# Copyright (c) 2017-2023 Florian Fischer. All rights reserved.
#
# This file is part of geldschieberbot.
#
# geldschieberbot is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# geldschieberbot is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# geldschieberbot found in the LICENSE file. If not,
# see <https://www.gnu.org/licenses/>.
"""Bot to manage a groups finances"""

from datetime import date, datetime, timedelta
import json
import os
import typing as T

from models import MessageContext, Modification, Change, GeldschieberbotJSONEncoder, Reply
from utils import to_euro, to_cent


class Geldschieberbot:
    """
    State of the geldschieberbot

    The state is stored in a central dict for convenient writing to and
    reading from disk.

    The state contains:
    * balance - dict of dicts associating two persons to an amount
    * name2num, num2name - dicts associating numbers to names and vice versa
    * cars - dict associating car names to their service charge
    * scheduled_cmds - dict associating names to cmds, their schedule,
                       and their last execution
    * changes - dict associating users with their changes
    * aliases - list of names mapping to multiple other names

    The central component of the geldschieberbot's state is the balance dictionary
    assigning a cent amount to each pair of participants (following A and B).
    The tracked amount represents the money the first component has to provide
    to the second to even out the balance.
    If money is transferred from A to B it is expected from B to give the same amount
    of money back to A.
    Moving money from A to B is tracked in both balances A->B and B->A.
    The amount is subtracted from the A->B balance and added to the B->A balance
    meaning that B has to give A money to even out the balance.

    """

    STATE_KEYS = ("balance", "name2num", "num2name", "available_cars",
                  "scheduled_cmds", "changes", "aliases")

    def load_state(self, state_path=''):
        """Load state from disk"""
        state_path = state_path or self.state_path
        if os.path.isfile(state_path):
            with open(state_path, 'r', encoding='utf-8') as state_f:
                self.state = json.load(state_f)
        else:
            self.state = {key: {} for key in self.STATE_KEYS}

        try:
            # decode JSON changes
            self.state['changes'] = {
                name: [
                    Change(ch['cmd'], [
                        Modification(*mod.values())
                        for mod in ch['modifications']
                    ], ch['timestamp'], ch['rewind_cmds']) for ch in changes
                ]
                for name, changes in self.state['changes'].items()
            }
        except (KeyError, TypeError):
            # convert from old plain changes format
            if isinstance(list(self.state['changes'].values())[0], list):
                for name, changes in self.state['changes'].items():
                    user_changes = []
                    for ch in changes:
                        try:
                            user_changes.append(
                                Change(ch[0], [
                                    Modification(r, d, a) for r, d, a in ch[1:]
                                ], None))
                        except (ValueError, TypeError):
                            continue

                    self.state['changes'][name] = user_changes

        for key in self.STATE_KEYS:
            # add missing keys to an existsing state
            setattr(self, key, self.state.setdefault(key, {}))

        # Do this simply to allow pylint to lint the Geldschieberbot and
        # prevent false positive 'no-member' errors.
        self.balance = self.state["balance"]
        self.name2num = self.state["name2num"]
        self.num2name = self.state["num2name"]
        # Workaround old states using the cars key instead of available_cars
        if 'cars' in self.state:
            all_cars = self.state['cars']
            del self.state['cars']
            all_cars.update(self.state['available_cars'])
            self.state['available_cars'] = all_cars
        self.available_cars = self.state["available_cars"]
        self.scheduled_cmds = self.state["scheduled_cmds"]
        self.changes = self.state["changes"]
        self.aliases = self.state["aliases"]

    def save_state(self, state_path=''):
        """Load state from disk"""
        state_path = state_path or self.state_path
        with open(state_path, 'w', encoding='utf-8') as state_file:
            json.dump(self.state, state_file, cls=GeldschieberbotJSONEncoder)

    def record(self, recipient: str, donor: str,
               amount: int) -> T.Optional[Modification]:
        """Apply changes to the balance"""

        return self.apply(Modification(recipient, donor, amount))

    def apply(self, mod: Modification) -> T.Optional[Modification]:
        """Apply a single modification to the balance"""

