Refactor error handling for system commands

src/pluralkit/errors.py

@@ -1,36 +1,57 @@
+from typing import Tuple
+
+
 class PluralKitError(Exception):
-    pass
+    def __init__(self, message):
+        self.message = message
+        self.help_page = None
+
+    def with_help(self, help_page: Tuple[str, str]):
+        self.help_page = help_page
 
 
 class ExistingSystemError(PluralKitError):
-    pass
+    def __init__(self):
+        super().__init__("You already have a system registered. To delete your system, use `pk;system delete`, or to unlink your system from this account, use `pk;system unlink`.")
 
 
 class DescriptionTooLongError(PluralKitError):
-    pass
+    def __init__(self):
+        super().__init__("You can't have a description longer than 1024 characters.")
 
 
 class TagTooLongError(PluralKitError):
-    pass
+    def __init__(self):
+        super().__init__("You can't have a system tag longer than 32 characters.")
 
 
 class TagTooLongWithMembersError(PluralKitError):
     def __init__(self, member_names):
+        super().__init__("The maximum length of a name plus the system tag is 32 characters. The following members would exceed the limit: {}. Please reduce the length of the tag, or rename the members.".format(", ".join(member_names)))
         self.member_names = member_names
 
 
 class CustomEmojiError(PluralKitError):
-    pass
+    def __init__(self):
+        super().__init__("Due to a Discord limitation, custom emojis aren't supported. Please use a standard emoji instead.")
 
 
 class InvalidAvatarURLError(PluralKitError):
-    pass
+    def __init__(self):
+        super().__init__("Invalid image URL.")
+
+
+class AccountInOwnSystemError(PluralKitError):
+    def __init__(self):
+        super().__init__("That account is already linked to your own system.")
 
 
 class AccountAlreadyLinkedError(PluralKitError):
     def __init__(self, existing_system):
+        super().__init__("The mentioned account is already linked to a system (`{}`)".format(existing_system.hid))
         self.existing_system = existing_system
 
 
 class UnlinkingLastAccountError(PluralKitError):
-    pass
+    def __init__(self):
+        super().__init__("This is the only account on your system, so you can't unlink it.")