Add preferences for AirPods Identity and Encryption Keys

This commit introduces settings for users to input their AirPods' Identity Resolving Key (IRK) and Encryption Key. These keys, obtainable via a MacBook, allow CAPod to reliably identify the AirPods and decrypt detailed status information.

Key changes:
- Added new preferences in General Settings for IRK and Encryption Key.
- Implemented a custom dialog for key input, including validation and a link to a guide.
- Added a Moshi adapter for serializing/deserializing `ByteArray` to/from Base64 for storing the keys.
- Included new string resources for labels, descriptions, and explanations related to the keys.
- Added new icons for the key preferences.

app/src/main/java/eu/darken/capod/main/ui/settings/general/AirPodKeyInputDialog.kt

@@ -0,0 +1,71 @@
+package eu.darken.capod.main.ui.settings.general
+
+import android.content.Context
+import androidx.appcompat.app.AlertDialog
+import androidx.core.widget.doOnTextChanged
+import com.google.android.material.dialog.MaterialAlertDialogBuilder
+import com.google.android.material.textfield.TextInputEditText
+import com.google.android.material.textfield.TextInputLayout
+import eu.darken.capod.R
+import eu.darken.capod.common.UIConverter
+
+class AirPodKeyInputDialog(private val context: Context) {
+    fun create(
+        mode: Mode,
+        current: String,
+        onKey: (String) -> Unit,
+        onGuide: () -> Unit,
+    ): AlertDialog {
+        val inputEditText = TextInputEditText(context).apply {
+            setText(current)
+        }
+        val inputLayout =
+            TextInputLayout(context, null, com.google.android.material.R.attr.textInputOutlinedStyle).apply {
+                hint = context.getString(
+                    R.string.general_example_label,
+                    "FE-D0-1C-54-11-81-BC-BC-87-D2-C4-3F-31-64-5F-EE"
+                )
+                addView(inputEditText)
+                val padding = UIConverter.convertDpToPixels(context, 24f)
+                setPadding(padding, padding / 2, padding, 0)
+            }
+
+        val dialog = MaterialAlertDialogBuilder(context).apply {
+            setView(inputLayout)
+            when (mode) {
+                Mode.IRK -> {
+                    setTitle(R.string.settings_maindevice_identitykey_label)
+                    setMessage(R.string.settings_maindevice_identitykey_explanation)
+                }
+
+                Mode.ENC -> {
+                    setTitle(R.string.settings_maindevice_encryptionkey_label)
+                    setMessage(R.string.settings_maindevice_encryptionkey_explanation)
+                }
+            }
+
+            setPositiveButton(R.string.general_save_action) { _, _ -> onKey(inputEditText.text.toString()) }
+            setNegativeButton(R.string.general_cancel_action) { _, _ -> }
+            setNeutralButton(R.string.general_guide_action) { _, _ -> onGuide() }
+        }.create()
+
+        dialog.setOnShowListener {
+            val saveButton = dialog.getButton(AlertDialog.BUTTON_POSITIVE)
+
+            val keyRegex = Regex("^([0-9A-F]{2}-){15}[0-9A-F]{2}$")
+            fun validateInput() {
+                val isValid = inputEditText.text.toString().matches(keyRegex)
+                saveButton.isEnabled = isValid || inputEditText.length() == 0
+            }
+            inputEditText.doOnTextChanged { _, _, _, _ -> validateInput() }
+            validateInput()
+        }
+        return dialog
+    }
+
+    enum class Mode {
+        IRK,
+        ENC,
+        ;
+    }
+}

app/src/main/java/eu/darken/capod/main/ui/settings/general/GeneralSettingsFragment.kt

