feat(chat): stabilize multi-image attachment picker (#986)

app/src/main/java/com/m57/hermescontrol/ExternalActivityLifecycleGuard.kt

@@ -0,0 +1,104 @@
+package com.m57.hermescontrol
+
+import android.os.Handler
+import android.os.Looper
+
+/** Coordinates background reply handling and a bounded connection lease for external activities. */
+object ExternalActivityLifecycleGuard {
+    private const val CONNECTION_LEASE_TIMEOUT_MS = 10 * 60 * 1_000L
+
+    private val lock = Any()
+    private var generation = 0L
+    private var externalActivityInFlight = false
+    private var resultDelivered = false
+    private var hostResumed = true
+    private var releaseConnectionLease: (() -> Unit)? = null
+
+    fun launchExternalActivity(
+        acquireConnectionLease: () -> Unit,
+        releaseConnectionLease: () -> Unit,
+        prepareForBackground: () -> Unit,
+        cleanupAfterLaunchFailure: () -> Unit,
+        scheduleTimeout: (Long, () -> Unit) -> Unit = ::scheduleTimeout,
+        launch: () -> Unit,
+    ) {
+        val launchGeneration =
+            synchronized(lock) {
+                generation += 1
+                externalActivityInFlight = true
+                resultDelivered = false
+                this.releaseConnectionLease = releaseConnectionLease
+                generation
+            }
+
+        try {
+            acquireConnectionLease()
+            scheduleTimeout(CONNECTION_LEASE_TIMEOUT_MS) {
+                finishExternalActivity(launchGeneration)
+            }
+            prepareForBackground()
+            launch()
+        } catch (error: Throwable) {
+            cleanupAfterLaunchFailure()
+            finishExternalActivity(launchGeneration)
+            throw error
+        }
+    }
+
+    fun onHostPaused() {
+        synchronized(lock) {
+            hostResumed = false
+        }
+    }
+
+    fun onHostResumed() {
+        val release =
+            synchronized(lock) {
+                hostResumed = true
+                if (externalActivityInFlight && resultDelivered) finishExternalActivityLocked() else null
+            }
+        release?.invoke()
+    }
+
+    fun externalActivityReturned() {
+        val release =
+            synchronized(lock) {
+                if (!externalActivityInFlight) return
+                resultDelivered = true
+                if (hostResumed) finishExternalActivityLocked() else null
+            }
+        release?.invoke()
+    }
+
+    internal fun resetForTest() {
+        synchronized(lock) {
+            generation += 1
+            externalActivityInFlight = false
+            resultDelivered = false
+            hostResumed = true
+            releaseConnectionLease = null
+        }
+    }
+
+    private fun finishExternalActivity(expectedGeneration: Long) {
+        val release =
+            synchronized(lock) {
+                if (!externalActivityInFlight || generation != expectedGeneration) return
+                finishExternalActivityLocked()
+            }
+        release?.invoke()
+    }
+
+    private fun finishExternalActivityLocked(): (() -> Unit)? {
+        externalActivityInFlight = false
+        resultDelivered = false
+        return releaseConnectionLease.also { releaseConnectionLease = null }
+    }
+
+    private fun scheduleTimeout(
+        delayMs: Long,
+        action: () -> Unit,
+    ) {
+        Handler(Looper.getMainLooper()).postDelayed(action, delayMs)
+    }
+}