add service state machine

src/service/index.ts

@@ -1,5 +1,8 @@
 import process from 'process';
 
+/**
+ * @deprecated use `ServiceState` instead
+ */
 export class RequestState {
   loading: boolean;
   success: boolean;
@@ -9,6 +12,62 @@ export class RequestState {
   }
 }
 
+/**
+ * Service state machine
+ *
+ * @example
+ * let former = that.state.service;
+ * that.setState({
+ *   service: former.trans(true),
+ * })
+ *
+ */
+export class ServiceState {
+  private state: 'loading' | 'success' | 'failed';
+
+  constructor() {
+    this.state = 'loading';
+  }
+
+  /**
+   * Transist from `loading` to `success` or `failed`
+   * @param success request succeeded or not
+   */
+  trans(success: boolean) {
+    if (this.state == 'loading') {
+      if (success) {
+        this.state = 'success';
+      } else {
+        this.state = 'failed';
+      }
+    }
+  }
+
+  /**
+   * Check if state is `loading`.
+   * @returns in `loading` state or not.
+   */
+  isLoading(): boolean {
+    return this.state == 'loading';
+  }
+
+  /**
+   * Check if state is `success`.
+   * @returns in `success state or not.
+   */
+  isSuccess(): boolean {
+    return this.state == 'success';
+  }
+
+  /**
+   * Check if state is `failed`.
+   * @returns in `failed` state or not.
+   */
+  isFailed(): boolean {
+    return this.state == 'failed';
+  }
+}
+
 /**
  * Get URL of backend
  * @param path Relative path to base url, begins with `/`