database_resetter.rb

class DatabaseResetter
  def initialize(options)
    @environment = options[:environment]
    @files_to_watch = options[:files_to_watch] || "schema/migrations/**/*.rb"
  end
  
  def reset_if_required
    if migrations_changed_since_last_database_reset?
      reset
    else
      puts "*** Skipping database reset (migrations not changed since last run)"
      puts "*** Run `#{reset_command}` if necessary, or touch a migration"
    end
  end
  
  private
  
  def database_reset_time_file
    "log/database_reset_time_#{@environment}"
  end
  
  def reset
    puts "*** Resetting #{@environment} database"
    run_reset_command_or_raise
    log_database_reset_time
    puts "*** #{@environment.capitalize} database reset"
  end
  
  def migrations_changed_since_last_database_reset?
    most_recent_migration_file_change_timestamp > last_database_reset_timestamp
  end
  
  def most_recent_migration_file_change_timestamp
    Dir[@files_to_watch].map { |filename|
      File.mtime(filename)
    }.max
  end
  
  def last_database_reset_timestamp
    File.open(database_reset_time_file) do |file|
      Time.parse(file.readline)
    end
  rescue Errno::ENOENT
    Time.at(0)
  end
  
  def log_database_reset_time
    File.open(database_reset_time_file, "w") do |file|
      file.puts(Time.new)
    end 
  end
  
  def run_reset_command_or_raise
    raise "Command failed: #{reset_command}" unless run_reset_command
  end
  
  def run_reset_command
    system(reset_command)
  end
  
  def reset_command
    "rake db:reset MERB_ENV=#{@environment}"
  end
end