feat(vscode): allow invoking Dart Frog daemon (#925)

Author: alestiago

extensions/vscode/src/daemon/dart-frog-daemon.ts

@@ -1,3 +1,33 @@
+import { ChildProcessWithoutNullStreams, spawn } from "child_process";
+import {
+  DaemonEvent,
+  DaemonMessage,
+  DaemonRequest,
+  DaemonResponse,
+  isDaemonEvent,
+  isDaemonRequest,
+  isDaemonResponse,
+  isReadyDaemonEvent,
+} from "./protocol";
+import { EventEmitter } from "events";
+
+/**
+ * The types of events that are emitted by the {@link DartFrogDaemon}.
+ *
+ * The possible types of events are:
+ * - "request": When a request is sent to the Dart Frog daemon. The
+ * {@link DaemonRequest} is passed as an argument to the event handler.
+ * - "response": When a response is received from the Dart Frog daemon. The
+ * {@link DaemonResponse} is passed as an argument to the event handler.
+ * - "event": When an event is received from the Dart Frog daemon. The
+ * {@link DaemonEvent} is passed as an argument to the event handler.
+ */
+export enum DartFrogDaemonEventEmitterTypes {
+  request = "request",
+  response = "response",
+  event = "event",
+}
+
 /**
  * The Dart Frog daemon is a long-running process that is responsible for
  * managing a single or multiple Dart Frog projects simultaneously.
@@ -15,4 +45,128 @@ export class DartFrogDaemon {
   public static get instance() {
     return this._instance || (this._instance = new this());
   }
+
+  private daemonMessagesEventEmitter = new EventEmitter();
+
+  /**
+   * The process that is running the Dart Frog daemon.
+   *
+   * Undefined until the Dart Frog daemon is {@link invoke}d.
+   */
+  private process: ChildProcessWithoutNullStreams | undefined;
+
+  private _isReady: boolean = false;
+
+  /**
+   * Whether the Dart Frog daemon is ready to accept requests.
+   *
+   * The Dart Frog daemon is ready to accept requests when it has emmitted
+   * the "ready" event after being {@link invoke}d.
+   *
+   * @see {@link invoke} to invoke the Dart Frog daemon.
+   */
+  public get isReady(): boolean {
+    return this._isReady;
+  }
+
+  /**
+   * Invokes the Dart Frog daemon.
+   *
+   * If the Dart Frog daemon is already running, this method will immediately
+   * return.
+   *
+   * After invoking the Dart Frog daemon, it will be ready to accept requests.
+   *
+   * @param workingDirectory The working directory of the Dart Frog daemon,
+   * usually the root directory of the Dart Frog project.
+   */
+  public async invoke(workingDirectory: string): Promise<void> {
+    if (this.isReady || this.process) {
+      return Promise.resolve();
+    }
+
+    const readyPromise = new Promise<void>((resolve) => {
+      const readyEventListener = (message: DaemonEvent) => {
+        if (!this._isReady && isReadyDaemonEvent(message)) {
+          this._isReady = true;
+          resolve();
+          this.off(DartFrogDaemonEventEmitterTypes.event, readyEventListener);
+        }
+      };
+      this.on(
+        DartFrogDaemonEventEmitterTypes.event,
+        readyEventListener.bind(this)
+      );
+    });
+
+    this.process = spawn("dart_frog", ["daemon"], {
+      cwd: workingDirectory,
+    });
+    this.process.stdout.on("data", this.stdoutDataListener.bind(this));
+
+    return readyPromise;
+  }
+
+  /**
+   * Decodes the stdout and emits events accordingly via the
+   * {@link daemonMessagesEventEmitter}.
+   *
+   * @param data The data that was received from the stdout of the Dart Frog
+   * Daemon.
+   * @see {@link daemonMessagesEventEmitter} for listening to the events that
+   * are emitted.
+   */
+  private stdoutDataListener(data: Buffer): void {
+    const daemonMessages = DaemonMessage.decode(data);
+    for (const message of daemonMessages) {
+      if (isDaemonEvent(message)) {
+        this.daemonMessagesEventEmitter.emit(
+          DartFrogDaemonEventEmitterTypes.event,
+          message
+        );
+      } else if (isDaemonResponse(message)) {
+        this.daemonMessagesEventEmitter.emit(
+          DartFrogDaemonEventEmitterTypes.response,
+          message
+        );
+      } else if (isDaemonRequest(message)) {
+        this.daemonMessagesEventEmitter.emit(
+          DartFrogDaemonEventEmitterTypes.request,
+          message
+        );
+      }
+    }
+  }
+
+  /**
+   * Starts listening to events related to this Dart Frog daemon.
+   *
+   * @returns A reference to this Dart Frog daemon, so that calls can be
+   * chained.
+   * @see {@link DartFrogDaemonEventEmitterTypes} for the types of events that
+   * are emitted.
+   */
+  public on(
+    type: DartFrogDaemonEventEmitterTypes,
+    listener: (...args: any[]) => void
+  ): DartFrogDaemon {
+    this.daemonMessagesEventEmitter.on(type, listener);
+    return this;
+  }
+
+  /**
+   * Unsubscribes a listener from events related to this Dart Frog daemon.
+   *
+   * @param type The type of event to unsubscribe from.
+   * @param listener The listener to unsubscribe.
+   * @returns A reference to this Dart Frog daemon, so that calls can be
+   * chained.
+   */
+  public off(
+    type: DartFrogDaemonEventEmitterTypes,
+    listener: (...args: any[]) => void
+  ): DartFrogDaemon {
+    this.daemonMessagesEventEmitter.off(type, listener);
+    return this;
+  }
 }