# Part of accounting-api project:
# https://gitorious.org/conservancy/accounting-api
# License: AGPLv3-or-later

import sys
import subprocess
import logging
import time
import re

from datetime import datetime
from xml.etree import ElementTree
from contextlib import contextmanager

from accounting.exceptions import AccountingException
from accounting.models import Account, Transaction, Posting, Amount
from accounting.storage import Storage, TransactionNotFound

_log = logging.getLogger(__name__)


class Ledger(Storage):
    def __init__(self, app=None, ledger_file=None, ledger_bin=None):
        if app:
            ledger_file = app.config['LEDGER_FILE']

        if ledger_file is None:
            raise ValueError('ledger_file cannot be None')

        self.ledger_bin = ledger_bin or 'ledger'
        self.ledger_file = ledger_file
        _log.info('ledger file: %s', ledger_file)

        self.locked = False
        self.ledger_process = None

    @contextmanager
    def locked_process(self):
        r'''
        Context manager that checks that the ledger process is not already
        locked, then "locks" the process and yields the process handle and
        unlocks the process when execution is returned.

        Since this decorated as a :func:`contextlib.contextmanager` the
        recommended use is with the ``with``-statement.

        .. code-block:: python

            with self.locked_process() as p:
                p.stdin.write(b'bal\n')

                output = self.read_until_prompt(p)

        '''
        if self.locked:
            raise RuntimeError('The process has already been locked,'
                               ' something\'s out of order.')

            # XXX: This code has no purpose in a single-threaded process
            timeout = 5  # Seconds

            for i in range(1, timeout + 2):
                if i > timeout:
                    raise RuntimeError('Ledger process is already locked')

                if not self.locked:
                    break
                else:
                    _log.info('Waiting for one second... %d/%d', i, timeout)
                    time.sleep(1)

        process = self.get_process()

        self.locked = True
        _log.debug('Lock enabled')

        yield process

        self.locked = False
        _log.debug('Lock disabled')

    def assemble_arguments(self):
        '''
        Returns a list of arguments suitable for :class:`subprocess.Popen`
        based on :attr:`self.ledger_bin` and :attr:`self.ledger_file`.
        '''
        return [
            self.ledger_bin,
            '-f',
            self.ledger_file,
        ]

    def init_process(self):
        '''
        Creates a new (presumably) ledger subprocess based on the args from
        :meth:`Ledger.assemble_arguments()` and then runs
        :meth:`Ledger.read_until_prompt()` once (which should return the banner
        text) and discards the output.
        '''
        _log.debug('Starting ledger process...')
        self.ledger_process = subprocess.Popen(
            self.assemble_arguments(),
            stdout=subprocess.PIPE,
            stdin=subprocess.PIPE,
            stderr=subprocess.PIPE)

        # Swallow the banner
        with self.locked_process() as p:
            self.read_until_prompt(p)

        return self.ledger_process

    def get_process(self):
        '''
        Returns :attr:`self.ledger_process` if it evaluates to ``True``. If
        :attr:`self.ledger_process` is not set the result of
        :meth:`self.init_process() <Ledger.init_process>` is returned.
        '''
        return self.ledger_process or self.init_process()

    def read_until_prompt(self, process):
        r'''
        Reads from the subprocess instance :data:`process` until it finds a
        combination of ``\n]\x20`` (the prompt), then returns the output
        without the prompt.
        '''
        output = b''

        while True:
            line = process.stdout.read(1)  # XXX: This is a hack

            output += line

            if b'\n] ' in output:
                _log.debug('Found prompt!')
                break

        output = output[:-3]  # Cut away the prompt

        _log.debug('output: %s', output)

        return output

    def send_command(self, command):
        output = None

        with self.locked_process() as p:
            if isinstance(command, str):
                command = command.encode('utf8')

            p.stdin.write(command + b'\n')
            p.stdin.flush()

            output = self.read_until_prompt(p)

            self.ledger_process.send_signal(subprocess.signal.SIGTERM)
            _log.debug('Waiting for ledger to shut down')
            self.ledger_process.wait()
            self.ledger_process = None

            return output

    def add_transaction(self, transaction):
        '''
        Writes a transaction to the ledger file by opening it in 'ab' mode and
        writing a ledger transaction based on the
        :class:`~accounting.models.Transaction` instance in
        :data:`transaction`.
        '''
        if transaction.id is None:
            _log.debug('No ID found. Generating an ID.')
            transaction.generate_id()

        transaction.metadata.update({'Id': transaction.id})

        transaction_template = ('\n{date} {t.payee}\n'
                                '{metadata}'
                                '{postings}')

        metadata_template = '   ;{0}: {1}\n'

