From 6e3053dd1cf6815cc0ea968edbf71f76738b4af6 Mon Sep 17 00:00:00 2001
From: Ray Speth <speth@mit.edu>
Date: Tue, 18 Dec 2018 14:17:14 -0500
Subject: [PATCH] Add function for setting default units from a std::map

This is the form that will be used when reading units from a YAML
input file.
---
 include/cantera/base/Units.h | 14 ++++++++++++++
 src/base/Units.cpp           | 32 ++++++++++++++++++++++++++++++++
 test/general/test_units.cpp  | 26 ++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)

diff --git a/include/cantera/base/Units.h b/include/cantera/base/Units.h
index 03504fb66..2bf9d6fc5 100644
--- a/include/cantera/base/Units.h
+++ b/include/cantera/base/Units.h
@@ -111,6 +111,20 @@ public:
     //! * To use CGS+mol: `setDefaults({"cm", "g", "mol"});`
     void setDefaults(std::initializer_list<std::string> units);
 
+    //! Set the default units using a map of dimension to unit pairs.
+    //!
+    //! Defaults for dimensions not specified will be left unchanged. To use
+    //! Cantera's default units:
+    //! ```
+    //! UnitSystem system;
+    //! std::map<string, string> defaults{
+    //!     {"length", "m"}, {"mass", "kg"}, {"time", "s"},
+    //!     {"quantity", "kmol"}, {"pressure", "Pa"}, {"molar-energy", "J/kmol"}
+    //! };
+    //! setDefaults(defaults);
+    //! ```
+    void setDefaults(const std::map<std::string, std::string>& units);
+
     //! Set the default units to convert from when using the `convertMolarEnergy`
     //! function.
     void setDefaultMolarEnergy(const std::string& e_units);
diff --git a/src/base/Units.cpp b/src/base/Units.cpp
index 5ab9303f5..19bae0487 100644
--- a/src/base/Units.cpp
+++ b/src/base/Units.cpp
@@ -68,6 +68,9 @@ const std::map<std::string, Units> knownUnits{
     {"ohm", Units(1.0, 1, 2, -3, 0, -2)}, // kg*m^2/s^3/A^2
     {"V", Units(1.0, 1, 2, -3, 0, -1)}, // kg*m^2/s^3/A
     {"coulomb", Units(1.0, 0, 0, 1, 0, 1)}, // A*s
+
+    //! Molar energy units [M*L^2/T^2/Q]
+    {"J/kmol", Units(1.0, 1, 2, -2, 0, 0, -1)},
 };
 
 const std::map<std::string, double> prefixes{
@@ -245,6 +248,35 @@ void UnitSystem::setDefaults(std::initializer_list<std::string> units)
     }
 }
 
+void UnitSystem::setDefaults(const std::map<std::string, std::string>& units)
+{
+    for (const auto& item : units) {
+        auto& name = item.first;
+        Units unit(item.second);
+        if (name == "mass" && unit.convertible(knownUnits.at("kg"))) {
+            m_mass_factor = unit.factor();
+        } else if (name == "length" && unit.convertible(knownUnits.at("m"))) {
+            m_length_factor = unit.factor();
+        } else if (name == "time" && unit.convertible(knownUnits.at("s"))) {
+            m_time_factor = unit.factor();
+        } else if (name == "temperature" && item.second == "K") {
+            // do nothing - no other temperature scales are supported
+        } else if (name == "current" && item.second == "A") {
+            // do nothing - no other current scales are supported
+        } else if (name == "quantity" && unit.convertible(knownUnits.at("kmol"))) {
+            m_quantity_factor = unit.factor();
+        } else if (name == "pressure" && unit.convertible(knownUnits.at("Pa"))) {
+            m_pressure_factor = unit.factor();
+        } else if (name == "molar-energy" && unit.convertible(knownUnits.at("J/kmol"))) {
+            m_molar_energy_factor = unit.factor();
+        } else {
+            throw CanteraError("UnitSystem::setDefaults",
+                "Unable to set default unit for '{}' to '{}' ({}).",
+                name, item.second, unit.str());
+        }
+    }
+}
+
 void UnitSystem::setDefaultMolarEnergy(const std::string& e_units)
 {
     Units u(e_units);
diff --git a/test/general/test_units.cpp b/test/general/test_units.cpp
index 330edb0b3..26e5dcdfd 100644
--- a/test/general/test_units.cpp
+++ b/test/general/test_units.cpp
@@ -51,6 +51,32 @@ TEST(Units, with_defaults) {
     EXPECT_DOUBLE_EQ(U.convert(1.0, "Pa*m^6/kmol"), 101325*1e-12*1000);
 }
 
+TEST(Units, with_defaults_map) {
+    std::map<std::string, std::string> defaults{
+        {"length", "cm"}, {"mass", "g"}, {"quantity", "mol"},
+        {"pressure", "atm"}
+    };
+    UnitSystem U;
+    U.setDefaults(defaults);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "m"), 0.01);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "kmol/m^3"), 1000);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "kg/kmol"), 1.0);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "cm^2"), 1.0);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "Pa"), 101325);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "hPa"), 1013.25);
+    EXPECT_DOUBLE_EQ(U.convert(1.0, "Pa*m^6/kmol"), 101325*1e-12*1000);
+
+}
+
+TEST(Units, bad_defaults) {
+    UnitSystem U;
+    std::map<std::string, std::string> bad_key{{"length", "m"}, {"joy", "MJ"}};
+    EXPECT_THROW(U.setDefaults(bad_key), CanteraError);
+    std::map<std::string, std::string> bad_value{{"length", "m"}, {"time", "J"}};
+    EXPECT_THROW(U.setDefaults(bad_value), CanteraError);
+}
+
+
 TEST(Units, activation_energies) {
     UnitSystem U;
     EXPECT_DOUBLE_EQ(U.convertMolarEnergy(1000, "J/kmol", "J/mol"), 1.0);