feat: add CompositeAsyncHandler to support multiple handlers

src/util/AsyncHandler.ts

@@ -1,17 +1,35 @@
 /**
  * Simple interface for classes that can potentially handle a specific kind of data asynchronously.
  */
-export interface AsyncHandler<TInput, TOutput = void> {
+export abstract class AsyncHandler<TInput, TOutput = void> {
   /**
    * Checks if the input data can be handled by this class.
+   * Throws an error if it can't handle the data.
    * @param input - Input data that would be handled potentially.
-   * @returns A promise resolving to if this input can be handled.
+   *
+   * @returns A promise resolving if this input can be handled, rejecting with an Error if not.
    */
-  canHandle: (input: TInput) => Promise<boolean>;
+  public abstract canHandle (input: TInput): Promise<void>;
+
   /**
    * Handles the given input. This should only be done if the {@link canHandle} function returned `true`.
    * @param input - Input data that needs to be handled.
+   *
    * @returns A promise resolving when the handling is finished. Return value depends on the given type.
    */
-  handle: (input: TInput) => Promise<TOutput>;
+  public abstract handle (input: TInput): Promise<TOutput>;
+
+  /**
+   * Helper function that first runs the canHandle function followed by the handle function.
+   * Throws the error of the {@link canHandle} function if the data can't be handled,
+   * or returns the result of the {@link handle} function otherwise.
+   * @param data - The data to handle.
+   *
+   * @returns The result of the handle function of the handler.
+   */
+  public async handleSafe (data: TInput): Promise<TOutput> {
+    await this.canHandle(data);
+
+    return this.handle(data);
+  }
 }