From 9809fa0f9b82a9818e4eb40cacd22d3b7c14d8a0 Mon Sep 17 00:00:00 2001
From: Scott Nelson <scott@scottnelson.co>
Date: Mon, 15 Jul 2024 10:52:33 -0400
Subject: [PATCH] Handle time normalization for nonexistent and ambiguous times

---
 docs/sphinx/source/whatsnew/v0.11.1.rst |  3 ++-
 pvlib/solarposition.py                  | 13 ++++++++++++-
 pvlib/tests/test_solarposition.py       | 23 +++++++++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/docs/sphinx/source/whatsnew/v0.11.1.rst b/docs/sphinx/source/whatsnew/v0.11.1.rst
index 5ffb0e564a..04ee918db7 100644
--- a/docs/sphinx/source/whatsnew/v0.11.1.rst
+++ b/docs/sphinx/source/whatsnew/v0.11.1.rst
@@ -17,7 +17,8 @@ Enhancements
 
 Bug fixes
 ~~~~~~~~~
-
+* Handle DST transitions that happen at midnight in :py:func:`pvlib.solarposition.hour_angle`
+  (:issue:`2132` :pull:`2133`)
 
 Testing
 ~~~~~~~
diff --git a/pvlib/solarposition.py b/pvlib/solarposition.py
index af59184727..fa1bcc2340 100644
--- a/pvlib/solarposition.py
+++ b/pvlib/solarposition.py
@@ -1392,7 +1392,18 @@ def hour_angle(times, longitude, equation_of_time):
         times = times.tz_localize('utc')
     tzs = np.array([ts.utcoffset().total_seconds() for ts in times]) / 3600
 
-    hrs_minus_tzs = (times - times.normalize()) / pd.Timedelta('1h') - tzs
+    # Some timezones have a DST shift at midnight:
+    #   11:59pm -> 1:00am - results in a nonexistent midnight
+    #   12:59am -> 12:00am - results in an ambiguous midnight
+    # We remove the timezone before normalizing for this reason.
+    naive_normalized_times = times.tz_localize(None).normalize()
+
+    # Use Pandas functionality for shifting nonexistent times forward
+    # or infering ambiguous times (which arose from normalizing)
+    normalized_times = naive_normalized_times.tz_localize(
+        times.tz, nonexistent='shift_forward', ambiguous='infer')
+
+    hrs_minus_tzs = (times - normalized_times) / pd.Timedelta('1h') - tzs
 
     # ensure array return instead of a version-dependent pandas <T>Index
     return np.asarray(
diff --git a/pvlib/tests/test_solarposition.py b/pvlib/tests/test_solarposition.py
index 472383acce..ece41a60b4 100644
--- a/pvlib/tests/test_solarposition.py
+++ b/pvlib/tests/test_solarposition.py
@@ -673,6 +673,29 @@ def test_hour_angle():
     assert np.allclose(hours, expected)
 
 
+def test_hour_angle_with_tricky_timezones():
+    # tests timezones that have a DST shift at midnight
+
+    eot = np.array([-3.935172, -4.117227])
+
+    longitude = 70.6693
+    times = pd.DatetimeIndex([
+        '2014-09-07 10:00:00',
+        '2014-09-07 11:00:00',
+    ]).tz_localize('America/Santiago')
+    # should not raise `pytz.exceptions.NonExistentTimeError`
+    solarposition.hour_angle(times, longitude, eot)
+
+    longitude = 82.3666
+    times = pd.DatetimeIndex([
+        '2014-11-02 10:00:00',
+        '2014-11-02 11:00:00',
+    ]).tz_localize('America/Havana')
+    # should not raise `pytz.exceptions.AmbiguousTimeError`
+    solarposition.hour_angle(times, longitude, eot)
+
+
+
 def test_sun_rise_set_transit_geometric(expected_rise_set_spa, golden_mst):
     """Test geometric calculations for sunrise, sunset, and transit times"""
     times = expected_rise_set_spa.index