Refactor: Override ruler class instead of hooking each function individually

src/ruler.js

@@ -0,0 +1,80 @@
+import {measure} from "./foundry_imports.js"
+import {settingsKey} from "./settings.js";
+import {getSnapPointForToken} from "./util.js";
+
+export class DragRulerRuler extends Ruler {
+	// Functions below are overridden versions of functions in Ruler
+	async moveToken(event) {
+		// This function is invoked by left clicking
+		if (!this.isDragRuler)
+			return await super.moveToken(event);
+		if (!game.settings.get(settingsKey, "swapSpacebarRightClick")) {
+			const snap = !event.shiftKey;
+			this.dragRulerAddWaypoint(this.destination, snap);
+		}
+		else {
+			this.dragRulerDeleteWaypoint();
+		}
+	}
+
+	toJSON() {
+		const json = super.toJSON();
+		if (this.draggedToken)
+			json["draggedToken"] = this.draggedToken.data._id;
+		return json;
+	}
+
+	update(data) {
+		// Don't show a GMs drag ruler to non GM players
+		if (data.draggedToken && this.user.isGM && !game.user.isGM && !game.settings.get(settingsKey, "showGMRulerToPlayers"))
+			return;
+
+		if (data.draggedToken) {
+			this.draggedToken = canvas.tokens.get(data.draggedToken);
+		}
+		super.update(data);
+	}
+
+	measure(destination, options={}) {
+		if (this.isDragRuler) {
+			return measure.call(this, destination, options);
+		}
+		else {
+			return super.measure(mestination, options);
+		}
+	}
+
+	_endMeasurement() {
+		super._endMeasurement();
+		this.draggedToken = null;
+	}
+
+	// The functions below aren't present in the orignal Ruler class and are added by Drag Ruler
+	dragRulerAddWaypoint(point, snap=true) {
+		if (snap)
+			point = getSnapPointForToken(point.x, point.y, this.draggedToken);
+		this.waypoints.push(new PIXI.Point(point.x, point.y));
+		this.labels.addChild(new PreciseText("", CONFIG.canvasTextStyle));
+	}
+
+	dragRulerDeleteWaypoint() {
+		if (this.waypoints.length > 1) {
+			const mousePosition = canvas.app.renderer.plugins.interaction.mouse.getLocalPosition(canvas.tokens);
+			const rulerOffset = this.rulerOffset;
+			this._removeWaypoint({x: mousePosition.x + rulerOffset.x, y: mousePosition.y + rulerOffset.y});
+			game.user.broadcastActivity({ruler: this});
+		}
+		else {
+			const token = this.draggedToken;
+			this._endMeasurement();
+
+			// Deactivate the drag workflow in mouse
+			token.mouseInteractionManager._deactivateDragEvents();
+			token.mouseInteractionManager.state = token.mouseInteractionManager.states.HOVER;
+
+			// This will cancel the current drag operation
+			// Pass in a fake event that hopefully is enough to allow other modules to function
+			token._onDragLeftCancel({preventDefault: () => {return}});
+		}
+	}
+}