Don't compute axle weights from a degenerate truck geometry

include/packingsolver/algorithms/truck.hpp

@@ -4,6 +4,7 @@
 
 #include <fstream>
 #include <iomanip>
+#include <stdexcept>
 
 namespace packingsolver
 {
@@ -87,6 +88,33 @@ struct SemiTrailerTruckData
         return {middle_axle_weight, rear_axle_weight};
     }
 
+    /**
+     * Check that the provided truck data is consistent.
+     *
+     * A bin type that is not a semi-trailer truck needs no truck data:
+     * compute_axle_weights returns {0, 0} without looking at any other
+     * field, so the other fields can hold any value. A semi-trailer truck
+     * needs 'harness_rear_axle_distance' and 'front_axle_middle_axle_distance'
+     * to compute the rear and middle axle weights.
+     */
+    void check() const
+    {
+        if (!is)
+            return;
+        if (harness_rear_axle_distance <= 0) {
+            throw std::invalid_argument(
+                    FUNC_SIGNATURE + ": "
+                    "a semi-trailer truck bin type must have a strictly "
+                    "positive 'harness_rear_axle_distance'.");
+        }
+        if (front_axle_middle_axle_distance <= 0) {
+            throw std::invalid_argument(
+                    FUNC_SIGNATURE + ": "
+                    "a semi-trailer truck bin type must have a strictly "
+                    "positive 'front_axle_middle_axle_distance'.");
+        }
+    }
+
     void read(std::string label, std::string value)
     {
         if (label == "IS_SEMI_TRAILER_TRUCK") {

src/boxstacks/instance_builder.cpp

@@ -684,7 +684,6 @@ void InstanceBuilder::read_bin_types(
         double maximum_stack_density = std::numeric_limits<double>::max();
 
         SemiTrailerTruckData semi_trailer_truck_data;
-        semi_trailer_truck_data.is = true;
 
         for (Counter i = 0; i < (Counter)line.size(); ++i) {
             if (labels[i] == "X") {
@@ -1001,6 +1000,8 @@ Instance InstanceBuilder::build()
             bin_type_id < instance_.number_of_bin_types();
             ++bin_type_id) {
         const BinType& bin_type = instance_.bin_type(bin_type_id);
+        // Check truck data consistency.
+        bin_type.semi_trailer_truck_data.check();
         // Update bin_type.copies.
         if (bin_type.copies == -1)
             instance_.bin_types_[bin_type_id].copies = instance_.number_of_items();

src/rectangle/instance_builder.cpp

@@ -1131,6 +1131,8 @@ Instance InstanceBuilder::build()
             bin_type_id < instance_.number_of_bin_types();
             ++bin_type_id) {
         const BinType& bin_type = instance_.bin_type(bin_type_id);
+        // Check truck data consistency.
+        bin_type.semi_trailer_truck_data.check();
         // Update bin_type.copies.
         if (bin_type.copies == -1)
             instance_.bin_types_[bin_type_id].copies = instance_.number_of_items();

test/algorithms/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_executable(PackingSolver_algorithms_test)
 target_sources(PackingSolver_algorithms_test PRIVATE
-    meet_in_the_middle_test.cpp)
+    meet_in_the_middle_test.cpp
+    truck_test.cpp)
 target_include_directories(PackingSolver_algorithms_test PRIVATE
     ${PROJECT_SOURCE_DIR}/src)
 target_link_libraries(PackingSolver_algorithms_test

test/algorithms/truck_test.cpp

@@ -0,0 +1,64 @@
+#include "packingsolver/algorithms/truck.hpp"
+
+#include <gtest/gtest.h>
+
+#include <stdexcept>
+
+using namespace packingsolver;
+
+namespace
+{
+
+/** Semi-trailer truck with a complete geometry. */
+SemiTrailerTruckData complete_truck()
+{
+    SemiTrailerTruckData semi_trailer_truck_data;
+    semi_trailer_truck_data.is = true;
+    semi_trailer_truck_data.tractor_weight = 8000;
+    semi_trailer_truck_data.front_axle_middle_axle_distance = 380;
+    semi_trailer_truck_data.front_axle_tractor_gravity_center_distance = 100;
+    semi_trailer_truck_data.front_axle_harness_distance = 320;
+    semi_trailer_truck_data.empty_trailer_weight = 6000;
+    semi_trailer_truck_data.harness_rear_axle_distance = 800;
+    semi_trailer_truck_data.trailer_gravity_center_rear_axle_distance = 400;
+    semi_trailer_truck_data.trailer_start_harness_distance = 100;
+    return semi_trailer_truck_data;
+}
+
+}
+
+TEST(Truck, ComputeAxleWeights)
+{
+    SemiTrailerTruckData semi_trailer_truck_data = complete_truck();
+    std::pair<Weight, Weight> axle_weights
+        = semi_trailer_truck_data.compute_axle_weights(200000, 2000);
+    EXPECT_NEAR(axle_weights.first, 6315.789473684211, 1e-6);
+    EXPECT_NEAR(axle_weights.second, 3000.0, 1e-6);
+}
+
+TEST(Truck, CheckNotATruck)
+{
+    // A bin type that isn't a semi-trailer truck needs no truck data.
+    SemiTrailerTruckData semi_trailer_truck_data;
+    EXPECT_NO_THROW(semi_trailer_truck_data.check());
+}
+
+TEST(Truck, CheckWithoutHarnessRearAxleDistance)
+{
+    // Every axle weight is computed from 'harness_weight', which divides by
+    // 'harness_rear_axle_distance', so a semi-trailer truck without it is an
+    // inconsistent input, not a case to silently skip.
+    SemiTrailerTruckData semi_trailer_truck_data = complete_truck();
+    semi_trailer_truck_data.harness_rear_axle_distance = 0;
+    EXPECT_THROW(semi_trailer_truck_data.check(), std::invalid_argument);
+}
+
+TEST(Truck, CheckWithoutFrontAxleMiddleAxleDistance)
+{
+    // The middle axle weight is computed from 'harness_weight', which
+    // divides by 'front_axle_middle_axle_distance', so a semi-trailer truck
+    // without it is an inconsistent input, not a case to silently skip.
+    SemiTrailerTruckData semi_trailer_truck_data = complete_truck();
+    semi_trailer_truck_data.front_axle_middle_axle_distance = 0;
+    EXPECT_THROW(semi_trailer_truck_data.check(), std::invalid_argument);
+}