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Mudassar
An Overview of Labs project

Intro to LABS projects

In this markdown, you will learn about the technologies and architecture of some of Labs projects. You can find all the projects at CERP Github organization.

Table of Content

Technologies

We're building system using latest technologies, here's the list but we're not limited to them:

  • Frontend

    • Javascript
    • Typescript
    • ReactJS + Redux
    • MaterialUI

  • Backend

    • Elixir
    • Postgres

  • Platform

    • Google Cloud Platform
    • Docker
    • Kubernetes

Tool We Built

Here are some tools that we build which are currently used in most of our projects

  • Syncr

    Make asynchronous requests to a server over WebSocket/Http connection

    Learn More

  • Former

    Handle HTMLFormEvents and mutate the state. Currently support class based components

    Learn More

  • Dynamic

    Provide useful tooling to manipulate the complex Objects (JS) and Maps (Elixir)

    Learn More

Projects overview

At Labs we built MISchool and IlmxExchange as our starter products. Below are some stuff which we follow and reuse for every project that we already built and will building in future.

Actions

To make change to redux store or to send payload to server, we divide actions into two category

These actions can be futher categorized into Core and Simple (based on core actions) actions. Let's see how core actions works

Core Actions

For now we have createMerges() and createDeletes() actions which help to manipulate to complex deep object in state

  • createMerges()

    createMerges() takes single argument of type Merge[] and return void. Here we're only looking at the prototype and usage of createMerges().

    API

    type Merge = {
  path: Array<string>
  value: any
}
createMerges(merges: Merge[]): void
    What does merge mean?
Basically merge is an object which contains path and value. "Path" is composed of 
complex deep object properties and "value" is any thing that we want to to store
or update against the path.

    Usage

    Let's see createMerges in actions. Consider we have state like below

    State A

    "db": {
  "students": {
    [1]: {
      id: 1
      Name: "ABC",
      Gender: "M",
      "attendance": {}
    }
  }
}

    1st Merge: Let's add a single student entry to state, so we create a merge like

    // merge to create or update a student
const student = {
  id: 2
  Name: "XYZ",
  Gender: "X",
  payments: {}
}

const merges = [
  {
    path: ["db", "students", student.id],
    value: student
  }
]

dispatch(createMerges(merges))

    After the merge action, state changes from A => B with a new student of id:2

    State B

    "db": {
  "students": {
    [1]: {
      id: 1
      Name: "ABC",
      Gender: "M",
      "attendance": {}
    },
    [2]: {
      id: 2
      Name: "XYZ",
      Gender: "M",
      "attendance": {}
    }
  }
}

    2nd Merge: Let's add an attendance entry against a student (deep object), so we create a merge like

    // merge to create or update a student
const student_id = 2
const attendance = {
  date: "04-07-2020",
  status: "PRESENT",
  time: 1593806556000
}

const merges = [
  {
    path: ["db", "students", student_id, "attendance", attendance.date],
    value: attendance
  }
]

dispatch(createMerges(merges))

    After the 2nd merge action, state changes from B => C with an attendance entry of student id:2

    State C

    "db": {
  "students": {
    [1]: {
      id: 1
      Name: "ABC",
      Gender: "M",
      "attendance": {}
    },
    [2]: {
      id: 2
      Name: "XYZ",
      Gender: "M",
      "attendance": {
        ["04-07-2020"]: {
          date: "04-07-2020",
          status: "PRESENT",
          time: 1593806556000
        }
      }
    }
  }
}

  • createDeletes()

    createDeletes() takes single argument of type Delete[] and return void. Here we're only looking at the prototype and usage of createDeletes().

    API

    type Delete = {
  path: Array<string>
}
createDeletes(deletes: Delete[]): void

    Usage

    1st Delete: Let's say we want to delete a student of id: 1, so we create a delete like

    const student_id = 1
const deletes = [
  {
    path: ["db", "students", student_id]
  }
]
dispatch(createDeletes(deletes))

    After a createDeletes() action, state changes from C => D, deleted student with id:1

    State D

      "db": {
    "students": {
      [2]: {
        id: 2
        Name: "XYZ",
        Gender: "M",
      "attendance": {
          ["04-07-2020"]: {
            date: "04-07-2020",
            status: "PRESENT",
            time: 1593806556000
          }
        }
      }
    }
  }

Async Actions

async actions help to send data to server using Syncr.

How a state manipulated by createMerges() or createDeletes encoded as an action and send to server. Let's see with createDeletes() in below steps. Assuming that we're working on MISchool

  • Step 1: Dispatch createDeletes()

    const student_id = 1
const delete = [
  {
    path: ["db", "students", student_id]
  }
]
dispatch(createDeletes(delete))

  • Step-2: Prepare merges as an action for server (in createDeletes())

    const new_deletes = deletes.reduce((agg, curr) => ({
  ...agg,
  [curr.path.join(',')]: {
    action: {
      type: "DELETE",
      path: curr.path.map(p => p === undefined ? "" : p),
      value: 1 // what's the reason behind this?
    },
    date: new Date().getTime()
  }
}), {})

const state = getState()
const rationalized_deletes = getRationalizedQueuePayload(new_deletes, "mutations", state)

  • Step-3: Rationalize state.queued items with new delete mutations (in getRationalizedQueuePayload())

    In this step, we're making sure, if there's anything else in queue(not send to server before), merge them together and send to server if state.connected === true

    // we're mainly dealing with three types of payload, deletes, merges fall in "mutations"
type QueuedType = "mutations" | "images" | "analytics"
type Queued = { mutataions: {}; analytics: {}, images:{}}
getRationalizedQueuePayload = (payload: any, key: QueuedType, state: Queued) => {
  return {
    ...state.queued,
    images: {},
    [key]: {
      ...state.queued[key],
      ...payload
    }
  }
}

    Here's what RootReducerState looks like

    root reducer state

  • Step-4: Send payload to server using Syncr

      const state = getState()
  syncr.send({
    type: SYNC,
    school_id: state.auth.school_id,
    client_type: client_type,
    lastSnapshot: state.lastSnapshot,
    payload
  })

Abstract view of Syncing

To achieve real-time functionality in MISchool and IlmExchange, syncing played an import role. In the following diagram, it's an abstract view of how does syncing happen among the connected clients.

abstract-syncing

Broadcasting

In progress

What happen when Action Fired

Let's say we want to reset fees for student in MISchool, following diagram shows what happen behind the scene when we press reset fee button.

when an action fired

Service Worker in MISchool

Service worker allows you to support offline experiences, giving engineers and developers end-to-end control over the user’s interactions with the app. A service worker enables you to run Javascript before a page even exists, makes your site faster, and allows you to display content even if there is no internet connection. A few properties of service worker are:

  • Runs in its own global script context
  • Is not directly tied to any particular page
  • Cannot access the DOM
  • Is event-driven (it’s terminated when it’s not in use and run again when needed)
  • Is HTTPS only

Abstract Workflow of SW

service worker

For MISchool, we're using WorkBox, a high-level set of libraries. It provides a solid foundation for any service worker's caching, routing, and response generation logic. Currently we're intercepting follow URLs with image caching (using CacheFirst) to support MISchool offline-first user experience.

  workbox.routing.registerRoute(
    ({ url, event }) => {
      const match = url.host === "storage.googleapis.com" ||
        url.host === "fonts.googleapis.com" ||
        url.host === "googleapis.com" ||
        url.host === "www.googleapis.com"
      return match
    },
    // fetch from cache, but also fetch from network and update cache
    new workbox.strategies.CacheFirst({
      cacheName: 'images',
      plugins: [
        new workbox.expiration.Plugin({
          maxAgeSeconds: 60 * 60 * 24 * 30 // 30 days,
          purgeOnQuotaError: true
        })
      ]
    })
  )

Check if an update is available

For MISchool we're adopting CacheFirst (fetch from cache, but also fetch from network and update cache) strategy. We can hook into onupdatefound function on the registered Service Worker. Even though we can cache tons of files, the Service Worker only checks the hash of registered service-worker.js. If that file has only 1 little change in it, it will be treated as a new version. Here's simple demonstration of Cache First strategy:

cache-first-strategy

The cache access failed and the Service Worker uses the network as a fallback.

Code Formatting + Linting

For code formatting and liting we use ESLint for Typescript for frontends

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