Implement InvalidRequestError with field-level validation details

src/shade/errors.py

@@ -1,6 +1,9 @@
 from __future__ import annotations
 
-from typing import Optional
+import json
+from typing import Any, Optional
+
+INVALID_REQUEST_STATUS_CODES = (400, 422)
 
 
 class ShadeError(Exception):
@@ -28,7 +31,47 @@ class AuthenticationError(ShadeError):
 
 
 class InvalidRequestError(ShadeError):
-    """Raised when a request is malformed or rejected by validation."""
+    """Raised on HTTP 400/422 responses for malformed or invalid parameters."""
+
+    def __init__(
+        self,
+        message: str,
+        status_code: Optional[int] = None,
+        response_body: Optional[str] = None,
+        param: Optional[str] = None,
+        field_errors: Optional[dict[str, Any]] = None,
+    ) -> None:
+        super().__init__(message, status_code, response_body)
+        parsed = _parse_error_response(response_body)
+        self.param: Optional[str] = param if param is not None else parsed.get("param")
+        self.field_errors: dict[str, Any] = (
+            field_errors if field_errors is not None else parsed.get("field_errors", {})
+        )
+
+    def __str__(self) -> str:
+        message = self.message
+        if self.param:
+            message = f"{message} (param: {self.param})"
+        if self.status_code is None:
+            return message
+        return f"{message} (status code: {self.status_code})"
+
+    @classmethod
+    def from_response(
+        cls,
+        status_code: int,
+        response_body: Optional[str] = None,
+    ) -> "InvalidRequestError":
+        """Construct from a raw 400/422 API response body."""
+        parsed = _parse_error_response(response_body)
+        message = parsed.get("message") or "Invalid request"
+        return cls(
+            message,
+            status_code=status_code,
+            response_body=response_body,
+            param=parsed.get("param"),
+            field_errors=parsed.get("field_errors", {}),
+        )
 
 
 class NotFoundError(ShadeError):
@@ -37,3 +80,45 @@ class NotFoundError(ShadeError):
 
 class NetworkError(ShadeError):
     """Raised when the SDK cannot complete a network request."""
+
+
+def raise_for_invalid_request(
+    status_code: int,
+    response_body: Optional[str] = None,
+) -> None:
+    """Raise InvalidRequestError when the API returns 400 or 422."""
+    if status_code in INVALID_REQUEST_STATUS_CODES:
+        raise InvalidRequestError.from_response(status_code, response_body)
+
+
+def _parse_body(response_body: Optional[str]) -> dict[str, Any]:
+    if not response_body:
+        return {}
+    try:
+        data = json.loads(response_body)
+        return data if isinstance(data, dict) else {}
+    except (json.JSONDecodeError, ValueError):
+        return {}
+
+
+def _parse_error_response(response_body: Optional[str]) -> dict[str, Any]:
+    data = _parse_body(response_body)
+    error = data.get("error", {})
+    if not isinstance(error, dict):
+        error = {}
+
+    field_errors = error.get("field_errors")
+    if not isinstance(field_errors, dict):
+        field_errors = data.get("field_errors")
+    if not isinstance(field_errors, dict):
+        field_errors = {}
+
+    message = error.get("message")
+    if not message:
+        message = data.get("message")
+
+    return {
+        "message": message,
+        "param": error.get("param"),
+        "field_errors": field_errors,
+    }

tests/test_errors.py

@@ -1,3 +1,4 @@
+import pytest
 import shade
 from shade import (
     AuthenticationError,
@@ -6,6 +7,7 @@
     NotFoundError,
     ShadeError,
 )
+from shade.errors import raise_for_invalid_request
 
 
 def test_shade_error_can_be_raised_standalone():
@@ -49,3 +51,87 @@ def test_package_root_exports_error_classes():
     assert shade.InvalidRequestError is InvalidRequestError
     assert shade.NetworkError is NetworkError
     assert shade.NotFoundError is NotFoundError
+
+
+def test_invalid_request_error_parses_param_from_body():
+    body = (
+        '{"error": {"code": "invalid_param", "param": "amount", '
+        '"message": "Amount must be greater than zero"}}'
+    )
+    error = InvalidRequestError("invalid request", status_code=400, response_body=body)
+
+    assert error.param == "amount"
+    assert error.message == "invalid request"
+
+
+def test_invalid_request_error_parses_field_errors_from_body():
+    body = (
+        '{"error": {"code": "invalid_param", "param": "amount", "message": "Validation failed", '
+        '"field_errors": {"amount": "must be positive", "currency": "is required"}}}'
+    )
+    error = InvalidRequestError.from_response(400, body)
+
+    assert error.param == "amount"
+    assert error.field_errors == {
+        "amount": "must be positive",
+        "currency": "is required",
+    }
+
+
+def test_invalid_request_error_str_includes_param():
+    body = (
+        '{"error": {"code": "invalid_param", "param": "amount", '
+        '"message": "Amount must be greater than zero"}}'
+    )
+    error = InvalidRequestError.from_response(400, body)
+
+    assert "amount" in str(error)
+    assert "Amount must be greater than zero" in str(error)
+    assert str(error) == "Amount must be greater than zero (param: amount) (status code: 400)"
+
+
+def test_invalid_request_error_explicit_attrs_override_body():
+    body = (
+        '{"error": {"param": "currency", "field_errors": {"currency": "invalid"}}, '
+        '"field_errors": {"amount": "too small"}}'
+    )
+    error = InvalidRequestError(
+        "invalid request",
+        status_code=422,
+        response_body=body,
+        param="amount",
+        field_errors={"amount": "required"},
+    )
+
+    assert error.param == "amount"
+    assert error.field_errors == {"amount": "required"}
+
+
+def test_400_response_raises_invalid_request_error():
+    body = (
+        '{"error": {"code": "invalid_param", "param": "amount", '
+        '"message": "Amount must be greater than zero"}}'
+    )
+
+    with pytest.raises(InvalidRequestError) as exc_info:
+        raise_for_invalid_request(400, body)
+
+    error = exc_info.value
+    assert error.status_code == 400
+    assert error.param == "amount"
+    assert isinstance(error, ShadeError)
+
+
+def test_422_response_raises_invalid_request_error():
+    body = '{"error": {"param": "email", "message": "Invalid email format"}}'
+
+    with pytest.raises(InvalidRequestError) as exc_info:
+        raise_for_invalid_request(422, body)
+
+    assert exc_info.value.param == "email"
+    assert exc_info.value.status_code == 422
+
+
+def test_raise_for_invalid_request_ignores_other_status_codes():
+    raise_for_invalid_request(404, '{"error": {"message": "not found"}}')
+    raise_for_invalid_request(500, '{"error": {"message": "server error"}}')