require 'time'

module Longleaf
  # Helper methods for interacting with dates/timestamps on services
  class ServiceDateHelper
    # Adds the amount of time from modifier to the provided timestamp
    # @param timestamp [String] ISO-8601 timestamp string
    # @param modifier [String] amount of time to add to the timestamp. It must follow the syntax
    # "<quantity> <time unit>", where quantity must be a positive whole number and time unit
    # must be second, minute, hour, day, week, month or year (unit may be plural).
    # Any info after a comma will be ignored.
    # @return [String] the original timestamp in ISO-8601 format with the provided amount of time added.
    def self.add_to_timestamp(timestamp, modifier)
      if modifier =~ /^(\d+) *(second|minute|hour|day|week|month|year)s?(,.*)?/
        value = $1.to_i
        unit = $2
      else
        raise ArgumentError.new("Cannot parse time modifier #{modifier}")
      end

      datetime = Time.iso8601(timestamp)
      case unit
      when 'second'
        unit_modifier = 1
      when 'minute'
        unit_modifier = 60
      when 'hour'
        unit_modifier = 3600
      when 'day'
        unit_modifier = 24 * 3600
      when 'week'
        unit_modifier = 7 * 24 * 3600
      when 'month'
        unit_modifier = 30 * 24 * 3600
      when 'year'
        unit_modifier = 365 * 24 * 3600
      end

      modified_time = datetime + (value * unit_modifier)
      modified_time.iso8601(3)
    end

    # Get a timestamp in the format expected for service timestamps.
    # @param timestamp [Time] the time to format. Defaults to now.
    # @return [String] the time formatted as iso8601
    def self.formatted_timestamp(timestamp = Time.now)
      timestamp.utc.iso8601(3).to_s
    end

    # Get the timestamp for the next time the provided service would need to be run
    # for the object described by md_rec
    # @param md_rec [MetadataRecord] metadata record for the file
    # @param service_def [ServiceDefinition] definition for the service
    # @return [String] iso8601 timestamp for the next time the service will need to run, or
    #    nil if the service does not need to run again.
    def self.next_run_needed(md_rec, service_def)
      raise ArgumentError.new('Must provide a md_rec parameter') if md_rec.nil?
      raise ArgumentError.new('Must provide a service_def parameter') if service_def.nil?

      service_name = service_def.name
      service_rec = md_rec.service(service_name)

      if service_rec.nil? || service_rec.timestamp.nil?
        if service_def.delay.nil?
          return md_rec.registered
        else
          return ServiceDateHelper.add_to_timestamp(md_rec.registered, service_def.delay)
        end
      end

      if service_def.frequency.nil?
        return nil
      else
        return ServiceDateHelper.add_to_timestamp(service_rec.timestamp, service_def.frequency)
      end
    end
  end
end