✨ Add Facebook Trigger Node (#1106)

* ⚡ Facebook trigger from webhooks

Uses tokens just like the GraphQL API but this one requires an app token
instead of an user access token.

* ⚡ Improvements
:zap Improvements

* 🐛 Fix credential file name

Co-authored-by: Omar Ajoue <krynble@gmail.com>

packages/nodes-base/nodes/Facebook/GenericFunctions.ts

@@ -0,0 +1,53 @@
+import {
+	OptionsWithUri,
+} from 'request';
+
+import {
+	IExecuteFunctions,
+	IExecuteSingleFunctions,
+	IHookFunctions,
+	ILoadOptionsFunctions,
+	IWebhookFunctions,
+} from 'n8n-core';
+
+import {
+	IDataObject,
+} from 'n8n-workflow';
+
+export async function facebookApiRequest(this: IHookFunctions | IExecuteFunctions | IExecuteSingleFunctions | ILoadOptionsFunctions | IWebhookFunctions, method: string, resource: string, body: any = {}, qs: IDataObject = {}, uri?: string, option: IDataObject = {}): Promise<any> { // tslint:disable-line:no-any
+
+	let credentials;
+
+	if (this.getNode().name.includes('Trigger')) {
+		credentials = this.getCredentials('facebookGraphSubscriptionApi') as IDataObject;
+	} else {
+		credentials = this.getCredentials('facebookGraphApi') as IDataObject;
+	}
+
+	qs.access_token = credentials!.accessToken;
+
+	const options: OptionsWithUri = {
+		headers: {
+			accept: 'application/json,text/*;q=0.99',
+		},
+		method,
+		qs,
+		body,
+		gzip: true,
+		uri: uri ||`https://graph.facebook.com/v8.0${resource}`,
+		json: true,
+	};
+
+	try {
+		return await this.helpers.request!(options);
+	} catch (error) {
+
+		if (error.response.body && error.response.body.error) {
+			const message = error.response.body.error.message;
+			throw new Error(
+				`Facebook Trigger error response [${error.statusCode}]: ${message}`,
+			);
+		}
+		throw new Error(error);
+	}
+}