split up FUE class

lib/flight/impact_model/fuel_use_equation.rb

@@ -1,24 +1,22 @@
+require 'flight/impact_model/fuel_use_equation/derived'
+require 'flight/impact_model/fuel_use_equation/given'
+
 module BrighterPlanet
   module Flight
     module ImpactModel
       class FuelUseEquation
         class << self
           def from_coefficients(m3, m2, m1, b)
-            equation = new
-            equation.m3 = m3
-            equation.m2 = m2
-            equation.m1 = m1
-            equation.b = b
+            equation = Given.new(m3, m2, m1, b)
             if equation.valid?
               equation
             else
               nil
             end
           end
 
-          def from_flight_segments(relation)
-            equation = new
-            equation.where_sql = relation.where_sql
+          def from_flight_segments(flight_segments)
+            equation = Derived.new flight_segments
             if equation.valid?
               equation
             else
@@ -27,121 +25,13 @@ def from_flight_segments(relation)
           end
         end
 
-        attr_writer :m3, :m2, :m1, :b
-        attr_accessor :where_sql
-
         def valid?
           coefficients.all?(&:present?) and coefficients.any?(&:nonzero?)
         end
 
-        def m3
-          calculate!
-          @m3
-        end
-
-        def m2
-          calculate!
-          @m2
-        end
-
-        def m1
-          calculate!
-          @m1
-        end
-
-        def b
-          calculate!
-          @b
-        end
-
         def coefficients
           [ m3, m2, m1, b ]
         end
-
-        private
-
-        def calculate!
-          return if @calculated == true
-          @calculated = true
-          return unless where_sql
-
-          # - Create a temporary table to hold the values we need
-          c = ::ActiveRecord::Base.connection
-
-          table_name = "flight_fuel_use_coefficients_#{::Kernel.rand(1e11)}"
-
-          create_table_sql = %{
-            CREATE TEMPORARY TABLE #{table_name} (
-              description VARCHAR(255),
-              m3 FLOAT,
-              m2 FLOAT,
-              m1 FLOAT,
-              b FLOAT,
-              passengers INT
-            )
-          }
-
-          # make this run faster if you're on mysql
-          create_table_sql << 'ENGINE=MEMORY' if c.adapter_name =~ /mysql/i
-
-          c.execute create_table_sql
-
-          # - Look up the unique aircraft descriptions in `where_sql`
-          aircraft_descriptions = c.select_values %{
-            SELECT DISTINCT aircraft_description
-            FROM #{::FlightSegment.quoted_table_name}
-            #{where_sql}
-          }
-
-          # - For each unique aircraft description:
-          # - 1. look up all the aircraft it refers to
-          # - 2. average those aircraft's fuel use coefficients
-          # - 3. store the resulting values in the temporary table along with the unique aircraft_description
-          c.execute %{
-            INSERT INTO #{table_name} (description, m3, m2, m1, b)
-              SELECT t1.b, AVG(t2.m3), AVG(t2.m2), AVG(t2.m1), AVG(t2.b)
-              FROM #{::FuzzyMatch::CachedResult.quoted_table_name} AS t1
-                INNER JOIN #{::Aircraft.quoted_table_name} AS t2
-                ON t1.a = t2.description
-              WHERE t1.b IN ('#{aircraft_descriptions.join("', '")}')
-              GROUP BY t1.b
-          }
-
-          # - For each unique aircraft description:
-          # - 1. look up all the flight segments in `where_sql` that match the aircraft description
-          # - 2. sum passengers across those flight segments
-          # - 3. store the resulting value in the temporary table
-          c.execute %{
-            UPDATE #{table_name}
-            SET passengers = (
-              SELECT SUM(passengers)
-              FROM #{::FlightSegment.quoted_table_name}
-              #{where_sql} AND #{::FlightSegment.quoted_table_name}.aircraft_description = #{table_name}.description
-            )
-          }
-
-          # - Calculate the average of the coefficients in the temporary table, weighted by passengers
-          row = c.select_one %{
-            SELECT
-              SUM(1.0 * m3 * passengers)/SUM(passengers) AS a_m3,
-              SUM(1.0 * m2 * passengers)/SUM(passengers) AS a_m2,
-              SUM(1.0 * m1 * passengers)/SUM(passengers) AS a_m1,
-              SUM(1.0 * b * passengers)/SUM(passengers)  AS a_b
-            FROM #{table_name}
-            WHERE
-              m3 IS NOT NULL
-              AND m2 IS NOT NULL
-              AND m1 IS NOT NULL
-              AND b IS NOT NULL
-              AND passengers > 0
-          }
-
-          @m3, @m2, @m1, @b = row['a_m3'], row['a_m2'], row['a_m1'], row['a_b']
-
-          c.execute %{
-            DROP TABLE #{table_name}
-          }
-        end
       end
     end
   end

