Machine Coding

Requirements Gathering, Clarifying Questions

1. Basic problem and fundamental requirements
2. Generalize the design & ask questions about that
3. Future Scope

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E-R Diagram

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

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Coding

1. Clean Architecture - way/guideline for structuring and building your code
2. Your directory structure / code structure should tell you exactly what you're building
3. 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

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

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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

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Enum vs Entity

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

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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

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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

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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

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// 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
}