Add preliminary js upload

src/main/resources/static/css/customAssets.css

@@ -0,0 +1,51 @@
+.modal {
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100vh;
+    background-color: rgba(0, 0, 0, 0.45);
+}
+
+.modal .modal-inner {
+    width: 1024px;
+    background-color: #0a0e1a;
+    border-radius: 8px;
+    padding: 12px;
+    color: white;
+    border: 1px solid #504768;
+    max-height: 90vh;
+    overflow: auto;
+}
+
+.modal .modal-inner form {
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+}
+
+.modal .modal-inner .form-group {
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+}
+
+.modal .modal-inner .form-actions {
+    display: flex;
+    justify-content: space-between;
+}
+
+.modal .modal-inner textarea {
+    max-width: 100%;
+    resize: vertical;
+}
+
+.modal .modal-inner .form-error {
+    padding: 8px;
+    background-color: rgba(200, 0, 0, 0.3);
+    border: 1px solid #a00;
+    border-radius: 4px;
+}

src/main/resources/static/js/customAssets.js

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+const assetModal = document.getElementById("custom-asset-modal");
+const userSourceTextArea = document.getElementById("custom-asset-code");
+const formErrorWrapper = document.getElementById("custom-asset-error");
+const jsErrorTitle = document.getElementById("js-error-title");
+const jsErrorDetails = document.getElementById("js-error-details");
+
+function toggleCustomAssetModal(event) {
+    if (event !== undefined && event.target !== event.currentTarget) {
+        return;
+    }
+    if (assetModal.classList.contains("hidden")) {
+        assetModal.classList.remove("hidden");
+    } else {
+        assetModal.classList.add("hidden");
+    }
+}
+
+function submitCodeAsset(formEvent) {
+    formEvent.preventDefault();
+    const src = userSourceTextArea.value;
+    const error = getUserJavaScriptSourceError(src);
+    if (error) {
+        jsErrorTitle.textContent = error.title;
+        jsErrorDetails.textContent = error.details;
+        formErrorWrapper.classList.remove("hidden");
+        return false;
+    }
+    formErrorWrapper.classList.add("hidden");
+    jsErrorTitle.textContent = "";
+    jsErrorDetails.textContent = "";
+    return false;
+}
+
+function getUserJavaScriptSourceError(src) {
+    let ast;
+
+    try {
+        ast = acorn.parse(src, {
+            ecmaVersion: "latest",
+            sourceType: "script",
+        });
+    } catch (e) {
+        return { title: "Syntax Error", details: e.message };
+    }
+
+    const functionNames = ast.body.filter((node) => node.type === "FunctionDeclaration").map((node) => node.id.name);
+    if (!functionNames.includes("init")) {
+        return { title: "Missing function: init", details: "Your code must include a function named 'init'." };
+    }
+    if (!functionNames.includes("tick")) {
+        return { title: "Missing function: tick", details: "Your code must include a function named 'tick'." };
+    }
+
+    return undefined;
+}