refactor: replace transactionType String with TransactionType enum

tgbotapi.core/src/commonMain/kotlin/dev/inmo/tgbotapi/types/payments/stars/TransactionPartner.kt

@@ -49,7 +49,7 @@ sealed interface TransactionPartner {
         @SerialName(userField)
         val user: PreviewUser,
         @SerialName(transactionTypeField)
-        val transactionType: String,
+        val transactionType: TransactionType,
         @SerialName(affiliateField)
         val affiliate: AffiliateInfo? = null,
         @SerialName(invoicePayloadField)
@@ -156,7 +156,7 @@ sealed interface TransactionPartner {
             val paid_media_payload: PaidMediaPayload? = null,
             val gift: Gift? = null,
             val premium_subscription_duration: Int? = null,
-            val transaction_type: String? = null,
+            val transaction_type: TransactionType? = null,
             val request_count: Int? = null,
             val sponsor_user: PreviewBot? = null,
             val commission_per_mille: Int? = null,

tgbotapi.core/src/commonMain/kotlin/dev/inmo/tgbotapi/types/payments/stars/TransactionType.kt

@@ -0,0 +1,38 @@
+package dev.inmo.tgbotapi.types.payments.stars
+
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.descriptors.PrimitiveKind
+import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+
+@Serializable(with = TransactionTypeSerializer::class)
+enum class TransactionType {
+    INVOICE_PAYMENT,
+    PAID_MEDIA_PAYMENT,
+    GIFT_PURCHASE,
+    PREMIUM_PURCHASE,
+    BUSINESS_ACCOUNT_TRANSFER,
+    UNKNOWN
+}
+
+private object TransactionTypeSerializer : KSerializer<TransactionType> {
+    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor(
+        serialName = "dev.inmo.tgbotapi.types.payments.stars.TransactionType",
+        kind = PrimitiveKind.STRING
+    )
+
+    override fun deserialize(decoder: Decoder): TransactionType {
+        return try {
+            TransactionType.valueOf(decoder.decodeString())
+        } catch (e: IllegalArgumentException) {
+            TransactionType.UNKNOWN
+        }
+    }
+
+    override fun serialize(encoder: Encoder, value: TransactionType) {
+        encoder.encodeString(value.name)
+    }
+}