Machine Coding

Requirements Gathering, Clarifying Questions

Basic problem and fundamental requirements
Generalize the design & ask questions about that
Future Scope

E-R Diagram

Entities
- attributes
- behavior
Relationships
- cardinality
- generalization (is-a)
- association (has-a)
  - aggregation (no-ownership)
  - composition (ownership)

Coding

Clean Architecture - way/guideline for structuring and building your code
Your directory structure / code structure should tell you exactly what you're building
A good architecture allows you to delay the important decisions to as late as possible

Central thing of our problem statement

Entities, Relations b/w the entities & business logic
Are we knowledgeable enough to decide exactly what DB we should use?
Are we knowledgeable enough to decide exactly framework we should use?
- web
  - http
  - websockets
- commandline
- desktop application
- android app

Code the entities & relations & business logic (Domain)
Usecases
- user logging in / logging out / updating profile
- ticket booking / cancel
How to interact with the outside world?
- webserver
- command line interface
Frameworks / libraries

User should be minimal

users can be of multiple types
customer / employees / partnerships
we don't want to put private/profile information in the user object
have ONLY the authentication & autorization info in the User
authentication: checking if the user is the person who they claim to be
- username (maybe your phone/email/string)
- password
authorization: does the user have the required permissions/authority
- Role Based Authorization Control (RBAC)
  - roles: instructor, mentor, admin
  - privileges: add a new lecture / shift a lecture / message any mentee / view someones resume

Enum vs Entity

enums are good for static analysis and for code
drawback: add / remove an option, you have to make a code change!

Best Practices around password storage

https://github.com/plaintextoffenders/plaintextoffenders/blob/master/offenders.csv
password must be b/w 8 .. 20 chars: varchar(20)
hashing & salting your password
Ashish - "Prashant"
Hash(Prashant) => shfsduhf => database
Hash(Prashant) => shfsduhf => does this match the value in my db?
if Ashish and Aakash had the same password -> qwerty, password1, abcdefgh, zaqwsx
hash(qwerty) => kjdbfsf
hash(qwerty) => kjdbfsf
dictionary of commonly used password -> hash => rainbow table attack
Ashish => ;sdf;sduf
Aakash => poqjojesf
hash(password+salt)
hash(qwerty;sdf;sduf) => wbf;ewbf;owe, ;sdf;sduf
hash(qwerypoqjojesf) => sdbf;sdkbf;n, poqjojesf

Encoding:

Representing information in some or another manner
Image -> jpeg, png, gif, svg, bmp, raw --------lossy----------- --lossless--
Audio -> mp3, wav, au3, wmv, aac, mp4
Text -> base64, ASCII, utf-8, unicode
Numbers -> hex, binary

Encryption:

Making the information garbage for everyone except the authorized/intended reader
If you don't have the "key" -> you can't make sense of the info
If you do have the "key" -> you can easily reverse the encryption and get the plaintext back

Symmetric Key Cryptography: same key for locking an unlocking

Ceaser / AES / DES Assymteric/Public Key Cryptogrpahy: 1 key to lock and a different key to unlock
RSA

Hashing:

Compressing the information in a lossy manner
Making the information random
a single bit change to the file contents will completely change the hash
it IMPOSSIBLE to go back from the has to the plaintext
MD5, BCrypt, SHA
do NOT use MD5

UUID Long -> Auto-generated monotonic

Scaler.com Google.com / IBM / Oracle you architect some software today

Integer -> 32bit integers (4 bytes) -2^31 .. 2^31 - 1 (signed) 0 .. 2^32 - 1 (unsigned) 2^32 ~ 4 billion Number of people in the world? 7-8 billion Number of devices? Trillions

String -> not a good idea. Take up a lot of space, comparisons are slow rtl/ltr, ascii/unicode

Auto Base64 string - X ObjectId - X

// Uber

enum Color {
    GREEN,
    ..
}

class Car {
    String licensePlate;
    String model;
    String color; // arbitrary?
    // turquoise blue
    // brick red
    // mauve
    // hooloovoo
}

public enum Role {
    ADMIN,
    CUSTOMER,
    PaidCustomer, // run the test, make the pull request // reviewed // merged // qa // staging server // AB-tested on 5% of production // public
    PARTNERSHIP
}

avinashkk1/bookmyshow