Be able to parse cron:

Gemfile.lock

@@ -2,6 +2,7 @@ PATH
   remote: .
   specs:
     arask (0.1.2)
+      fugit (~> 1.1)
       rails (~> 5.1)
 
 GEM
@@ -54,6 +55,11 @@ GEM
     crass (1.0.4)
     diff-lcs (1.3)
     erubi (1.7.1)
+    et-orbi (1.1.2)
+      tzinfo
+    fugit (1.1.1)
+      et-orbi (~> 1.1, >= 1.1.1)
+      raabro (~> 1.1)
     globalid (0.4.1)
       activesupport (>= 4.2.0)
     i18n (1.0.1)
@@ -73,6 +79,7 @@ GEM
     nio4r (2.3.1)
     nokogiri (1.8.2)
       mini_portile2 (~> 2.3.0)
+    raabro (1.1.5)
     rack (2.0.5)
     rack-test (1.0.0)
       rack (>= 1.0, < 3)

arask.gemspec

@@ -17,6 +17,7 @@ Gem::Specification.new do |s|
   s.files = Dir["{app,config,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
 
   s.add_dependency "rails", "~> 5.1"
+  s.add_dependency "fugit", "~> 1.1"
 
   s.add_development_dependency "sqlite3"
   s.add_development_dependency "rspec"

lib/arask.rb

@@ -2,6 +2,7 @@
 require "arask/arask_job"
 require "arask/run_jobs"
 require "arask/setup"
+require 'fugit' # To parse cron
 
 module Arask
   class << self; attr_accessor :jobs_touched, :exception_email, :exception_email_from; end

lib/arask/arask_job.rb

@@ -2,8 +2,10 @@ module Arask
   require 'rake'
 
   class AraskJob < ActiveRecord::Base
+    after_create :calculate_new_execute_at
+
     def run
-      self.update_attribute(:execute_at, self.interval.seconds.from_now)
+      calculate_new_execute_at
       begin
         if self.job.start_with?('Rake::Task')
           Rake.load_rakefile Rails.root.join( 'Rakefile' )
@@ -24,5 +26,15 @@ def run
         end
       end
     end
+
+    private
+    def calculate_new_execute_at
+      if self.interval.start_with?('cron: ')
+        cron = Fugit::Cron.parse(self.interval.split(' ', 2)[1])
+        self.update_attribute(:execute_at, cron.next_time.to_t)
+      else
+        self.update_attribute(:execute_at, self.interval.to_i.seconds.from_now)
+      end
+    end
   end
 end

lib/arask/setup.rb

@@ -6,16 +6,25 @@ def self.on_exception(email: nil, from: 'robot@server')
       puts "Arask could not parse parameter for on_exception!" unless email.class == String
     end
 
-    def self.create(script: nil, task: nil, interval:, run_first_time: false)
-      case interval
-      when :hourly
-        interval = 1.hour
-      when :daily
-        interval = 1.day
-      when :monthly
-        interval = 1.month
+    def self.create(script: nil, task: nil, interval: nil, cron: nil, run_first_time: false)
+      unless interval.nil?
+        case interval
+        when :hourly
+          interval = 1.hour
+        when :daily
+          interval = 1.day
+        when :monthly
+          interval = 1.month
+        end
+        interval = interval.to_s.to_i
+      end
+      unless cron.nil?
+        interval = 'cron: ' + cron
+      end
+      if interval.nil?
+        puts 'Arask: You did not specify either cron: or interval:! When should the task run?'
+        return
       end
-      interval = interval.to_s.to_i
       unless task.nil?
         script = "Rake::Task['#{task}'].invoke"
       end
@@ -28,7 +37,7 @@ def self.create(script: nil, task: nil, interval:, run_first_time: false)
         if job
           Arask.jobs_touched << job.id
         else
-          job = AraskJob.create(job: script, interval: interval, execute_at: interval.seconds.from_now)
+          job = AraskJob.create(job: script, interval: interval)
           Arask.jobs_touched << job.id
           if run_first_time===true
             job.run

lib/generators/arask/install_generator.rb

@@ -8,6 +8,6 @@ def initialize(*args, &block)
     Arask::InstallGenerator.source_root File.expand_path('../../arask', __FILE__)
     copy_file '../../arask/initialize.rb', 'config/initializers/arask.rb'
 
-    generate 'migration', 'create_arask_jobs job:string execute_at:datetime:index interval:integer'
+    generate 'migration', 'create_arask_jobs job:string execute_at:datetime:index interval:string'
   end
 end