        # Only change anything if this is not a dry run
        if self.dry_run:
            return None

        self.balance[mod.donor][mod.recipient] += mod.amount
        self.balance[mod.recipient][mod.donor] -= mod.amount

        return mod

    def reverse(self, mod: Modification) -> Modification:
        """Reverse the effect of a single modification to the balance"""

        self.balance[mod.donor][mod.recipient] -= mod.amount
        self.balance[mod.recipient][mod.donor] += mod.amount

        return Modification(mod.donor, mod.recipient, mod.amount)

    def create_summary(self, user, include=None) -> str:
        """Create a summary for a user"""
        msg = ''
        cars_summary = ""
        total = 0
        cars_total = 0
        p_balances = self.balance[user]  # failes if user is not in balance
        for person in p_balances:
            if include and not person in include:
                continue

            amount = p_balances[person]
            if amount == 0:
                continue
            if person in self.available_cars:
                cars_total -= amount
                cars_summary += f'\t{"<-" if amount < 0 else "->"} {person} {to_euro(abs(amount))}\n'
            else:
                total -= amount
                msg += f'\t{"<-" if amount < 0 else "->"} {person} {to_euro(abs(amount))}\n'

        if not msg:
            msg = '\tAll fine :)'
        else:
            msg += f'\tBalance: {to_euro(total)}'

        ret_summary = f'{user}:\n{msg}'

        if cars_summary:
            cars_summary += f'\tLiability: {to_euro(cars_total)}'
            ret_summary += f'\n\tCars:\n{cars_summary}'

        return ret_summary

    def create_total_summary(self) -> str:
        """Create a summary of all balances"""
        msg = 'Summary:'

        cars_summary = ''
        for person in self.balance:
            p_summary = self.create_summary(person)
            if person in self.available_cars:
                cars_summary += f'\n{p_summary}'
            else:
                msg += f'\n{p_summary}'

        if cars_summary:
            msg += f'\nCars:{cars_summary}'
        return msg

    def create_members(self) -> str:
        """Create a list of all group members"""
        out = ""
        for member in self.name2num:
            out += f'{member}: {self.name2num[member]}\n'
        return out

    def add_to_balance(self, name: str):
        """Add a new user balance"""
        new_balance = {}
        for member in self.balance:
            self.balance[member][name] = 0
            new_balance[member] = 0
        self.balance[name] = new_balance

    def remove_from_balance(self, name: str):
        """Remove a user balance"""
        del self.balance[name]
        for member in self.balance:
            del self.balance[member][name]

    def expand_aliases(self,
                       users: list[str],
                       exclude_users=None) -> list[str]:
        """Expand any alias

        Any user name in exclude_users will not be expanded. This is usefull
        when using aliases with commands implicitly adding a user like !split.
        """
        ret = []
        for user in users:
            if not user in self.aliases and user != 'all':
                ret.append(user)
                continue

            expanded_users = []
            if user in self.aliases:
                expanded_users += self.aliases[user]
            else:
                expanded_users += list(self.name2num.keys())

            ret.extend([
                u for u in expanded_users
                if not exclude_users or u not in exclude_users
            ])

        return ret

    @classmethod
    def create_help(cls) -> str:
        """Return a help message explaining how to use geldschieberbot"""
        return """
    Usage: send a message starting with '!' followed by a command
    Commands:
    ls | list - print all registered members
    help - print this help message
    reg name - register the sender with the name: name
    sum [name] - print summary of specific users
    full-sum - print summary of all users

    alias - list registered aliases
    alias name person [persons] - create an alias for one or multiple persons
    alias remove name - remove an alias

    split amount person [persons] - split amount between the sender and persons
    teil amount person [persons] - split amount between the sender and persons

    schieb amount recipient [recipients ...] - give money to one or more recipients
    gib amount recipient [recipients ...] - give money to one or more recipients
    zieh amount donor [donor ...] - get money from one or more donors
    nimm amount donor [donor ...] - get money from one or more donors

    transfer amount source destination - transfer amount of your balance from source to destination

    cars [cmd] - interact with the available cars
    cars [list | ls] - list available cars and their service charge
    cars add car-name service-charge - add new car
    cars new car-name service-charge - add new car
    cars remove car-name - remove a car
    cars pay car-name amount - pay a bill for the specified car

    tanken amount [person] [car] [info] - calculate fuel costs, service charge and add them to the person's and car's balance respectively

    fuck [change] - rewind last or specific change
    list-changes [n] [first] - list the last n changes starting at first

    export-state - send the state file

    weekly name cmd -  repeat cmd each week
    monthly name cmd - repeat cmd each month
    yearly name cmd - repeat cmd each year
    cancel name - stop repeating cmd

    Happy Geldschieben!
    """

    def register(self, msg: MessageContext) -> dict[str, str]:
        """Register a new user"""
        if len(msg.args) != 2:
            return {'err': f'not in form "{msg.args[0]} name"'}
        name = msg.args[1]

        try:
            to_cent(name)
            return {'err': 'pure numerical names are not allowed'}
        except (ValueError, TypeError):
            pass

        if name in self.name2num:
            return {'err': f'{name} already registered'}

        if msg.sender:
            return {'err': f'you are already registered as {msg.sender}'}

        self.num2name[msg.sender_number] = name
        self.name2num[name] = msg.sender_number

        self.add_to_balance(name)

