MSC4141: Time based notification filtering

proposals/xxxx-time-based-notification-filtering.md

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+# MSC3XXXX: Time based notification filtering
+Do not disturb / focus features are becoming standard across operating systems and networking products. Users expect to
+be able to manage the level of noisiness from an application based on day and time.
+
+Users should be able to configure many periods of notification levels during the day; for example before work, lunch
+hour, and after work. They should also be able to schedule notification levels for a particular day of the week; for
+example a quieter notification setting all day on No Meeting Wednesday, or complete silence over the weekend.
+
+## Proposal
+
+We introduce a push notification [condition](https://spec.matrix.org/v1.2/client-server-api/#push-rules) `time_and_day`
+to filter based on time of day and day of week.
+
+**`time_and_day` condition definition**
+
+| key | type | value | description | Required |
+| ---- | ----| ----- | ----------- | -------- |
+| `kind` | string | 'dnd_time_of_day' | | **Required** |
+| `timezone` | string | user's [Olson formatted timezone](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) | The timezone to use for time comparison. This format allows for automatic DST handling | Optional. Defaults to UTC |
+| `intervals` | array | array of time matching intervals (see below) | Intervals representing time periods in which the rule should match. Evaluated with an OR condition | **Required** |
+
+**Time matching interval definition**
+
+| key | type | value                 | description                                                                                                                                                                                                                                             | Required |
+| ---- | ----|-----------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| -------- |
+| `time_of_day` | string[] | tuple of `hh:mm` time | Tuple representing start and end of a time interval in which the rule should match. Times are [ISO 8601 formatted times](https://en.wikipedia.org/wiki/ISO_8601#:~:text=As%20of%20ISO%208601%2D1,minute%20between%2000%20and%2059.). Times are inclusive | Optional. When omitted all times are matched.  |
+| `day_of_week` | number[] | array of integers 0-6 | An array of integers representing days of the week on which the rule should match, where 0 = Sunday, 1 = Monday, .., 6 = Saturday                                                                                                                       | **Required** |
+
+
+- `time_of_day` condition is met when the server's timezone-adjusted time is between the values of the tuple, or when no
+  `time_of_day` is set on the interval. Values are inclusive.
+- `day_of_week` condition is met when the server's timezone-adjusted day is included in the array.
+
+When both `time_of_day` and `day_of_week` conditions are met for an interval in the `intervals` array the rule evaluates
+to true.
+
+```json5
+{
+    "kind": "time_and_day",
+    "timezone": "Europe/Berlin",
+    "intervals": [
+        {
+            "time_of_day": ["00:00", "09:00"],
+            "day_of_week": [1, 2, 3, 4, 5] // Monday - Fri
+        },
+        {
+            "time_of_day": ["17:00", "23:59"],
+            "day_of_week": [1, 2, 3, 4, 5] // Monday - Fri
+        },
+        {
+            // no time_of_day, all day is matched
+            "day_of_week": [0, 6] // Weekend
+        }
+    ]
+}
+```
+
+A primary use case for this condition is creating 'do not disturb' behaviour.
+For example, Wednesday morning focus time rule:
+```json5
+{
+    "rule_id": ".m.rule.master",
+    "default": true,
+    "enabled": true,
+    "conditions": {
+        "kind": "time_and_day",
+        "timezone": "Europe/Berlin",
+        "intervals": [
+            {
+                "time_of_day": ["09:00", "11:00"],
+                "day_of_week": [3] // Wednesday
+            },
+        ]
+    },
+    "actions": [
+        "dont_notify" // See note below
+    ]
+}
+```
+
+##### `dont_notify` and Do Not Disturb behaviour
+`dont_notify` will stop badges from being
+updated in the client during 'do not disturb' hours, so the user will not be
+able to locate messages that were silenced when they are back online.
+To silence push notifications but allow discovery of missed messages in app, `notify_in_app` as proposed in
+[MSC3768](https://github.com/matrix-org/matrix-spec-proposals/pull/3768) should
+be used.
+
+## Potential issues
+- If a user changes timezone their push rules will not automatically update. 
+
+## Alternatives
+
+#### System
+Some systems (e.g. iOS) have their own DND / focus mode but this is only an option if all of your devices are within
+that vendor ecosystem (here Apple) and doesn't help when you have e.g. an iPad and an Android phone. This also needs to
+be configured per device.
+
+#### `room_member_count` style comparison
+```json5
+{
+    "conditions": [
+        {
+            "kind": "time_of_day",
+            "is": ">=18000000" // 17:00 NZST, 5:00 UTC 
+        },
+        {
+            "kind": "time_of_day",
+            "is": "<=75600000" // 9:00 NZST, 21:00 UTC
+        },
+    ]
+}
+```
+As only one rule per `kind` + `rule_id` is allowed and rule conditions are an `AND` this allows only one contiguous
+range to be defined. This precludes one of the main usecases for the feature - ignoring notifications outside of
+work/waking hours.
+
+#### Device assessment
+An alternative version of the `time_and_day` defined above used timezone agnostic times and did not define a timezone.
+This rule would be assessed only on the device. This is not easily achieved on every platform. 
+
+#### ms offsets for time intervals
+Previous proposals used ms offsets to represent time of day instead of `hh:mm`. Ms offsets may behave incorrectly on
+days with a DST jump and are less intuitive.
+
+## Security considerations
+- Stores user's timezone on the server. DND periods saved to the server without timezone information would reveal
+  information about a user's approximate timezone anyway. Users who do not wish to store their timezone can set DND
+  periods in UTC (this option should be available in clients implementing time based notification filtering).
+
+## Unstable prefix
+
+- While this MSC is not considered stable `time_and_day` should be referred to as `org.matrix.mscxxxx.time_and_day`
+
+## Dependencies
+None.