refactor: migrate to kotlinx serialization, eliminate gson dependency

app/src/main/java/com/bitcointxoko/gudariwallet/api/Models.kt

@@ -1,50 +1,66 @@
 package com.bitcointxoko.gudariwallet.api
 
 import androidx.compose.runtime.Immutable
-import com.google.gson.TypeAdapter
-import com.google.gson.annotations.JsonAdapter
-import com.google.gson.annotations.SerializedName
-import com.google.gson.stream.JsonReader
-import com.google.gson.stream.JsonToken
-import com.google.gson.stream.JsonWriter
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.descriptors.buildClassSerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+import kotlinx.serialization.json.JsonDecoder
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonEncoder
+import kotlinx.serialization.json.JsonNull
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 
 // ── Wallet ────────────────────────────────────────────────────────────────────
+@Serializable
 data class WalletResponse(
-    val id: String,
-    val name: String,
-    val balance: Long       // millisatoshis
+    val id: String = "",
+    val name: String = "",
+    val balance: Long = 0L      // millisatoshis
 )
 
 // ── Create invoice ────────────────────────────────────────────────────────────
+@Serializable
 data class CreateInvoiceRequest(
     val out: Boolean,
     val amount: Long,       // satoshis
     val memo: String
 )
 
+@Serializable
 data class CreateInvoiceResponse(
-    @SerializedName("payment_hash")    val paymentHash: String,
-    @SerializedName("payment_request") val paymentRequest: String,
-    @SerializedName("expiry")          val expiry        : String?
+    @SerialName("payment_hash")    val paymentHash: String,
+    @SerialName("payment_request") val paymentRequest: String,
+    @SerialName("expiry")          val expiry: String?
 )
 
 // ── Pay invoice ───────────────────────────────────────────────────────────────
+@Serializable
 data class PayInvoiceRequest(
     val out: Boolean,
     val bolt11: String
 )
 
+@Serializable
 data class PayInvoiceResponse(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String
+    @SerialName("payment_hash") val paymentHash: String,
+    @SerialName("checking_id")  val checkingId: String
 )
 
 // ── Check payment ─────────────────────────────────────────────────────────────
+@Serializable
 data class PaymentStatusResponse(
     val paid: Boolean,
     val details: PaymentDetails? = null
 )
 
+@Serializable
 data class PaymentDetails(
     val amount: Long?,
     val fee: Long?,
@@ -52,82 +68,80 @@ data class PaymentDetails(
 )
 
 // ── Decode BOLT-11 ────────────────────────────────────────────────────────────
+@Serializable
 data class DecodeInvoiceRequest(
     val data: String
 )
 
+@Serializable
 data class DecodeInvoiceResponse(
-    @SerializedName("payment_hash") val paymentHash  : String? = null,
-    @SerializedName("amount_msat")  val amountMsat   : Long?   = null,
-    @SerializedName("description")  val description  : String? = null,
-    @SerializedName("payee")        val payee        : String? = null,
-    @SerializedName("route_hints")  val routeHints   : List<List<RouteHintHop>>? = null
+    @SerialName("payment_hash") val paymentHash: String?            = null,
+    @SerialName("amount_msat")  val amountMsat: Long?               = null,
+    @SerialName("description")  val description: String?            = null,
+    @SerialName("payee")        val payee: String?                  = null,
+    @SerialName("route_hints")  val routeHints: List<List<RouteHintHop>>? = null
 )
 
-
+@Serializable
 data class RouteHintHop(
-    @SerializedName("public_key")         val publicKey       : String,
-    @SerializedName("short_channel_id")   val shortChannelId  : String? = null,
-    @SerializedName("base_fee")           val baseFeeMsat     : Long    = 0,
-    @SerializedName("ppm_fee")            val ppmFee          : Long    = 0,
-    @SerializedName("cltv_expiry_delta")  val cltvExpiryDelta : Int     = 0
+    @SerialName("public_key")        val publicKey: String,
+    @SerialName("short_channel_id")  val shortChannelId: String?  = null,
+    @SerialName("base_fee")          val baseFeeMsat: Long        = 0,
+    @SerialName("ppm_fee")           val ppmFee: Long             = 0,
+    @SerialName("cltv_expiry_delta") val cltvExpiryDelta: Int     = 0
 )
 
