# Copyright BigchainDB GmbH and BigchainDB contributors
# SPDX-License-Identifier: (Apache-2.0 AND CC-BY-4.0)
# Code is Apache-2.0 and docs are CC-BY-4.0
from collections import OrderedDict

import base58
from uuid import uuid4

from bigchaindb import backend
from bigchaindb.elections.vote import Vote
from bigchaindb.common.exceptions import (InvalidSignature,
                                          MultipleInputsError,
                                          InvalidProposer,
                                          UnequalValidatorSet,
                                          DuplicateTransaction)
from bigchaindb.tendermint_utils import key_from_base64, public_key_to_base64
from bigchaindb.common.crypto import (public_key_from_ed25519_key)
from bigchaindb.common.transaction import Transaction
from bigchaindb.common.schema import (_validate_schema,
                                      TX_SCHEMA_COMMON,
                                      TX_SCHEMA_CREATE)


class Election(Transaction):
    """Represents election transactions.

       To implement a custom election, create a class deriving from this one
       with OPERATION set to the election operation, ALLOWED_OPERATIONS
       set to (OPERATION,), CREATE set to OPERATION.
    """

    OPERATION = None
    # Custom validation schema
    TX_SCHEMA_CUSTOM = None
    # Election Statuses:
    ONGOING = 'ongoing'
    CONCLUDED = 'concluded'
    INCONCLUSIVE = 'inconclusive'
    # Vote ratio to approve an election
    ELECTION_THRESHOLD = 2 / 3

    @classmethod
    def get_validator_change(cls, bigchain):
        """Return the validator set from the most recent approved block

        :return: {
            'height': <block_height>,
            'validators': <validator_set>
        }
        """
        latest_block = bigchain.get_latest_block()
        if latest_block is None:
            return None
        return bigchain.get_validator_change(latest_block['height'])

    @classmethod
    def get_validators(cls, bigchain, height=None):
        """Return a dictionary of validators with key as `public_key` and
           value as the `voting_power`
        """
        validators = {}
        for validator in bigchain.get_validators(height):
            # NOTE: we assume that Tendermint encodes public key in base64
            public_key = public_key_from_ed25519_key(key_from_base64(validator['public_key']['value']))
            validators[public_key] = validator['voting_power']

        return validators

    @classmethod
    def recipients(cls, bigchain):
        """Convert validator dictionary to a recipient list for `Transaction`"""

        recipients = []
        for public_key, voting_power in cls.get_validators(bigchain).items():
            recipients.append(([public_key], voting_power))

        return recipients

    @classmethod
    def is_same_topology(cls, current_topology, election_topology):
        voters = {}
        for voter in election_topology:
            if len(voter.public_keys) > 1:
                return False

            [public_key] = voter.public_keys
            voting_power = voter.amount
            voters[public_key] = voting_power

        # Check whether the voters and their votes is same to that of the
        # validators and their voting power in the network
        return current_topology == voters

    def validate(self, bigchain, current_transactions=[]):
        """Validate election transaction

        NOTE:
        * A valid election is initiated by an existing validator.

        * A valid election is one where voters are validators and votes are
          allocated according to the voting power of each validator node.

        Args:
            :param bigchain: (BigchainDB) an instantiated bigchaindb.lib.BigchainDB object.
            :param current_transactions: (list) A list of transactions to be validated along with the election

        Returns:
            Election: a Election object or an object of the derived Election subclass.

        Raises:
            ValidationError: If the election is invalid
        """
        input_conditions = []

        duplicates = any(txn for txn in current_transactions if txn.id == self.id)
        if bigchain.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.')

        current_validators = self.get_validators(bigchain)

        # NOTE: Proposer should be a single node
        if len(self.inputs) != 1 or len(self.inputs[0].owners_before) != 1:
            raise MultipleInputsError('`tx_signers` must be a list instance of length one')

        # NOTE: Check if the proposer is a validator.
        [election_initiator_node_pub_key] = self.inputs[0].owners_before
        if election_initiator_node_pub_key not in current_validators.keys():
            raise InvalidProposer('Public key is not a part of the validator set')

        # NOTE: Check if all validators have been assigned votes equal to their voting power
        if not self.is_same_topology(current_validators, self.outputs):
            raise UnequalValidatorSet('Validator set much be exactly same to the outputs of election')

        return self

    @classmethod
    def generate(cls, initiator, voters, election_data, metadata=None):
        # Break symmetry in case we need to call an election with the same properties twice
        uuid = uuid4()
        election_data['seed'] = str(uuid)

        (inputs, outputs) = cls.validate_create(initiator, voters, election_data, metadata)
        election = cls(cls.OPERATION, {'data': election_data}, inputs, outputs, metadata)
        cls.validate_schema(election.to_dict())
        return election

    @classmethod
    def validate_schema(cls, tx):
        """Validate the election transaction. Since `ELECTION` extends `CREATE` transaction, all the validations for
        `CREATE` transaction should be inherited
        """
        _validate_schema(TX_SCHEMA_COMMON, tx)
        _validate_schema(TX_SCHEMA_CREATE, tx)
        if cls.TX_SCHEMA_CUSTOM:
            _validate_schema(cls.TX_SCHEMA_CUSTOM, tx)

    @classmethod
    def create(cls, tx_signers, recipients, metadata=None, asset=None):
        raise NotImplementedError

    @classmethod
    def transfer(cls, tx_signers, recipients, metadata=None, asset=None):
        raise NotImplementedError

    @classmethod
    def to_public_key(cls, election_id):
        return base58.b58encode(bytes.fromhex(election_id)).decode()

