Added a TemplateManager singleton for creating movable previewTemplates (#580)

module/documents/templateManager.mjs

@@ -0,0 +1,99 @@
+/**
+ * A singleton class that handles preview templates.
+ */
+
+export default class DhTemplateManager {
+    #activePreview;
+
+    /**
+     * Create a template preview, deactivating any existing ones.
+     * @param {object} data
+     */
+    async createPreview(data) {
+        const template = await canvas.templates._createPreview(data, { renderSheet: false });
+
+        this.#activePreview = {
+            document: template.document,
+            object: template,
+            origin: { x: template.document.x, y: template.document.y }
+        };
+
+        this.#activePreview.events = {
+            contextmenu: this.#cancelTemplate.bind(this),
+            mousedown: this.#confirmTemplate.bind(this),
+            mousemove: this.#onDragMouseMove.bind(this),
+            wheel: this.#onMouseWheel.bind(this)
+        };
+        canvas.stage.on('mousemove', this.#activePreview.events.mousemove);
+        canvas.stage.on('mousedown', this.#activePreview.events.mousedown);
+
+        canvas.app.view.addEventListener('wheel', this.#activePreview.events.wheel, true);
+        canvas.app.view.addEventListener('contextmenu', this.#activePreview.events.contextmenu);
+    }
+
+    /**
+     * Handles the movement of the temlate preview on mousedrag.
+     * @param {mousemove Event} event
+     */
+    #onDragMouseMove(event) {
+        event.stopPropagation();
+        const { moveTime, object } = this.#activePreview;
+        const update = {};
+
+        const now = Date.now();
+        if (now - (moveTime || 0) <= 16) return;
+        this.#activePreview.moveTime = now;
+
+        let cursor = event.getLocalPosition(canvas.templates);
+
+        Object.assign(update, canvas.grid.getCenterPoint(cursor));
+
+        object.document.updateSource(update);
+        object.renderFlags.set({ refresh: true });
+    }
+
+    /**
+     * Handles the rotation of the preview template on scrolling.
+     * @param {wheel Event} event
+     */
+    #onMouseWheel(event) {
+        if (!event.shiftKey) return;
+        event.stopPropagation();
+        event.preventDefault();
+        const { moveTime, object } = this.#activePreview;
+
+        const now = Date.now();
+        if (now - (moveTime || 0) <= 16) return;
+        this.#activePreview.moveTime = now;
+
+        object.document.updateSource({
+            direction: object.document.direction + event.deltaY * 0.2
+        });
+        object.renderFlags.set({ refresh: true });
+    }
+
+    /**
+     * Cancels the preview template on right-click.
+     * @param {contextmenu Event} event
+     */
+    #cancelTemplate(event) {
+        const { mousemove, mousedown, contextmenu } = this.#activePreview.events;
+        canvas.templates._onDragLeftCancel(event);
+
+        canvas.stage.off('mousemove', mousemove);
+        canvas.stage.off('mousedown', mousedown);
+        canvas.app.view.removeEventListener('contextmenu', contextmenu);
+    }
+
+    /**
+     * Creates a real MeasuredTemplate at the preview location and cancels the preview.
+     * @param {click Event} event
+     */
+    #confirmTemplate(event) {
+        event.stopPropagation();
+
+        canvas.scene.createEmbeddedDocuments('MeasuredTemplate', [this.#activePreview.document.toObject()]);
+
+        this.#cancelTemplate(event);
+    }
+}