Implement ADMIN_MODIFY_DB logs

When an admin requests /admin/umbrella/edit and the request succeeds, an
ADMIN_MODIFY_DB log is kept. `Database.update` will keep track of the
updated columns.

1 files changed, 16 insertions, 3 deletions

diff --git a/jimbrella/database.py b/jimbrella/database.py
index a8d480b..9b6e51f 100644
--- a/jimbrella/database.py
+++ b/jimbrella/database.py
@@ -91,7 +91,7 @@ class Database(CsvTable):
                 umbrellas[idx]["lent_time_ago_str"] = human_timedelta(lent_time_ago)
         return umbrellas
 
-    def update(self, umb) -> list:
+    def update(self, umb) -> dict:
         """An interface to `_update()` with added convenience and safeguards.
 
         Convenience:    Not all fields in an umbrella dict need to be present in `umb`. If an
@@ -117,7 +117,8 @@ class Database(CsvTable):
                         fields mentioned above are made blank, and these fields supplied in `umb`
                         are ignored.
 
-        Returns updated database (same as `_update()`).
+        Returns a dict, where the keys are all modified columns of the updated row, and the value
+        of each is a 2-tuple (<past value>, <new value>).
         """
         # `serial` must be specified.
         if "serial" not in umb:
@@ -169,7 +170,19 @@ class Database(CsvTable):
             if not umb["lent_at"]:
                 raise UmbrellaValueError("lent_at")
 
-        return self._update(umb)
+        # commit update
+        self._update(umb)
+
+        # find updated columns
+        # essentially "diff umb_in_db umb"
+        diff = {}
+        for key, new in umb.items():
+            past = umb_in_db[key]
+            if any([new, past]) and new != past:
+                # new and past are not both null values, and they are unequal
+                diff[key] = (past, new)
+
+        return diff
 
     @staticmethod
     def group_by_status(umbrellas) -> dict: