Retrigger events that arrive too early

d2m/actions/retrigger.js

@@ -0,0 +1,61 @@
+// @ts-check
+
+const {EventEmitter} = require("events")
+const passthrough = require("../../passthrough")
+const {select} = passthrough
+
+const DEBUG_RETRIGGER = false
+
+function debugRetrigger(message) {
+	if (DEBUG_RETRIGGER) {
+		console.log(message)
+	}
+}
+
+const emitter = new EventEmitter()
+
+/**
+ * Due to Eventual Consistency(TM) an update/delete may arrive before the original message arrives
+ * (or before the it has finished being bridged to an event).
+ * In this case, wait until the original message has finished bridging, then retrigger the passed function.
+ * @template {(...args: any) => Promise<any>} T
+ * @param {string} messageID
+ * @param {T} fn
+ * @param {Parameters<T>} rest
+ * @returns {boolean} false if the event was found and the function will be ignored, true if the event was not found and the function will be retriggered
+ */
+function eventNotFoundThenRetrigger(messageID, fn, ...rest) {
+	const eventID = select("event_message", "event_id", {message_id: messageID}).pluck().get()
+	if (eventID) {
+		debugRetrigger(`[retrigger] OK mid <-> eid = ${messageID} <-> ${eventID}`)
+		return false // event was found so don't retrigger
+	}
+
+	debugRetrigger(`[retrigger] WAIT mid <-> eid = ${messageID} <-> ${eventID}`)
+	emitter.addListener(messageID, () => {
+		debugRetrigger(`[retrigger] TRIGGER mid = ${messageID}`)
+		fn(...rest)
+	})
+	// if the event never arrives, don't trigger the callback, just clean up
+	setTimeout(() => {
+		if (emitter.listeners(messageID).length) {
+			debugRetrigger(`[retrigger] EXPIRE mid = ${messageID}`)
+		}
+		emitter.removeAllListeners(messageID)
+	}, 60 * 1000) // 1 minute
+	return true // event was not found, then retrigger
+}
+
+/**
+ * Triggers any pending operations that were waiting on the corresponding event ID.
+ * @param {string} messageID
+ */
+function messageFinishedBridging(messageID) {
+	if (emitter.listeners(messageID).length) {
+		debugRetrigger(`[retrigger] EMIT mid = ${messageID}`)
+	}
+	emitter.emit(messageID)
+}
+
+module.exports.eventNotFoundThenRetrigger = eventNotFoundThenRetrigger
+module.exports.messageFinishedBridging = messageFinishedBridging