planetmint/planetmint/transactions/common/transaction.py

# Copyright © 2020 Interplanetary Database Association e.V.,
# Planetmint and IPDB software contributors.
# SPDX-License-Identifier: (Apache-2.0 AND CC-BY-4.0)
# Code is Apache-2.0 and docs are CC-BY-4.0

"""Transaction related models to parse and construct transaction
payloads.

Attributes:
    UnspentOutput (namedtuple): Object holding the information
        representing an unspent output.

"""
from collections import namedtuple
from copy import deepcopy
from functools import lru_cache
import rapidjson

import base58
from cryptoconditions import Fulfillment, ThresholdSha256, Ed25519Sha256, ZenroomSha256
from cryptoconditions.exceptions import ParsingError, ASN1DecodeError, ASN1EncodeError
from cid import is_cid

from hashlib import sha3_256

from planetmint.transactions.common.crypto import PrivateKey, hash_data
from planetmint.transactions.common.exceptions import (
    KeypairMismatchException,
    InputDoesNotExist,
    DoubleSpend,
    InvalidHash,
    InvalidSignature,
    AmountError,
    AssetIdMismatch,
    DuplicateTransaction,
)
from planetmint.backend.schema import validate_language_key
from planetmint.transactions.common.schema import validate_transaction_schema
from planetmint.transactions.common.utils import serialize, validate_txn_obj, validate_key
from .memoize import memoize_from_dict, memoize_to_dict
from .input import Input
from .output import Output
from .transaction_link import TransactionLink

UnspentOutput = namedtuple(
    "UnspentOutput",
    (
        # TODO 'utxo_hash': sha3_256(f'{txid}{output_index}'.encode())
        # 'utxo_hash',   # noqa
        "transaction_id",
        "output_index",
        "amount",
        "asset_id",
        "condition_uri",
    ),
)

VALIDATOR_ELECTION = "VALIDATOR_ELECTION"
CHAIN_MIGRATION_ELECTION = "CHAIN_MIGRATION_ELECTION"
VOTE = "VOTE"


class Transaction(object):
    """A Transaction is used to create and transfer assets.

    Note:
        For adding Inputs and Outputs, this class provides methods
        to do so.

    Attributes:
        operation (str): Defines the operation of the Transaction.
        inputs (:obj:`list` of :class:`~planetmint.transactions.common.
            transaction.Input`, optional): Define the assets to
            spend.
        outputs (:obj:`list` of :class:`~planetmint.transactions.common.
            transaction.Output`, optional): Define the assets to lock.
        asset (dict): Asset payload for this Transaction. ``CREATE``
            Transactions require a dict with a ``data``
            property while ``TRANSFER`` Transactions require a dict with a
            ``id`` property.
        metadata (dict):
            Metadata to be stored along with the Transaction.
        version (string): Defines the version number of a Transaction.
    """

    CREATE = "CREATE"
    TRANSFER = "TRANSFER"
    VALIDATOR_ELECTION = VALIDATOR_ELECTION
    CHAIN_MIGRATION_ELECTION = CHAIN_MIGRATION_ELECTION
    VOTE = VOTE
    ALLOWED_OPERATIONS = (CREATE, TRANSFER)
    ASSET = "asset"
    METADATA = "metadata"
    DATA = "data"
    VERSION = "2.0"

    def __init__(
        self,
        operation,
        asset,
        inputs=None,
        outputs=None,
        metadata=None,
        version=None,
        hash_id=None,
        tx_dict=None,
        script=None,
    ):
        """The constructor allows to create a customizable Transaction.

        Note:
            When no `version` is provided, one is being
            generated by this method.

        Args:
            operation (str): Defines the operation of the Transaction.
            asset (dict): Asset payload for this Transaction.
            inputs (:obj:`list` of :class:`~planetmint.transactions.common.
                transaction.Input`, optional): Define the assets to
            outputs (:obj:`list` of :class:`~planetmint.transactions.common.
                transaction.Output`, optional): Define the assets to
                lock.
            metadata (dict): Metadata to be stored along with the
                Transaction.
            version (string): Defines the version number of a Transaction.
            hash_id (string): Hash id of the transaction.
        """
        if operation not in self.ALLOWED_OPERATIONS:
            allowed_ops = ", ".join(self.__class__.ALLOWED_OPERATIONS)
            raise ValueError("`operation` must be one of {}".format(allowed_ops))

        # Asset payloads for 'CREATE' operations must be None or
        # dicts holding a `data` property. Asset payloads for 'TRANSFER'
        # operations must be dicts holding an `id` property.
        if operation == self.CREATE and asset is not None:
            if not isinstance(asset, dict):
                raise TypeError(
                    (
                        "`asset` must be None or a dict holding a `data` "
                        " property instance for '{}' Transactions".format(operation)
                    )
                )

            if "data" in asset:
                if asset["data"] is not None and not isinstance(asset["data"], str):
                    if is_cid(asset["data"]) == False:
                        raise TypeError("`asset.data` not valid CID")

                    raise TypeError(
                        (
                            "`asset` must be None or a dict holding a `data` "
                            " property instance for '{}' Transactions".format(operation)
                        )
                    )

        elif operation == self.TRANSFER and not (isinstance(asset, dict) and "id" in asset):
            raise TypeError(("`asset` must be a dict holding an `id` property " "for 'TRANSFER' Transactions"))

        if outputs and not isinstance(outputs, list):
            raise TypeError("`outputs` must be a list instance or None")

        if inputs and not isinstance(inputs, list):
            raise TypeError("`inputs` must be a list instance or None")

        if metadata is not None and not isinstance(metadata, str):
            if is_cid(metadata) == False:
                raise TypeError("`metadata` not valid CID")

            raise TypeError("`metadata` must be a CID string or None")

        if script is not None and not isinstance(script, dict):
            raise TypeError("`script` must be a dict or None")

        self.version = version if version is not None else self.VERSION
        self.operation = operation
        self.asset = asset
        self.inputs = inputs or []
        self.outputs = outputs or []
        self.metadata = metadata
        self.script = script
        self._id = hash_id
        self.tx_dict = tx_dict

    def validate(self, planet, current_transactions=[]):
        """Validate transaction spend
        Args:
            planet (Planetmint): an instantiated planetmint.Planetmint object.
        Returns:
            The transaction (Transaction) if the transaction is valid else it
            raises an exception describing the reason why the transaction is
            invalid.
        Raises:
            ValidationError: If the transaction is invalid
        """
        input_conditions = []

        if self.operation == Transaction.CREATE:
            duplicates = any(txn for txn in current_transactions if txn.id == self.id)
            if planet.is_committed(self.id) or duplicates:
                raise DuplicateTransaction("transaction `{}` already exists".format(self.id))

            if not self.inputs_valid(input_conditions):
                raise InvalidSignature("Transaction signature is invalid.")

        elif self.operation == Transaction.TRANSFER:
            self.validate_transfer_inputs(planet, current_transactions)

        return self

    @property
    def unspent_outputs(self):
        """UnspentOutput: The outputs of this transaction, in a data
        structure containing relevant information for storing them in
        a UTXO set, and performing validation.
        """
        if self.operation == self.CREATE:
            self._asset_id = self._id
        elif self.operation == self.TRANSFER:
            self._asset_id = self.asset["id"]
        return (
            UnspentOutput(
                transaction_id=self._id,
                output_index=output_index,
                amount=output.amount,
                asset_id=self._asset_id,
                condition_uri=output.fulfillment.condition_uri,
            )
            for output_index, output in enumerate(self.outputs)
        )

    @property
    def spent_outputs(self):
        """Tuple of :obj:`dict`: Inputs of this transaction. Each input
        is represented as a dictionary containing a transaction id and
        output index.
        """
        return (input_.fulfills.to_dict() for input_ in self.inputs if input_.fulfills)

    @property
    def serialized(self):
        return Transaction._to_str(self.to_dict())

    def _hash(self):
        self._id = hash_data(self.serialized)

    def __eq__(self, other):
        try:
            other = other.to_dict()
        except AttributeError:
            return False
        return self.to_dict() == other

    def to_inputs(self, indices=None):
        """Converts a Transaction's outputs to spendable inputs.

