class CostQuery::SqlStatement
  class Union

    COMMON_FIELDS = %w[
      user_id project_id issue_id rate_id
      comments spent_on created_on updated_on tyear tmonth tweek
      costs overridden_costs type
    ]

    ##
    # Generates SqlStatement that maps time_entries and cost_entries to a common structure.
    #
    # Mapping for direct fields:
    #
    #   Result                    | Time Entires             | Cost entries
    #   --------------------------|--------------------------|--------------------------
    #   id                        | id                       | id
    #   user_id                   | user_id                  | user_id
    #   project_id                | project_id               | project_id
    #   issue_id                  | issue_id                 | issue_id
    #   rate_id                   | rate_id                  | rate_id
    #   comments                  | comments                 | comments
    #   spent_on                  | spent_on                 | spent_on
    #   created_on                | created_on               | created_on
    #   updated_on                | updated_on               | updated_on
    #   tyear                     | tyear                    | tyear
    #   tmonth                    | tmonth                   | tmonth
    #   tweek                     | tweek                    | tweek
    #   costs                     | costs                    | costs
    #   overridden_costs          | overridden_costs         | overridden_costs
    #   units                     | hours                    | units
    #   activity_id               | activity_id              | -1
    #   cost_type_id              | -1                       | cost_type_id
    #   type                      | "TimeEntry"              | "CostEntry"
    #   count                     | 1                        | 1
    #
    # Also: This _should_ handle joining activities and cost_types, as the logic differs for time_entries
    # and cost_entries.
    #
    # @param [#table_name] model The model to map
    # @return [CostQuery::SqlStatement] Generated statement
    def self.unified_entry(model)
      table = table_name_for model
      new(table).tap do |query|
        query.select COMMON_FIELDS
        query.desc = "Subquery for #{table}"
        query.select({
          :count => 1, :id => [model, :id], :display_costs => 1,
          :real_costs => switch("#{table}.overridden_costs IS NULL" => [model, :costs], :else => [model, :overridden_costs]),
          :week => iso_year_week(:spent_on, model),
          :singleton_value => 1
          })
          #FIXME: build this subquery from a sql_statement
          query.from "(SELECT *, #{typed :text, model.model_name} AS type FROM #{table}) AS #{table}"
          send("unify_#{table}", query)
      end
    end

    ##
    # Applies logic for mapping time entries to general entries structure.
    #
    # @param [CostQuery::SqlStatement] query The statement to adjust
    def self.unify_time_entries(query)
      query.select :activity_id, :units => :hours, :cost_type_id => -1
      query.select :cost_type => quoted_label(:caption_labor)
    end

    ##
    # Applies logic for mapping cost entries to general entries structure.
    #
    # @param [CostQuery::SqlStatement] query The statement to adjust
    def self.unify_cost_entries(query)
      query.select :units, :cost_type_id, :activity_id => -1
      query.select :cost_type => "cost_types.name"
      query.join CostType
    end

    ##
    # Generates a statement based on all entries (i.e. time entries and cost entries) mapped to the general entries structure,
    # and therefore usable by filters and such.
    #
    # @return [CostQuery::SqlStatement] Generated statement
    def self.for_entries
      new unified_entry(TimeEntry).union(unified_entry(CostEntry), "entries")
    end
  end
end