diff --git a/lib/main.rb b/lib/main.rb
new file mode 100644
index 00000000..a5c3be3b
--- /dev/null
+++ b/lib/main.rb
@@ -0,0 +1,126 @@
+require_relative 'planet'
+require_relative 'solar_system'
+
+def main
+=begin 
+  # For wave 1 
+  # Create two different instances of Planet and print out some of their attributes  
+  earth = Planet.new('Earth', 'blue-green', 5.972e24, 1.496e8, 'Only planet known to support life')
+  puts "#{ earth.name } is #{ earth.color }"
+  puts earth.summary  
+
+  mars = Planet.new('Mars', 'red', 6.39e23, 14.16e8, 'The second-smallest planet in the solar system')  
+  puts "#{ mars.name } is #{ mars.fun_fact.downcase }"
+  puts mars.summary  
+
+  # For wave 2
+  # create an instance of SolarSystem, add all your Planets to it, and then print the list
+  solar_system = SolarSystem.new("Sol")
+  saturn = Planet.new('Saturn', 'pale yellow', 5.683e26, 92.802e8, 'The second-largest planet in the solar system')
+  solar_system.add_planet(saturn)
+
+  list = solar_system.list_planets
+  puts list
+
+  # Exercise SolarSystem#find_planet_by_name
+  found_planet = solar_system.find_planet_by_name('saturn')
+  # puts found_planet
+  # puts found_planet.summary if found_planet.class == Planet
+  puts "We couldn't find this planet, please try agian" if found_planet.nil?
+  found_planet.each { |planet| puts "#{ planet.summary }\n"}
+=end
+
+  # For wave 3
+  solar_system = SolarSystem.new("Sol")
+  earth = Planet.new('Earth', 'blue-green', 5.972e24, 1.496e8, 'Only planet known to support life')
+  solar_system.add_planet(earth)
+
+  mars = Planet.new('Mars', 'red', 6.39e23, 14.16e8, 'The second-smallest planet in the solar system')
+  solar_system.add_planet(mars)
+
+  saturn = Planet.new('Saturn', 'pale yellow', 5.683e26, 92.802e8, 'The second-largest planet in the solar system')
+  solar_system.add_planet(saturn)
+  
+  options = ["list planets", "planet details", "add planet", "distance between planets", "exit"]
+  stop_loop = false
+  until stop_loop
+    puts "\nWhat do you want to see?"
+    options.each_with_index { |option, index| puts "#{ index+1 }. #{ option }" }
+    user_response = gets.chomp.downcase
+    
+    case user_response
+    when "list planets", "1"
+      puts "\n", list = solar_system.list_planets 
+    when "planet details", "2"
+      puts "\nYay, let's see more details about the planets. Which planet do you want to see?"
+      puts list = solar_system.list_planets 
+      print "==> "
+      user_planet = gets.chomp.downcase
+      found_planet = solar_system.find_planet_by_name(user_planet)
+      
+      while found_planet.count == 0
+        puts "\nSorry, we don't have this planet. Please try again.", list = solar_system.list_planets 
+        print "==> "
+        user_planet = gets.chomp.downcase
+        found_planet = solar_system.find_planet_by_name(user_planet)
+      end
+      
+      puts "\nThe information for planet #{ user_planet.capitalize } is as below:"
+      found_planet.each { |planet| puts "#{ planet.summary }"}
+    when "add planet", "3"
+      puts "\nSo exciting, you're to add a new planet!"  
+      new_planet = Hash.new
+      elements_to_give = ["name", "color", "mass_kg", "distance_from_sun_km", "fun_fact"]
+      elements_to_give.each do |element|
+        print "What's the #{ element } of this planet: "
+        user_new_planet = gets.chomp.downcase
+        if element == "name"
+          check_name = solar_system.find_planet_by_name(user_new_planet)
+          until check_name.count == 0
+            print "Sorry, this name is used, please try another name ==> "
+            user_new_planet = gets.chomp.downcase
+          end
+        end
+        new_planet[element] = user_new_planet
+      end
+      
+      rescue_status = false
+      begin
+        user_planet = Planet.new(new_planet["name"].capitalize, new_planet["color"], new_planet["mass_kg"], new_planet["distance_from_sun_km"], new_planet["fun_fact"])
+      rescue ArgumentError => exception
+        puts "\n#{ exception.message }"
+        puts "Your new planet is not added, please try again."
+        rescue_status = true
+      end 
+      
+      solar_system.add_planet(user_planet) if rescue_status == false
+      puts "\nNow, want to see your new planet on the main menu? Please go check \"list planets\"" if rescue_status == false
+    when "distance between planets", "4"
+      puts "\n Which two planets do you want to see their distance?"
+      puts list = solar_system.list_planets 
+      two_planet = 1
+      planets_for_distance = Hash(first: "", second:"")
+      until two_planet == 3
+        print "Planet #{two_planet}: "
+        user_distance_planet = gets.chomp.downcase
+        found_planet = solar_system.find_planet_by_name(user_distance_planet)
+
+        if found_planet.nil? || found_planet.count == 0
+          puts "Sorry, we don't have this planet: #{ user_distance_planet }" 
+        else
+          planets_for_distance[:first] = user_distance_planet if two_planet == 1
+          planets_for_distance[:second] = user_distance_planet if two_planet == 2
+          two_planet += 1
+        end
+      end      
+      puts "\nThe distance between #{ planets_for_distance[:first] } and #{ planets_for_distance[:second] } is #{ solar_system.distance_between(planets_for_distance[:first], planets_for_distance[:second]) }km." 
+    when "exit", "5"
+      stop_loop = true 
+    else
+      puts "Please enter the options listed."
+    end
+  end
+
+end
+
+main
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diff --git a/lib/planet.rb b/lib/planet.rb
new file mode 100644
index 00000000..aced9783
--- /dev/null
+++ b/lib/planet.rb
@@ -0,0 +1,19 @@
+class Planet
+  attr_reader :name, :color, :mass_kg, :distance_from_sun_km, :fun_fact
+
+  def initialize(name, color, mass_kg, distance_from_sun_km, fun_fact)  
+    raise ArgumentError.new("Mass(kg) should be a number that greater than zero: #{ mass_kg }") if !(mass_kg.to_f > 0)
+    @mass_kg = mass_kg.to_f
+    
+    raise ArgumentError.new("Distance from sun (km) should be a number that greater than zero: #{ distance_from_sun_km }") if !(distance_from_sun_km.to_f > 0)
+    @distance_from_sun_km = distance_from_sun_km.to_f
+
+    @name = name
+    @color = color
+    @fun_fact = fun_fact
+  end
+
+  def summary
+    return "#{ @name } is #{ @color }, and it weights #{ @mass_kg } kg and #{ @distance_from_sun_km } km away from sun. \nThe fun fact about it: #{ @fun_fact.downcase }\n\n"
+  end
+end
diff --git a/lib/solar_system.rb b/lib/solar_system.rb
new file mode 100644
index 00000000..1317628b
--- /dev/null
+++ b/lib/solar_system.rb
@@ -0,0 +1,30 @@
+class SolarSystem
+  attr_reader :star_name, :planets
+
+  def initialize(star_name)
+    @star_name = star_name
+    @planets = Array.new
+  end
+
+  def add_planet(planet)
+    @planets.push(planet)
+  end
+
+  def list_planets
+    my_string = "Planets orbiting <#{ @star_name }>\n"
+    @planets.each { |planet| my_string += "- #{ planet.name }\n" }
+    return my_string
+  end
+
+  def find_planet_by_name(planet_name)
+    found_planet = @planets.select { |planet| planet.name.downcase == planet_name.downcase }
+    return found_planet
+  end
+
+  def distance_between(planet1, planet2)
+    first_planet = find_planet_by_name(planet1)
+    second_planet = find_planet_by_name(planet2)
+    distance_between_two_planets = (first_planet[0].distance_from_sun_km - second_planet[0].distance_from_sun_km).abs
+    return distance_between_two_planets
+  end
+end
