import { Lambda } from 'aws-sdk';

const lambda = new Lambda({ region: 'us-east-1' });

/**
 * Invokes the function and returns the parsed body
 * @param  {[type]} functionName [description]
 * @param  {[type]} body         [description]
 * @return {[type]}              [description]
 */
export async function invoke<T>(functionName: string, body: object | string): Promise<T> {
    return lambda
        .invoke({
            FunctionName: functionName,
            Payload: createPayload(body),
        })
        .promise()
        .then(data => parseResponse<T>(functionName, data));
}

/**
 * Invokes the event
 * @param  {[type]} functionName [description]
 * @param  {[type]} body         [description]
 * @return {[type]}              [description]
 */
export async function invokeEvent(functionName: string, body: object | string): Promise<boolean> {
    return lambda
        .invoke({
            FunctionName: functionName,
            InvocationType: 'Event',
            Payload: createPayload(body),
        })
        .promise()
        .then(data => data.StatusCode === 200);
}

/////////////////////////////

function createPayload(body: object | string): string {
    if (body === undefined) return undefined;
    else if (typeof body === 'string') {
        return body;
    } else if (typeof body === 'object') {
        return JSON.stringify(body);
    }
}

function parseResponse<T>(functionName: string, res: Lambda.InvocationResponse): any {
    let result;
    if (res.StatusCode === 200) {
        result = JSON.parse(res.Payload.toString());
    }

    if (!result) {
        return;
    }

    // errors will be serialized with errorMessage, errorType, and stack properties
    if (result.errorMessage) {
        let error = new Error(`Invocation of ${functionName} failed.`);
        console.log(result);
        error.stack = result.stack;
        throw error;
    } else {
        return result;
    }
}