        Note:
            Takes the Transaction's outputs and derives inputs
            from that can then be passed into `Transaction.transfer` as
            `inputs`.
            A list of integers can be passed to `indices` that
            defines which outputs should be returned as inputs.
            If no `indices` are passed (empty list or None) all
            outputs of the Transaction are returned.

        Args:
            indices (:obj:`list` of int): Defines which
                outputs should be returned as inputs.

        Returns:
            :obj:`list` of :class:`~planetmint.transactions.common.transaction.
                Input`
        """
        # NOTE: If no indices are passed, we just assume to take all outputs
        #       as inputs.
        indices = indices or range(len(self.outputs))
        return [
            Input(
                self.outputs[idx].fulfillment,
                self.outputs[idx].public_keys,
                TransactionLink(self.id, idx),
            )
            for idx in indices
        ]

    def add_input(self, input_):
        """Adds an input to a Transaction's list of inputs.

        Args:
            input_ (:class:`~planetmint.transactions.common.transaction.
                Input`): An Input to be added to the Transaction.
        """
        if not isinstance(input_, Input):
            raise TypeError("`input_` must be a Input instance")
        self.inputs.append(input_)

    def add_output(self, output):
        """Adds an output to a Transaction's list of outputs.

        Args:
            output (:class:`~planetmint.transactions.common.transaction.
                Output`): An Output to be added to the
                Transaction.
        """
        if not isinstance(output, Output):
            raise TypeError("`output` must be an Output instance or None")
        self.outputs.append(output)

    def sign(self, private_keys):
        """Fulfills a previous Transaction's Output by signing Inputs.

        Note:
            This method works only for the following Cryptoconditions
            currently:
                - Ed25519Fulfillment
                - ThresholdSha256
                - ZenroomSha256
            Furthermore, note that all keys required to fully sign the
            Transaction have to be passed to this method. A subset of all
            will cause this method to fail.

        Args:
            private_keys (:obj:`list` of :obj:`str`): A complete list of
                all private keys needed to sign all Fulfillments of this
                Transaction.

        Returns:
            :class:`~planetmint.transactions.common.transaction.Transaction`
        """
        # TODO: Singing should be possible with at least one of all private
        #       keys supplied to this method.
        if private_keys is None or not isinstance(private_keys, list):
            raise TypeError("`private_keys` must be a list instance")

        # NOTE: Generate public keys from private keys and match them in a
        #       dictionary:
        #                   key:     public_key
        #                   value:   private_key
        def gen_public_key(private_key):
            # TODO FOR CC: Adjust interface so that this function becomes
            #              unnecessary

            # cc now provides a single method `encode` to return the key
            # in several different encodings.
            public_key = private_key.get_verifying_key().encode()
            # Returned values from cc are always bytestrings so here we need
            # to decode to convert the bytestring into a python str
            return public_key.decode()

        key_pairs = {gen_public_key(PrivateKey(private_key)): PrivateKey(private_key) for private_key in private_keys}

        tx_dict = self.to_dict()
        tx_dict = Transaction._remove_signatures(tx_dict)
        tx_serialized = Transaction._to_str(tx_dict)
        for i, input_ in enumerate(self.inputs):
            self.inputs[i] = self._sign_input(input_, tx_serialized, key_pairs)

        self._hash()

        return self

    @classmethod
    def _sign_input(cls, input_, message, key_pairs):
        """Signs a single Input.

        Note:
            This method works only for the following Cryptoconditions
            currently:
                - Ed25519Fulfillment
                - ThresholdSha256.
                - ZenroomSha256
        Args:
            input_ (:class:`~planetmint.transactions.common.transaction.
                Input`) The Input to be signed.
            message (str): The message to be signed
            key_pairs (dict): The keys to sign the Transaction with.
        """
        if isinstance(input_.fulfillment, Ed25519Sha256):
            return cls._sign_simple_signature_fulfillment(input_, message, key_pairs)
        elif isinstance(input_.fulfillment, ThresholdSha256):
            return cls._sign_threshold_signature_fulfillment(input_, message, key_pairs)
        elif isinstance(input_.fulfillment, ZenroomSha256):
            return cls._sign_zenroom_fulfillment(input_, message, key_pairs)
        else:
            raise ValueError("Fulfillment couldn't be matched to " "Cryptocondition fulfillment type.")

    @classmethod
    def _sign_zenroom_fulfillment(cls, input_, message, key_pairs):
        """Signs a Zenroomful.

        Args:
            input_ (:class:`~planetmint.transactions.common.transaction.
                Input`) The input to be signed.
            message (str): The message to be signed
            key_pairs (dict): The keys to sign the Transaction with.
        """
        # NOTE: To eliminate the dangers of accidentally signing a condition by
        #       reference, we remove the reference of input_ here
        #       intentionally. If the user of this class knows how to use it,
        #       this should never happen, but then again, never say never.
        input_ = deepcopy(input_)
        public_key = input_.owners_before[0]
        message = sha3_256(message.encode())
        if input_.fulfills:
            message.update("{}{}".format(input_.fulfills.txid, input_.fulfills.output).encode())

        try:
            # cryptoconditions makes no assumptions of the encoding of the
            # message to sign or verify. It only accepts bytestrings
            input_.fulfillment.sign(message.digest(), base58.b58decode(key_pairs[public_key].encode()))
        except KeyError:
            raise KeypairMismatchException(
                "Public key {} is not a pair to " "any of the private keys".format(public_key)
            )
        return input_

    @classmethod
    def _sign_simple_signature_fulfillment(cls, input_, message, key_pairs):
        """Signs a Ed25519Fulfillment.

        Args:
            input_ (:class:`~planetmint.transactions.common.transaction.
                Input`) The input to be signed.
            message (str): The message to be signed
            key_pairs (dict): The keys to sign the Transaction with.
        """
        # NOTE: To eliminate the dangers of accidentally signing a condition by
        #       reference, we remove the reference of input_ here
        #       intentionally. If the user of this class knows how to use it,
        #       this should never happen, but then again, never say never.
        input_ = deepcopy(input_)
        public_key = input_.owners_before[0]
        message = sha3_256(message.encode())
        if input_.fulfills:
            message.update("{}{}".format(input_.fulfills.txid, input_.fulfills.output).encode())

        try:
            # cryptoconditions makes no assumptions of the encoding of the
            # message to sign or verify. It only accepts bytestrings
            input_.fulfillment.sign(message.digest(), base58.b58decode(key_pairs[public_key].encode()))
        except KeyError:
            raise KeypairMismatchException(
                "Public key {} is not a pair to " "any of the private keys".format(public_key)
            )
        return input_

    @classmethod
    def _sign_threshold_signature_fulfillment(cls, input_, message, key_pairs):
        """Signs a ThresholdSha256.

        Args:
            input_ (:class:`~planetmint.transactions.common.transaction.
                Input`) The Input to be signed.
            message (str): The message to be signed
            key_pairs (dict): The keys to sign the Transaction with.
        """
        input_ = deepcopy(input_)
        message = sha3_256(message.encode())
        if input_.fulfills:
            message.update("{}{}".format(input_.fulfills.txid, input_.fulfills.output).encode())

        for owner_before in set(input_.owners_before):
            # TODO: CC should throw a KeypairMismatchException, instead of
            #       our manual mapping here

            # TODO FOR CC: Naming wise this is not so smart,
            #              `get_subcondition` in fact doesn't return a
            #              condition but a fulfillment

            # TODO FOR CC: `get_subcondition` is singular. One would not
            #              expect to get a list back.
            ccffill = input_.fulfillment
            subffills = ccffill.get_subcondition_from_vk(base58.b58decode(owner_before))
            if not subffills:
                raise KeypairMismatchException(
                    "Public key {} cannot be found " "in the fulfillment".format(owner_before)
                )
            try:
                private_key = key_pairs[owner_before]
            except KeyError:
                raise KeypairMismatchException(
                    "Public key {} is not a pair " "to any of the private keys".format(owner_before)
                )

            # cryptoconditions makes no assumptions of the encoding of the
            # message to sign or verify. It only accepts bytestrings
            for subffill in subffills:
                subffill.sign(message.digest(), base58.b58decode(private_key.encode()))
        return input_

    def inputs_valid(self, outputs=None):
        """Validates the Inputs in the Transaction against given
        Outputs.

            Note:
                Given a `CREATE` Transaction is passed,
                dummy values for Outputs are submitted for validation that
                evaluate parts of the validation-checks to `True`.

            Args:
                outputs (:obj:`list` of :class:`~planetmint.transactions.common.
                    transaction.Output`): A list of Outputs to check the
                    Inputs against.

            Returns:
                bool: If all Inputs are valid.
        """
        if self.operation == self.CREATE:
            # NOTE: Since in the case of a `CREATE`-transaction we do not have
            #       to check for outputs, we're just submitting dummy
            #       values to the actual method. This simplifies it's logic
            #       greatly, as we do not have to check against `None` values.
            return self._inputs_valid(["dummyvalue" for _ in self.inputs])
        elif self.operation == self.TRANSFER:
            return self._inputs_valid([output.fulfillment.condition_uri for output in outputs])
        elif self.operation == self.VALIDATOR_ELECTION:
            return self._inputs_valid(["dummyvalue" for _ in self.inputs])
        elif self.operation == self.CHAIN_MIGRATION_ELECTION:
            return self._inputs_valid(["dummyvalue" for _ in self.inputs])
        else:
            allowed_ops = ", ".join(self.__class__.ALLOWED_OPERATIONS)
            raise TypeError("`operation` must be one of {}".format(allowed_ops))

    def _inputs_valid(self, output_condition_uris):
        """Validates an Input against a given set of Outputs.

        Note:
            The number of `output_condition_uris` must be equal to the
            number of Inputs a Transaction has.

        Args:
            output_condition_uris (:obj:`list` of :obj:`str`): A list of
                Outputs to check the Inputs against.

        Returns:
            bool: If all Outputs are valid.
        """

        if len(self.inputs) != len(output_condition_uris):
            raise ValueError("Inputs and " "output_condition_uris must have the same count")

        tx_dict = self.tx_dict if self.tx_dict else self.to_dict()
        tx_dict = Transaction._remove_signatures(tx_dict)
        tx_dict["id"] = None
        tx_serialized = Transaction._to_str(tx_dict)

        def validate(i, output_condition_uri=None):
            """Validate input against output condition URI"""
            return self._input_valid(self.inputs[i], self.operation, tx_serialized, output_condition_uri)

        return all(validate(i, cond) for i, cond in enumerate(output_condition_uris))

    @lru_cache(maxsize=16384)
    def _input_valid(self, input_, operation, message, output_condition_uri=None):
        """Validates a single Input against a single Output.

        Note:
            In case of a `CREATE` Transaction, this method
            does not validate against `output_condition_uri`.

        Args:
            input_ (:class:`~planetmint.transactions.common.transaction.
                Input`) The Input to be signed.
            operation (str): The type of Transaction.
            message (str): The fulfillment message.
            output_condition_uri (str, optional): An Output to check the
                Input against.