 // ── LNURL scan ────────────────────────────────────────────────────────────────
+@Serializable
 data class LnurlScanResponse(
     val tag: String?,
-    // ── payRequest fields ────────────────────────────────────────────────────
-    val callback: String?                = null,
-    @SerializedName("minSendable")    val minSendable: Long?    = null,
-    @SerializedName("maxSendable")    val maxSendable: Long?    = null,
-    val metadata: String?                = null,
-    @SerializedName("commentAllowed") val commentAllowed: Int?  = null,
-    @SerializedName("allowsNostr")    val allowsNostr: Boolean? = null,
-    @SerializedName("nostrPubkey")    val nostrPubkey: String?  = null,
-    val bolt11: String?                  = null,
-    @SerializedName("amount_msat")    val amountMsat: Long?     = null,
-    val disposable: Boolean?             = null,  // LUD-06: null means treat as true (do not cache)
-    // ── withdrawRequest fields ───────────────────────────────────────────────
-    val k1               : String?  = null,
-    @SerializedName("defaultDescription")
-    val defaultDescription: String? = null,
-    @SerializedName("minWithdrawable")
-    val minWithdrawable  : Long?    = null,
-    @SerializedName("maxWithdrawable")
-    val maxWithdrawable  : Long?    = null,
-    @SerializedName("balanceCheck")
-    val balanceCheck     : String?  = null,
-    @SerializedName("currentBalance")
-    val currentBalance   : Long?    = null,
-    // ── Error fields ─────────────────────────────────────────────────────────
-    val status         : String?  = null,   // "OK" or "ERROR"
-    val reason         : String?  = null    // error message when status == "ERROR"
+    // ── payRequest fields ─────────────────────────────────────────────────────
+    val callback: String?                       = null,
+    @SerialName("minSendable")    val minSendable: Long?           = null,
+    @SerialName("maxSendable")    val maxSendable: Long?           = null,
+    val metadata: String?                       = null,
+    @SerialName("commentAllowed") val commentAllowed: Int?         = null,
+    @SerialName("allowsNostr")    val allowsNostr: Boolean?        = null,
+    @SerialName("nostrPubkey")    val nostrPubkey: String?         = null,
+    val bolt11: String?                         = null,
+    @SerialName("amount_msat")    val amountMsat: Long?            = null,
+    val disposable: Boolean?                    = null,  // LUD-06: null means treat as true (do not cache)
+    // ── withdrawRequest fields ────────────────────────────────────────────────
+    val k1: String?                             = null,
+    @SerialName("defaultDescription") val defaultDescription: String? = null,
+    @SerialName("minWithdrawable")    val minWithdrawable: Long?   = null,
+    @SerialName("maxWithdrawable")    val maxWithdrawable: Long?   = null,
+    @SerialName("balanceCheck")       val balanceCheck: String?    = null,
+    @SerialName("currentBalance")     val currentBalance: Long?    = null,
+    // ── Error fields ──────────────────────────────────────────────────────────
+    val status: String?                         = null,  // "OK" or "ERROR"
+    val reason: String?                         = null   // error message when status == "ERROR"
 )
 
 // ── LNURL-pay callback response (LUD-06) ─────────────────────────────────────
+@Serializable
 data class LnurlCallbackResponse(
-    val pr            : String,           // BOLT-11 invoice to pay
-    val routes        : List<Any>?  = null,
-    @SerializedName("successAction")
-    val successAction : SuccessAction? = null,
-    // Error fields (server may return status=ERROR instead of pr)
-    val status        : String?     = null,
-    val reason        : String?     = null
+    val pr: String,
+    val routes: List<JsonElement>? = null,
+    @SerialName("successAction") val successAction: SuccessAction? = null,
+    val status: String? = null,
+    val reason: String? = null
 )
 
-
 // ── LNURL pay ─────────────────────────────────────────────────────────────────
+@Serializable
 data class LnurlPayRes(
     val tag: String?,
     val callback: String?,
-    @SerializedName("minSendable")    val minSendable: Long?,
-    @SerializedName("maxSendable")    val maxSendable: Long?,
+    @SerialName("minSendable")    val minSendable: Long?,
+    @SerialName("maxSendable")    val maxSendable: Long?,
     val metadata: String?,
-    @SerializedName("commentAllowed") val commentAllowed: Int?,
-    @SerializedName("allowsNostr")    val allowsNostr: Boolean? = null,
-    @SerializedName("nostrPubkey")    val nostrPubkey: String?  = null
+    @SerialName("commentAllowed") val commentAllowed: Int?,
+    @SerialName("allowsNostr")    val allowsNostr: Boolean? = null,
+    @SerialName("nostrPubkey")    val nostrPubkey: String?  = null
 )
 
