sessionMonitor.ts

Manages the active monitoring session lifecycle across iOS and Android

Purpose

This module manages the user-initiated “active monitoring session” — the equivalent of a workout mode. On iOS it uses a continuous GPS location watch to keep the app alive in the background, throttled to run the prediction pipeline at most once per minute. On Android it delegates to the react-native-background-actions foreground service.

Its responsibilities include:

Persisting session active state to AsyncStorage so it survives app restarts
Starting and stopping iOS GPS location watching with appropriate options
Starting and stopping the Android background foreground service
Throttling iOS pipeline runs to at most one per MIN_INTERVAL_MS
Notifying registered prediction listeners after each pipeline run
Exposing a subscription API for the PredictionScreen to react to new results

Invariants

Single Watch Guard

startSession no-ops if watchId is already set, preventing duplicate location watchers from being registered.

Throttle Gate

On iOS, each location update checks Date.now() - lastRunMs < MIN_INTERVAL_MS before running the pipeline.

Throttled updates log a debug message with the remaining cooldown in seconds but do not run inference.

AsyncStorage Session Flag

Session state is persisted to AsyncStorage under "heatsafe_session_active" so isSessionActive() can return the correct value even after a cold start.

stopSession explicitly writes "false" rather than deleting the key, ensuring the flag is always present after the first session.

iOS Location Options

Option	Value	Rationale
`enableHighAccuracy`	`false`	Low-power; only approximate location needed for weather
`distanceFilter`	`0`	Fire on every update; throttle handles rate limiting
`showsBackgroundLocationIndicator`	`true`	Required for App Store transparency (blue status-bar pill)
`pauseUpdatesAutomatically`	`false`	Prevent iOS from pausing updates during inactivity

Android Permission Before Service Start

requestPersistenceNotificationPermission is called before BackgroundService.start to satisfy the Android 13+ foreground service notification requirement.

If the service is already running (BackgroundService.isRunning()), startSession does not start a second instance.

Exports

`predictionListeners`

let predictionListeners: PredictionListener[]

Mutable array of listener callbacks invoked after each successful pipeline run. Also used by background.ts to notify the foreground after Android background predictions.

`subscribeToPredictions(...)`

function subscribeToPredictions(listener: () => void): () => void

Registers a prediction listener and returns an unsubscribe function.

`isSessionActive()`

async function isSessionActive(): Promise<boolean>

Returns true if the session flag in AsyncStorage is "true". Returns false on storage errors.

`startSession()`

async function startSession(): Promise<void>

Starts the monitoring session for the current platform. On iOS, begins GPS location watching. On Android, starts the foreground service.

`stopSession()`

async function stopSession(): Promise<void>

Stops the monitoring session. Clears the GPS watcher (iOS), stops the background service (Android), and writes "false" to the session flag.