        Returns:
            bool: If the Input is valid.
        """
        ccffill = input_.fulfillment
        try:
            parsed_ffill = Fulfillment.from_uri(ccffill.serialize_uri())
        except TypeError as e:
            print(f"Exception TypeError : {e}")
            return False
        except ValueError as e:
            print(f"Exception ValueError : {e}")
            return False
        except ParsingError as e:
            print(f"Exception ParsingError : {e}")
            return False
        except ASN1DecodeError as e:
            print(f"Exception ASN1DecodeError : {e}")
            return False
        except ASN1EncodeError as e:
            print(f"Exception ASN1EncodeError : {e}")
            return False

        if operation in [self.CREATE, self.CHAIN_MIGRATION_ELECTION, self.VALIDATOR_ELECTION]:
            # NOTE: In the case of a `CREATE` transaction, the
            #       output is always valid.
            output_valid = True
        else:
            output_valid = output_condition_uri == ccffill.condition_uri

        ffill_valid = False
        if isinstance(parsed_ffill, ZenroomSha256):
            import json

            msg = json.loads(message)
            ffill_valid = parsed_ffill.validate(message=json.dumps(msg["script"]))
        else:
            message = sha3_256(message.encode())
            if input_.fulfills:
                message.update("{}{}".format(input_.fulfills.txid, input_.fulfills.output).encode())

            # NOTE: We pass a timestamp to `.validate`, as in case of a timeout
            #       condition we'll have to validate against it

            # cryptoconditions makes no assumptions of the encoding of the
            # message to sign or verify. It only accepts bytestrings
            ffill_valid = parsed_ffill.validate(message=message.digest())
        return output_valid and ffill_valid

    # This function is required by `lru_cache` to create a key for memoization
    def __hash__(self):
        return hash(self.id)

    @memoize_to_dict
    def to_dict(self):
        """Transforms the object to a Python dictionary.

        Returns:
            dict: The Transaction as an alternative serialization format.
        """
        tx_dict = {
            "inputs": [input_.to_dict() for input_ in self.inputs],
            "outputs": [output.to_dict() for output in self.outputs],
            "operation": str(self.operation),
            "metadata": self.metadata,
            "asset": self.asset,
            "version": self.version,
            "id": self._id,
        }
        if self.script:
            tx_dict["script"] = self.script
        return tx_dict

    @staticmethod
    # TODO: Remove `_dict` prefix of variable.
    def _remove_signatures(tx_dict):
        """Takes a Transaction dictionary and removes all signatures.

        Args:
            tx_dict (dict): The Transaction to remove all signatures from.

        Returns:
            dict

        """
        # NOTE: We remove the reference since we need `tx_dict` only for the
        #       transaction's hash
        tx_dict = deepcopy(tx_dict)
        for input_ in tx_dict["inputs"]:
            # NOTE: Not all Cryptoconditions return a `signature` key (e.g.
            #       ThresholdSha256), so setting it to `None` in any
            #       case could yield incorrect signatures. This is why we only
            #       set it to `None` if it's set in the dict.
            input_["fulfillment"] = None
        return tx_dict

    @staticmethod
    def _to_hash(value):
        return hash_data(value)

    @property
    def id(self):
        return self._id

    def to_hash(self):
        return self.to_dict()["id"]

    @staticmethod
    def _to_str(value):
        return serialize(value)

    # TODO: This method shouldn't call `_remove_signatures`
    def __str__(self):
        _tx = self.to_dict()
        tx = Transaction._remove_signatures(_tx)
        return Transaction._to_str(tx)

    @classmethod
    def get_asset_id(cls, transactions):
        """Get the asset id from a list of :class:`~.Transactions`.

        This is useful when we want to check if the multiple inputs of a
        transaction are related to the same asset id.

        Args:
            transactions (:obj:`list` of :class:`~planetmint.transactions.common.
                transaction.Transaction`): A list of Transactions.
                Usually input Transactions that should have a matching
                asset ID.

        Returns:
            str: ID of the asset.

