Add basic implementation and tests

Gemfile

@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
-source "https://rubygems.org"
+source 'https://rubygems.org'
 
 # Specify your gem's dependencies in cron_calc.gemspec
 gemspec
 
-gem "rake", "~> 13.1"
+gem 'rake', '~> 13.1'
 
-gem "rspec", "~> 3.12"
+gem 'rspec', '~> 3.12'
 
-gem "rubocop", "~> 1.57"
+gem 'rubocop', '~> 1.57'

Rakefile

@@ -1,11 +1,11 @@
 # frozen_string_literal: true
 
-require "bundler/gem_tasks"
-require "rspec/core/rake_task"
+require 'bundler/gem_tasks'
+require 'rspec/core/rake_task'
 
 RSpec::Core::RakeTask.new(:spec)
 
-require "rubocop/rake_task"
+require 'rubocop/rake_task'
 
 RuboCop::RakeTask.new
 

bin/console

@@ -1,11 +1,11 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
-require "bundler/setup"
-require "cron_calc"
+require 'bundler/setup'
+require 'cron_calc'
 
 # You can add fixtures and/or initialization code here to make experimenting
 # with your gem easier. You can also use a different console, if you like.
 
-require "irb"
+require 'irb'
 IRB.start(__FILE__)

cron_calc.gemspec

@@ -1,24 +1,22 @@
 # frozen_string_literal: true
 
-require_relative "lib/cron_calc/version"
+require_relative 'lib/cron_calc/version'
 
 Gem::Specification.new do |spec|
-  spec.name = "cron_calc"
+  spec.name = 'cron_calc'
   spec.version = CronCalc::VERSION
-  spec.authors = ["Jakub Miziński"]
-  spec.email = ["[email protected]"]
+  spec.authors = ['Jakub Miziński']
+  spec.email = ['[email protected]']
 
-  spec.summary = "calculates cron job occurrences"
-  spec.description = "calculates cron job occurrences within a specified period"
-  spec.homepage = "TODO: Put your gem's website or public repo URL here."
-  spec.license = "MIT"
-  spec.required_ruby_version = ">= 2.6.0"
+  spec.summary = 'calculates cron job occurrences'
+  spec.description = 'calculates cron job occurrences within a specified period'
+  spec.homepage = 'https://github.com/mizinsky/cron_calc'
+  spec.license = 'MIT'
+  spec.required_ruby_version = '>= 2.6.0'
 
-  spec.metadata["allowed_push_host"] = "TODO: Set to your gem server 'https://example.com'"
-
-  spec.metadata["homepage_uri"] = spec.homepage
-  spec.metadata["source_code_uri"] = "TODO: Put your gem's public repo URL here."
-  spec.metadata["changelog_uri"] = "TODO: Put your gem's CHANGELOG.md URL here."
+  spec.metadata['homepage_uri'] = spec.homepage
+  spec.metadata['source_code_uri'] = 'https://github.com/mizinsky/cron_calc'
+  spec.metadata['changelog_uri'] = 'https://github.com/mizinsky/cron_calc/blob/main/CHANGELOG.md'
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
@@ -28,12 +26,12 @@ Gem::Specification.new do |spec|
         f.start_with?(*%w[bin/ test/ spec/ features/ .git .github appveyor Gemfile])
     end
   end
-  spec.bindir = "exe"
+  spec.bindir = 'exe'
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
-  spec.require_paths = ["lib"]
+  spec.require_paths = ['lib']
 
   # Uncomment to register a new dependency of your gem
-  # spec.add_dependency "example-gem", "~> 1.0"
+  spec.add_dependency 'rspec', '~> 3.12'
 
   # For more information and examples about making a new gem, check out our
   # guide at: https://bundler.io/guides/creating_gem.html

lib/cron_calc.rb

@@ -1,8 +1,80 @@
 # frozen_string_literal: true
 
-require_relative "cron_calc/version"
+require_relative 'cron_calc/version'
+require 'time'
 
 module CronCalc
   class Error < StandardError; end
-  # Your code goes here...
+
+  def self.new(cron_string, period)
+    Parser.new(cron_string, period)
+  end
+
+  class Parser
+    attr_reader :cron_string, :cron_parts, :period
+
+    RANGE = {
+      minutes: 0..59,
+      hours: 0..23,
+      days: 1..31,
+      months: 1..12
+    }.freeze
+
+    def initialize(cron_string, period)
+      @cron_string = cron_string
+      @period = period
+      @cron_parts = split_cron_string
+    end
+
+    def occurrences
+      raise 'Cron expression is not supported or invalid' unless cron_string_valid?
+
+      minutes, hours, days, months, years = parse_cron_expression
+
+      years.product(months, days, hours, minutes).each_with_object([]) do |(year, month, day, hour, minute), occ|
+        time = Time.new(year, month, day, hour, minute)
+        occ << time if Date.valid_date?(year, month, day) && period.include?(time)
+      end
+    end
+
+    private
+
+    def split_cron_string
+      splitted = cron_string.split
+
+      {
+        minutes: splitted[0],
+        hours: splitted[1],
+        days: splitted[2],
+        months: splitted[3]
+      }
+    end
+
+    def parse_cron_expression
+      %i[minutes hours days months].map { |unit| parse_cron_part(unit) } << (period.min.year..period.max.year).to_a
+    end
+
+    def parse_cron_part(time_unit)
+      range = RANGE[time_unit]
+      part = cron_parts[time_unit]
+
+      case part
+      when '*'
+        range.to_a
+      when /,/
+        part.split(',').map(&:to_i)
+      when /-/
+        (part.split('-').first.to_i..part.split('-').last.to_i).to_a
+      when %r{/}
+        range.step(part.split('/').last.to_i).to_a
+      else
+        [part.to_i]
+      end
+    end
+
+    def cron_string_valid?
+      regex = %r{\A(\*|([0-5]?\d)(,([0-5]?\d))*|(\*/\d+)|(\d+-\d+)) (\*|([01]?\d|2[0-3])(,([01]?\d|2[0-3]))*|(\*/\d+)|(\d+-\d+)) (\*|([12]?\d|3[01])(,([12]?\d|3[01]))*|(\*/\d+)|(\d+-\d+)) (\*|([1-9]|1[0-2])(,([1-9]|1[0-2]))*|(\*/\d+)|(\d+-\d+)) \*\z}
+      cron_string.match?(regex)
+    end
+  end
 end