@@ -8,6 +8,7 @@ import androidx.preference.ListPreference
 import androidx.preference.Preference
 import dagger.hilt.android.AndroidEntryPoint
 import eu.darken.capod.R
+import eu.darken.capod.common.WebpageTool
 import eu.darken.capod.common.bluetooth.ScannerMode
 import eu.darken.capod.common.preferences.PercentSliderPreference
 import eu.darken.capod.common.uix.PreferenceFragment3
@@ -25,6 +26,7 @@ class GeneralSettingsFragment : PreferenceFragment3() {
 
     @Inject lateinit var generalSettings: GeneralSettings
     @Inject lateinit var upgradeRepo: UpgradeRepo
+    @Inject lateinit var webpageTool: WebpageTool
 
     override val settings: GeneralSettings
         get() = generalSettings
@@ -35,6 +37,8 @@ class GeneralSettingsFragment : PreferenceFragment3() {
     private val scanModePref by lazy { findPreference<ListPreference>(generalSettings.scannerMode.key)!! }
     private val mainDeviceAddressPref by lazy { findPreference<Preference>(generalSettings.mainDeviceAddress.key)!! }
     private val mainDeviceModelPref by lazy { findPreference<Preference>(generalSettings.mainDeviceModel.key)!! }
+    private val mainDeviceIdentityKeyPref by lazy { findPreference<Preference>(generalSettings.mainDeviceIdentityKey.key)!! }
+    private val mainDeviceEncryptionKeyPref by lazy { findPreference<Preference>(generalSettings.mainDeviceEncryptionKey.key)!! }
 
     override fun onPreferencesCreated() {
         monitorModePref.apply {
@@ -45,9 +49,32 @@ class GeneralSettingsFragment : PreferenceFragment3() {
             entries = ScannerMode.values().map { getString(it.labelRes) }.toTypedArray()
             entryValues = ScannerMode.values().map { settings.scannerMode.rawWriter(it) as String }.toTypedArray()
         }
+        mainDeviceIdentityKeyPref.setOnPreferenceClickListener {
+            AirPodKeyInputDialog(requireContext()).create(
+                mode = AirPodKeyInputDialog.Mode.IRK,
+                current = generalSettings.mainDeviceIdentityKey.value?.toHumanReadable() ?: "",
+                onKey = { generalSettings.mainDeviceIdentityKey.value = it.fromHumanReadable() },
+                onGuide = { webpageTool.open("https://github.com/d4rken-org/capod/wiki/airpod-Keys") }
+            ).show()
+            true
+        }
+        mainDeviceEncryptionKeyPref.setOnPreferenceClickListener {
+            AirPodKeyInputDialog(requireContext()).create(
+                mode = AirPodKeyInputDialog.Mode.ENC,
+                current = generalSettings.mainDeviceEncryptionKey.value?.toHumanReadable() ?: "",
+                onKey = { generalSettings.mainDeviceEncryptionKey.value = it.fromHumanReadable() },
+                onGuide = { webpageTool.open("https://github.com/d4rken-org/capod/wiki/airpod-Keys") }
+            ).show()
+            true
+        }
+
         super.onPreferencesCreated()
     }
 
+    private fun ByteArray.toHumanReadable(): String = joinToString("-") { "%02X".format(it) }
+
+    private fun String.fromHumanReadable(): ByteArray = split("-").map { it.toInt(16).toByte() }.toByteArray()
+
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         vm.bondedDevices.observe2 { devices ->
             mainDeviceAddressPref.setOnPreferenceClickListener {

app/src/main/res/drawable/ic_key_24.xml

@@ -0,0 +1,11 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorControlNormal"
+    android:autoMirrored="true">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M7 14C5.9 14 5 13.1 5 12S5.9 10 7 10 9 10.9 9 12 8.1 14 7 14M12.6 10C11.8 7.7 9.6 6 7 6C3.7 6 1 8.7 1 12S3.7 18 7 18C9.6 18 11.8 16.3 12.6 14H16V18H20V14H23V10H12.6Z" />
+</vector>

