From 2b583fd822b4a89fb19d320bb471c368a743c238 Mon Sep 17 00:00:00 2001
From: Jedd Morgan <45512892+JR-Morgan@users.noreply.github.com>
Date: Wed, 6 Sep 2023 12:34:16 +0100
Subject: [PATCH] Added unit scaling functions in units.py

---
 src/specklepy/objects/units.py  | 37 ++++++++++++++++++++--
 tests/unit/test_unit_scaling.py | 56 +++++++++++++++++++++++++++++++++
 2 files changed, 91 insertions(+), 2 deletions(-)
 create mode 100644 tests/unit/test_unit_scaling.py

diff --git a/src/specklepy/objects/units.py b/src/specklepy/objects/units.py
index 182ea1d3..d795738c 100644
--- a/src/specklepy/objects/units.py
+++ b/src/specklepy/objects/units.py
@@ -35,6 +35,7 @@ class Units(Enum):
     Units.none: ["none", "null"],
 }
 
+
 UNITS_ENCODINGS = {
     Units.none: 0,
     None: 0,
@@ -49,6 +50,20 @@ class Units(Enum):
 }
 
 
+UNIT_SCALE = {
+    Units.none: 1,
+    Units.mm: 0.001,
+    Units.cm: 0.01,
+    Units.m: 1.0,
+    Units.km: 1000.0,
+    Units.inches: 0.0254,
+    Units.feet: 0.3048,
+    Units.yards: 0.9144,
+    Units.miles: 1609.340,
+}
+"""Unit scaling factor to meters"""
+
+
 def get_units_from_string(unit: str) -> Units:
     if not isinstance(unit, str):
         raise SpeckleInvalidUnitException(unit)
@@ -59,10 +74,10 @@ def get_units_from_string(unit: str) -> Units:
     raise SpeckleInvalidUnitException(unit)
 
 
-def get_units_from_encoding(unit: int):
+def get_units_from_encoding(unit: int) -> Units:
     for name, encoding in UNITS_ENCODINGS.items():
         if unit == encoding:
-            return name
+            return name or Units.none
 
     raise SpeckleException(
         message=(
@@ -87,3 +102,21 @@ def get_encoding_from_units(unit: Union[Units, str, None]):
                 f"Please enter a valid unit to encode (eg {UNITS_ENCODINGS})."
             )
         ) from e
+
+
+def get_scale_factor_from_string(fromUnits: str, toUnits: str) -> float:
+    """Returns a scalar to convert distance values from one unit system to another"""
+    return get_scale_factor(get_units_from_string(fromUnits), get_units_from_string(toUnits))
+
+
+def get_scale_factor(fromUnits: Units, toUnits: Units) -> float:
+    """Returns a scalar to convert distance values from one unit system to another"""
+    return get_scale_factor_to_meters(fromUnits) / get_scale_factor_to_meters(toUnits)
+
+
+def get_scale_factor_to_meters(fromUnits: Units) -> float:
+    """Returns a scalar to convert distance values from one unit system to meters"""
+    if fromUnits not in UNIT_SCALE:
+        raise ValueError(f"Invalid units provided: {fromUnits}")
+
+    return UNIT_SCALE[fromUnits]
\ No newline at end of file
diff --git a/tests/unit/test_unit_scaling.py b/tests/unit/test_unit_scaling.py
new file mode 100644
index 00000000..34627462
--- /dev/null
+++ b/tests/unit/test_unit_scaling.py
@@ -0,0 +1,56 @@
+
+
+import pytest
+
+from specklepy.objects.units import Units, get_scale_factor
+
+
+@pytest.mark.parametrize(
+    "fromUnits, toUnits, inValue, expectedOutValue",
+    [
+        #To self
+        (Units.km, Units.km, 1.5, 1.5),
+        (Units.km, Units.km, 0, 0),
+        (Units.m, Units.m, 1.5, 1.5),
+        (Units.m, Units.m, 0, 0),
+        (Units.cm, Units.cm, 1.5, 1.5),
+        (Units.cm, Units.cm, 0, 0),
+        (Units.mm, Units.mm, 1.5, 1.5),
+        (Units.mm, Units.mm, 0, 0),
+        (Units.miles, Units.miles, 1.5, 1.5),
+        (Units.miles, Units.miles, 0, 0),
+        (Units.yards, Units.yards, 1.5, 1.5),
+        (Units.yards, Units.yards, 0, 0),
+        (Units.feet, Units.feet, 1.5, 1.5),
+        (Units.feet, Units.feet, 0, 0),
+
+        #To Meters
+        (Units.km, Units.m, 987654.321, 987654321),
+        (Units.m, Units.m, 987654.321, 987654.321),
+        (Units.mm, Units.m, 98765432.1, 98765.4321),
+        (Units.cm, Units.m, 9876543.21, 98765.4321),
+
+        #To negative meters
+        (Units.km, Units.m, -987654.321, -987654321),
+        (Units.m, Units.m,- 987654.321, -987654.321),
+        (Units.mm, Units.m, -98765432.1, -98765.4321),
+        (Units.cm, Units.m, -9876543.21, -98765.4321),
+
+        (Units.m, Units.km, 987654.321, 987.654321),
+        (Units.m, Units.cm, 987654.321, 98765432.1),
+        (Units.m, Units.mm, 987654.321, 987654321),
+
+        #Imperial
+        (Units.miles, Units.m, 123.45, 198673.517),
+        (Units.miles, Units.inches, 123.45, 7821792),
+        (Units.yards, Units.m, 123.45, 112.88268),
+        (Units.yards, Units.inches, 123.45, 4444.2),
+        (Units.feet, Units.m, 123.45, 37.62756),
+        (Units.feet, Units.inches, 123.45, 1481.4),
+        (Units.inches, Units.m, 123.45, 3.13563),
+    ],
+)
+def test_get_scale_factor_between_units(fromUnits: Units, toUnits: Units, inValue: float, expectedOutValue: float):
+    Tolerance = 1e-10
+    actual = inValue * get_scale_factor(fromUnits, toUnits)
+    assert(actual - expectedOutValue < Tolerance)