feat: add strftimedelta pattern

src/earthkit/data/utils/patterns.py

@@ -11,6 +11,7 @@
 import re
 
 from .dates import to_datetime
+from .dates import to_timedelta
 
 RE1 = re.compile(r"{([^}]*)}")
 RE2 = re.compile(r"\(([^}]*)\)")
@@ -62,6 +63,31 @@ def substitute(self, value, name):
         return to_datetime(value).strftime(self.format)
 
 
+class DatetimeDelta:
+    def __init__(self, params):
+        params_list = params.split(";")
+        if len(params_list) != 2:
+            raise ValueError(
+                "Invalid parameters '{}' for class DatetimeDelta, expected (delta;format)".format(params)
+            )
+        self.delta = params_list[0].strip()
+        self.format = params_list[1].strip()
+
+    def substitute(self, value, name):
+        sign = -1 if self.delta[0] == "-" else 1
+        if re.fullmatch(r"[-\+]?\d+[hms]?", self.delta):
+            delta = re.search(r"\d+[hms]?", self.delta).group(0)
+        else:
+            raise ValueError(
+                "Invalid value '{}' for delta, expected time in hour (h), minute (m) or second (s)".format(
+                    self.delta
+                )
+            )
+
+        valid_date = to_datetime(value) + sign * to_timedelta(delta)
+        return valid_date.strftime(self.format)
+
+
 class Str:
     def __init__(self, format="%s"):
         self.format = format
@@ -78,6 +104,7 @@ def substitute(self, value, name):
     "float": Float,
     "date": Datetime,
     "strftime": Datetime,
+    "strftimedelta": DatetimeDelta,
     "enum": Enum,
 }
 

tests/utils/test_patterns.py

@@ -26,6 +26,16 @@
             {"my_date": datetime.datetime(2020, 5, 13), "name": ["t2", "msl"]},
             ["test_2020-05-13_t2.grib", "test_2020-05-13_msl.grib"],
         ),
+        (
+            "test_{date:strftimedelta(-6;%Y-%m-%d_%H)}.grib",
+            {"date": [datetime.datetime(2020, 5, 11), datetime.datetime(2020, 5, 11, 6)]},
+            ["test_2020-05-10_18.grib", "test_2020-05-11_00.grib"],
+        ),
+        (
+            "test_{date:strftimedelta(60m;%Y-%m-%d_%H)}.grib",
+            {"date": [datetime.datetime(2020, 5, 11), datetime.datetime(2020, 5, 11, 6)]},
+            ["test_2020-05-11_01.grib", "test_2020-05-11_07.grib"],
+        ),
     ],
 )
 def test_pattern_core(pattern, values, expected_value):