From 5bdcd393a14f6fd3305929cea90b41baa2e924b9 Mon Sep 17 00:00:00 2001
From: Filipe Fernandes <ocefpaf@gmail.com>
Date: Thu, 20 Jun 2024 10:31:13 +0200
Subject: [PATCH] Use pint instead of cf_units

---
 compliance_checker/cfutil.py |  10 ++-
 compliance_checker/units.py  | 120 +++++++++++++++++++++++++++++++++++
 requirements.txt             |   1 +
 3 files changed, 129 insertions(+), 2 deletions(-)
 create mode 100644 compliance_checker/units.py

diff --git a/compliance_checker/cfutil.py b/compliance_checker/cfutil.py
index 8bcce331..01671bf2 100644
--- a/compliance_checker/cfutil.py
+++ b/compliance_checker/cfutil.py
@@ -11,6 +11,8 @@
 from cf_units import Unit
 from importlib_resources import files
 
+from compliance_checker.units import units
+
 _UNITLESS_DB = None
 _SEA_NAMES = None
 
@@ -111,8 +113,12 @@ def is_dimensionless_standard_name(standard_name_table, standard_name):
         f".//entry[@id='{standard_name}']",
     )
     if found_standard_name is not None:
-        canonical_units = Unit(found_standard_name.find("canonical_units").text)
-        return canonical_units.is_dimensionless()
+        canonical_units = units(found_standard_name.find("canonical_units").text)
+        print(f"{canonical_units=}")
+        print(f"{type(canonical_units)=}")
+        if isinstance(canonical_units, (int, float)):
+            return True
+        return canonical_units.dimensionless
     # if the standard name is not found, assume we need units for the time being
     else:
         return False
diff --git a/compliance_checker/units.py b/compliance_checker/units.py
new file mode 100644
index 00000000..cae8dd9f
--- /dev/null
+++ b/compliance_checker/units.py
@@ -0,0 +1,120 @@
+"""Module to provide unit support via pint approximating UDUNITS/CF."""
+
+import functools
+import re
+
+import pint
+from pint import (  # noqa: F401
+    DimensionalityError,
+    UndefinedUnitError,
+    UnitStrippedWarning,
+)
+
+# from `xclim`'s unit support module with permission of the maintainers
+try:
+
+    @pint.register_unit_format("cf")
+    def short_formatter(unit, registry, **options):
+        """Return a CF-compliant unit string from a `pint` unit.
+
+        Parameters
+        ----------
+        unit : pint.UnitContainer
+            Input unit.
+        registry : pint.UnitRegistry
+            the associated registry
+        **options
+            Additional options (may be ignored)
+
+        Returns
+        -------
+        out : str
+            Units following CF-Convention, using symbols.
+        """
+        import re
+
+        # convert UnitContainer back to Unit
+        unit = registry.Unit(unit)
+        # Print units using abbreviations (millimeter -> mm)
+        s = f"{unit:~D}"
+
+        # Search and replace patterns
+        pat = r"(?P<inverse>(?:1 )?/ )?(?P<unit>\w+)(?: \*\* (?P<pow>\d))?"
+
+        def repl(m):
+            i, u, p = m.groups()
+            p = p or (1 if i else "")
+            neg = "-" if i else ""
+
+            return f"{u}{neg}{p}"
+
+        out, n = re.subn(pat, repl, s)
+
+        # Remove multiplications
+        out = out.replace(" * ", " ")
+        # Delta degrees:
+        out = out.replace("Δ°", "delta_deg")
+        return out.replace("percent", "%")
+
+except ImportError:
+    pass
+
+# ------
+# Reused with modification from MetPy under the terms of the BSD 3-Clause License.
+# Copyright (c) 2015,2017,2019 MetPy Developers.
+# Create registry, with preprocessors for UDUNITS-style powers (m2 s-2) and percent signs
+units = pint.UnitRegistry(
+    autoconvert_offset_to_baseunit=True,
+    preprocessors=[
+        functools.partial(
+            re.compile(
+                r"(?<=[A-Za-z])(?![A-Za-z])(?<![0-9\-][eE])(?<![0-9\-])(?=[0-9\-])",
+            ).sub,
+            "**",
+        ),
+        lambda string: string.replace("%", "percent"),
+    ],
+    force_ndarray_like=True,
+)
+# ----- end block copied from metpy
+
+# need to insert to make sure this is the first preprocessor
+# This ensures we convert integer `1` to string `"1"`, as needed by pint.
+units.preprocessors.insert(0, str)
+
+# -----
+units.define("percent = 0.01 = %")
+units.define("count = 1 = constant")
+
+# Define commonly encountered units (both CF and non-CF) not defined by pint
+units.define("@alias meter = gpm")
+# ----- end block copied from metpy
+
+# -----
+# The following redefinitions were copied from xclim under the terms of their Apache-2 license
+# In pint, the default symbol for year is "a" which is not CF-compliant (stands for "are")
+units.define("year = 365.25 * day = yr")
+
+# Define commonly encountered units not defined by pint
+units.define("@alias degC = C = deg_C = Celsius = degrees_Celsius")
+units.define("@alias degK = deg_K")
+units.define("@alias day = d")
+units.define("@alias hour = h")  # Not the Planck constant...
+units.define(
+    "degrees_north = degree = degrees_north = degrees_N = degreesN = degree_north = degree_N = degreeN",
+)
+units.define(
+    "degrees_east = degree = degrees_east = degrees_E = degreesE = degree_east = degree_E = degreeE",
+)
+# degrees for grid_longitude / grid_latitude for grid_mappings
+units.define("degrees = degree = degrees")
+units.define("[speed] = [length] / [time]")
+# ----- end block copied from xclim
+
+# Add other specific aliases (by cf_xarray developers)
+units.define("practical_salinity_unit = [] = psu = PSU")
+
+# end of vendored code from MetPy
+
+# Set as application registry
+pint.set_application_registry(units)
diff --git a/requirements.txt b/requirements.txt
index 914faa1e..7de1880c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,6 +9,7 @@ netcdf4>=1.6.4
 owslib>=0.8.3
 packaging
 pendulum>=1.2.4
+pint
 pygeoif>=0.6
 pyproj>=2.2.1
 regex>=2017.07.28