Ruby Programming

puts "Hello, World!"
puts 42.class    # Integer
puts "hi".class  # String

# Variables
name = "Mayank"
age = 15
puts "#{name} is #{age}"

# Run: ruby file.rb

name = "Mayank"      # String
age = 15              # Integer
pi = 3.14             # Float
alive = true          # TrueClass
nothing = nil         # NilClass

nums = [1, 2, 3, 4, 5]  # Array
hash = {name: "Mayank", age: 15}  # Hash with symbol keys

puts name.class       # String
puts nums.class       # Array
puts hash.class       # Hash

# String interpolation
greeting = "Hello, #{name}!"
puts greeting

# Multiline string
html = <<~HTML
  <h1>Hello</h1>
  <p>World</p>
HTML
puts html

puts 10 + 3   # 13
puts 10 - 3   # 7
puts 10 * 3   # 30
puts 10 / 3   # 3 (integer division)
puts 10 % 3   # 1
puts 10 ** 3  # 1000

# String concatenation
puts "Hello" + " " + "World"
puts "Hello" << " World"

# Spaceship operator
puts (1 <=> 2)   # -1
puts (2 <=> 2)   # 0
puts (3 <=> 2)   # 1

# Range
puts (1..5).to_a   # [1, 2, 3, 4, 5]
puts (1...5).to_a  # [1, 2, 3, 4]

# Regex
puts "hello123".match?(/\d+/)  # true

score = 85
if score >= 90
  puts 'A'
elsif score >= 80
  puts 'B'
else
  puts 'C'
end

# Unless (opposite of if)
unless score < 50
  puts 'You passed'
end

# Case
day = 3
case day
when 1 then puts 'Monday'
when 2 then puts 'Tuesday'
when 3 then puts 'Wednesday'
else puts 'Other'
end

# Loops
5.times { |i| puts i }
1.upto(5) { |i| puts i }
[1,2,3,4,5].each { |n| puts n }

# Iterator methods
[1,2,3,4,5].select { |n| n.even? }  # [2, 4]
[1,2,3,4,5].map { |n| n * 2 }       # [2, 4, 6, 8, 10]
[1,2,3,4,5].reduce(:+)               # 15

def add(a, b)
  a + b
end
puts add(3, 4)

# Default params
def greet(name, prefix = 'Hello')
  "#{prefix}, #{name}!"
end
puts greet('Mayank')
puts greet('World', 'Hi')

# Yield (pass block)
def timer
  start = Time.now
  yield
  puts "Took #{Time.now - start}s"
end
timer { sleep 0.1 }

# Block
[1,2,3].each do |n|
  puts n * 10
end

# Lambda
square = ->(x) { x * x }
puts square.call(5)

# Proc
double = Proc.new { |x| x * 2 }
puts [1,2,3].map(&double)

class Dog
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def bark
    "#{@name}: Woof!"
  end

  def to_s
    "Dog(#{@name}, #{@age})"
  end
end

d = Dog.new('Rex', 5)
puts d.bark
puts d.name
puts d

module Swimmable
  def swim
    "#{@name} is swimming!"
  end
end

class Duck
  include Swimmable
  def initialize(name) @name = name end
end

class Fish
  include Swimmable
  def initialize(name) @name = name end
end

puts Duck.new('Donald').swim
puts Fish.new('Nemo').swim

# Module as namespace
module Math
  def self.circle_area(r)
    Math::PI * r * r
  end
end
puts Math.circle_area(5)

nums = [5, 3, 1, 4, 2]

puts nums.sort
puts nums.reverse
puts nums.select { |n| n > 2 }
puts nums.reject { |n| n > 2 }
puts nums.map { |n| n * 10 }
puts nums.reduce(:+)
puts nums.min
puts nums.max
puts nums.include?(3)
puts nums.count

# Hash iteration
hash = {a: 1, b: 2, c: 3}
hash.each { |k, v| puts "#{k}=#{v}" }
puts hash.keys
puts hash.values

# Chaining
result = (1..100)
  .select(&:odd?)
  .map { |n| n ** 2 }
  .select { |n| n > 100 }
  .first(5)
puts result.inspect

# Symbols
s1 = :hello
s2 = :hello
puts s1.object_id == s2.object_id  # true (same object)

# Metaprogramming
class Dynamic
  def method_missing(name, *args)
    if name.to_s.start_with?('say_')
      msg = name.to_s[4..]
      define_singleton_method(name) { "#{msg}!" }
      send(name)
    else
      super
    end
  end
end

d = Dynamic.new
dputs d.say_hello   # "hello!"
puts d.say_world    # "world!"

# define_method
class Greeter
  define_method(:greet) { |name| "Hello, #{name}" }
end
puts Greeter.new.greet('Mayank')

# File operations
File.write('test.txt', 'Hello Ruby!\n')
puts File.read('test.txt')

# Line by line
File.foreach('test.txt') { |line| puts line }

# Append
File.open('log.txt', 'a') { |f| f.puts "#{Time.now} event" }

# Shell commands
output = `ls -la`
puts output

system('echo "Hello from shell"')

# Dir operations
puts Dir.glob('*.rb')
Dir.mkdir('test_dir') unless Dir.exist?('test_dir')

# Path
require 'pathname'
puts Pathname.new(__FILE__).dirname

class CustomError < StandardError; end

def risky_operation(n)
  raise CustomError, "Bad value: #{n}" if n < 0
  Math.sqrt(n)
end

begin
  puts risky_operation(16)
  puts risky_operation(-1)
rescue CustomError => e
  puts "Error: #{e.message}"
rescue => e
  puts "Other: #{e.message}"
ensure
  puts "Always runs"
end

# Retry
attempts = 0
begin
  attempts += 1
  raise 'fail' if attempts < 3
  puts 'success'
rescue
  retry if attempts < 3
end

# Gemfile
source 'https://rubygems.org'

gem 'rails', '~> 7.0'
gem 'rspec', '~> 3.12'
gem 'pry', '~> 0.14'

# Terminal:
# bundle install
# bundle exec rspec

# Creating a gem
# gem build mygem.gemspec
# gem push mygem-1.0.0.gem

# Using gems
require 'json'
data = { name: 'Mayank' }.to_json
puts data

require 'date'
puts Date.today
puts DateTime.now

# Popular gems:
# rails - web framework
# sinatra - lightweight web
# rspec - testing
# pry - debugging
# nokogiri - HTML parsing
# sidekiq - background jobs