lib/flight/impact_model/fuel_use_equation/derived.rb

@@ -0,0 +1,118 @@
+module BrighterPlanet
+  module Flight
+    module ImpactModel
+      class FuelUseEquation
+        class Derived < FuelUseEquation
+          def initialize(flight_segments)
+            @where_sql = flight_segments.where_sql
+          end
+
+          def m3
+            calculate!
+            @m3
+          end
+
+          def m2
+            calculate!
+            @m2
+          end
+
+          def m1
+            calculate!
+            @m1
+          end
+
+          def b
+            calculate!
+            @b
+          end
+
+          private
+
+          def calculate!
+            return if @calculated == true
+            @calculated = true
+            raise ArgumentError if @where_sql.blank?
+
+            # - Create a temporary table to hold the values we need
+            c = ::ActiveRecord::Base.connection
+
+            table_name = "flight_fuel_use_coefficients_#{::Kernel.rand(1e11)}"
+
+            create_table_sql = %{
+              CREATE TEMPORARY TABLE #{table_name} (
+                description VARCHAR(255),
+                m3 FLOAT,
+                m2 FLOAT,
+                m1 FLOAT,
+                b FLOAT,
+                passengers INT
+              )
+            }
+
+            # make this run faster if you're on mysql
+            create_table_sql << 'ENGINE=MEMORY' if c.adapter_name =~ /mysql/i
+
+            c.execute create_table_sql
+
+            # - Look up the unique aircraft descriptions in `@where_sql`
+            aircraft_descriptions = c.select_values %{
+              SELECT DISTINCT aircraft_description
+              FROM #{::FlightSegment.quoted_table_name}
+              #{@where_sql}
+            }
+
+            # - For each unique aircraft description:
+            # - 1. look up all the aircraft it refers to
+            # - 2. average those aircraft's fuel use coefficients
+            # - 3. store the resulting values in the temporary table along with the unique aircraft_description
+            c.execute %{
+              INSERT INTO #{table_name} (description, m3, m2, m1, b)
+                SELECT t1.b, AVG(t2.m3), AVG(t2.m2), AVG(t2.m1), AVG(t2.b)
+                FROM #{::FuzzyMatch::CachedResult.quoted_table_name} AS t1
+                  INNER JOIN #{::Aircraft.quoted_table_name} AS t2
+                  ON t1.a = t2.description
+                WHERE t1.b IN ('#{aircraft_descriptions.join("', '")}')
+                GROUP BY t1.b
+            }
+
+            # - For each unique aircraft description:
+            # - 1. look up all the flight segments in `@where_sql` that match the aircraft description
+            # - 2. sum passengers across those flight segments
+            # - 3. store the resulting value in the temporary table
+            c.execute %{
+              UPDATE #{table_name}
+              SET passengers = (
+                SELECT SUM(passengers)
+                FROM #{::FlightSegment.quoted_table_name}
+                #{@where_sql} AND #{::FlightSegment.quoted_table_name}.aircraft_description = #{table_name}.description
+              )
+            }
+
+            # - Calculate the average of the coefficients in the temporary table, weighted by passengers
+            row = c.select_one %{
+              SELECT
+                SUM(1.0 * m3 * passengers)/SUM(passengers) AS a_m3,
+                SUM(1.0 * m2 * passengers)/SUM(passengers) AS a_m2,
+                SUM(1.0 * m1 * passengers)/SUM(passengers) AS a_m1,
+                SUM(1.0 * b * passengers)/SUM(passengers)  AS a_b
+              FROM #{table_name}
+              WHERE
+                m3 IS NOT NULL
+                AND m2 IS NOT NULL
+                AND m1 IS NOT NULL
+                AND b IS NOT NULL
+                AND passengers > 0
+            }
+
+            @m3, @m2, @m1, @b = row['a_m3'], row['a_m2'], row['a_m1'], row['a_b']
+
+            c.execute %{
+              DROP TABLE #{table_name}
+            }
+          end
+        end
+      end
+    end
+  end
+end

lib/flight/impact_model/fuel_use_equation/given.rb

@@ -0,0 +1,17 @@
+module BrighterPlanet
+  module Flight
+    module ImpactModel
+      class FuelUseEquation
+        class Given < FuelUseEquation
+          attr_reader :m3, :m2, :m1, :b
+          def initialize(m3, m2, m1, b)
+            @m3 = m3
+            @m2 = m2
+            @m1 = m1
+            @b = b
+          end
+        end
+      end
+    end
+  end
+end