        # TODO: Generate metadata for postings
        posting_template = ('  {account} {p.amount.symbol}'
                            ' {p.amount.amount}\n')

        output = b''

        # XXX: Even I hardly understands what this does, however I indent it it
        # stays unreadable.
        output += transaction_template.format(
            date=transaction.date.strftime('%Y-%m-%d'),
            t=transaction,
            metadata=''.join([
                metadata_template.format(k, v)
                for k, v in transaction.metadata.items()]),
            postings=''.join([posting_template.format(
                p=p,
                account=p.account + ' ' * (
                    80 - (len(p.account) + len(p.amount.symbol) +
                          len(str(p.amount.amount)) + 1 + 2)
                )) for p in transaction.postings
            ])
        ).encode('utf8')

        with open(self.ledger_file, 'ab') as f:
            f.write(output)

        _log.debug('written to file: %s', output)

        return transaction.id

    def bal(self):
        output = self.send_command('xml')

        if output is None:
            raise RuntimeError('bal call returned no output')

        accounts = []

        xml = ElementTree.fromstring(output.decode('utf8'))

        accounts = self._recurse_accounts(xml.find('./accounts'))

        return accounts

    def _recurse_accounts(self, root):
        accounts = []

        for account in root.findall('./account'):
            name = account.find('./fullname').text

            amounts = []

            # Try to find an account total value, then try to find the account
            # balance
            account_amounts = account.findall(
                './account-total/balance/amount') or \
                account.findall('./account-amount/amount') or \
                account.findall('./account-total/amount')

            if account_amounts:
                for amount in account_amounts:
                    quantity = amount.find('./quantity').text
                    symbol = amount.find('./commodity/symbol').text

                    amounts.append(Amount(amount=quantity, symbol=symbol))
            else:
                _log.warning('Account %s does not have any amounts', name)

            accounts.append(Account(name=name,
                                    amounts=amounts,
                                    accounts=self._recurse_accounts(account)))

        return accounts

    def get_transactions(self):
        return self.reg()

    def get_transaction(self, transaction_id):
        transactions = self.get_transactions()

        for transaction in transactions:
            if transaction.id == transaction_id:
                return transaction

        raise TransactionNotFound('No transaction with id %s found',
                                  transaction_id)

    def reg(self):
        output = self.send_command('xml')

        if output is None:
            raise RuntimeError('reg call returned no output')

        entries = []

        reg_xml = ElementTree.fromstring(output.decode('utf8'))

        for transaction in reg_xml.findall('./transactions/transaction'):
            date = datetime.strptime(transaction.find('./date').text,
                                     '%Y/%m/%d')
            payee = transaction.find('./payee').text

            postings = []

            for posting in transaction.findall('./postings/posting'):
                account = posting.find('./account/name').text
                amount = posting.find('./post-amount/amount/quantity').text
                symbol = posting.find(
                    './post-amount/amount/commodity/symbol').text

                # Get the posting metadata
                metadata = {}

                values = posting.findall('./metadata/value')
                if values:
                    for value in values:
                        key = value.get('key')
                        value = value.find('./string').text

                        _log.debug('metadata: %s: %s', key, value)

                        metadata.update({key: value})

                postings.append(
                    Posting(account=account,
                            metadata=metadata,
                            amount=Amount(amount=amount, symbol=symbol)))

            # Get the transaction metadata
            metadata = {}

            values = transaction.findall('./metadata/value')
            if values:
                for value in values:
                    key = value.get('key')
                    value = value.find('./string').text

                    _log.debug('metadata: %s: %s', key, value)

                    metadata.update({key: value})

            # Add a Transaction instance to the list
            id = metadata.pop('Id')
            entries.append(
                Transaction(id=id, date=date, payee=payee, postings=postings,
                            metadata=metadata))

        return entries

    def delete_transaction(self, transaction_id):
        '''
        Delete a transaction from the ledger file.