        # add changes list
        self.changes[name] = []
        return {'msg': f'Happy geldschiebing {name}!'}

    def summary(self, msg: MessageContext) -> dict[str, str]:
        """Print summary for one or multiple balances"""
        if len(msg.args) == 1:
            if not msg.sender:
                return {'err': 'You must register first to print your summary'}
            return {'msg': f'Summary:\n{self.create_summary(msg.sender)}'}

        out = "Summary:\n"
        for name in self.expand_aliases(msg.args[1:]):
            if name in self.name2num or name in self.available_cars:
                out += self.create_summary(name) + "\n"
            else:
                return {'err': f'name "{name}" not registered'}
        return {'msg': out}

    def full_summary(self, msg: MessageContext) -> dict[str, str]:
        """Print a summary of all balances"""
        if len(msg.args) == 1:
            return {'msg': self.create_total_summary()}

        return {'err': f'{msg.args[0][1:]} takes no arguments'}

    def list_users(self, msg: MessageContext) -> dict[str, str]:  # pylint: disable=unused-argument
        """List all registered users"""
        return {'msg': self.create_members()}

    @classmethod
    def usage(cls, msg: MessageContext) -> dict[str, str]:  # pylint: disable=unused-argument
        """Return the usage"""
        return {'msg': cls.create_help()}

    def split(self, msg: MessageContext) -> dict[str, str]:
        """Split a fixed amount across multiple persons"""
        if not msg.sender:
            return {'err': 'you must register first'}

        if len(msg.args) < 3:
            return {'err': f'not in form "{msg.args[0]} amount [name]+"'}

        try:
            amount = to_cent(msg.args[1])
            persons = msg.args[2:]
        except (ValueError, TypeError):
            # support !split name amount
            if len(msg.args) == 3:
                try:
                    amount = to_cent(msg.args[2])
                    persons = [msg.args[1]]
                except (ValueError, TypeError):
                    return {'err': 'amount must be a positive number'}
            else:
                return {'err': 'amount must be a positive number'}

        recipient = msg.sender
        # exclude the implicit recipient from alias expension
        persons = self.expand_aliases(persons, exclude_users=[recipient])
        # persons + sender
        npersons = len(persons) + 1
        amount_per_person = int(amount / npersons)

        output = f"Split {to_euro(amount)} between {npersons} -> {to_euro(amount_per_person)} each\n"
        modifications: list[Modification] = []
        for person in persons:
            if person in self.name2num:
                if person == recipient:
                    output += (
                        f'{person}, you will be charged multiple times. '
                        'This may not be what you want\n')
                else:
                    modification = self.record(recipient, person,
                                               amount_per_person)
                    if modification:
                        modifications.append(modification)
            else:
                output += f"{person} not known. Please take care manually\n"

        self.may_record_change(recipient,
                               Change(msg.args, modifications, msg.timestamp))

        output += "New Balance:\n"
        output += self.create_summary(recipient)
        return {'msg': output}

    def _transaction(self, initiator: str, recipients: list[str],
                     amount: int) -> tuple[str, list[Modification]]:
        """Record a transaction"""
        transaction_sum = ''

        modifications: list[Modification] = []
        for recipient in recipients:
            modification = self.record(initiator, recipient, amount)
            if modification:
                modifications.append(modification)

            p_balance = self.balance[initiator][recipient]

            transaction_sum += f'{"->" if amount > 0 else "<-"} {recipient} {to_euro(abs(amount))}\n'

        output = ''
        if len(recipients) > 1:
            output += transaction_sum
            output += 'New Balance:\n'
            output += self.create_summary(initiator, recipients)
        else:
            output = f'New Balance: {initiator} {"->" if p_balance > 0 else "<-"} {to_euro(abs(p_balance))} {recipients[0]}\n'
        return output, modifications

    def transaction(self, msg: MessageContext) -> dict[str, str]:
        """Record a transaction received in a message"""
        if len(msg.args) < 3:
            return {
                'err':
                f'not in form "{msg.args[0]} amount recipient [recipient ...]"'
            }

        if not msg.sender:
            return {'err': 'you must register first'}

        if len(msg.args) == 3:
            if msg.args[1] in self.balance or msg.args[1] in self.aliases:
                recipient, _amount = msg.args[1:3]
            elif msg.args[2] in self.balance or msg.args[2] in self.aliases:
                _amount, recipient = msg.args[1:3]
            else:
                return {'err': 'recipient not known'}

            recipients = self.expand_aliases([recipient])
        else:
            _amount, recipients = msg.args[1], msg.args[2:]

        if msg.sender in recipients:
            return {'err': 'you can not transfer money to or from yourself'}

        try:
            amount = to_cent(_amount)
        except (ValueError, TypeError):
            return {'err': 'amount must be a positive number'}

        for recipient in recipients:
            if recipient not in self.balance:
                return {'err': f'recipient "{recipient}" not known'}

        if msg.args[0] in ["!zieh", "!nimm"]:
            amount *= -1

        output, modifications = self._transaction(msg.sender, recipients,
                                                  amount)
        self.may_record_change(msg.sender,
                               Change(msg.args, modifications, msg.timestamp))
        return {'msg': output}

    def _transfer(self, sender: str, source: str, destination: str,
                  amount: int) -> tuple[str, list[Modification]]:
        """Transfer amount from one balance to another"""
        # Sender <- X Source
        output, modifications = self._transaction(sender, [source], -amount)