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diff --git a/test/planet_test.rb b/test/planet_test.rb
new file mode 100644
index 00000000..3672d525
--- /dev/null
+++ b/test/planet_test.rb
@@ -0,0 +1,46 @@
+require 'minitest'
+require 'minitest/spec'
+require 'minitest/autorun'
+require 'minitest/reporters'
+require 'minitest/pride'
+
+require_relative '../lib/planet'
+
+Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
+
+describe 'tests for planet class' do
+  it 'mass_kg and distance_from_sun_km are both a number greater than zero' do
+    # Arrange && Act
+    tiny_planet = Planet.new('Tiny planet', 'pale pink', 1, 10000, 'Pale pink color is becuase of cherry blossom')
+
+    # Assert 
+    expect(tiny_planet.mass_kg).must_equal 1
+    expect(tiny_planet.distance_from_sun_km).must_equal 10000
+
+    tiny_planet2 = Planet.new('Tiny planet', 'pale pink', "4", 10000, 'Pale pink color is becuase of cherry blossom')
+    expect(tiny_planet2.mass_kg.to_f).must_equal 4.0
+
+    tiny_planet3 = Planet.new('Tiny planet', 'pale pink', 1, "40000", 'Pale pink color is becuase of cherry blossom')
+    expect(tiny_planet3.distance_from_sun_km.to_f).must_equal 40000.0
+
+
+  end
+
+  it 'raises an ArgumentError for mass_kg is not a number greater than 0' do
+
+    expect {Planet.new('Tiny planet', 'pale pink', 'super tiny planet', 10000, 'Pale pink color is becuase of cherry blossom')}.must_raise ArgumentError
+
+    expect {Planet.new('Tiny planet', 'pale pink', -100, 10000, 'Pale pink color is becuase of cherry blossom')}.must_raise ArgumentError
+
+    expect {Planet.new('Tiny planet', 'pale pink', '', 10000, 'Pale pink color is becuase of cherry blossom')}.must_raise ArgumentError
+  end
+
+  it 'raises an ArgumentError for distance_from_sun_km is not a number greater than 0' do
+
+    expect {Planet.new('Tiny planet', 'pale pink', 1, 'not so far away', 'Pale pink color is becuase of cherry blossom')}.must_raise ArgumentError
+
+    expect {Planet.new('Tiny planet', 'pale pink', 1, 0, 'Pale pink color is becuase of cherry blossom')}.must_raise ArgumentError
+
+    expect {Planet.new('Tiny planet', 'pale pink', 1, nil, 'Pale pink color is becuase of cherry blossom')}.must_raise ArgumentError
+  end
+end
\ No newline at end of file
diff --git a/test/solar_system_test.rb b/test/solar_system_test.rb
new file mode 100644
index 00000000..2ff5d95d
--- /dev/null
+++ b/test/solar_system_test.rb
@@ -0,0 +1,27 @@
+require 'minitest'
+require 'minitest/spec'
+require 'minitest/autorun'
+require 'minitest/reporters'
+require 'minitest/pride'
+
+require_relative '../lib/planet'
+require_relative '../lib/solar_system'
+
+Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
+
+describe 'tests for solar_system class' do
+  it 'has the distance between two planets' do
+    # Arrange 
+    first_planet = Planet.new('Tiny planet', 'pale pink', 1, 10_000, 'Pale pink color is becuase of cherry blossom')
+    second_planet = Planet.new('Huge planet', 'green and blue', 100_000_000, 100_000, 'The biggest volumn of planet')
+
+    # Act
+    space_system = SolarSystem.new("Sol")
+    space_system.add_planet(first_planet)
+    space_system.add_planet(second_planet)
+    distance_between_them = space_system.distance_between(first_planet.name, second_planet.name)
+
+    # Assert 
+    expect(distance_between_them).must_equal 90_000
+  end
+end
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