Fix: Read the charger-maximum extras by their literal keys

BatteryManager.EXTRA_MAX_CHARGING_CURRENT/VOLTAGE are @hide constants:
BatteryService puts both into ACTION_BATTERY_CHANGED, but the symbols
are absent from the public SDK's android.jar, so referencing them fails
to compile. The extras themselves are readable (only the constants are
missing), so the reader uses the stable AOSP string keys instead. No
reflection is involved.

Author: d4rken

app/src/main/java/eu/darken/amply/battery/core/BatteryReader.kt

@@ -51,8 +51,8 @@ class BatteryReader @Inject constructor(
             currentNowMicroamps = manager.propertyOrAbsent(BatteryManager.BATTERY_PROPERTY_CURRENT_NOW),
             chargeCounterMicroampHours = manager.propertyOrAbsent(BatteryManager.BATTERY_PROPERTY_CHARGE_COUNTER),
             cycleCount = cycleCount(battery),
-            maxChargingCurrentMicroamps = battery.getIntExtra(BatteryManager.EXTRA_MAX_CHARGING_CURRENT, ABSENT),
-            maxChargingVoltageMicrovolts = battery.getIntExtra(BatteryManager.EXTRA_MAX_CHARGING_VOLTAGE, ABSENT),
+            maxChargingCurrentMicroamps = battery.getIntExtra(EXTRA_MAX_CHARGING_CURRENT, ABSENT),
+            maxChargingVoltageMicrovolts = battery.getIntExtra(EXTRA_MAX_CHARGING_VOLTAGE, ABSENT),
         )
     }
 
@@ -68,5 +68,11 @@ class BatteryReader @Inject constructor(
 
         // BatteryManager.EXTRA_CYCLE_COUNT — inlined to avoid a hard API-34 symbol reference.
         const val EXTRA_CYCLE_COUNT = "android.os.extra.CYCLE_COUNT"
+
+        // BatteryManager.EXTRA_MAX_CHARGING_CURRENT/VOLTAGE are @hide: BatteryService puts them into
+        // ACTION_BATTERY_CHANGED, but the constants are absent from the public SDK. The literal keys
+        // are stable AOSP identifiers.
+        const val EXTRA_MAX_CHARGING_CURRENT = "max_charging_current"
+        const val EXTRA_MAX_CHARGING_VOLTAGE = "max_charging_voltage"
     }
 }

app/src/main/java/eu/darken/amply/battery/core/BatteryReadout.kt

@@ -24,9 +24,13 @@ data class BatteryReadout(
     val chargeCounterMicroampHours: Int? = null,
     val cycleCount: Int? = null,
     /**
-     * Charger-advertised maximum, not a measurement: what the connected supply says it can deliver
-     * ([android.os.BatteryManager.EXTRA_MAX_CHARGING_CURRENT] / `EXTRA_MAX_CHARGING_VOLTAGE`). Only
-     * meaningful while something is connected, and never a substitute for the measured draw.
+     * Charger-advertised maximum, not a measurement: what the connected supply says it can deliver.
+     * Only meaningful while something is connected, and never a substitute for the measured draw.
+     *
+     * Sourced from the `max_charging_current` / `max_charging_voltage` extras of
+     * [android.content.Intent.ACTION_BATTERY_CHANGED]. The framework populates them, but their
+     * `BatteryManager` constants are `@hide` and absent from the public SDK, so `BatteryReader` reads
+     * the literal AOSP keys.
      */
     val maxChargingCurrentMicroamps: Int? = null,
     val maxChargingVoltageMicrovolts: Int? = null,