Merge pull request #8 from hotwired/new-message

Create new message instance from existing message

strada/src/main/kotlin/dev/hotwire/strada/Message.kt

@@ -22,4 +22,19 @@ data class Message(
      * For a "page" component, this might be `{"title": "Page Title"}`
      */
     val jsonData: String
-)
+) {
+    /**
+     * Convenience method for creating a new message from an existing message,
+     * replacing its `event` and/or `jsonData`. The new message can be sent
+     * back to the over the bridge to notify the web of a change/action.
+     */
+    fun replacing(
+        event: String = this.event,
+        jsonData: String = this.jsonData
+    ) = Message(
+        id = this.id,
+        component = this.component,
+        event = event,
+        jsonData = jsonData
+    )
+}

strada/src/test/kotlin/dev/hotwire/strada/MessageTest.kt

@@ -0,0 +1,26 @@
+package dev.hotwire.strada
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class MessageTest {
+    @Test
+    fun replacing() {
+        val message = Message(
+            id = "1",
+            component = "page",
+            event = "connect",
+            jsonData = """{"title":"Page-title","subtitle":"Page-subtitle"}"""
+        )
+
+        val newMessage = message.replacing(
+            event = "disconnect",
+            jsonData = "{}"
+        )
+
+        assertEquals("1", newMessage.id)
+        assertEquals("page", newMessage.component)
+        assertEquals("disconnect", newMessage.event)
+        assertEquals("{}", newMessage.jsonData)
+    }
+}