Improve easy of specifying window on metrics

We want end users to be able to specify metric windows like
```
window: 14 days
```
instead of having to do
```
window:
  count: 14
  granularity: day
```

core/dbt/contracts/graph/unparsed.py

@@ -599,18 +599,12 @@ class UnparsedMetricInputMeasure(dbtClassMixin):
     alias: Optional[str] = None
 
 
-@dataclass
-class UnparsedMetricTimeWindow(dbtClassMixin):
-    count: int
-    granularity: str  # an TimeGranularity Enum
-
-
 @dataclass
 class UnparsedMetricInput(dbtClassMixin):
     name: str
     filter: Optional[str] = None
     alias: Optional[str] = None
-    offset_window: Optional[UnparsedMetricTimeWindow] = None
+    offset_window: Optional[str] = None
     offset_to_grain: Optional[str] = None  # str is really a TimeGranularity Enum
 
 
@@ -621,7 +615,7 @@ class UnparsedMetricTypeParams(dbtClassMixin):
     numerator: Optional[Union[UnparsedMetricInputMeasure, str]] = None
     denominator: Optional[Union[UnparsedMetricInputMeasure, str]] = None
     expr: Optional[str] = None
-    window: Optional[UnparsedMetricTimeWindow] = None
+    window: Optional[str] = None
     grain_to_date: Optional[str] = None  # str is really a TimeGranularity Enum
     metrics: Optional[List[Union[UnparsedMetricInput, str]]] = None
 

core/dbt/parser/schema_yaml_readers.py

@@ -7,7 +7,6 @@
     UnparsedMetric,
     UnparsedMetricInput,
     UnparsedMetricInputMeasure,
-    UnparsedMetricTimeWindow,
     UnparsedMetricTypeParams,
 )
 from dbt.contracts.graph.nodes import (
@@ -183,12 +182,44 @@ def _get_input_measures(
 
     def _get_time_window(
         self,
-        unparsed_window: Optional[UnparsedMetricTimeWindow],
+        unparsed_window: Optional[str],
     ) -> Optional[MetricTimeWindow]:
         if unparsed_window is not None:
+            parts = unparsed_window.split(" ")
+            if len(parts) != 2:
+                raise YamlParseDictError(
+                    self.yaml.path,
+                    "window",
+                    {"window": unparsed_window},
+                    f"Invalid window ({unparsed_window}) in cumulative metric. Should be of the form `<count> <granularity>`, "
+                    "e.g., `28 days`",
+                )
+
+            granularity = parts[1]
+            # once we drop python 3.8 this could just be `granularity = parts[0].removesuffix('s')
+            if granularity.endswith("s"):
+                # months -> month
+                granularity = granularity[:-1]
+            if granularity not in [item.value for item in TimeGranularity]:
+                raise YamlParseDictError(
+                    self.yaml.path,
+                    "window",
+                    {"window": unparsed_window},
+                    f"Invalid time granularity {granularity} in cumulative metric window string: ({unparsed_window})",
+                )
+
+            count = parts[0]
+            if not count.isdigit():
+                raise YamlParseDictError(
+                    self.yaml.path,
+                    "window",
+                    {"window": unparsed_window},
+                    f"Invalid count ({count}) in cumulative metric window string: ({unparsed_window})",
+                )
+
             return MetricTimeWindow(
-                count=unparsed_window.count,
-                granularity=TimeGranularity(unparsed_window.granularity),
+                count=int(count),
+                granularity=TimeGranularity(granularity),
             )
         else:
             return None

tests/functional/metrics/fixtures.py

@@ -96,9 +96,7 @@
       measure:
         name: years_tenure
         filter: "loves_dbt is true"
-      window:
-        count: 14
-        granularity: day
+      window: 14 days
 
 """