Introduce singleton API client with retry policy (#130)

* Add singleton http client
* Removed refresh token logic
* Further cleanup after refresh token
* Make tests faster maybe

src/ApiClient.ts

@@ -0,0 +1,91 @@
+import axios, { AxiosRequestConfig, AxiosResponse, AxiosInstance, AxiosError } from 'axios';
+import axiosRetry, { isNetworkOrIdempotentRequestError } from 'axios-retry';
+import { Session } from './Types';
+
+export class ApiClient {
+    private static instance: ApiClient;
+    private axiosInstance?: AxiosInstance;
+    private session?: Session;
+
+    private constructor(session?: Session) {
+        this.session = session;
+        this.axiosInstance = axios.create({
+            baseURL: session?.ApiGatewayUri,
+            timeout: 7000,
+            headers: { 'User-Agent': 'destreamer/2.0 (Hammer of Dawn)' }
+        });
+        axiosRetry(this.axiosInstance, {
+            shouldResetTimeout: true,
+            retries: 6,
+            retryDelay: (retryCount) => {
+                return retryCount * 2000;
+            },
+            retryCondition: (err: AxiosError) => {
+                const retryCodes = [429, 500, 502, 503];
+                if (isNetworkOrIdempotentRequestError(err)) {
+                    console.warn(`${err}. Retrying request...`);
+
+                    return true;
+                }   
+                console.warn(`Got HTTP ${err?.response?.status}. Retrying request...`);
+                const condition = retryCodes.includes(err?.response?.status ?? 0);
+
+                return condition;
+            }
+        });
+    }
+
+    public static getInstance(session?: Session): ApiClient {
+        if (!ApiClient.instance) {
+            ApiClient.instance = new ApiClient(session);
+        }
+
+        return ApiClient.instance;
+    }
+
+    /**
+     * Call Microsoft Stream API. Base URL is sourced from
+     * the session object and prepended automatically.
+     */
+    public async callApi(
+        path: string,
+        method: AxiosRequestConfig['method'] = 'get',
+        payload?: any): Promise<AxiosResponse | undefined> {
+
+        const delimiter = path.split('?').length === 1 ? '?' : '&';
+
+        const headers: object = {
+            'Authorization': 'Bearer ' + this.session?.AccessToken
+        };
+
+        return this.axiosInstance?.request({
+            method: method,
+            headers: headers,
+            data: payload ?? undefined,
+            url: path + delimiter + 'api-version=' + this.session?.ApiGatewayVersion
+        });
+    }
+
+    /**
+     * Call an absolute URL
+     */
+    public async callUrl(
+        url: string,
+        method: AxiosRequestConfig['method'] = 'get',
+        payload?: any,
+        responseType: AxiosRequestConfig['responseType'] = 'json'): Promise<AxiosResponse | undefined> {
+            
+        const headers: object = {
+            'Authorization': 'Bearer ' + this.session?.AccessToken
+        };
+
+        return this.axiosInstance?.request({
+            method: method,
+            headers: headers,
+            data: payload ?? undefined,
+            url: url,
+            responseType: responseType
+        });
+    }
+
+}