lib/cron_calc/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module CronCalc
-  VERSION = "0.1.0"
+  VERSION = '0.1.0'
 end

spec/cron_calc_spec.rb

@@ -1,11 +1,121 @@
 # frozen_string_literal: true
 
 RSpec.describe CronCalc do
-  it "has a version number" do
+  it 'has a version number' do
     expect(CronCalc::VERSION).not_to be nil
   end
 
-  it "does something useful" do
-    expect(false).to eq(true)
+  describe '#occurrences' do
+    let(:subject) { described_class.new(cron_string, period).occurrences }
+
+    context 'when "," is used' do
+      let(:cron_string) { '30 22,23 * * *' }
+      let(:period) { Time.new(2023, 11, 23)..Time.new(2023, 11, 27) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2023, 11, 23, 22, 30),
+                                Time.new(2023, 11, 23, 23, 30),
+                                Time.new(2023, 11, 24, 22, 30),
+                                Time.new(2023, 11, 24, 23, 30),
+                                Time.new(2023, 11, 25, 22, 30),
+                                Time.new(2023, 11, 25, 23, 30),
+                                Time.new(2023, 11, 26, 22, 30),
+                                Time.new(2023, 11, 26, 23, 30)
+                              ])
+      end
+    end
+
+    context 'when day is used' do
+      let(:cron_string) { '5 5 12 * *' }
+      let(:period) { Time.new(2023, 11, 10)..Time.new(2024, 2, 20) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2023, 11, 12, 5, 5),
+                                Time.new(2023, 12, 12, 5, 5),
+                                Time.new(2024, 1, 12, 5, 5),
+                                Time.new(2024, 2, 12, 5, 5)
+                              ])
+      end
+    end
+
+    context 'when month is used' do
+      let(:cron_string) { '5 5 12 1 *' }
+      let(:period) { Time.new(2023, 11, 10)..Time.new(2024, 2, 20) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2024, 1, 12, 5, 5)
+                              ])
+      end
+    end
+
+    context 'when range "-" is used' do
+      let(:cron_string) { '5 5 15-17 * *' }
+      let(:period) { Time.new(2023, 1, 10)..Time.new(2023, 2, 20) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2023, 1, 15, 5, 5),
+                                Time.new(2023, 1, 16, 5, 5),
+                                Time.new(2023, 1, 17, 5, 5),
+                                Time.new(2023, 2, 15, 5, 5),
+                                Time.new(2023, 2, 16, 5, 5),
+                                Time.new(2023, 2, 17, 5, 5)
+                              ])
+      end
+    end
+
+    context 'when step "/" is used' do
+      let(:cron_string) { '5 5 28 */3 *' }
+      let(:period) { Time.new(2023, 1, 1)..Time.new(2024, 1, 31) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2023, 1, 28, 5, 5),
+                                Time.new(2023, 4, 28, 5, 5),
+                                Time.new(2023, 7, 28, 5, 5),
+                                Time.new(2023, 10, 28, 5, 5),
+                                Time.new(2024, 1, 28, 5, 5)
+                              ])
+      end
+    end
+
+    context 'when there is an occurrence with 0 minutes' do
+      let(:cron_string) { '* 11-12 28 * *' }
+      let(:period) { Time.new(2023, 1, 28, 11, 58)..Time.new(2023, 1, 28, 12, 2) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2023, 1, 28, 11, 58),
+                                Time.new(2023, 1, 28, 11, 59),
+                                Time.new(2023, 1, 28, 12),
+                                Time.new(2023, 1, 28, 12, 1),
+                                Time.new(2023, 1, 28, 12, 2)
+                              ])
+      end
+    end
+
+    context 'when invalid cron string is used' do
+      let(:cron_string) { '* 40 * * *' }
+      let(:period) { Time.new(2023, 1, 1)..Time.new(2023, 1, 2) }
+
+      it do
+        expect { subject }.to raise_error(RuntimeError, 'Cron expression is not supported or invalid')
+      end
+    end
+
+    context 'when there is short month' do
+      let(:cron_string) { '5 5 31 1,2,3,4 *' }
+      let(:period) { Time.new(2023, 1, 1, 0, 0)..Time.new(2023, 6, 1, 0, 0) }
+
+      it do
+        expect(subject).to eq([
+                                Time.new(2023, 1, 31, 5, 5),
+                                Time.new(2023, 3, 31, 5, 5)
+                              ])
+      end
+    end
   end
 end

spec/spec_helper.rb

@@ -1,10 +1,10 @@
 # frozen_string_literal: true
 
-require "cron_calc"
+require 'cron_calc'
 
 RSpec.configure do |config|
   # Enable flags like --only-failures and --next-failure
-  config.example_status_persistence_file_path = ".rspec_status"
+  config.example_status_persistence_file_path = '.rspec_status'
 
   # Disable RSpec exposing methods globally on `Module` and `main`
   config.disable_monkey_patching!