+@Serializable
 data class PayLnurlRequest(
     val res: LnurlPayRes,
     val lnurl: String,
@@ -135,45 +149,48 @@ data class PayLnurlRequest(
     val comment: String? = null
 )
 
+@Serializable
 data class PayLnurlResponse(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String
+    @SerialName("payment_hash") val paymentHash: String,
+    @SerialName("checking_id")  val checkingId: String
 )
 
+@Serializable
 data class WithdrawCallbackResponse(
-    val status : String,
-    val reason : String? = null
+    val status: String,
+    val reason: String? = null
 )
 
 // ── LNURLp pay link (lightning address) ──────────────────────────────────────
+@Serializable
 data class LnurlpLink(
-    val id          : String,
-    val wallet      : String,
-    val username    : String?,      // the part before the @ in the lightning address
-    val description : String?,
-    val min         : Long,
-    val max         : Long
+    val id: String,
+    val wallet: String,
+    val username: String?,      // the part before the @ in the lightning address
+    val description: String?,
+    @Serializable(with = LongAsDoubleSerializer::class) val min: Long,
+    @Serializable(with = LongAsDoubleSerializer::class) val max: Long
 )
 
-
 // ── Payment history ───────────────────────────────────────────────────────────
 @Immutable
+@Serializable
 data class PaymentRecord(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String,
-    @SerializedName("amount")       val amountMsat: Long,
-    @SerializedName("fee")          val feeMsat: Long,
-    @SerializedName("memo")         val memo: String?,
-    @SerializedName("time")         val time: String,
-    @SerializedName("status")       val status: String,
-    @SerializedName("bolt11")       val bolt11: String?,
-    @SerializedName("pending")      val pending: Boolean,
-    @SerializedName("preimage")     val preimage: String?,
-    @SerializedName("extra")        val extra: PaymentExtra?,
+    @SerialName("payment_hash") val paymentHash: String = "",
+    @SerialName("checking_id")  val checkingId: String  = "",
+    @SerialName("amount")       val amountMsat: Long     = 0L,
+    @SerialName("fee")          val feeMsat: Long        = 0L,
+    @SerialName("memo")         val memo: String?        = null,
+    @SerialName("time")         val time: String         = "",
+    @SerialName("status")       val status: String       = "",
+    @SerialName("bolt11")       val bolt11: String?      = null,
+    @SerialName("pending")      val pending: Boolean     = false,
+    @SerialName("preimage")     val preimage: String?    = null,
+    @SerialName("extra")        val extra: PaymentExtra? = null,
     // Not from the API — populated only when loaded from Room via toDomain()
     val createdAt: Long? = null,
-    val pubkey: String? = null,
-    val alias:  String? = null
+    val pubkey: String?  = null,
+    val alias: String?   = null
 ) {
     val amountSat: Long     get() = kotlin.math.abs(amountMsat) / 1000L
     val feeSat: Long        get() = kotlin.math.abs(feeMsat)    / 1000L
@@ -181,13 +198,13 @@ data class PaymentRecord(
 
     companion object {
         fun fromPayment(
-            paymentHash : String,
-            amountSats  : Long,
-            feeSats     : Long?,
-            bolt11      : String?,
-            memo        : String?,
-            pubkey      : String?,
-            alias       : String?,
+            paymentHash: String,
+            amountSats: Long,
+            feeSats: Long?,
+            bolt11: String?,
+            memo: String?,
+            pubkey: String?,
+            alias: String?,
         ): PaymentRecord = PaymentRecord(
             paymentHash = paymentHash,
             checkingId  = paymentHash,
@@ -207,23 +224,25 @@ data class PaymentRecord(
 }
 
 @Immutable
-
+@Serializable
 data class PaymentExtra(
-    @SerializedName("tag")            val tag: String?,
-    @JsonAdapter(FlexibleStringAdapter::class)
-    val comment: String?,
-    @SerializedName("success_action") val successAction: SuccessAction?,
-    @SerializedName("wallet_id")      val walletId: String?,
-    @SerializedName("destination")    val destination: String?,
-    @SerializedName("expires_at")     val expiresAt: String?
+    @SerialName("tag")            val tag: String?            = null,
+    @Serializable(with = FlexibleStringSerializer::class)
+    val comment: String?        = null,
+    @SerialName("success_action") @Serializable(with = SuccessActionSerializer::class)
+    val successAction: SuccessAction? = null,
+    @SerialName("wallet_id")      val walletId: String?       = null,
+    @SerialName("destination")    val destination: String?    = null,
+    @SerialName("expires_at")     val expiresAt: String?      = null
 )
 
