chore(BACK-8009): update slices support (#144)

- start and end are optional
- end is exclusive

src/erc7730/model/paths/__init__.py

@@ -67,24 +67,30 @@ class ArraySlice(Model):
         description="The path component type identifier (discriminator for path components discriminated union).",
     )
 
-    start: ArrayIndex = PydanticField(
+    start: ArrayIndex | None = PydanticField(
+        default=None,
         title="Slice Start Index",
-        description="The start index of the slice. Must be lower than the end index.",
+        description="The start index of the slice (inclusive). Must be lower than the end index. If unset, slice "
+        "starts from the beginning of the array.",
     )
 
-    end: ArrayIndex = PydanticField(
+    end: ArrayIndex | None = PydanticField(
+        default=None,
         title="Slice End Index",
-        description="The end index of the slice. Must be greater than the start index.",
+        description="The end index of the slice (exclusive). Must be greater than the start index. If unset, slice "
+        "ends at the end of the array.",
     )
 
     @model_validator(mode="after")
     def _validate(self) -> Self:
-        if self.start > self.end:
-            raise ValueError("Array slice start index must be lower than end index.")
+        if (start := self.start) is None or (end := self.end) is None:
+            return self
+        if 0 <= end <= start or end <= start < 0:
+            raise ValueError("Array slice start index must be strictly lower than end index.")
         return self
 
     def __str__(self) -> str:
-        return f"[{self.start}:{self.end}]"
+        return f"[{'' if self.start is None else self.start}:{'' if self.end is None else self.end}]"
 
 
 class Array(Model):

src/erc7730/model/paths/path_parser.py

@@ -36,7 +36,8 @@
         array: "[]"
         array_index: /-?[0-9]+/
         array_element: "[" array_index "]"
-        array_slice: "[" array_index ":" array_index "]"
+        slice_array_index: array_index?
+        array_slice: "[" slice_array_index ":" slice_array_index "]"
     """,
     start="path",
 )
@@ -60,6 +61,12 @@ def array_element(self, ast: Any) -> ArrayElement:
         (value,) = ast
         return ArrayElement(index=value)
 
+    def slice_array_index(self, ast: Any) -> ArrayIndex | None:
+        if len(ast) == 1:
+            (value,) = ast
+            return value
+        return None
+
     def array_slice(self, ast: Any) -> ArraySlice:
         (start, end) = ast
         return ArraySlice(start=start, end=end)

tests/model/paths/test_path_parser.py

@@ -42,14 +42,16 @@ def test_valid_input_container_path() -> None:
 
 def test_valid_input_data_path_absolute() -> None:
     _test_valid_input_path(
-        string="#.params.[].[-2].[1:5].amountIn",
+        string="#.params.[].[-2].[1:5].[:5].[5:].amountIn",
         obj=DataPath(
             absolute=True,
             elements=[
                 Field(identifier="params"),
                 Array(),
                 ArrayElement(index=-2),
                 ArraySlice(start=1, end=5),
+                ArraySlice(start=None, end=5),
+                ArraySlice(start=5, end=None),
                 Field(identifier="amountIn"),
             ],
         ),
@@ -62,6 +64,8 @@ def test_valid_input_data_path_absolute() -> None:
                 { "type": "array" },
                 { "type": "array_element", "index": -2 },
                 { "type": "array_slice", "start": 1, "end": 5 },
+                { "type": "array_slice", "end": 5 },
+                { "type": "array_slice", "start": 5 },
                 { "type": "field", "identifier": "amountIn" }
               ]
             }
@@ -211,7 +215,7 @@ def test_invalid_array_slice_inverted() -> None:
     message = str(e.value)
     assert "Invalid path" in message
     assert "#.[1:0]" in message
-    assert "Array slice start index must be lower than end index" in message
+    assert "Array slice start index must be strictly lower than end index" in message
 
 
 def test_invalid_array_slice_used_in_descriptor_path() -> None: