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.

3 files changed, 39 insertions, 6 deletions

diff --git a/jimbrella/admin.py b/jimbrella/admin.py
index 9a9f6c8..eaf0e54 100644
--- a/jimbrella/admin.py
+++ b/jimbrella/admin.py
@@ -72,9 +72,8 @@ def umbrellas_edit():
     ]:
         data[key] = request.form.get(key)
 
-    error = None
     try:
-        db.update(data)
+        diff = db.update(data)
     except UmbrellaValueError as e:
         # invalid field is in `e.message`.
         return redirect(
@@ -85,6 +84,19 @@ def umbrellas_edit():
     except UmbrellaNotFoundError:
         pass  # impossible on web console
 
+    for column, value_pair in diff.items():
+        past, new = value_pair
+        admin_log.log(
+            "ADMIN_MODIFY_DB",
+            {
+                "admin_name": session["username"],
+                "serial": data["serial"],
+                "column": column,
+                "past_value": past,
+                "new_value": new,
+            },
+        )
+
     return redirect(url_for("admin.umbrellas"))
 
 
diff --git a/jimbrella/admin_log.py b/jimbrella/admin_log.py
index 8b5bb09..622abec 100644
--- a/jimbrella/admin_log.py
+++ b/jimbrella/admin_log.py
@@ -106,7 +106,15 @@ class AdminLog:
                     "{name} missed the due for umbrella #{key}. " + tenant_info
                 )
             elif event == "ADMIN_MODIFY_DB":
-                description = "{admin_name} changed {column} of umbrella #{serial} from {past_value} to {new_value}."
+                if not entry["past_value"]:
+                    description = "{admin_name} set {column} of umbrella #{serial} to {new_value}."
+                elif not entry["new_value"]:
+                    description = "{admin_name} cleared {column} of umbrella #{serial} (was {past_value})."
+                else:
+                    description = (
+                        "{admin_name} changed {column} of umbrella #{serial} "
+                        "from {past_value} to {new_value}."
+                    )
 
             friendly_logs.append(
                 {
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: