Module mydata_did.v1_0.utils.jsonld.create_verify_data

"""
Contains the functions needed to produce and verify a json-ld signature.

This file was ported from
https://github.com/transmute-industries/Ed25519Signature2018/blob/master/src/createVerifyData/index.js
"""

import datetime
import hashlib

from pyld import jsonld

cache = {}
def caching_document_loader(url, options):
    loader = jsonld.requests_document_loader()
    if url in cache:
        return cache[url]
    resp = loader(url)
    cache[url] = resp
    return resp

jsonld.set_document_loader(caching_document_loader)


def _canonize(data):
    return jsonld.normalize(
        data, {"algorithm": "URDNA2015", "format": "application/n-quads"}
    )


def _sha256(data):
    return hashlib.sha256(data.encode("utf-8")).hexdigest()


def _cannonize_signature_options(signatureOptions):
    _signatureOptions = {**signatureOptions,
                        "@context": "https://w3id.org/security/v2"}
    _signatureOptions.pop("jws", None)
    _signatureOptions.pop("signatureValue", None)
    _signatureOptions.pop("proofValue", None)
    return _canonize(_signatureOptions)


def _cannonize_document(doc, proof_chain: bool = False):
    _doc = {**doc}
    if not proof_chain:
        _doc.pop("proof", None)
    return _canonize(_doc)


class DroppedAttributeException(Exception):
    """Exception used to track that an attribute was removed."""

    pass


def create_verify_data(data, signature_options, proof_chain: bool = False):
    """Encapsulate the process of constructing the string used during sign and verify."""

    if "creator" in signature_options:
        signature_options["verificationMethod"] = signature_options["creator"]

    if not signature_options["verificationMethod"]:
        raise Exception("signature_options.verificationMethod is required")

    if "created" not in signature_options:
        signature_options["created"] = datetime.datetime.now(
            datetime.timezone.utc
        ).strftime("%Y-%m-%dT%H:%M:%SZ")

    if (
        "type" not in signature_options
        or signature_options["type"] != "Ed25519Signature2018"
    ):
        signature_options["type"] = "Ed25519Signature2018"

    [expanded] = jsonld.expand(data)
    framed = jsonld.compact(
        expanded, "https://w3id.org/security/v2", {"skipExpansion": True}
    )

    # Detect any dropped attributes during the expand/contract step.

    if len(data) != len(framed):
        raise DroppedAttributeException("Extra Attribute Detected")
    if (
        "proof" in data
        and "proof" in framed
        and len(data["proof"]) != len(framed["proof"])
    ):
        raise DroppedAttributeException("Extra Attribute Detected")

    cannonized_signature_options = _cannonize_signature_options(
        signature_options)

    hash_of_cannonized_signature_options = _sha256(
        cannonized_signature_options)

    cannonized_document = _cannonize_document(framed, proof_chain)

    hash_of_cannonized_document = _sha256(cannonized_document)

    return (framed, hash_of_cannonized_signature_options + hash_of_cannonized_document)