
+
+    Page 1 of reference [2] says: "This manual supercedes TM-11-380, 27 April
+    1942, and TM-11-380B, 20 September 1943."
+
+    """
+    lugs = generate_lugs()
+    pin_list = generate_pin_list()
+    letter_check = generate_letter_check(lugs, pin_list)
+
+    return KeyList(indicator=indicator, lugs=lugs, pin_list=pin_list,
+            letter_check=letter_check)
+
+
+def generate_lugs():
+    """Return random lug settings based on Army procedure."""
+    return ''
+
+
+def generate_pin_list():
+    """Return a random pin list based on Army procedure."""
+
+    cards = ['R'] * 78
+    cards.extend(['L'] * (156 - len(cards)))
+
+    for n in range(MAX_ATTEMPTS):
+        random.shuffle(cards)
+        deck = collections.deque(cards)
+        pin_list = []
+        for letters, _ in KEY_WHEEL_DATA:
+            pins = [c for c in letters if 'R' == deck.pop()]
+            pin_list.append(''.join(pins))
+
+        if pin_list_check(pin_list):
+            break
+    else:
+        raise M209Error("generate_pin_list: too many attempts")
+
+    return pin_list
+
+
+def generate_letter_check(pin_list, lugs):
+    """Return a letter check string for the given pin list and lug settings."""
+
+    m_209 = M209(lugs, pin_list)
+    m_209.set_key_wheels('A' * 6)
+    return m_209.encrypt('A' * 26, group=True)
+
+
+def pin_list_check(pin_list):
+    """Returns True if the supplied pin list meets Army procedure criteria.
+
+    To pass the check, the number of effective pins must be between 40-60%.
+    Furthermore, there cannot be more than 6 consecutive effective or
+    non-effective pins on any wheel.
+
+    """
+    num_eff = sum(len(s) for s in pin_list)
+    ratio = num_eff / TOTAL_PINS
+
+    if not (0.4 <= ratio <= 0.6):
+        return False
+
+    # Check for more than 6 consecutive effective pins
+    # TODO
+
+    # Check for more than 6 consecutive ineffective pins
+    # TODO
+
+    return True