require "groupdate/version"
require "active_record"

module Groupdate
  extend ActiveSupport::Concern

  # Pattern from kaminari
  # https://github.com/amatsuda/kaminari/blob/master/lib/kaminari/models/active_record_extension.rb
  included do
    # Future subclasses will pick up the model extension
    class << self
      def inherited_with_groupdate(kls) #:nodoc:
        inherited_without_groupdate kls
        kls.send(:include, ClassMethods) if kls.superclass == ActiveRecord::Base
      end
      alias_method_chain :inherited, :groupdate
    end

    # Existing subclasses pick up the model extension as well
    self.descendants.each do |kls|
      kls.send(:include, ClassMethods) if kls.superclass == ActiveRecord::Base
    end
  end

  module ClassMethods
    extend ActiveSupport::Concern

    included do
      # Field list from
      # http://www.postgresql.org/docs/9.1/static/functions-datetime.html
      fields = %w(second minute hour day week month year day_of_week hour_of_day)
      fields.each do |field|
        self.scope :"group_by_#{field}", lambda {|unsafe_column, time_zone = Time.zone|
          column = connection.quote_column_name(unsafe_column)
          time_zone ||= "Etc/UTC"
          if time_zone.is_a?(ActiveSupport::TimeZone) or time_zone = ActiveSupport::TimeZone[time_zone]
            time_zone = time_zone.tzinfo.name
          else
            raise "Unrecognized time zone"
          end
          query =
            case connection.adapter_name
            when "MySQL", "Mysql2"
              case field
              when "day_of_week" # Sunday = 0, Monday = 1, etc
                # use CONCAT for consistent return type (String)
                ["DAYOFWEEK(CONVERT_TZ(#{column}, '+00:00', ?)) - 1", time_zone]
              when "hour_of_day"
                ["EXTRACT(HOUR from CONVERT_TZ(#{column}, '+00:00', ?))", time_zone]
              when "week"
                ["CONVERT_TZ(DATE_FORMAT(CONVERT_TZ(DATE_SUB(#{column}, INTERVAL (DAYOFWEEK(CONVERT_TZ(#{column}, '+00:00', ?)) - 1) DAY), '+00:00', ?), '%Y-%m-%d 00:00:00'), ?, '+00:00')", time_zone, time_zone, time_zone]
              else
                format =
                  case field
                  when "second"
                    "%Y-%m-%d %H:%i:%S"
                  when "minute"
                    "%Y-%m-%d %H:%i:00"
                  when "hour"
                    "%Y-%m-%d %H:00:00"
                  when "day"
                    "%Y-%m-%d 00:00:00"
                  when "month"
                    "%Y-%m-01 00:00:00"
                  else # year
                    "%Y-01-01 00:00:00"
                  end

                ["CONVERT_TZ(DATE_FORMAT(CONVERT_TZ(#{column}, '+00:00', ?), '#{format}'), ?, '+00:00')", time_zone, time_zone]
              end
            when "PostgreSQL"
              case field
              when "day_of_week"
                ["EXTRACT(DOW from #{column}::timestamptz AT TIME ZONE ?)", time_zone]
              when "hour_of_day"
                ["EXTRACT(HOUR from #{column}::timestamptz AT TIME ZONE ?)", time_zone]
              when "week" # start on Sunday, not PostgreSQL default Monday
                ["(DATE_TRUNC('#{field}', (#{column}::timestamptz + INTERVAL '1 day') AT TIME ZONE ?) - INTERVAL '1 day') AT TIME ZONE ?", time_zone, time_zone]
              else
                ["DATE_TRUNC('#{field}', #{column}::timestamptz AT TIME ZONE ?) AT TIME ZONE ?", time_zone, time_zone]
              end
            else
              raise "Connection adapter not supported: #{connection.adapter_name}"
            end

          group(Groupdate::OrderHack.new(sanitize_sql_array(query), field))
        }
      end
    end
  end

  class OrderHack < String
    attr_reader :field

    def initialize(str, field)
      super(str)
      @field = field
    end
  end
end

ActiveRecord::Base.send :include, Groupdate

# hack for **unfixed** rails issue
# https://github.com/rails/rails/issues/7121
module ActiveRecord
  module Calculations

    def column_alias_for_with_hack(*keys)
      if keys.first.is_a?(Groupdate::OrderHack)
        keys.first.field
      else
        column_alias_for_without_hack(*keys)
      end
    end
    alias_method_chain :column_alias_for, :hack

  end
end