Parameterize UrlDefinedSource construction with the URL authority part

Allows the associated Dataset and Narrative subclasses to be simpler and
similar to other sources by using source.baseUrl.

src/getDatasetHelpers.js

@@ -64,6 +64,11 @@ const splitPrefixIntoParts = (prefix) => {
       source = new Source(...prefixParts.splice(0, 2));
       break;
 
+    // UrlDefined source requires a URL authority part
+    case "fetch":
+      source = new Source(prefixParts.shift());
+      break;
+
     default:
       source = new Source();
   }
@@ -102,6 +107,12 @@ const joinPartsIntoPrefix = ({source, prefixParts, isNarrative = false}) => {
     case "community":
       leadingParts.push(source.owner, source.repoNameWithBranch);
       break;
+
+    // UrlDefined source requires a URL authority part
+    case "fetch":
+      leadingParts.push(source.authority);
+      break;
+
     // no default
   }
 

src/sources.js

@@ -296,12 +296,19 @@ class CommunityNarrative extends Narrative {
 
 
 class UrlDefinedSource extends Source {
-
   static get _name() { return "fetch"; }
-  get baseUrl() {
-    throw new Error("UrlDefinedSource does not use `this.baseUrl`");
+
+  constructor(authority) {
+    super();
+
+    if (!authority) throw new Error(`Cannot construct a ${this.constructor.name} without a URL authority`);
+
+    this.authority = authority;
   }
 
+  get baseUrl() {
+    return `https://${this.authority}`;
+  }
   dataset(pathParts) {
     return new UrlDefinedDataset(this, pathParts);
   }
@@ -316,49 +323,26 @@ class UrlDefinedSource extends Source {
 }
 
 class UrlDefinedDataset extends Dataset {
-  get baseParts() {
-    return this.pathParts;
-  }
-  get isRequestValidWithoutDataset() {
-    return false;
-  }
   baseNameFor(type) {
-    // mandate https
-    const datasetUrl = "https://" + this.baseParts.join("/");
-    if (type==="main") {
-      return datasetUrl;
-    }
-    // if the request is for A.json, then return A_<type>.json.
-    if (datasetUrl.endsWith(".json")) {
-      return `${datasetUrl.replace(/\.json$/, '')}_${type}.json`;
+    const baseName = this.baseParts.join("/");
+
+    if (type === "main") {
+      return baseName;
     }
-    // if the request if for B, where B doesn't end with `.json`, then return B_<type>
-    return `${datasetUrl}_${type}`;
-  }
-  urlFor(type) {
-    // when `parsePrefix()` runs (which it does for each /charon/getDataset API request), it preemtively defines
-    // a `urlFor` tree, meta and main types. For `UrlDefinedDataset`s we can only serve v2 datasets, but be aware
-    // the `urlFor` function is still called for tree + meta "types".
-    if (type==="tree" || type==="meta") return undefined;
-    const url = new URL(this.baseNameFor(type));
-    return url.toString();
+
+    return baseName.endsWith(".json")
+      ? `${baseName.replace(/\.json$/, '')}_${type}.json`
+      : `${baseName}_${type}`;
   }
 }
 
 class UrlDefinedNarrative extends Narrative {
-  get baseParts() {
-    return this.pathParts;
-  }
   get baseName() {
-    // mandate https
-    return "https://" + this.baseParts.join("/");
-  }
-  url() {
-    const url = new URL(this.baseName);
-    return url.toString();
+    return this.baseParts.join("/");
   }
 }
 
+
 class S3Source extends Source {
   get bucket() {
     throw new InvalidSourceImplementation("bucket() must be implemented by subclasses");