        This method opens the ledger file, loads all lines into memory and
        looks for the transaction_id, then looks for the bounds of that
        transaction in the ledger file, removes all lines within the bounds of
        the transaction and removes them, then writes the lines back to the
        ledger file.

        Exceptions:

        -   RuntimeError: If all boundaries to the transaction are not found
        -   TransactionNotFound: If no such transaction_id can be found in
            :data:`self.ledger_file`
        '''
        f = open(self.ledger_file, 'r')

        lines = [i for i in f]

        # A mapping of line meanings and their line numbers as found by the
        # following logic
        semantic_lines = dict(
            id_location=None,
            transaction_start=None,
            next_transaction_or_eof=None
        )

        for i, line in enumerate(lines):
            if transaction_id in line:
                semantic_lines['id_location'] = i
                break

        if not semantic_lines['id_location']:
            raise TransactionNotFound(
                'No transaction with ID "{0}" found'.format(transaction_id))

        transaction_start_pattern = re.compile(r'^\S')

        cursor = semantic_lines['id_location'] - 1

        # Find the first line of the transaction
        while True:
            if transaction_start_pattern.match(lines[cursor]):
                semantic_lines['transaction_start'] = cursor
                break

            cursor -= 1

        cursor = semantic_lines['id_location'] + 1

        # Find the last line of the transaction
        while True:
            try:
                if transaction_start_pattern.match(lines[cursor]):
                    semantic_lines['next_transaction_or_eof'] = cursor
                    break
            except IndexError:
                # Set next_line_without_starting_space_or_end_of_file to
                # the cursor. The cursor will be an index not included in the
                # list of lines
                semantic_lines['next_transaction_or_eof'] = cursor
                break

            cursor += 1

        if not all(map(lambda v: v is not None, semantic_lines.values())):
            raise RuntimeError('Could not find all the values necessary for'
                               ' safe deletion of a transaction.')

        del_start = semantic_lines['transaction_start']

        if len(lines) == semantic_lines['next_transaction_or_eof']:
            _log.debug('There are no transactions below the transaction being'
                       ' deleted. The line before the first line of the'
                       ' transaction will be deleted.')
            # Delete the preceding line to make the file
            del_start -= 1

        del lines[del_start:semantic_lines['next_transaction_or_eof']]

        with open(self.ledger_file, 'w') as f:
            for line in lines:
                f.write(line)

    def update_transaction(self, transaction):
        '''
        Update a transaction in the ledger file.

        Takes a :class:`~accounting.models.Transaction` object and removes
        the old transaction using :data:`transaction.id` from the passed
        :class:`~accounting.models.Transaction` instance and adds
        :data:`transaction` to the database.
        '''
        if not transaction.id:
            return AccountingException(('The transaction {0} has no'
                                        ' id attribute').format(transaction))

        old_transaction = self.get_transaction(transaction.id)

        self.delete_transaction(transaction.id)

        self.add_transaction(transaction)

        _log.debug('Updated transaction from: %s to: %s', old_transaction,
                   transaction)


def main(argv=None):
    import argparse
    if argv is None:
        argv = sys.argv

    parser = argparse.ArgumentParser()
    parser.add_argument('-v', '--verbosity',
                        default='INFO',
                        help=('Filter logging output. Possible values:' +
                              ' CRITICAL, ERROR, WARNING, INFO, DEBUG'))

    args = parser.parse_args(argv[1:])
    logging.basicConfig(level=getattr(logging, args.verbosity, 'INFO'))
    ledger = Ledger(ledger_file='non-profit-test-data.ledger')
    print(ledger.bal())
    print(ledger.reg())


if __name__ == '__main__':
    sys.exit(main())