index_impl.js

const snsApi = require('./snsApi.js');
const response = require("cf-fetch-response");

exports.handler = async (event, context) => {

    let {
        RequestType,
        ResourceProperties: {
            FilterPolicy,
            SubscriptionArn,
        }
    } = event;

    switch (RequestType.toLowerCase()) {
        case 'create': {
            console.log('Create sns filter policy');
            return create({FilterPolicy, SubscriptionArn})
                .then(() => response.sendSuccess(event, context));
        }
        case 'update': {
            console.log('Update sns filter policy');
            let OldSubscriptionArn = event.OldResourceProperties.SubscriptionArn;
            if (OldSubscriptionArn === SubscriptionArn) {
                console.log('Update filter policy on same subscription arn');
                return create({FilterPolicy, SubscriptionArn})
                    .then(() => response.sendSuccess(event, context))
            } else {
                console.log('Update filter policy on new subscription arn');
                console.log('Delete old filter policy');
                await deleteFn({SubscriptionArn: OldSubscriptionArn});
                console.log('Create new filter policy');
                return create({FilterPolicy, SubscriptionArn})
                    .then(() => response.sendSuccess(event, context));
            }
        }
        case 'delete': {
            console.log('Delete sns filter policy');
            return deleteFn({SubscriptionArn})
                .then(() => response.sendSuccess(event, context));
        }
    }
};


let create = async ({FilterPolicy, SubscriptionArn} = {}) => {
    if (!FilterPolicy || !SubscriptionArn || !Array.isArray(FilterPolicy)) {
        throw `missing mandatory argument: FilterPolicy=${FilterPolicy} SubscriptionArn=${SubscriptionArn}`
    }

    let value = FilterPolicy.reduce((acc, cur) => {
        if (acc[cur.Attribute]) {
            throw `Duplicate entry: ${cur.Attribute}`;
        }
        acc[cur.Attribute] = JSON.parse(cur.Policy);
        console.log(`Attribute: ${cur.Attribute} Policy: ${acc[cur.Attribute]}`);
        return acc;
    }, {});

    return snsApi.setSubscriptionAttributes({
        AttributeName: 'FilterPolicy',
        SubscriptionArn: SubscriptionArn,
        AttributeValue: JSON.stringify(value)
    });
};

let deleteFn = async ({SubscriptionArn} = {}) => {
    if (!SubscriptionArn) {
        return;
    }

    return snsApi.setSubscriptionAttributes({
        AttributeName: 'FilterPolicy',
        SubscriptionArn: SubscriptionArn,
        AttributeValue: '{}'
    });
};