feat(settings): NIP-78 cross-device sync of Interface preferences

WALLET_PARITY.md

@@ -772,25 +772,25 @@ existing wallet have no obvious entry point.
 
 **Restructure per §2.6**:
 
-- [ ] Replace the top-level layout with the two-row picker (Spark /
+- [x] Replace the top-level layout with the two-row picker (Spark /
       NWC) described in §2.6 Screen 1.
-- [ ] Add a Spark sub-screen matching §2.6 Screen 2 with four option
+- [x] Add a Spark sub-screen matching §2.6 Screen 2 with four option
       rows (or three when `hasKeypair() == false`).
-- [ ] Move the `maybeAutoCreateDefaultWallet()` entry point to the new
+- [x] Move the `maybeAutoCreateDefaultWallet()` entry point to the new
       "Use my default wallet" row at the top of the Spark sub-screen.
       Ignore `skipAutoCreate` on explicit tap.
-- [ ] Add the string resources from §2.6 to `strings.xml`.
-- [ ] Verify the existing flows still wire through:
+- [x] Add the string resources from §2.6 to `strings.xml`.
+- [x] Verify the existing flows still wire through:
       - Create new wallet → existing BIP39-generate + confirm-backup flow
       - Restore from seed phrase → existing 12-word entry flow
       - Restore from relays → existing NIP-78 backup search flow
       - Nostr Wallet Connect → existing NWC paste-string flow
-- [ ] Disconnect flow on a default wallet says **"Switch Wallet"** and
+- [x] Disconnect flow on a default wallet says **"Switch Wallet"** and
       the body copy refers to the wallet as your *default wallet* —
       never "Wisp wallet" or "wisp wallet".
-- [ ] Settings section header renamed from "Danger Zone" to
+- [x] Settings section header renamed from "Danger Zone" to
       **"Disconnect Wallet"** (per §4.8).
-- [ ] Dashboard welcome banner for default wallets per §3.5 (blue/accent
+- [x] Dashboard welcome banner for default wallets per §3.5 (blue/accent
       tint, key icon, "secured by your key" copy) — separate from the
       existing amber warning banner for custom wallets.
 

app/src/main/kotlin/com/wisp/app/nostr/Nip78.kt

@@ -128,4 +128,97 @@ object Nip78 {
     /** Extract the d-tag value from an event, or null. */
     fun extractDTag(event: NostrEvent): String? =
         event.tags.firstOrNull { it.size >= 2 && it[0] == "d" }?.get(1)
+
+    // ─── App Settings Backup ──────────────────────────────────────────────────
+
+    const val APP_SETTINGS_D_TAG = "wisp-app-settings:v1"
+
+    /**
+     * Versioned, NIP-44-encrypted UI-prefs payload stored as kind 30078.
+     * Every field is optional so older / newer clients round-trip without
+     * data loss. JSON keys match iOS Nip78Backup.AppSettingsPayload
+     * byte-for-byte so the backups are bit-compatible across platforms.
+     */
+    @kotlinx.serialization.Serializable
+    data class AppSettingsPayload(
+        // Reactions (iOS-only UI today; Android round-trips defaultReaction
+        // + defaultReactionEnabled as opaque values so iOS settings survive
+        // an Android publish.)
+        val defaultReaction: String? = null,
+        val defaultReactionEnabled: Boolean? = null,
+        // Quick zaps
+        val quickZapEnabled: Boolean? = null,
+        val quickZapAmountSats: Long? = null,
+        val quickZapAmountFiat: Double? = null,
+        val quickZapMessage: String? = null,
+        val zapIconStyle: String? = null,
+        // Fiat prefs
+        val fiatModeEnabled: Boolean? = null,
+        val fiatCurrency: String? = null,
+        // Zap presets
+        val zapPresetsCSV: String? = null,
+        // Reaction popup state (Android: unicodeEmojis + frequency map in
+        // CustomEmojiRepository; iOS: EmojiRepository).
+        val quickReactions: List<String>? = null,
+        val frequency: Map<String, Int>? = null,
+        // Appearance
+        val largeText: Boolean? = null,
+        val themeName: String? = null,
+        // iOS-only light/dark override today; Android round-trips it.
+        val colorScheme: String? = null,
+        // iOS encodes ARGB as Swift `Int` (64-bit), so values like
+        // 0xFFFF9800 (4_294_940_672) overflow Kotlin's signed 32-bit
+        // Int. Use Long here and convert at the setter — the lower 32
+        // bits round-trip correctly even when Int reads them negative.
+        val accentColorARGB: Long? = null,
+        // Media
+        val autoLoadMedia: Boolean? = null,
+        val videoAutoplay: Boolean? = null,
+        // iOS-only toggle for animated avatars; Android always animates,
+        // so this is round-tripped opaquely.
+        val animateAvatars: Boolean? = null,
+        val mediaLayoutStyle: String? = null,
+        // Posting
+        val clientTagEnabled: Boolean? = null,
+        val postUndoTimerEnabled: Boolean? = null,
+        val postUndoTimerSeconds: Int? = null,
+        val postUndoTimerForReplies: Boolean? = null,
+        val version: Int? = 1
+    )
+
+    private val lenientJson = kotlinx.serialization.json.Json {
+        ignoreUnknownKeys = true
+        encodeDefaults = false
+    }
+
+    /** Build and sign a kind 30078 event carrying the NIP-44-encrypted settings JSON. */
+    suspend fun createAppSettingsEvent(signer: NostrSigner, payload: AppSettingsPayload): NostrEvent {
+        val json = lenientJson.encodeToString(AppSettingsPayload.serializer(), payload)
+        val encrypted = signer.nip44Encrypt(json, signer.pubkeyHex)
+        val tags = listOf(
+            listOf("d", APP_SETTINGS_D_TAG),
+            listOf("encryption", "nip44")
+        )
+        return signer.signEvent(kind = KIND, content = encrypted, tags = tags)
+    }
+
+    /** Decrypt a kind 30078 app-settings event and parse the JSON payload. Returns null on any failure. */
+    suspend fun decryptAppSettings(signer: NostrSigner, event: NostrEvent): AppSettingsPayload? {
+        if (event.content.isBlank()) return null
+        return try {
+            val decrypted = signer.nip44Decrypt(event.content, event.pubkey)
+            lenientJson.decodeFromString(AppSettingsPayload.serializer(), decrypted)
+        } catch (e: Exception) {
+            android.util.Log.w("AppSettingsSync", "decryptAppSettings exception: ${e.javaClass.simpleName}: ${e.message}", e)
+            null
+        }
+    }
+
+    /** Filter to fetch this user's app-settings backup (single addressable event). */
+    fun appSettingsFilter(pubkeyHex: String): Filter = Filter(
+        kinds = listOf(KIND),
+        authors = listOf(pubkeyHex),
+        dTags = listOf(APP_SETTINGS_D_TAG),
+        limit = 1
+    )
 }