adding exchange state machine class

protocol/src/main/kotlin/tbdex/sdk/protocol/ExceptionDeclarations.kt

@@ -0,0 +1,25 @@
+package tbdex.sdk.protocol
+
+/**
+ * InvalidNextMessageException
+ *
+ * @param message the exception message detailing the error
+ */
+class InvalidNextMessageException(message: String? = null)
+  : RuntimeException(message)
+
+/**
+ * ExchangeIdNotFoundException
+ *
+ * @param message the exception message detailing the error
+ */
+class ExchangeIdNotFoundException(message: String? = null)
+  : RuntimeException(message)
+
+/**
+ * UnknownMessageKindException
+ *
+ * @param message the exception message detailing the error
+ */
+class UnknownMessageKindException(message: String? = null)
+  : RuntimeException(message)

protocol/src/main/kotlin/tbdex/sdk/protocol/Exchange.kt

@@ -0,0 +1,83 @@
+package tbdex.sdk.protocol
+
+import tbdex.sdk.protocol.models.Close
+import tbdex.sdk.protocol.models.Message
+import tbdex.sdk.protocol.models.MessageKind
+import tbdex.sdk.protocol.models.Order
+import tbdex.sdk.protocol.models.OrderStatus
+import tbdex.sdk.protocol.models.Quote
+import tbdex.sdk.protocol.models.Rfq
+
+class Exchange(
+  var rfq: Rfq? = null,
+  var quote: Quote? = null,
+  var order: Order? = null,
+  var orderStatus: MutableList<OrderStatus> = mutableListOf(),
+  var close: Close? = null
+) {
+
+  fun addMessages(messages: List<Message>) {
+
+    val sortedMessages = messages.sortedBy { it.metadata.createdAt }
+
+    for (message in sortedMessages) {
+      this.addNextMessage(message)
+    }
+  }
+
+  fun addNextMessage(message: Message) {
+    if (!this.isValidNext(message.metadata.kind)) {
+      throw InvalidNextMessageException(
+        "Could not add message ${message.metadata.id} to Exchange because" +
+          "${message.metadata.kind} is not a valid next message for this Exchange"
+      )
+    }
+
+    if (this.exchangeId() != null &&
+      message.metadata.exchangeId.toString() != this.exchangeId()) {
+      throw ExchangeIdNotFoundException(
+        "Could not add message ${message.metadata.id} to Exchange because" +
+          "it does not have matching exchange id ${this.exchangeId()}"
+      )
+    }
+
+    when (message.metadata.kind) {
+      MessageKind.rfq -> this.rfq = message as Rfq
+      MessageKind.quote -> this.quote = message as Quote
+      MessageKind.order -> this.order = message as Order
+      MessageKind.orderstatus -> {
+        this.orderStatus.add(message as OrderStatus)
+      }
+
+      MessageKind.close -> this.close = message as Close
+      else -> throw UnknownMessageKindException("Unrecognized message kind")
+    }
+
+  }
+
+  fun isValidNext(kind: MessageKind): Boolean {
+    val validNext = this.latestMessage()?.validNext ?: setOf(MessageKind.rfq)
+    return validNext.contains(kind)
+  }
+
+  fun latestMessage(): Message? {
+    return when {
+      this.close != null -> this.close
+      this.orderStatus.isNotEmpty() -> this.orderStatus.last()
+      this.order != null -> this.order
+      this.quote != null -> this.quote
+      this.rfq != null -> this.rfq
+      else -> null
+    }
+  }
+
+  fun exchangeId(): String? {
+    return this.rfq?.metadata?.exchangeId?.toString()
+  }
+
+  fun messages(): List<Message> {
+    return listOfNotNull(this.rfq, this.quote, this.order, this.close) +
+      (this.orderStatus)
+  }
+
+}