        Raises:
            :exc:`AssetIdMismatch`: If the inputs are related to different
                assets.
        """

        if not isinstance(transactions, list):
            transactions = [transactions]

        # create a set of the transactions' asset ids
        asset_ids = {
            tx.id if tx.operation in [tx.CREATE, tx.VALIDATOR_ELECTION] else tx.asset["id"] for tx in transactions
        }

        # check that all the transasctions have the same asset id
        if len(asset_ids) > 1:
            raise AssetIdMismatch(("All inputs of all transactions passed" " need to have the same asset id"))
        return asset_ids.pop()

    @staticmethod
    def validate_id(tx_body):
        """Validate the transaction ID of a transaction

        Args:
            tx_body (dict): The Transaction to be transformed.
        """
        # NOTE: Remove reference to avoid side effects
        tx_body = deepcopy(tx_body)
        tx_body = rapidjson.loads(rapidjson.dumps(tx_body))

        try:
            proposed_tx_id = tx_body["id"]
        except KeyError:
            raise InvalidHash("No transaction id found!")

        tx_body["id"] = None

        tx_body_serialized = Transaction._to_str(tx_body)
        valid_tx_id = Transaction._to_hash(tx_body_serialized)
        if proposed_tx_id != valid_tx_id:
            err_msg = "The transaction's id '{}' isn't equal to " "the hash of its body, i.e. it's not valid."
            raise InvalidHash(err_msg.format(proposed_tx_id))

    @classmethod
    @memoize_from_dict
    def from_dict(cls, tx, skip_schema_validation=True):
        """Transforms a Python dictionary to a Transaction object.

        Args:
            tx_body (dict): The Transaction to be transformed.

        Returns:
            :class:`~planetmint.transactions.common.transaction.Transaction`
        """
        operation = tx.get("operation", Transaction.CREATE) if isinstance(tx, dict) else Transaction.CREATE
        cls = Transaction.resolve_class(operation)

        id = None
        try:
            id = tx["id"]
        except KeyError:
            id = None
        # tx['asset'] = tx['asset'][0] if isinstance( tx['asset'], list) or isinstance( tx['asset'], tuple) else tx['asset'],  # noqa: E501
        local_dict = {
            "inputs": tx["inputs"],
            "outputs": tx["outputs"],
            "operation": operation,
            "metadata": tx["metadata"],
            "asset": tx[
                "asset"
            ],  # [0] if isinstance( tx['asset'], list) or isinstance( tx['asset'], tuple) else tx['asset'],  # noqa: E501
            "version": tx["version"],
            "id": id,
        }
        try:
            script_ = tx["script"]
            script_dict = {"script": script_}
        except KeyError:
            script_ = None
            pass
        else:
            local_dict = {**local_dict, **script_dict}

        if not skip_schema_validation:
            cls.validate_id(local_dict)
            cls.validate_schema(local_dict)

        inputs = [Input.from_dict(input_) for input_ in tx["inputs"]]
        outputs = [Output.from_dict(output) for output in tx["outputs"]]
        return cls(
            tx["operation"],
            tx["asset"],
            inputs,
            outputs,
            tx["metadata"],
            tx["version"],
            hash_id=tx["id"],
            tx_dict=tx,
            script=script_,
        )

    @classmethod
    def from_db(cls, planet, tx_dict_list):
        """Helper method that reconstructs a transaction dict that was returned
        from the database. It checks what asset_id to retrieve, retrieves the
        asset from the asset table and reconstructs the transaction.

        Args:
            planet (:class:`~planetmint.tendermint.Planetmint`): An instance
                of Planetmint used to perform database queries.
            tx_dict_list (:list:`dict` or :obj:`dict`): The transaction dict or
                list of transaction dict as returned from the database.