app/src/main/res/drawable/ic_key_outline_24.xml

@@ -0,0 +1,11 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorControlNormal"
+    android:autoMirrored="true">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M21 18H15V15H13.3C12.2 17.4 9.7 19 7 19C3.1 19 0 15.9 0 12S3.1 5 7 5C9.7 5 12.2 6.6 13.3 9H24V15H21V18M17 16H19V13H22V11H11.9L11.7 10.3C11 8.3 9.1 7 7 7C4.2 7 2 9.2 2 12S4.2 17 7 17C9.1 17 11 15.7 11.7 13.7L11.9 13H17V16M7 15C5.3 15 4 13.7 4 12S5.3 9 7 9 10 10.3 10 12 8.7 15 7 15M7 11C6.4 11 6 11.4 6 12S6.4 13 7 13 8 12.6 8 12 7.6 11 7 11Z" />
+</vector>

app/src/main/res/values/strings.xml

@@ -7,6 +7,11 @@
     <string name="general_upgrade_action">Upgrade</string>
     <string name="general_check_action">Check</string>
     <string name="general_close_action">Close</string>
+    <string name="general_save_action">Save</string>
+    <string name="general_guide_action">Guide</string>
+    <string name="general_continue_action">Continue</string>
+
+    <string name="general_example_label">E.g.: %s</string>
 
     <string name="upgrade_capod_label">Upgrade CAPod</string>
     <string name="upgrade_capod_description">Get additional features and support the developer.</string>
@@ -49,6 +54,13 @@
     <string name="settings_maindevice_address_none">None</string>
     <string name="settings_maindevice_model_label">Your device model</string>
     <string name="settings_maindevice_model_description">The model of your main device. This helps the app recognize your device when it is not connected to your phone.</string>
+    <string name="settings_maindevice_identitykey_label">Identity Key</string>
+    <string name="settings_maindevice_identitykey_description">Your device\'s Identity Resolving Key (IRK), which helps CAPod identify it among nearby devices.</string>
+    <string name="settings_maindevice_identitykey_explanation">AirPods frequently change their Bluetooth address for privacy. The IRK helps CAPod recognize your device. You need one-time access to a MacBook.</string>
+    <string name="settings_maindevice_encryptionkey_label">Encryption Key</string>
+    <string name="settings_maindevice_encryptionkey_description">Your device\'s encryption key, which allows CAPod to retrieve detailed status information.</string>
+    <string name="settings_maindevice_encryptionkey_explanation">AirPods send a status message, part of which is encrypted. The encryption key allows CAPod to decrypt the full message. You need one-time access to a MacBook.</string>
+
     <string name="settings_onepod_mode_label">One pod mode</string>
     <string name="settings_onepod_mode_description">Wearing both pods is not required, wearing a single pod is sufficient to trigger reactions.</string>
     <string name="settings_popup_caseopen_label">Show case popup</string>
@@ -134,6 +146,4 @@
     <string name="onboarding_body3">CAPod has no ads and does not collect your data.</string>
     <string name="onboarding_body4">You can upgrade to CAPod Pro to gain extra features and support development.</string>
 
-    <string name="general_continue_action">Continue</string>
-
 </resources>

app/src/main/res/xml/preferences_general.xml

@@ -41,6 +41,18 @@
             android:key="core.maindevice.model"
             android:summary="@string/settings_maindevice_model_description"
             android:title="@string/settings_maindevice_model_label" />
+
+        <Preference
+            android:icon="@drawable/ic_key_outline_24"
+            android:key="core.maindevice.identitykey"
+            android:summary="@string/settings_maindevice_identitykey_description"
+            android:title="@string/settings_maindevice_identitykey_label" />
+
+        <Preference
+            android:icon="@drawable/ic_key_24"
+            android:key="core.maindevice.encryptionkey"
+            android:summary="@string/settings_maindevice_encryptionkey_description"
+            android:title="@string/settings_maindevice_encryptionkey_label" />
     </PreferenceCategory>
 
     <PreferenceCategory