npm install tslib // also to work in javascript
npm install payme-merchant-integrator

import { PaymeIntegrator } from 'payme-merchant-integrator';

const paymeIntegrator = new PaymeIntegrator({
    db_str: process.env.MONGODB_URL,
    collection: 'payme_transactions', // collection name to save transactions
    type: 'cumulative', // enum ['one-time', 'cumulative'] one time fee or cumulative
    password: process.env.PAYME_PASSWORD,
    isAccountExist,
    markAsPaid,
    getPayingCost, // optional for 'cumulative' type
    canCancel, // method to check cancellation
    markAsCancel, // method to mark as cancel
})

const isAccountExist = async (account) => {
    const is_user_exist = await UserModel.findOne({phone: account.phone});
    if(!is_user_exist) return false;
    return true;
}

const markAsPaid = async (account, amount) => {
    await UserModel.findOneAndUpdate(
        {phone: account.phone},
        { $inc: { balance: amount } }
    );
}

const canCancel = async (account) => {
    return false; // for no cancellation;
    // or check and return true or false 
}

const markAsCancel = async (account) => {
    // write function to update balance or cancel paid transaction 
}

const isAccountExist = async (account) => {
    const is_user_exist = await CheckModel.findOne({check_id: account.check_id});
    if(!is_user_exist) return false;
    return true;
}

const getPayingCost = async (account) => {
    const check = await CheckModel.findOne({check_id: account.check_id});
    return check.cost;
}

const markAsPaid = async (account, amount) => {
    await CheckModel.findOneAndUpdate(
        {check_id: account.check_id},
        { $set: { paid: true } }
    );
}

const authenticate = async (request, reply) => {
    await paymeIntegrator.authenticate(request, reply);
}

const handler = async (request, reply) => {
    return await paymeIntegrator.handler(request, reply);
}
fastify.post(
    '/payme',
    { preValidation: [authenticate] },
    handler
);