--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/purple/main.py	Tue Dec 03 21:14:52 2013 -0600
@@ -0,0 +1,116 @@
+# Copyright (C) 2013 by Brian Neal.
+# This file is part of purple, the PURPLE (Cipher Machine 97) simulation.
+# purple is released under the MIT License (see LICENSE.txt).
+
+"""This file contains the main routine for the command-line purple97 program."""
+
+import argparse
+import os
+import string
+
+from purple.machine import Purple97, Purple97Error
+from purple.switch import SteppingSwitchError
+
+
+DESC = """PURPLE cipher machine simulator"""
+
+EPILOG = """\
+Supply either -e or -d, but not both, to perform either an encrypt or decrypt. If
+the -s option is not supplied, the value of the environment variable
+PURPLE97_SWITCHES will be used. If the -a option is not supplied, the value of
+the environment variable PURPLE97_ALPHABET will be used. Input text is supplied
+either by the -t or by the -f options, but not both.
+"""
+
+DEFAULT_SWITCHES = '1-1,1,1-12'
+DEFAULT_ALPHABET = Purple97.STRAIGHT_PLUGBOARD
+
+LOWERCASE = set(string.ascii_lowercase)
+DIGITS = {
+    '0': 'ZERO',
+    '1': 'ONE',
+    '2': 'TWO',
+    '3': 'THREE',
+    '4': 'FOUR',
+    '5': 'FIVE',
+    '6': 'SIX',
+    '7': 'SEVEN',
+    '8': 'EIGHT',
+    '9': 'NINE',
+}
+
+
+def filter_plaintext(s):
+    """A generator to filter plaintext to ensure only valid input is fed to
+    the purple cipher machine:
+
+        * Uppercase letters A-Z are passed unchanged
+        * Lowercase letters a-z are converted to uppercase
+        * Digits are converted to words; e.g. 1 => ONE
+        * All other input is ignored (filtered out)
+
+    """
+    for c in s:
+        if c in Purple97.VALID_KEYS:
+            yield c
+        elif c in LOWERCASE:
+            yield c.upper()
+        else:
+            digit_name = DIGITS.get(c)
+            if digit_name:
+                for d in digit_name:
+                    yield d
+
+
+def main(argv=None):
+    """Entry point for the command-line purple97 simulation."""
+
+    parser = argparse.ArgumentParser(description=DESC, epilog=EPILOG)
+    parser.add_argument('-e', '--encrypt', action='store_true',
+        help='encrypt text from files or the command-line')
+    parser.add_argument('-d', '--decrypt', action='store_true',
+        help='decrypt text from files or the command-line')
+    parser.add_argument('-s', '--switches',
+        help='switch settings, e.g. 9-1,24,6-23')
+    parser.add_argument('-a', '--alphabet',
+        help='plugboard wiring string, 26-letters')
+    parser.add_argument('-t', '--text',
+        help='input text to encrypt/decrypt')
+    parser.add_argument('-f', '--files', nargs='+', metavar='FILE',
+        help='files to take input from, - for stdin')
+
+    args = parser.parse_args(args=argv)
+
+    if not args.encrypt and not args.decrypt:
+        parser.error("Please supply either -e or -d options")
+    if args.encrypt and args.decrypt:
+        parser.error("Please supply either -e or -d, not both")
+    if args.text and args.files:
+        parser.error("Please supply either -t or -f, not both")
+
+    # Get key settings
+    if args.switches:
+        switches = args.switches
+    else:
+        switches = os.environ.get('PURPLE97_SWITCHES', DEFAULT_SWITCHES)
+
+    if args.alphabet:
+        alphabet = args.alphabet
+    else:
+        alphabet = os.environ.get('PURPLE97_ALPHABET', DEFAULT_ALPHABET)
+
+    try:
+        purple = Purple97.from_key_sheet(switches, alphabet)
+    except (Purple97Error, SteppingSwitchError) as ex:
+        parser.error(str(ex))
+
+    if args.encrypt:
+        result = purple.encrypt(filter_plaintext(args.text))
+    else:
+        result = purple.decrypt(args.text)
+
+    print(result)
+
+
+if __name__ == '__main__':
+    main()