scripts: get_maintainer: add count function

For looking at statistics over time, it is helpful to be able to
quickly query the number of unique maintainers, collaborators,
areas, and the number of orphaned areas (without a maintainer).

This change adds the `count` subcommand to
`scripts/get_maintainer.py`.

```
% python3 ./scripts/get_maintainer.py count -h
usage: get_maintainer.py count [-h] [-a] [-c] [-n] [-o]

optional arguments:
  -h, --help            show this help message and exit
  -a, --count-areas     Count the number of areas
  -c, --count-collaborators
                        Count the number of unique collaborators
  -n, --count-maintainers
                        Count the number of unique maintainers
  -o, --count-orphaned  Count the number of orphaned areas

% python3 ./scripts/get_maintainer.py count
areas:          113
maintainers:    49
collaborators:  81
orphaned:       21

% python3 ./scripts/get_maintainer.py count -o
orphaned:       21
```

Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com>

scripts/get_maintainer.py

@@ -120,6 +120,31 @@ def _parse_args():
         help="Limit to files under PATH")
     orphaned_parser.set_defaults(cmd_fn=Maintainers._orphaned_cmd)
 
+    count_parser = subparsers.add_parser(
+        "count",
+        help="Count areas, unique maintainers, and / or unique collaborators")
+    count_parser.add_argument(
+        "-a",
+        "--count-areas",
+        action="store_true",
+        help="Count the number of areas")
+    count_parser.add_argument(
+        "-c",
+        "--count-collaborators",
+        action="store_true",
+        help="Count the number of unique collaborators")
+    count_parser.add_argument(
+        "-n",
+        "--count-maintainers",
+        action="store_true",
+        help="Count the number of unique maintainers")
+    count_parser.add_argument(
+        "-o",
+        "--count-orphaned",
+        action="store_true",
+        help="Count the number of orphaned areas")
+    count_parser.set_defaults(cmd_fn=Maintainers._count_cmd)
+
     args = parser.parse_args()
     if not hasattr(args, "cmd_fn"):
         # Called without a subcommand
@@ -261,6 +286,36 @@ class Maintainers:
             else:
                 print("{:25}\t{}".format(area.name, ",".join(area.maintainers)))
 
+    def _count_cmd(self, args):
+        # 'count' subcommand implementation
+
+        if not (args.count_areas or args.count_collaborators or args.count_maintainers or args.count_orphaned):
+            # if no specific count is provided, print them all
+            args.count_areas = True
+            args.count_collaborators = True
+            args.count_maintainers = True
+            args.count_orphaned = True
+
+        orphaned = 0
+        collaborators = set()
+        maintainers = set()
+
+        for area in self.areas.values():
+            if area.status == 'maintained':
+                maintainers = maintainers.union(set(area.maintainers))
+            elif area.status == 'orphaned':
+                orphaned += 1
+            collaborators = collaborators.union(set(area.collaborators))
+
+        if args.count_areas:
+            print('{:14}\t{}'.format('areas:', len(self.areas)))
+        if args.count_maintainers:
+            print('{:14}\t{}'.format('maintainers:', len(maintainers)))
+        if args.count_collaborators:
+            print('{:14}\t{}'.format('collaborators:', len(collaborators)))
+        if args.count_orphaned:
+            print('{:14}\t{}'.format('orphaned:', orphaned))
+
     def _list_cmd(self, args):
         # 'list' subcommand implementation