From 17b248f8f9122079cfae88c1353c323a8f8e950a Mon Sep 17 00:00:00 2001
From: Filipe Fernandes <ocefpaf@gmail.com>
Date: Tue, 12 Nov 2024 20:52:54 +0100
Subject: [PATCH] make cf-units optional

---
 compliance_checker/cfutil.py | 48 +++++++++++++++++++++++++++---------
 pyproject.toml               |  4 +--
 requirements.txt             |  1 -
 3 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/compliance_checker/cfutil.py b/compliance_checker/cfutil.py
index 25ebc874..345f8301 100644
--- a/compliance_checker/cfutil.py
+++ b/compliance_checker/cfutil.py
@@ -9,9 +9,6 @@
 from functools import lru_cache, partial
 
 from importlib_resources import files
-from pyudunits2 import UnitSystem, UnresolvableUnitException
-
-ut_system = UnitSystem.from_udunits2_xml()
 
 _UNITLESS_DB = None
 _SEA_NAMES = None
@@ -2032,30 +2029,59 @@ def guess_feature_type(nc, variable):
         return "reduced-grid"
 
 
+class _CCUnit:
+    def __init__(self, units):
+        import cf_units
+
+        self.u = cf_units.Unit(units)
+        self.is_time_reference = self.u.is_time_reference()
+
+    def __eq__(self, other):
+        return self.u == other.u
+
+    def is_convertible_to(self, other):
+        if isinstance(other, str):
+            ret = self.u.is_convertible(other)
+        else:
+            ret = self.u.is_convertible(other.u)
+        return ret
+
+    def is_dimensionless(self):
+        return self.u.is_dimensionless()
+
+    def expanded(self):
+        return self.u.definition
+
+
 def _units(units: str):
     """PLACEHOLDER."""
-    # FIXME:
-    # cf_units will create:
-    # cf_units.Unit(None)
-    # Unit('unknown')
-    # that will contain all the methods we use here.
+    # FIXME: Try to make cf_units optional
+    try:
+        return _CCUnit(units)
+    except ImportError:
+        from pyudunits2 import UnitSystem, UnresolvableUnitException
+
+        ut_system = UnitSystem.from_udunits2_xml()
+
+    # FIXME: cf_units.Unit(None) -> Unit('unknown')
     if units is None:
         units = ""
+    # FIXME: Syntax Error when HH:MM:SS is present in time reference.
     if "T00:00:00" in units:
         units = units.replace("T00:00:00", "")
 
+    # FIXME: cf_units raised only ValueError
     try:
         u = ut_system.unit(units)
     except (SyntaxError, UnresolvableUnitException) as err:
         raise ValueError from err
+    # FIXME: cf_units defined .is_time_reference for time reference units.
     u.is_time_reference = False
-    u.is_long_time_interval = False
     try:
         if hasattr(u._definition, "shift_from"):
             u.is_time_reference = True
-            if u._definition.unit.content in ("months", "years"):
-                u.is_long_time_interval = True
     except KeyError:
+        # FIXME: hasattr should return None in that case.
         # pyudunits2/_expr_graph.py:27, in Node.__getattr__(self, name)
         #      25 def __getattr__(self, name):
         #      26     # Allow the dictionary to raise KeyError if the key doesn't exist.
diff --git a/pyproject.toml b/pyproject.toml
index 696cf98f..618e9291 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -9,7 +9,7 @@ requires = [
 [project]
 name = "compliance-checker"
 description = "Checks Datasets and SOS endpoints for standards compliance"
-readme = "README.md"
+readme = { file = "README.md", content-type = "text/markdown" }
 license = { text = "Apache-2.0" }
 maintainers = [
   { name = "Dave Foster", email = "dave@axiomdatascience.com" },
@@ -40,6 +40,7 @@ dynamic = [
   "dependencies",
   "version",
 ]
+optional-dependencies.extras = [ "cf-units>=2" ]
 urls.documentation = "https://ioos.github.io/compliance-checker"
 urls.homepage = "https://compliance.ioos.us/index.html"
 urls.repository = "https://github.com/ioos/compliance-checker"
@@ -81,7 +82,6 @@ compliance_checker = [
 dependencies = { file = [
   "requirements.txt",
 ] }
-readme = { file = "README.md", content-type = "text/markdown" }
 
 [tool.setuptools_scm]
 write_to = "compliance_checker/_version.py"
diff --git a/requirements.txt b/requirements.txt
index 1a61c43b..40c38f38 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,3 @@
-cf-units>=2
 cftime>=1.1.0
 importlib-metadata
 importlib-resources