# 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

"""This module contains all the goodness to integrate BigchainDB
with Tendermint.
"""
import logging
import sys

from abci.application import BaseApplication
from abci import (
    ResponseInitChain,
    ResponseInfo,
    ResponseCheckTx,
    ResponseBeginBlock,
    ResponseDeliverTx,
    ResponseEndBlock,
    ResponseCommit,
)

from bigchaindb import BigchainDB
from bigchaindb.elections.election import Election
from bigchaindb.version import __tm_supported_versions__
from bigchaindb.utils import tendermint_version_is_compatible
from bigchaindb.tendermint_utils import (decode_transaction,
                                         calculate_hash)
from bigchaindb.lib import Block
import bigchaindb.upsert_validator.validator_utils as vutils
from bigchaindb.events import EventTypes, Event


CodeTypeOk = 0
CodeTypeError = 1
logger = logging.getLogger(__name__)


class App(BaseApplication):
    """Bridge between BigchainDB and Tendermint.

    The role of this class is to expose the BigchainDB
    transaction logic to Tendermint Core.
    """

    def __init__(self, bigchaindb=None, events_queue=None):
        self.events_queue = events_queue
        self.bigchaindb = bigchaindb or BigchainDB()
        self.block_txn_ids = []
        self.block_txn_hash = ''
        self.block_transactions = []
        self.validators = None
        self.new_height = None
        self.chain = self.bigchaindb.get_latest_abci_chain()

    def log_abci_migration_error(self, chain_id, validators):
        logger.error(f'An ABCI chain migration is in process. ' +
                     'Download the new ABCI client and configure it with ' +
                     'chain_id={chain_id} and validators={validators}.')

    def abort_if_abci_chain_is_not_synced(self):
        if self.chain is None or self.chain['is_synced']:
            return

        validators = self.bigchaindb.get_validators()
        self.log_abci_migration_error(self.chain['chain_id'], validators)
        sys.exit(1)

    def init_chain(self, genesis):
        """Initialize chain upon genesis or a migration"""

        app_hash = ''
        height = 0

        known_chain = self.bigchaindb.get_latest_abci_chain()
        if known_chain is not None:
            chain_id = known_chain['chain_id']

            if known_chain['is_synced']:
                msg = f'Got invalid InitChain ABCI request ({genesis}) - ' + \
                      'the chain {chain_id} is already synced.'
                logger.error(msg)
                sys.exit(1)

            if chain_id != genesis.chain_id:
                validators = self.bigchaindb.get_validators()
                self.log_abci_migration_error(chain_id, validators)
                sys.exit(1)

            # set migration values for app hash and height
            block = self.bigchaindb.get_latest_block()
            app_hash = '' if block is None else block['app_hash']
            height = 0 if block is None else block['height'] + 1

        known_validators = self.bigchaindb.get_validators()
        validator_set = [vutils.decode_validator(v)
                         for v in genesis.validators]

        if known_validators and known_validators != validator_set:
            self.log_abci_migration_error(known_chain['chain_id'],
                                          known_validators)
            sys.exit(1)

        block = Block(app_hash=app_hash, height=height, transactions=[])
        self.bigchaindb.store_block(block._asdict())
        self.bigchaindb.store_validator_set(height + 1, validator_set)
        abci_chain_height = 0 if known_chain is None else known_chain['height']
        self.bigchaindb.store_abci_chain(abci_chain_height,
                                         genesis.chain_id, True)
        self.chain = {'height': abci_chain_height, 'is_synced': True,
                      'chain_id': genesis.chain_id}
        return ResponseInitChain()

    def info(self, request):
        """Return height of the latest committed block."""

        self.abort_if_abci_chain_is_not_synced()

        # Check if BigchainDB supports the Tendermint version
        if not (hasattr(request, 'version') and tendermint_version_is_compatible(request.version)):
            logger.error(f'Unsupported Tendermint version: {getattr(request, "version", "no version")}.'
                         f' Currently, BigchainDB only supports {__tm_supported_versions__}. Exiting!')
            sys.exit(1)

        logger.info(f"Tendermint version: {request.version}")

        r = ResponseInfo()
        block = self.bigchaindb.get_latest_block()
        if block:
            chain_shift = 0 if self.chain is None else self.chain['height']
            r.last_block_height = block['height'] - chain_shift
            r.last_block_app_hash = block['app_hash'].encode('utf-8')
        else:
            r.last_block_height = 0
            r.last_block_app_hash = b''
        return r

    def check_tx(self, raw_transaction):
        """Validate the transaction before entry into
        the mempool.

