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"""
Implements JSON pointer resolution based on RFC 6901:
https://www.rfc-editor.org/rfc/rfc6901
"""
from typing import Any, Optional, Tuple, Union
# JSONPtrAddressable = Optional[Union[Dict[str, "JSONPtrAddressable"], List["JSONPtrAddressable"], int, float, bool, str, None]]
JSONPtrAddressable = Any # the recursive definition above is not valid :(
class _JSONPtr:
@staticmethod
def _decode_token(token: str) -> str:
"""
Resolves escaped characters ~ and /
"""
# the order of the replace statements is important, do not change without
# consulting the RFC
return token.replace("~1", "/").replace("~0", "~")
@staticmethod
def _encode_token(token: str) -> str:
return token.replace("~", "~0").replace("/", "~1")
def __init__(self, ptr: str):
if ptr == "":
# pointer to the root
self.tokens = []
else:
if ptr[0] != "/":
raise SyntaxError(
f"JSON pointer '{ptr}' invalid: the first character MUST be '/' or the pointer must be empty"
)
ptr = ptr[1:]
self.tokens = [_JSONPtr._decode_token(tok) for tok in ptr.split("/")]
def resolve(
self, obj: JSONPtrAddressable
) -> Tuple[Optional[JSONPtrAddressable], JSONPtrAddressable, Union[str, int, None]]:
"""
Returns (Optional[parent], Optional[direct value], key of value in the parent object)
"""
parent: Optional[JSONPtrAddressable] = None
current = obj
current_ptr = ""
token: Union[int, str, None] = None
for token in self.tokens:
if current is None:
raise ValueError(
f"JSON pointer cannot reference nested non-existent object: object at ptr '{current_ptr}' already points to None, cannot nest deeper with token '{token}'"
)
if isinstance(current, (bool, int, float, str)):
raise ValueError(f"object at '{current_ptr}' is a scalar, JSON pointer cannot point into it")
parent = current
if isinstance(current, list):
if token == "-":
current = None
else:
try:
token_num = int(token)
current = current[token_num]
except ValueError as e:
raise ValueError(
f"invalid JSON pointer: list '{current_ptr}' require numbers as keys, instead got '{token}'"
) from e
elif isinstance(current, dict):
current = current.get(token, None)
current_ptr += f"/{token}"
return parent, current, token
def json_ptr_resolve(
obj: JSONPtrAddressable,
ptr: str,
) -> Tuple[Optional[JSONPtrAddressable], Optional[JSONPtrAddressable], Union[str, int, None]]:
return _JSONPtr(ptr).resolve(obj)
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