 @Immutable
+@Serializable(with = SuccessActionSerializer::class)
 data class SuccessAction(
-    @SerializedName("tag")         val tag: String?,
-    @SerializedName("message")     val message: String?,
-    @SerializedName("url")         val url: String?,
-    @SerializedName("description") val description: String?
+    @SerialName("tag")         val tag: String?,
+    @SerialName("message")     val message: String?,
+    @SerialName("url")         val url: String?,
+    @SerialName("description") val description: String?
 )
 
 /**
@@ -232,99 +251,101 @@ data class SuccessAction(
  *   - a plain string "Thanks!"
  *   - null
  *
- * Gson's default deserialiser throws IllegalStateException when it sees a
- * string where it expects {. This adapter handles all three cases.
+ * kotlinx.serialization's default deserialiser throws when it sees a
+ * string where it expects {. This serializer handles all three cases.
  *
- * Registered centrally in [GsonProvider] — applies to all deserialization
- * paths automatically.
+ * Applied via @Serializable(with = SuccessActionSerializer::class) on
+ * the SuccessAction class and on PaymentExtra.successAction.
  */
-class SuccessActionAdapter : TypeAdapter<SuccessAction?>() {
+object SuccessActionSerializer : KSerializer<SuccessAction?> {
 
-    override fun write(out: JsonWriter, value: SuccessAction?) {
-        if (value == null) { out.nullValue(); return }
-        out.beginObject()
-        out.name("tag");         out.value(value.tag)
-        out.name("message");     out.value(value.message)
-        out.name("url");         out.value(value.url)
-        out.name("description"); out.value(value.description)
-        out.endObject()
+    override val descriptor: SerialDescriptor =
+        buildClassSerialDescriptor("SuccessAction")
+
+    override fun serialize(encoder: Encoder, value: SuccessAction?) {
+        val jsonEncoder = encoder as JsonEncoder
+        if (value == null) {
+            jsonEncoder.encodeJsonElement(JsonNull)
+        } else {
+            jsonEncoder.encodeJsonElement(
+                JsonObject(
+                    mapOf(
+                        "tag"         to JsonPrimitive(value.tag),
+                        "message"     to JsonPrimitive(value.message),
+                        "url"         to JsonPrimitive(value.url),
+                        "description" to JsonPrimitive(value.description)
+                    )
+                )
+            )
+        }
     }
 
-    override fun read(reader: JsonReader): SuccessAction? {
-        return when (reader.peek()) {
-            JsonToken.NULL -> { reader.nextNull(); null }
-
-            // Plain string — treat as a message-type success action
-            JsonToken.STRING -> {
-                val text = reader.nextString()
+    override fun deserialize(decoder: Decoder): SuccessAction? {
+        val jsonDecoder = decoder as JsonDecoder
+        return when (val element = jsonDecoder.decodeJsonElement()) {
+            is JsonNull      -> null
+            is JsonPrimitive -> {
+                // Plain string — treat as a message-type success action
+                val text = element.jsonPrimitive.content
                 if (text.isBlank()) null
                 else SuccessAction(tag = "message", message = text, url = null, description = null)
             }
-
-            // Normal object
-            JsonToken.BEGIN_OBJECT -> {
-                reader.beginObject()
-                var tag: String? = null
-                var message: String? = null
-                var url: String? = null
-                var description: String? = null
-                while (reader.hasNext()) {
-                    when (reader.nextName()) {
-                        "tag"         -> tag         = reader.nextString()
-                        "message"     -> message     = reader.nextString()
-                        "url"         -> url         = reader.nextString()
-                        "description" -> description = reader.nextString()
-                        else          -> reader.skipValue()
-                    }
-                }
-                reader.endObject()
-                SuccessAction(tag = tag, message = message, url = url, description = description)
+            is JsonObject    -> {
+                SuccessAction(
+                    tag         = element.jsonObject["tag"]?.jsonPrimitive?.content,
+                    message     = element.jsonObject["message"]?.jsonPrimitive?.content,
+                    url         = element.jsonObject["url"]?.jsonPrimitive?.content,
+                    description = element.jsonObject["description"]?.jsonPrimitive?.content
+                )
             }
-
-            else -> { reader.skipValue(); null }
+            else             -> null
         }
     }
 }
+
 data class PaymentDetailResponse(
     val paid: Boolean,
     val details: PaymentRecord?
 )
 
