/**
 * -------------------------------------------------------------------------------------------
 * Copyright (c) Microsoft Corporation.  All Rights Reserved.  Licensed under the MIT License.
 * See License in the project root for license information.
 * -------------------------------------------------------------------------------------------
 */

/**
 * @module TelemetryHandler
 */
import { isCustomHost, isGraphURL } from "../GraphRequestUtil";
import { Context } from "../IContext";
import { PACKAGE_VERSION } from "../Version";
import { Middleware } from "./IMiddleware";
import { MiddlewareControl } from "./MiddlewareControl";
import { appendRequestHeader, generateUUID, getRequestHeader, setRequestHeader } from "./MiddlewareUtil";
import { TelemetryHandlerOptions } from "./options/TelemetryHandlerOptions";

/**
 * @class
 * @implements Middleware
 * Class for TelemetryHandler
 */
export class TelemetryHandler implements Middleware {
	/**
	 * @private
	 * @static
	 * A member holding the name of the client request id header
	 */
	private static CLIENT_REQUEST_ID_HEADER = "client-request-id";

	/**
	 * @private
	 * @static
	 * A member holding the name of the sdk version header
	 */
	private static SDK_VERSION_HEADER = "SdkVersion";

	/**
	 * @private
	 * @static
	 * A member holding the language prefix for the sdk version header value
	 */
	private static PRODUCT_NAME = "graph-js";

	/**
	 * @private
	 * @static
	 * A member holding the key for the feature usage metrics
	 */
	private static FEATURE_USAGE_STRING = "featureUsage";

	/**
	 * @private
	 * A member to hold next middleware in the middleware chain
	 */
	private nextMiddleware: Middleware;

	/**
	 * @public
	 * @async
	 * To execute the current middleware
	 * @param {Context} context - The context object of the request
	 * @returns A Promise that resolves to nothing
	 */
	public async execute(context: Context): Promise<void> {
		const url = typeof context.request === "string" ? context.request : context.request.url;
		if (isGraphURL(url) || (context.customHosts && isCustomHost(url, context.customHosts))) {
			// Add telemetry only if the request url is a Graph URL.
			// Errors are reported as in issue #265 if headers are present when redirecting to a non Graph URL
			let clientRequestId: string = getRequestHeader(context.request, context.options, TelemetryHandler.CLIENT_REQUEST_ID_HEADER);
			if (!clientRequestId) {
				clientRequestId = generateUUID();
				setRequestHeader(context.request, context.options, TelemetryHandler.CLIENT_REQUEST_ID_HEADER, clientRequestId);
			}
			let sdkVersionValue = `${TelemetryHandler.PRODUCT_NAME}/${PACKAGE_VERSION}`;
			let options: TelemetryHandlerOptions;
			if (context.middlewareControl instanceof MiddlewareControl) {
				options = context.middlewareControl.getMiddlewareOptions(TelemetryHandlerOptions) as TelemetryHandlerOptions;
			}
			if (options) {
				const featureUsage: string = options.getFeatureUsage();
				sdkVersionValue += ` (${TelemetryHandler.FEATURE_USAGE_STRING}=${featureUsage})`;
			}
			appendRequestHeader(context.request, context.options, TelemetryHandler.SDK_VERSION_HEADER, sdkVersionValue);
		} else {
			// Remove telemetry headers if present during redirection.
			delete context.options.headers[TelemetryHandler.CLIENT_REQUEST_ID_HEADER];
			delete context.options.headers[TelemetryHandler.SDK_VERSION_HEADER];
		}
		return await this.nextMiddleware.execute(context);
	}

	/**
	 * @public
	 * To set the next middleware in the chain
	 * @param {Middleware} next - The middleware instance
	 * @returns Nothing
	 */
	public setNext(next: Middleware): void {
		this.nextMiddleware = next;
	}
}