    @classmethod
    def count_votes(cls, election_pk, transactions, getter=getattr):
        votes = 0
        for txn in transactions:
            if getter(txn, 'operation') == Vote.OPERATION:
                for output in getter(txn, 'outputs'):
                    # NOTE: We enforce that a valid vote to election id will have only
                    # election_pk in the output public keys, including any other public key
                    # along with election_pk will lead to vote being not considered valid.
                    if len(getter(output, 'public_keys')) == 1 and [election_pk] == getter(output, 'public_keys'):
                        votes = votes + int(getter(output, 'amount'))
        return votes

    def get_commited_votes(self, bigchain, election_pk=None):
        if election_pk is None:
            election_pk = self.to_public_key(self.id)
        txns = list(backend.query.get_asset_tokens_for_public_key(bigchain.connection,
                                                                  self.id,
                                                                  election_pk))
        return self.count_votes(election_pk, txns, dict.get)

    def has_concluded(self, bigchain, current_votes=[]):
        """Check if the election can be concluded or not.

        * Elections can only be concluded if the validator set has not changed
          since the election was initiated.
        * Elections can be concluded only if the current votes form a supermajority.

        Custom elections may override this function and introduce additional checks.
        """
        if self.has_validator_set_changed(bigchain):
            return False

        election_pk = self.to_public_key(self.id)
        votes_committed = self.get_commited_votes(bigchain, election_pk)
        votes_current = self.count_votes(election_pk, current_votes)

        total_votes = sum(output.amount for output in self.outputs)
        if (votes_committed < (2/3) * total_votes) and \
                (votes_committed + votes_current >= (2/3)*total_votes):
            return True

        return False

    def get_status(self, bigchain):
        election = self.get_election(self.id, bigchain)
        if election and election['is_concluded']:
            return self.CONCLUDED

        return self.INCONCLUSIVE if self.has_validator_set_changed(bigchain) else self.ONGOING

    def has_validator_set_changed(self, bigchain):
        latest_change = self.get_validator_change(bigchain)
        if latest_change is None:
            return False

        latest_change_height = latest_change['height']

        election = self.get_election(self.id, bigchain)

        return latest_change_height > election['height']

    def get_election(self, election_id, bigchain):
        return bigchain.get_election(election_id)

    def store(self, bigchain, height, is_concluded):
        bigchain.store_election(self.id, height, is_concluded)

    def show_election(self, bigchain):
        data = self.asset['data']
        if 'public_key' in data.keys():
            data['public_key'] = public_key_to_base64(data['public_key']['value'])
        response = ''
        for k, v in data.items():
            if k != 'seed':
                response += f'{k}={v}\n'
        response += f'status={self.get_status(bigchain)}'

        return response

    @classmethod
    def _get_initiated_elections(cls, height, txns):
        elections = []
        for tx in txns:
            if not isinstance(tx, Election):
                continue

            elections.append({'election_id': tx.id, 'height': height,
                              'is_concluded': False})
        return elections

    @classmethod
    def _get_votes(cls, txns):
        elections = OrderedDict()
        for tx in txns:
            if not isinstance(tx, Vote):
                continue

            election_id = tx.asset['id']
            if election_id not in elections:
                elections[election_id] = []
            elections[election_id].append(tx)
        return elections

    @classmethod
    def process_block(cls, bigchain, new_height, txns):
        """Looks for election and vote transactions inside the block, records
           and processes elections.

           Every election is recorded in the database.

           Every vote has a chance to conclude the corresponding election. When
           an election is concluded, the corresponding database record is
           marked as such.

           Elections and votes are processed in the order in which they
           appear in the block. Elections are concluded in the order of
           appearance of their first votes in the block.

           For every election concluded in the block, calls its `on_approval`
           method. The returned value of the last `on_approval`, if any,
           is a validator set update to be applied in one of the following blocks.

           `on_approval` methods are implemented by elections of particular type.
           The method may contain side effects but should be idempotent. To account
           for other concluded elections, if it requires so, the method should
           rely on the database state.
        """
        # elections initiated in this block
        initiated_elections = cls._get_initiated_elections(new_height, txns)

        if initiated_elections:
            bigchain.store_elections(initiated_elections)

        # elections voted for in this block and their votes
        elections = cls._get_votes(txns)

        validator_update = None
        for election_id, votes in elections.items():
            election = bigchain.get_transaction(election_id)
            if election is None:
                continue

            if not election.has_concluded(bigchain, votes):
                continue

            validator_update = election.on_approval(bigchain, new_height)
            election.store(bigchain, new_height, is_concluded=True)

        return [validator_update] if validator_update else []

    @classmethod
    def rollback(cls, bigchain, new_height, txn_ids):
        """Looks for election and vote transactions inside the block and
           cleans up the database artifacts possibly created in `process_blocks`.

           Part of the `end_block`/`commit` crash recovery.
        """

        # delete election records for elections initiated at this height and
        # elections concluded at this height
        bigchain.delete_elections(new_height)

        txns = [bigchain.get_transaction(tx_id) for tx_id in txn_ids]

        elections = cls._get_votes(txns)
        for election_id in elections:
            election = bigchain.get_transaction(election_id)
            election.on_rollback(bigchain, new_height)

    def on_approval(self, bigchain, new_height):
        """Override to update the database state according to the
           election rules. Consider the current database state to account for
           other concluded elections, if required.
        """
        raise NotImplementedError

    def on_rollback(self, bigchain, new_height):
        """Override to clean up the database artifacts possibly created
           in `on_approval`. Part of the `end_block`/`commit` crash recovery.
        """
        raise NotImplementedError