 // ── WebSocket payment message ─────────────────────────────────────────────────
+@Serializable
 data class WsPaymentMessage(
-    @SerializedName("wallet_balance") val walletBalance: Long?,
+    @SerialName("wallet_balance") val walletBalance: Long?,
     val payment: WsPayment?
 )
 
+@Serializable
 data class WsPayment(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String,
-    @SerializedName("amount")       val amount: Long,
-    @SerializedName("fee")          val fee: Long,
-    @SerializedName("memo")         val memo: String?,
-    @SerializedName("time")         val time: String,
-    @SerializedName("status")       val status: String,
-    @SerializedName("bolt11")       val bolt11: String?,
-    @SerializedName("pending")      val pending: Boolean,
-    @SerializedName("preimage")     val preimage: String?,
-    @SerializedName("extra")        val extra: PaymentExtra?
+    @SerialName("payment_hash") val paymentHash: String,
+    @SerialName("checking_id")  val checkingId: String,
+    @SerialName("amount")       val amount: Long,
+    @SerialName("fee")          val fee: Long,
+    @SerialName("memo")         val memo: String?,
+    @SerialName("time")         val time: String,
+    @SerialName("status")       val status: String,
+    @SerialName("bolt11")       val bolt11: String?,
+    @SerialName("pending")      val pending: Boolean,
+    @SerialName("preimage")     val preimage: String?,
+    @SerialName("extra")        val extra: PaymentExtra?
 )
 
-
-// ── Fiat rate ────────────────────────────────────────────────────────────────
+// ── Fiat rate ─────────────────────────────────────────────────────────────────
+@Serializable
 data class FiatRateResponse(
     val rate: Double,   // sat to fiat rate
-    val price : Double  // BTC price in the requested fiat currency
+    val price: Double   // BTC price in the requested fiat currency
 )
 
-// ── History sync ─────────────────────────────────────────────────────────────
+// ── History sync ──────────────────────────────────────────────────────────────
+@Serializable
 data class PaginatedPaymentsResponse(
-    @SerializedName("data")  val data:  List<PaymentRecord>,
-    @SerializedName("total") val total: Int
+    @SerialName("data")  val data: List<PaymentRecord>,
+    @SerialName("total") val total: Int
 )
 
 // ── NWC Provider models ───────────────────────────────────────────────────────
-
+@Serializable
 data class NwcKey(
     val pubkey: String,
     val wallet: String,
@@ -335,6 +356,7 @@ data class NwcKey(
     val last_used: Long
 )
 
+@Serializable
 data class NwcBudget(
     val id: Int,
     val pubkey: String,
@@ -344,22 +366,41 @@ data class NwcBudget(
     val used_budget_msats: Long = 0
 )
 
-/** Response for GET /nwc and GET /nwc/{pubkey} */
+@Serializable
 data class NwcGetResponse(
     val data: NwcKey,
     val budgets: List<NwcBudget>
 )
 
+@Serializable
 data class NwcNewBudget(
     val budget_msats: Long,
     val refresh_window: Int,        // seconds
-    val created_at    : Long = System.currentTimeMillis() / 1000L
+    val created_at: Long = System.currentTimeMillis() / 1000L
 )
 
-/** Request body for PUT /nwc/{pubkey} */
+@Serializable
 data class NwcRegistrationRequest(
     val permissions: List<String>,
     val description: String,
-    val expires_at: Long,          // unix timestamp; 0 = no expiry
+    val expires_at: Long,           // unix timestamp; 0 = no expiry
     val budgets: List<NwcNewBudget> = emptyList()
 )
+
+/**
+ * Deserializes a JSON number that may arrive as either an integer (1)
+ * or a float (1.0) into a Long, truncating any fractional part.
+ */
+object LongAsDoubleSerializer : KSerializer<Long> {
+    override val descriptor = buildClassSerialDescriptor("LongAsDouble")
+
+    override fun serialize(encoder: Encoder, value: Long) = encoder.encodeLong(value)
+
+    override fun deserialize(decoder: Decoder): Long {
+        val jsonDecoder = decoder as JsonDecoder
+        return when (val element = jsonDecoder.decodeJsonElement()) {
+            is JsonPrimitive -> element.content.toDouble().toLong()
+            else -> 0L
+        }
+    }
+}