argparser : adds subcommands to the argparser

this adds subcommands to the argparser using subparsers, we also set a
default value for func depending on which of the subcommands is
selected.
Also change the formatting of the epilog so it is on two lines.

src/unisync/argparser.py

@@ -3,20 +3,34 @@
 
 import argparse
 
-def create_argparser() -> argparse.ArgumentParser:
+def create_argparser(sync_function, add_function, mount_function) -> argparse.ArgumentParser:
+    """
+    Creates an argument parser to parse the command line arguments.
+    We use subparsers and set a default function for each to perform the correct action.
+    """
     parser = argparse.ArgumentParser(
             prog='unisync',
             description='File synchronisation application',
-            epilog="""
-            Copyright © 2025 Paul Retourné.
-            License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>."""
+            epilog="Copyright © 2025 Paul Retourné.\n"
+            "License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.",
+            formatter_class=argparse.RawDescriptionHelpFormatter
             )
     parser.add_argument("local", nargs="?")
     parser.add_argument("remote", nargs="?")
+    parser.set_defaults(func=sync_function)
 
     remote_addr_group = parser.add_mutually_exclusive_group()
     remote_addr_group.add_argument("--ip")
     remote_addr_group.add_argument("--hostname")
 
     parser.add_argument("--config", help="Path to the configuration file", metavar="path_to_config")
+
+    subparsers = parser.add_subparsers(help='Actions other than synchronisation')
+
+    parser_add = subparsers.add_parser('add', help='Add files to be synchronised.')
+    parser_add.set_defaults(func=add_function)
+
+    parser_mount = subparsers.add_parser('mount', help='Mount the remote.')
+    parser_mount.set_defaults(func=mount_function)
+
     return parser