Create ModInterfaceV2 for cool stuff

For now it only includes a helper function to resolve file URLs and a
method that adds a CSS stylesheet to the document.

src/js/mods/mod.ts

@@ -1,5 +1,5 @@
 import { Application } from "@/application";
-import { ModInterface } from "./mod_interface";
+import { ModInterfaceV2 } from "./mod_interface_v2";
 import { FrozenModMetadata, ModMetadata } from "./mod_metadata";
 import { MOD_SIGNALS } from "./mod_signals";
 import { ModLoader } from "./modloader";
@@ -20,7 +20,7 @@ export abstract class Mod {
     // TODO: Review what properties are necessary while improving ModInterface
     protected readonly app: Application;
     protected readonly modLoader: ModLoader;
-    protected readonly modInterface: ModInterface;
+    protected readonly modInterface: ModInterfaceV2;
     protected readonly signals = MOD_SIGNALS;
 
     // Exposed for convenience
@@ -31,11 +31,12 @@ export abstract class Mod {
     constructor(metadata: ModMetadata, app: Application, modLoader: ModLoader) {
         this.app = app;
         this.modLoader = modLoader;
-        // TODO: ModInterface should accept the mod instance
-        this.modInterface = new ModInterface(modLoader);
 
         this.id = metadata.id;
         this.metadata = freezeMetadata(metadata);
+
+        // ModInterfaceV2 assumes id to be set
+        this.modInterface = new ModInterfaceV2(this, modLoader);
     }
 
     abstract init(): void | Promise<void>;

src/js/mods/mod_interface_v2.ts

@@ -0,0 +1,38 @@
+import { Mod } from "./mod";
+import { ModInterface } from "./mod_interface";
+import { ModLoader } from "./modloader";
+
+export class ModInterfaceV2 extends ModInterface {
+    private readonly mod: Mod;
+    private readonly baseUrl: string;
+
+    constructor(mod: Mod, modLoader: ModLoader) {
+        super(modLoader);
+        this.mod = mod;
+        this.baseUrl = `mod://${mod.id}`;
+    }
+
+    resolve(path: string) {
+        path = path
+            .split("/")
+            .map(p => encodeURIComponent(p))
+            .join("/");
+
+        if (!path.startsWith("./")) {
+            // Assume relative if not specified
+            path = `./${path}`;
+        }
+
+        // Cannot use import.meta in webpack context
+        return new URL(path, this.baseUrl).toString();
+    }
+
+    addStylesheet(path: string) {
+        const link = document.createElement("link");
+        link.rel = "stylesheet";
+        link.href = this.resolve(path);
+        link.setAttribute("data-mod-id", this.mod.id);
+
+        document.head.append(link);
+    }
+}