From 992205da4a7cf9148ac11a3d6c814a2dd93f7100 Mon Sep 17 00:00:00 2001
From: "D. Berge" <dberge@aaltronav.eu>
Date: Sun, 15 May 2022 13:39:45 +0200
Subject: [PATCH] Add event handler for midnight shot detection.

This event handler checks if there is an UTC date jump between
consecutive shots. If a jump is detected, it sends to new entries
to the event log, for the last shot and first shot of the previous
and current dates, respectively.

Fixes #223.
---
 lib/www/server/events/handlers/detect-fdsp.js | 143 ++++++++++++++++++
 lib/www/server/events/handlers/index.js       |   3 +-
 2 files changed, 145 insertions(+), 1 deletion(-)
 create mode 100644 lib/www/server/events/handlers/detect-fdsp.js

diff --git a/lib/www/server/events/handlers/detect-fdsp.js b/lib/www/server/events/handlers/detect-fdsp.js
new file mode 100644
index 0000000..dec521d
--- /dev/null
+++ b/lib/www/server/events/handlers/detect-fdsp.js
@@ -0,0 +1,143 @@
+const { schema2pid } = require('../../lib/db/connection');
+const { event } = require('../../lib/db');
+const { ALERT, ERROR, INFO, DEBUG } = require('DOUGAL_ROOT/debug')(__filename);
+
+/** Midnight shot detection.
+ *
+ * This event handler checks if there is an UTC date jump between consecutive
+ * shots. If a jump is detected, it sends to new entries to the event log, for
+ * the last shot and first shot of the previous and current dates, respectively.
+ */
+class DetectFDSP {
+	/* Data may come much faster than we can process it, so we put it
+	 * in a queue and process it at our own pace.
+	 *
+	 * The run() method fills the queue with the necessary data and then
+	 * calls processQueue().
+	 *
+	 * The processQueue() method looks at the first two elements in
+	 * the queue and processes them if they are not already being taken
+	 * care of by a previous processQueue() call – this will happen when
+	 * data is coming in faster than it can be processed.
+	 *
+	 * If the processQueue() call is the first to see the two bottommost
+	 * two elements, it will process them and, when finished, it will set
+	 * the `isPending` flag of the bottommost element to `false`, thus
+	 * letting the next call know that it has work to do.
+	 *
+	 * If the queue was empty, run() will set the `isPending` flag of its
+	 * first element to a falsy value, thus bootstrapping the process.
+	 */
+	static MAX_QUEUE_SIZE = 125000;
+
+	queue = [];
+
+	async processQueue () {
+		DEBUG("Queue length", this.queue.length)
+		while (this.queue.length > 1) {
+
+			if (this.queue[0].isPending) {
+				setImmediate(() => this.processQueue());
+				return;
+			}
+
+			const prev = this.queue.shift();
+			const cur  = this.queue[0];
+
+			const sequence = Number(cur._sequence);
+
+			try {
+
+				if (prev.lineName == cur.lineName && prev._sequence == cur._sequence &&
+					prev.lineStatus == "online" && cur.lineStatus == "online" && sequence) {
+
+// 					DEBUG("Previous", prev);
+// 					DEBUG("Current", cur);
+
+					if (prev.time.substr(0, 10) != cur.time.substr(0, 10)) {
+						// Possible a date change, but could also be a missing timestamp
+						// or something else.
+
+						const ts0 = new Date(prev.time)
+						const ts1 = new Date(cur.time);
+
+						if (!isNaN(ts0) && !isNaN(ts1) &&  ts0.getUTCDay() != ts1.getUTCDay()) {
+							INFO("Sequence shot across midnight UTC detected", cur._sequence, cur.lineName);
+
+							const ldsp = {
+								sequence: prev._sequence,
+								point: prev._point,
+								remarks: "Last shotpoint of the day",
+								labels: ["LDSP", "Prod"],
+								meta: {auto: true, insertedBy: this.constructor.name}
+							};
+
+							const fdsp = {
+								sequence: cur._sequence,
+								point: cur._point,
+								remarks: "First shotpoint of the day",
+								labels: ["FDSP", "Prod"],
+								meta: {auto: true, insertedBy: this.constructor.name}
+							};
+
+							INFO("LDSP", ldsp);
+							INFO("FDSP", fdsp);
+
+							const projectId = await schema2pid(prev._schema);
+
+							if (projectId) {
+								await event.post(projectId, ldsp);
+								await event.post(projectId, fdsp);
+							} else {
+								ERROR("projectId not found for", prev._schema);
+							}
+						} else {
+							WARNING("False positive on these timestamps", prev.time, cur.time);
+							WARNING("No events were created");
+						}
+					}
+				}
+				// Processing of this shot has already been completed.
+				// The queue can now move forward.
+			} catch (err) {
+				ERROR(err);
+			} finally {
+				cur.isPending = false;
+			}
+		}
+	}
+
+	async run (data) {
+		if (!data || data.channel !== "realtime") {
+			return;
+		}
+
+		if (!(data.payload && data.payload.new && data.payload.new.meta)) {
+			return;
+		}
+
+		const meta = data.payload.new.meta;
+
+		if (this.queue.length < DetectFDSP.MAX_QUEUE_SIZE) {
+
+			const event = {
+				isPending: this.queue.length,
+				_schema: meta._schema,
+				time: meta.time,
+				lineStatus: meta.lineStatus,
+				_sequence: meta._sequence,
+				_point: meta._point,
+				lineName: meta.lineName
+			};
+			this.queue.push(event);
+// 			DEBUG("EVENT", event);
+
+		} else {
+			ALERT("Queue full at", this.queue.length);
+		}
+
+		this.processQueue();
+	}
+}
+
+module.exports = DetectFDSP;
diff --git a/lib/www/server/events/handlers/index.js b/lib/www/server/events/handlers/index.js
index 8739808..5fe9436 100644
--- a/lib/www/server/events/handlers/index.js
+++ b/lib/www/server/events/handlers/index.js
@@ -1,5 +1,6 @@
 const Handlers = [
-	require('./detect-soleol')
+	require('./detect-soleol'),
+	require('./detect-fdsp')
 ];
 
 function init () {