clockula/docs/BACKUP.md

# Clockula backup format

`clockula-backup-v1.json` is a documented, versioned JSON export of Clockula's
own data, written to (and read from) a user-chosen folder via SAF
(`docs/PLAN.md` §7). This file is the schema's source of truth; the codec
(`data/backup/BackupDto.kt`, `BackupCodec.kt`) implements exactly what is
written here.

## Top level

```json
{
  "format": "clockula-backup",
  "version": 1,
  "exportedAt": 1700000000000,
  "alarms": [ … ],
  "timers": [ … ],
  "worldClocks": [ … ],
  "settings": { … }
}
```

- `format`: must be exactly `"clockula-backup"`.
- `version`: must be exactly `1`. Any other value rejects the whole file:
  Clockula does not guess at a schema it has not implemented.
- `exportedAt`: epoch milliseconds, informational only (not re-imported).

## Parsing rules

- **Tolerant of unknown fields, at any level.** An older or newer client's
  extra field is ignored, never an error.
- **Strict about known fields.** A malformed value in a field this schema
  defines (`format`, `version`, an alarm's `hour`/`minute`, a world clock's
  `zone_id`, a timer's `duration_millis`) rejects the **whole file** with a
  specific reason. Nothing is imported half-way.
- Settings values (snooze minutes, volume ramp, …) are
  **not** range-checked at parse time; they pass through the same clamps
  `ClockPrefs`/`SettingsPrefs` already apply on every write, so a value from
  a future, more permissive version degrades to the nearest valid one instead
  of failing the import.
- An alarm's own `snooze_minutes`, `snooze_limit` and `volume_ramp_seconds`
  are clamped at parse time to the same ranges as the defaults they
  override, and a timer's `duration_millis` to the setup range (1 second to
  24 hours). Room has no clamp of its own, so this is where it happens.
- A missing `timer_presets` keeps the built-in presets. An empty list is a
  user who removed them all, and is imported as such.
- An enum field with a name this version does not recognise (a `dismiss_
  challenge` or `theme_mode` from a future version, say) degrades to that
  field's default, the same forgiving-read posture `AlarmMapper` already uses
  for a corrupt Room row. It does not fail the import.
- Import and export are limited to 8 MiB. Import also rejects more than 10,000
  alarms, 10,000 timers, 1,000 world clocks, oversized labels or ringtone URIs,
  and more than 1,000 timer presets. These limits keep a picked document from
  exhausting memory or creating an impractical number of rows.

## Import semantics

Import **replaces all state**: alarms, timers and world clocks are deleted
and re-created from the file, and every setting the file carries is written
over the current value. This is not a merge, and the backup screen says so
before the user confirms. Settings are written in one DataStore transaction;
the three Room tables are replaced in one database transaction. The live ring
and timer services are paused while the tables change. If the database replace
fails, the old rows remain, the previous settings are restored, and the ring
and timer registrations are resumed. Scheduling is reconciled after either
outcome. An imported timer always starts idle.

Export writes a complete temporary document before removing an older backup.
If the provider refuses the final rename, the complete temporary document is
kept in the chosen folder and the app reports the failure with its filename.

Every imported alarm and timer gets a **fresh id and fresh timestamps**.
The backup carries no id and no `created_at`/`updated_at`, since those are
local-database facts, not portable ones.

## Alarms

One object per row of `alarms`, config only:

| Field | Type | Notes |
|---|---|---|
| `hour` | Int | 0..23. Out of range rejects the whole file. |
| `minute` | Int | 0..59. Out of range rejects the whole file. |
| `label` | String | |
| `enabled` | Boolean | |
| `repeat_days` | Int | The 7-bit mask (`RepeatDays`); bit *n* is ISO day *n+1*. |
| `skip_next_occurrence` | Boolean | |
| `ringtone_uri` | String? | Exported as-is. See "Ringtone URIs" below. |
| `vibrate` | Boolean? | `null` = inherit the app default. |
| `snooze_minutes` | Int? | `null` = inherit. |
| `snooze_limit` | Int? | `null` = inherit. |
| `volume_ramp_seconds` | Int? | `null` = inherit. |
| `dismiss_challenge` | String? | `NONE`/`MATH`/`HOLD`, or `null` = inherit. |
| `delete_after_use` | Boolean | A transient, contract-created alarm. |

**Not exported:** the `alarm_states` ring-state table (snooze/ringing/handled-
occurrence bookkeeping). It is volatile, per-device state, not configuration,
and `docs/ARCHITECTURE.md` §4/§6 are explicit that it must never appear here.

## Timers

One object per row of `timers`, config only:

| Field | Type | Notes |
|---|---|---|
| `label` | String | |
| `duration_millis` | Long | ≥ 0. Negative rejects the whole file. |
| `ringtone_uri` | String? | |
| `sort_order` | Int | |
| `delete_after_use` | Boolean | |

**Not exported:** `state`, `remaining`, the elapsed-realtime anchors, or
`ends_at_wall_clock`. A timer's running state is meaningless on another
device or after a reboot (`docs/PLAN.md` §5). Every imported timer lands
`IDLE`, with `remaining` equal to `duration`.

## World clocks

| Field | Type | Notes |
|---|---|---|
| `zone_id` | String | Must be a zone id the *exporting* device's IANA tzdata knows (`Zones.isValid`). A bad id rejects the whole file. |
| `label` | String? | |
| `sort_order` | Int | |

## Settings

```json
"settings": {
  "theme_mode": "SYSTEM",
  "dynamic_color": true,
  "default_snooze_minutes": 10,
  "default_snooze_limit": 3,
  "default_vibrate": true,
  "default_volume_ramp_seconds": 15,
  "default_alarm_ringtone_uri": null,
  "default_timer_ringtone_uri": null,
  "default_dismiss_challenge": "NONE",
  "home_zone_id": null,
  "timer_presets": [60000, 120000, 180000, 300000, 600000, 900000, 1800000, 3600000],
  "bedtime": {
    "enabled": false,
    "bedtime_minutes": 1350,
    "wake_minutes": 420,
    "days": 127,
    "reminder_minutes": 0,
    "grayscale": true,
    "dim_wallpaper": true,
    "dark_theme": true,
    "hide_always_on_display": false
  }
}
```

`bedtime` is the opt-in bedtime schedule (issue #1). Its times are minutes
since local midnight, `days` is the same 7-bit mask as an alarm's
`repeat_days` (the nights bedtime is for, named by their evening), and `reminder_minutes` 0 means no
reminder. A file without `bedtime` (any file written before it existed)
leaves the device's current bedtime settings as they are, the one setting a
restore does not replace when its file is silent about it. Like the other settings it
is clamped rather than rejected: times into a day, the reminder into 0–120
minutes, and a `days` of 0 (which the screen never allows) into every night. The id of the Do Not Disturb rule a device created is not part of it;
the importing device creates its own (`docs/ARCHITECTURE.md` §18).

Field names mirror `ClockPrefs`'/`SettingsPrefs`' own on-disk keys. Older
files may also carry `default_timer_duration_millis`, from a default timer
length setting that has since been removed; it is ignored on import like any
other unknown field. Every
numeric/duration value is clamped on *apply* using the same ranges and encoding
as the existing preference setters, never on parse.

## Ringtone URIs

Exported exactly as stored (a `content://` URI, typically). On import the
URI is written back unchanged; if the *importing* device cannot resolve it
at ring/preview time, the existing ringtone-resolution fallback already used
elsewhere in the app applies (falls through to the device default). This is
not special-cased in the backup path itself.