        Returns:
            :class:`~Transaction`

        """
        return_list = True
        if isinstance(tx_dict_list, dict):
            tx_dict_list = [tx_dict_list]
            return_list = False

        tx_map = {}
        tx_ids = []
        for tx in tx_dict_list:
            tx.update({"metadata": None})
            tx_map[tx["id"]] = tx
            tx_ids.append(tx["id"])

        assets = list(planet.get_assets(tx_ids))
        for asset in assets:
            if asset is not None:
                # This is tarantool specific behaviour needs to be addressed
                tx = tx_map[asset[1]]
                tx["asset"] = asset[0]

        tx_ids = list(tx_map.keys())
        metadata_list = list(planet.get_metadata(tx_ids))
        for metadata in metadata_list:
            if "id" in metadata:
                tx = tx_map[metadata["id"]]
                tx.update({"metadata": metadata.get("metadata")})

        if return_list:
            tx_list = []
            for tx_id, tx in tx_map.items():
                tx_list.append(cls.from_dict(tx))
            return tx_list
        else:
            tx = list(tx_map.values())[0]
            return cls.from_dict(tx)

    type_registry = {}

    @staticmethod
    def register_type(tx_type, tx_class):
        Transaction.type_registry[tx_type] = tx_class

    def resolve_class(operation):
        """For the given `tx` based on the `operation` key return its implementation class"""

        create_txn_class = Transaction.type_registry.get(Transaction.CREATE)
        return Transaction.type_registry.get(operation, create_txn_class)

    @classmethod
    def validate_schema(cls, tx):
        validate_transaction_schema(tx)
        validate_txn_obj(cls.ASSET, tx[cls.ASSET], cls.DATA, validate_key)
        validate_txn_obj(cls.METADATA, tx, cls.METADATA, validate_key)
        validate_language_key(tx[cls.ASSET], cls.DATA)
        validate_language_key(tx, cls.METADATA)

    def validate_transfer_inputs(self, planet, current_transactions=[]):
        # store the inputs so that we can check if the asset ids match
        input_txs = []
        input_conditions = []
        for input_ in self.inputs:
            input_txid = input_.fulfills.txid
            input_tx = planet.get_transaction(input_txid)
            if input_tx is None:
                for ctxn in current_transactions:
                    if ctxn.id == input_txid:
                        input_tx = ctxn

            if input_tx is None:
                raise InputDoesNotExist("input `{}` doesn't exist".format(input_txid))

            spent = planet.get_spent(input_txid, input_.fulfills.output, current_transactions)
            if spent:
                raise DoubleSpend("input `{}` was already spent".format(input_txid))

            output = input_tx.outputs[input_.fulfills.output]
            input_conditions.append(output)
            input_txs.append(input_tx)

        # Validate that all inputs are distinct
        links = [i.fulfills.to_uri() for i in self.inputs]
        if len(links) != len(set(links)):
            raise DoubleSpend('tx "{}" spends inputs twice'.format(self.id))

        # validate asset id
        asset_id = self.get_asset_id(input_txs)
        if asset_id != self.asset["id"]:
            raise AssetIdMismatch(("The asset id of the input does not" " match the asset id of the" " transaction"))

        input_amount = sum([input_condition.amount for input_condition in input_conditions])
        output_amount = sum([output_condition.amount for output_condition in self.outputs])

        if output_amount != input_amount:
            raise AmountError(
                (
                    "The amount used in the inputs `{}`" " needs to be same as the amount used" " in the outputs `{}`"
                ).format(input_amount, output_amount)
            )

        if not self.inputs_valid(input_conditions):
            raise InvalidSignature("Transaction signature is invalid.")

        return True

    @classmethod
    def complete_tx_i_o(self, tx_signers, recipients):
        inputs = []
        outputs = []

        # generate_outputs
        for recipient in recipients:
            if not isinstance(recipient, tuple) or len(recipient) != 2:
                raise ValueError(
                    ("Each `recipient` in the list must be a" " tuple of `([<list of public keys>]," " <amount>)`")
                )
            pub_keys, amount = recipient
            outputs.append(Output.generate(pub_keys, amount))

        # generate inputs
        inputs.append(Input.generate(tx_signers))

        return (inputs, outputs)