From 0ae30508da3b8902c78b07760e51f92bf9783d31 Mon Sep 17 00:00:00 2001
From: Roland Reichwein <mail@reichwein.it>
Date: Sun, 27 Nov 2022 14:58:40 +0100
Subject: Dynamic reload times to limit server load

---
 html/whiteboard.js | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/html/whiteboard.js b/html/whiteboard.js
index 9018f92..d9f0904 100644
--- a/html/whiteboard.js
+++ b/html/whiteboard.js
@@ -3,6 +3,65 @@ function init() {
 	init_board();
 }
 
+class AdjustingTimer {
+	constructor() {
+		this.update_counter = 0; // counting seconds since last counter reset
+	}
+
+	fast_mode() {
+		if (this.update_counter < 5*60)
+			return true;
+		return false;
+	}
+
+	// private method
+	// returns current interval in ms
+	current_update_interval()
+	{
+	 if (this.fast_mode())
+	  return 2000; // 2s
+	 else
+	  return 5 * 60000; // 5min
+	};
+
+	// private
+	count() {
+		this.update_counter += this.current_update_interval() / 1000;
+	};
+
+	// private
+	on_timeout() {
+		this.m_fn();
+		this.count();
+		var _this = this;
+		this.update_timer = setTimeout(function(){_this.on_timeout();}, this.current_update_interval());
+	};
+
+	// to be called once on startup
+	start(fn) {
+		this.m_fn = fn;
+		var _this = this;
+		this.update_timer = setTimeout(function(){_this.on_timeout();}, this.current_update_interval());
+	};
+
+	// to be called on activity:
+	// * changes from remote
+	// * changes by ourselves
+	// * local activity, e.g. mouse move, or key presses
+	reset() {
+		if (!this.fast_mode()) {
+			this.update_counter = 0;
+			clearTimeout(this.update_timer);
+			var _this = this;
+			this.update_timer = setTimeout(function(){_this.on_timeout();}, this.current_update_interval());
+		} else {
+			this.update_counter = 0;
+		}
+	};
+}
+
+var timer = new AdjustingTimer();
+
 function init_board() {
 	var xhr = new XMLHttpRequest();
 	
@@ -35,7 +94,10 @@ function init_board() {
 					// Initialization done. Now we can start modifying.
 					board.addEventListener("input", function() {on_modify(); });
 
-					setInterval(function() {checkupdate();}, 2000);
+					// Initialization done. Now we can start modifying.
+					document.addEventListener("mousemove", function() {timer.reset(); });
+					
+					timer.start(checkupdate);
 				}
 				
 			        reader.readAsBinaryString(file);
@@ -121,8 +183,11 @@ function redirect_to_new_page()
 	//set_status("Please wait while server prepares " + filename + " ...");
 }
 
+// local change done
 function on_modify()
 {
+	timer.reset();
+
 	var xhr = new XMLHttpRequest();
 	
 	// run on data received back
@@ -196,6 +261,7 @@ function checkupdate() {
 
 				// no change if response is text/plain
 				if (this.getResponseHeader("Content-Type") == "application/octet-stream") {
+					timer.reset();
 					var file = new Blob([this.response]);
 					reader = new FileReader();
 					reader.onload = function() {
-- 
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