copy fetcher/ from inet-js

TODO.md

@@ -1,13 +1,17 @@
 # module system
 
-node/Node
-
 Mod -- has loader
 
 Place and Transition -- has modId
 
 Mod has definitions: Map<string, Definition>
 
+# loader
+
+copy `loader/` from inet-js
+
+# command-line
+
 # net
 
 [net] addPlace

src/fetcher/Fetcher.ts

@@ -0,0 +1,63 @@
+export type FetcherHandler = {
+  fetchText: (url: URL) => string | Promise<string>
+  formatURL?: (url: URL) => string
+}
+
+export class Fetcher {
+  handlers: Record<string, FetcherHandler> = {}
+
+  constructor() {
+    this.register("http", {
+      fetchText: async (url) => await (await fetch(url)).text(),
+    })
+
+    this.register("https", {
+      fetchText: async (url) => await (await fetch(url)).text(),
+    })
+  }
+
+  findHandler(url: URL): FetcherHandler | undefined {
+    const scheme = url.protocol.slice(0, url.protocol.length - 1)
+    return this.handlers[scheme]
+  }
+
+  formatURL(url: URL): string {
+    const handler = this.findHandler(url)
+    if (handler === undefined) {
+      throw new Error(
+        [
+          `[Fetcher.formatURL] I meet unknown protocol.`,
+          ``,
+          `  protocol: ${url.protocol}`,
+          `  url: ${url.href}`,
+        ].join("\n"),
+      )
+    }
+
+    if (handler.formatURL) {
+      return handler.formatURL(url)
+    } else {
+      return url.href
+    }
+  }
+
+  async fetchText(url: URL): Promise<string> {
+    const handler = this.findHandler(url)
+    if (handler === undefined) {
+      throw new Error(
+        [
+          `[Fetcher.fetchText] I meet unknown protocol.`,
+          ``,
+          `  protocol: ${url.protocol}`,
+          `  url: ${url.href}`,
+        ].join("\n"),
+      )
+    }
+
+    return handler.fetchText(url)
+  }
+
+  register(scheme: string, handler: FetcherHandler): void {
+    this.handlers[scheme] = handler
+  }
+}

src/fetcher/index.ts

@@ -0,0 +1 @@
+export * from "./Fetcher"