Refactor SOL/EOL real-time detection handler.

This also implements a generic handler mechanism that can be
reused for other purposes, such as sending email / XMPP notifications,
doing real-time QC checks and so on.

Fixes #113.

lib/www/server/events/handlers/detect-soleol.js

@@ -0,0 +1,146 @@
+const { schema2pid } = require('../../lib/db/connection');
+const { event } = require('../../lib/db');
+
+class DetectSOLEOL {
+	/* 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 takes 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 () {
+		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) {
+// 					console.log("TRANSITION TO ONLINE", prev, cur);
+					
+					// Check if there are already FSP, FGSP events for this sequence
+					const projectId = await schema2pid(cur._schema);
+					const sequenceEvents = await event.list(projectId, {sequence});
+					
+					const labels = ["FSP", "FGSP"].filter(l => !sequenceEvents.find(i => i.labels.includes(l)));
+					
+					if (labels.includes("FSP")) {
+						// At this point labels contains either FSP only or FSP + FGSP,
+						// depending on whether a FGSP event has already been entered.
+						
+						const remarks = `SEQ ${cur._sequence}, SOL ${cur.lineName}, BSP: ${(cur.speed*3.6/1.852).toFixed(1)} kt, Water depth: ${Number(cur.waterDepth).toFixed(0)} m.`;
+						const payload = {
+							type: "sequence",
+							sequence,
+							point: cur._point,
+							remarks,
+							labels
+						}
+						
+// 						console.log(projectId, payload);
+						await event.post(projectId, payload);
+					} else {
+						// A first shot point has been already entered in the log,
+						// so we have nothing to do here.
+					}
+				} else if (prev.lineStatus == "online" && cur.lineStatus != "online") {
+// 					console.log("TRANSITION TO OFFLINE", prev, cur);
+					
+					// Check if there are already LSP, LGSP events for this sequence
+					const projectId = await schema2pid(prev._schema);
+					const sequenceEvents = await event.list(projectId, {sequence});
+					
+					const labels = ["LSP", "LGSP"].filter(l => !sequenceEvents.find(i => i.labels.includes(l)));
+					
+					if (labels.includes("LSP")) {
+						// At this point labels contains either LSP only or LSP + LGSP,
+						// depending on whether a LGSP event has already been entered.
+						
+						const remarks = `SEQ ${prev._sequence}, EOL ${prev.lineName}, BSP: ${(prev.speed*3.6/1.852).toFixed(1)} kt, Water depth: ${Number(prev.waterDepth).toFixed(0)} m.`;
+						const payload = {
+							type: "sequence",
+							sequence,
+							point: prev._point,
+							remarks,
+							labels
+						}
+						
+// 						console.log(projectId, payload);
+						await event.post(projectId, payload);
+					} else {
+						// A first shot point has been already entered in the log,
+						// so we have nothing to do here.
+					}
+				}
+				// Processing of this shot has already been completed.
+				// The queue can now move forward.
+			} catch (err) {
+				console.error("DetectSOLEOL Error")
+				console.log(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 < DetectSOLEOL.MAX_QUEUE_SIZE) {
+		
+			this.queue.push({
+				isPending: this.queue.length,
+				_schema: meta._schema,
+				time: meta.time,
+				shot: meta.shot,
+				lineStatus: meta.lineStatus,
+				_sequence: meta._sequence,
+				_point: meta._point,
+				lineName: meta.lineName,
+				speed: meta.speed,
+				waterDepth: meta.waterDepth
+			});
+			
+		} else {
+			// FIXME Change to alert
+			console.error("DetectSOLEOL queue full at", this.queue.length);
+		}
+		
+		this.processQueue();
+	}
+}
+
+module.exports = DetectSOLEOL;