diff --git a/calendar/generate_dates/app.py b/calendar/generate_dates/app.py
index 72112e7..b22893d 100644
--- a/calendar/generate_dates/app.py
+++ b/calendar/generate_dates/app.py
@@ -1,14 +1,10 @@
-#!/usr/bin/env python3
-
 import argparse
 import copy
-import datetime
-import importlib.resources as pkg_resources
 import pathlib
 import sys
-import yaml
 
 from generate_dates import TeachingCalendar, config, templates
+from generate_dates.config import parse_command_line
 
 
 class PeriodError(KeyError):
@@ -21,118 +17,6 @@
     pass
 
 
-def parse_command_line():
-    """Parse command-line arguments.
-
-    Example command lines:
-    generate_dates --style calendar --format latex --year 2020 --period S1 --paper INFO201
-    generate_dates --style lecture --format xml --period S2 --paper INFO202
-    """
-    format_map = {
-        "t": "text",
-        "text": "text",
-        "l": "latex",
-        "latex": "latex",
-        "x": "xml",
-        "xml": "xml",
-    }
-    style_map = {
-        "c": "calendar",
-        "calendar": "calendar",
-        "l": "lecture",
-        "lecture": "lecture",
-        "i": "iso",
-        "iso": "iso",
-    }
-
-    parser = argparse.ArgumentParser(
-        prog="generate_dates",
-        description="")
-    
-    parser.add_argument(
-        "--config", "-c", default=None, dest="config_file",
-        help="file name of the configuration file "
-            "[default 'default.yml' in generate_dates.config]")
-    
-    parser.add_argument(
-        "--debug", "-d", action='store_true',
-        help="enable debugging output")
-    
-    parser.add_argument(
-        "--format", "-f", default="latex",
-        choices=["text", "t", "latex", "l", "xml", "x"],
-        help="output format [default 'latex']")
-    
-    parser.add_argument(
-        "--output", "-o",
-        type=argparse.FileType("w", encoding="UTF-8"),
-        help="file name to write the output to; existing "
-            "files of the same name will be overwritten!")
-    
-    parser.add_argument(
-        "--paper", "-p", default=None,
-        help="paper code (e.g., INFO201) [required for 'lecture' style, "
-            "ignored otherwise]")
-    
-    parser.add_argument(
-        "--style", "-s", default="calendar",
-        choices=["calendar", "c", "lecture", "l", "iso", "i"],
-        help="output style: 'calendar' for teaching calendars in course "
-            "outlines, 'lecture' for individual lecture dates, or 'iso'"
-            "for dates across the entire ISO-8601 year [default 'calendar']")
-    
-    parser.add_argument(
-        "--teaching-period", "-t", default=None,
-        choices=["SS", "S1", "S2", "FY"], dest="period",
-        help="teaching period [required]")
-    
-    parser.add_argument(
-        "--year", "-y", type=int, default=datetime.date.today().year,
-        help=("the year to generate dates for [default {y}]".format(
-            y=datetime.date.today().year)))
-    
-    args = parser.parse_args()
-    # normalise format and style
-    args.format = format_map[args.format]
-    args.style = style_map[args.style]
-
-    # Load the default config if none is explicitly specified.
-    if not args.config_file:
-        args.config = yaml.safe_load(
-            pkg_resources.read_text(config, "default.yml"))
-    else:
-        with open(args.config_file) as cfg:
-            args.config = yaml.safe_load(cfg.read())
-
-    if args.style == "calendar":
-        # --paper is irrelevant
-        if args.paper:
-            print("generate_dates: warning: --paper/-p is ignored for "
-                "'calendar' style")
-        # --teaching-period is required
-        if not args.period:
-            parser.exit(2, "generate_dates: error: --teaching-period/-t "
-                "is required for 'calendar' style\n")
-
-    elif args.style == "iso":
-        # both --paper and --teaching-period are irrelevant
-        if args.paper or args.period:
-            print("generate_dates: warning: --paper/-p and "
-                "--teaching-period/-t are ignored for 'iso' style")
-
-    elif args.style == "lecture":
-        # both --paper and --teaching-period are required
-        if not args.paper:
-            parser.exit(2, message="generate_dates: error: -paper/-p and "
-                "--teaching-period/-t are required for 'lecture' style\n")
-    
-    # --teaching-period must be specified if --style is "calendar" or "lecture"
-    else:
-        pass
-    
-    return args
-    
-
 def parse_config(config, args):
     """Validate and filter the top-level configuration.