feat: add options to list rules

The option `--list` is added that allow you to list rules matching a
pattern and the option `--show` is present that allow you to pick the
level of detail that you want to show for each rule.

Fixes #37

src/doctor/__init__.py

@@ -18,7 +18,8 @@
 database.
 """
 
-from textwrap import dedent, fill
+from fnmatch import fnmatch
+from textwrap import dedent, fill, TextWrapper
 from os.path import dirname, basename, isfile, join
 from abc import ABC
 from packaging.version import parse
@@ -92,6 +93,27 @@ def register(cls):
     return cls
 
 
+def list_rules(pattern, show):
+    """List all rules matching pattern.
+
+    Will list rules matching `pattern`, and print detailed message if
+    `details` is true. Note that since the detailed message contains
+    variables for expansion, and there is no replacements to use, the
+    message with the placeholders will be printed.
+    """
+    wrapper = TextWrapper(initial_indent="    ", subsequent_indent="    ")
+    for category, rules in RULES.items():
+        for name, cls in rules.items():
+            fullname = f"{category}.{name}"
+            if fnmatch(fullname, pattern):
+                print(f"{fullname}:")
+                print(wrapper.fill(cls.__doc__))
+                if show in ("details", "message"):
+                    print("\n    == MESSAGE ==", end="\n\n")
+                    print(wrapper.fill(cls.message), end="\n\n")
+                    if show == "details" and hasattr(cls, 'detail'):
+                        print(wrapper.fill(cls.detail), end="\n\n")
+
 def check_rules(dbname, user, host, port):
     """Check all rules with the database."""
     conn = psycopg2.connect(dbname=dbname, user=user,

src/doctor/cli.py

@@ -18,7 +18,7 @@
 import getpass
 import os
 
-from doctor import check_rules
+from doctor import check_rules, list_rules
 from doctor.rules import load_rules
 
 
@@ -42,10 +42,22 @@ def parse_arguments():
     parser.add_argument("--verbose", "-v", dest="log_level",
                         action="count", default=2,
                         help='Verbose logging. More options give higher verbosity.')
+    parser.add_argument("--list", nargs='?', const='*', metavar="PATTERN",
+                        help=("List rules matching pattern. "
+                              "If no pattern is given, will list all rules"))
+    parser.add_argument(
+        '--show', choices=['brief', 'message', 'details'], default="brief",
+        help=("What to show from the rule. The brief description is always shown, "
+              "but it is possible to show the message and the detailed message as "
+              "well.")
+    )
     return parser.parse_args()
 
 def main():
     """Run application."""
     load_rules()
     args = parse_arguments()
-    check_rules(user=args.user, dbname=args.dbname, port=args.port, host=args.host)
+    if args.show is not None:
+        list_rules(args.list, args.show)
+    else:
+        check_rules(user=args.user, dbname=args.dbname, port=args.port, host=args.host)