From 3e54b48321087597db39a731ca7bd89403d1173e Mon Sep 17 00:00:00 2001
From: Arthur Lu <learthurgo@gmail.com>
Date: Wed, 13 Sep 2023 20:03:36 +0000
Subject: [PATCH] improve draggable item style

---
 scripts/draggable.js | 66 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 54 insertions(+), 12 deletions(-)

diff --git a/scripts/draggable.js b/scripts/draggable.js
index 05d9395..7b8507a 100644
--- a/scripts/draggable.js
+++ b/scripts/draggable.js
@@ -1,3 +1,26 @@
+// Map valid UUIDs used by draggable-item elements in order to better validate data transfers to ignore random data transfers.
+const draggableItemUUIDs = {};
+
+/**
+ * Validate a data transfer object through its data types. Valid draggable-item events have one type of the format `application/json/${uuid}`.
+ * The function takes the entire type list from event.dataTransfer.types and returns true if the dataTransfer object is likely to be valid.
+ * @param {*} formatList from event.dataTransfer.types
+ * @returns {Boolean} true if dataTransfer is valid (from a draggable-item source on this page), false otherwise
+ */
+function getDragSource (typesList) {
+	if (typesList.length !== 1) {
+		return null;
+	}
+	const typeString = typesList[0];
+	const type = typeString.split("/");
+	if (type.length === 3 && type[0] === "application" && type[1] === "json" && draggableItemUUIDs[type[2]]) {
+		return { type: typeString, uuid: type[2], element: draggableItemUUIDs[type[2]] };
+	}
+	else {
+		return null;
+	}
+}
+
 class DraggableContainer extends HTMLElement {
 	constructor () {
 		super();
@@ -22,10 +45,14 @@ class DraggableContainer extends HTMLElement {
 	}
 
 	append (newNode) {
+		newNode.uuid = window.crypto.randomUUID();
+		draggableItemUUIDs[newNode.uuid] = newNode;
 		this.content.insertBefore(newNode, this.bottom);
 	}
 
 	insertBefore (newNode, referenceNode) {
+		newNode.uuid = window.crypto.randomUUID();
+		draggableItemUUIDs[newNode.uuid] = newNode;
 		this.content.insertBefore(newNode, referenceNode);
 	}
 
@@ -35,6 +62,7 @@ class DraggableContainer extends HTMLElement {
 
 	removeChild (node) {
 		if (node && this.content.contains(node)) {
+			draggableItemUUIDs[node.uuid] = null;
 			this.content.removeChild(node);
 			return true;
 		}
@@ -57,20 +85,25 @@ class DraggableContainer extends HTMLElement {
 }
 
 class DraggableItem extends HTMLElement {
+	uuid = null;
 	constructor () {
 		super();
 		this.attachShadow({ mode: "open" });
 		// for whatever reason, only grid layout seems to respect the parent's content bounds
 		this.shadowRoot.innerHTML = `
 			<style>
-				#drag {
-					cursor: move;
+				#drag-over {
+					height: 1.5em; 
+					border: 1px dotted var(--main-text-color); 
+					border-radius: 5px; 
+					background-color: rgba(0,0,0,0.25); 
 				}
 				img {
 					height: 1em;
 					width: 1em;
 				}
 			</style>
+			<div id="drag-over" style="display: none;"></div>
 			<div id="wrapper">
 				<div style="min-height: 1.5em;"></div>
 			</div>
@@ -80,8 +113,14 @@ class DraggableItem extends HTMLElement {
 		this.addEventListener("dragstart", (event) => {
 			this.content.style.opacity = "0.5";
 			const data = { id: this.id, data: this.data, content: this.content.innerHTML, value: this.value };
-			event.dataTransfer.setData("application/json", JSON.stringify(data));
+			event.dataTransfer.setData(`application/json/${this.uuid}`, JSON.stringify(data));
 			event.dataTransfer.effectAllowed = "move";
+			const blank = document.createElement("img");
+			event.dataTransfer.setDragImage(blank, 0, 0);
+			setTimeout(() => {
+				this.content.style.visibility = "hidden";
+				this.content.style.height = "0";
+			}, 0);
 		});
 		this.addEventListener("dragend", (event) => {
 			if (event.dataTransfer.dropEffect === "move") {
@@ -92,13 +131,14 @@ class DraggableItem extends HTMLElement {
 			}
 		});
 		this.addEventListener("dragenter", (event) => {
-			if (event.target.dropTarget) {
-				event.target.dragOver = true;
+			const sourceElement = getDragSource(event.dataTransfer.types);
+			if (event.target.dropTarget && sourceElement) {
+				event.target.dragOver = sourceElement.element.innerHTML;
 			}
 			event.preventDefault();
 		});
 		this.addEventListener("dragleave", (event) => {
-			if (event.target.dragOver) {
+			if (event.target.dragOver && getDragSource(event.dataTransfer.types)) {
 				event.target.dragOver = false;
 			}
 			event.preventDefault();
@@ -110,8 +150,9 @@ class DraggableItem extends HTMLElement {
 			if (event.target.dragOver) {
 				event.target.dragOver = false;
 			}
-			if (event.target.dropTarget) {
-				const transfer = JSON.parse(event.dataTransfer.getData("application/json"));
+			const sourceElement = getDragSource(event.dataTransfer.types);
+			if (event.target.dropTarget && sourceElement) {
+				const transfer = JSON.parse(event.dataTransfer.getData(sourceElement.type));
 				const item = document.createElement("draggable-item");
 				item.data = transfer.data;
 				item.innerHTML = transfer.content;
@@ -119,6 +160,7 @@ class DraggableItem extends HTMLElement {
 				item.dropTarget = true;
 				item.id = transfer.id;
 				item.value = transfer.data.value;
+				item.uuid = sourceElement.uuid;
 				event.target.parentElement.insertBefore(item, event.target);
 			}
 			this.content.attributeStyleMap.clear();
@@ -154,13 +196,13 @@ class DraggableItem extends HTMLElement {
 	set dragOver (dragOver) {
 		if (dragOver) {
 			this.classList.add("drag-over");
-			// temp hover over effect
-			this.content.style.borderTop = "1px dotted";
+			this.shadowRoot.querySelector("#drag-over").style.display = "block";
+			this.shadowRoot.querySelector("#drag-over").innerHTML = dragOver;
 		}
 		else {
 			this.classList.remove("drag-over");
-			// temp hover over effect
-			this.content.style.borderTop = "";
+			this.shadowRoot.querySelector("#drag-over").style.display = "none";
+			this.shadowRoot.querySelector("#drag-over").innerHTML = "";
 		}
 	}
 }