checks: add target_member_id to guild_perm_check

litecord/blueprints/checks.py

@@ -113,18 +113,66 @@ async def channel_check(
         return ctype, owner_id
 
 
-async def guild_perm_check(user_id, guild_id, permission: str):
-    """Check guild permissions for a user."""
+async def guild_perm_check(
+    user_id,
+    guild_id,
+    permission: str,
+    target_member_id: Optional[int] = None,
+    raise_err: bool = True,
+) -> bool:
+    """Check guild permissions for a user.
+
+    Accepts optional target argument for actions that are done TO another member
+    in the guild."""
     base_perms = await base_permissions(user_id, guild_id)
     hasperm = getattr(base_perms.bits, permission)
 
-    if not hasperm:
+    # if we have the PERM and there's a target member involved,
+    # check on the target's max(role.position), if its equal or greater,
+    # raise MissingPermissions
+    if hasperm and target_member_id:
+
+        # there is no internal function to fetch full role objects
+        # (likely because it would be too expensive to do it here),
+        # so instead do a raw sql query.
+        target_max_position = await app.db.fetchval(
+            """
+            SELECT MAX(role.position)
+            FROM member_roles
+            JOIN roles ON roles.id = member_roles.role_id
+            WHERE member_roles.member_id = $1
+            """,
+            target_member_id,
+        )
+        user_max_position = await app.db.fetchval(
+            """
+            SELECT MAX(role.position)
+            FROM member_roles
+            JOIN roles ON roles.id = member_roles.role_id
+            WHERE member_roles.member_id = $1
+            """,
+            user_id,
+        )
+
+        assert target_max_position is not None
+        assert user_max_position is not None
+
+        if user_max_position <= target_max_position:
+            hasperm = False
+
+    if not hasperm and raise_err:
         raise MissingPermissions("Missing permissions.")
 
     return bool(hasperm)
 
 
-async def channel_perm_check(user_id, channel_id, permission: str, raise_err=True):
+# TODO add target semantics
+async def channel_perm_check(
+    user_id,
+    channel_id,
+    permission: str,
+    raise_err=True,
+):
     """Check channel permissions for a user."""
     base_perms = await get_permissions(user_id, channel_id)
     hasperm = getattr(base_perms.bits, permission)