        Args:
            raw_tx: a raw string (in bytes) transaction.
        """

        self.abort_if_abci_chain_is_not_synced()

        logger.debug('check_tx: %s', raw_transaction)
        transaction = decode_transaction(raw_transaction)
        if self.bigchaindb.is_valid_transaction(transaction):
            logger.debug('check_tx: VALID')
            return ResponseCheckTx(code=CodeTypeOk)
        else:
            logger.debug('check_tx: INVALID')
            return ResponseCheckTx(code=CodeTypeError)

    def begin_block(self, req_begin_block):
        """Initialize list of transaction.
        Args:
            req_begin_block: block object which contains block header
            and block hash.
        """
        self.abort_if_abci_chain_is_not_synced()

        chain_shift = 0 if self.chain is None else self.chain['height']
        logger.debug('BEGIN BLOCK, height:%s, num_txs:%s',
                     req_begin_block.header.height + chain_shift,
                     req_begin_block.header.num_txs)

        self.block_txn_ids = []
        self.block_transactions = []
        return ResponseBeginBlock()

    def deliver_tx(self, raw_transaction):
        """Validate the transaction before mutating the state.

        Args:
            raw_tx: a raw string (in bytes) transaction.
        """

        self.abort_if_abci_chain_is_not_synced()

        logger.debug('deliver_tx: %s', raw_transaction)
        transaction = self.bigchaindb.is_valid_transaction(
            decode_transaction(raw_transaction), self.block_transactions)

        if not transaction:
            logger.debug('deliver_tx: INVALID')
            return ResponseDeliverTx(code=CodeTypeError)
        else:
            logger.debug('storing tx')
            self.block_txn_ids.append(transaction.id)
            self.block_transactions.append(transaction)
            return ResponseDeliverTx(code=CodeTypeOk)

    def end_block(self, request_end_block):
        """Calculate block hash using transaction ids and previous block
        hash to be stored in the next block.

        Args:
            height (int): new height of the chain.
        """

        self.abort_if_abci_chain_is_not_synced()

        chain_shift = 0 if self.chain is None else self.chain['height']

        height = request_end_block.height + chain_shift
        self.new_height = height

        # store pre-commit state to recover in case there is a crash during
        # `end_block` or `commit`
        logger.debug(f'Updating pre-commit state: {self.new_height}')
        pre_commit_state = dict(height=self.new_height,
                                transactions=self.block_txn_ids)
        self.bigchaindb.store_pre_commit_state(pre_commit_state)

        block_txn_hash = calculate_hash(self.block_txn_ids)
        block = self.bigchaindb.get_latest_block()

        if self.block_txn_ids:
            self.block_txn_hash = calculate_hash([block['app_hash'], block_txn_hash])
        else:
            self.block_txn_hash = block['app_hash']

        validator_update = Election.process_block(self.bigchaindb,
                                                  self.new_height,
                                                  self.block_transactions)

        return ResponseEndBlock(validator_updates=validator_update)

    def commit(self):
        """Store the new height and along with block hash."""

        self.abort_if_abci_chain_is_not_synced()

        data = self.block_txn_hash.encode('utf-8')

        # register a new block only when new transactions are received
        if self.block_txn_ids:
            self.bigchaindb.store_bulk_transactions(self.block_transactions)

        block = Block(app_hash=self.block_txn_hash,
                      height=self.new_height,
                      transactions=self.block_txn_ids)
        # NOTE: storing the block should be the last operation during commit
        # this effects crash recovery. Refer BEP#8 for details
        self.bigchaindb.store_block(block._asdict())

        logger.debug('Commit-ing new block with hash: apphash=%s ,'
                     'height=%s, txn ids=%s', data, self.new_height,
                     self.block_txn_ids)

        if self.events_queue:
            event = Event(EventTypes.BLOCK_VALID, {
                'height': self.new_height,
                'transactions': self.block_transactions
            })
            self.events_queue.put(event)

        return ResponseCommit(data=data)


def rollback(b):
    pre_commit = b.get_pre_commit_state()

    if pre_commit is None:
        # the pre_commit record is first stored in the first `end_block`
        return

    latest_block = b.get_latest_block()
    if latest_block is None:
        logger.error('Found precommit state but no blocks!')
        sys.exit(1)

    # NOTE: the pre-commit state is always at most 1 block ahead of the commited state
    if latest_block['height'] < pre_commit['height']:
        Election.rollback(b, pre_commit['height'], pre_commit['transactions'])
        b.delete_transactions(pre_commit['transactions'])