        # Sender -> X Destination
        out, modification = self._transaction(sender, [destination], amount)
        output += out
        modifications += modification

        # Destination -> X Source
        out, modification = self._transaction(source, [destination], -amount)
        output += out
        modifications += modification

        return output, modifications

    def transfer(self, msg: MessageContext) -> dict[str, str]:
        """Message handler wrapping the transfer function"""
        if len(msg.args) < 4:
            return {
                'err': f'not in form "{msg.args[0]} amount source destination"'
            }

        if not msg.sender:
            return {'err': 'you must register first'}

        try:
            amount_raw = msg.args[1]
            amount_cent = to_cent(amount_raw)
        except (ValueError, TypeError):
            return {'err': 'amount must be a positive number'}

        source, destination = msg.args[2:4]
        if source not in self.balance:
            return {'err': f'source "{source}" not known'}

        if destination not in self.balance:
            return {'err': f'destination "{destination}" not known'}

        out, modifications = self._transfer(msg.sender, source, destination,
                                            amount_cent)
        self.may_record_change(msg.sender,
                               Change(msg.args, modifications, msg.timestamp))
        return {'msg': out}

    def cars(self, msg: MessageContext) -> dict[str, str]:
        """Manage available cars

        List, add, remove or pay a bill for a car.
        """
        # list cars
        if len(msg.args) < 2 or msg.args[1] in ["ls", "list"]:
            if len(self.available_cars) == 0:
                return {'msg': 'No cars registered yet.'}

            ret_msg = ""

            if len(msg.args) > 2:
                cars_to_list = msg.args[2:]
            else:
                cars_to_list = self.available_cars

            for car in cars_to_list:
                if car in self.available_cars:
                    ret_msg += f"{car} - service charge {self.available_cars[car]}ct/km\n"
                    ret_msg += self.create_summary(car) + "\n"
                else:
                    return {'err': f'"{car}" is no available car\n'}

            return {'msg': ret_msg[:-1]}

        # add car
        if msg.args[1] in ["add", "new"]:
            if len(msg.args) < 4:
                return {
                    'err':
                    f'not in form "{msg.args[0]} {msg.args[1]} car-name service-charge"'
                }

            car = msg.args[2]
            if car in self.available_cars:
                return {'err': f'"{car}" already registered'}

            if car in self.balance:
                return {
                    'err':
                    f'A user named "{car}" already exists. Please use a different name for this car'
                }

            try:
                service_charge = to_cent(msg.args[3])
            except (ValueError, TypeError):
                return {'err': 'service-charge must be a positive number'}

            self.available_cars[car] = service_charge
            self.add_to_balance(car)
            return {'msg': f'added "{car}" as an available car'}

        # remove car
        if msg.args[1] in ["rm", "remove"]:
            if len(msg.args) < 3:
                return {
                    'err':
                    f'not in form "{msg.args[0]} {msg.args[1]} car-name"'
                }

            car = msg.args[2]
            if car not in self.available_cars:
                return {'err': f'A car with the name "{car}" does not exists'}

            del self.available_cars[car]
            self.remove_from_balance(car)
            return {'msg': f'removed "{car}" from the available cars'}

        # pay bill
        if msg.args[1] in ["pay"]:
            if len(msg.args) < 4:
                return {
                    'err':
                    f'not in form "{msg.args[0]} {msg.args[1]} car-name amount"'
                }

            if not msg.sender:
                return {'err': 'you must register first'}

            car = msg.args[2]
            # print(self.state, self.available_cars)
            if car not in self.available_cars:
                return {'err': f'car "{car}" not known'}

            try:
                amount = to_cent(msg.args[3])
                amount_euro = to_euro(amount)
            except (ValueError, TypeError):
                return {'err': 'amount must be a positive number'}

            output = ""

            total_available_charge = 0
            available_charges = []
            for person in self.balance[car]:
                _amount = self.balance[car][person]
                if _amount < 0:
                    total_available_charge -= _amount
                    available_charges.append((person, _amount))

            proportion = -1.0
            if amount < total_available_charge:
                proportion = -1 * (amount / total_available_charge)

            _, modifications = self._transaction(msg.sender, [car], amount)
            output += f"{msg.sender} payed {amount_euro}\n"

            # transfer money
            output += f"Transferring {proportion * -100:.2f}% of everybody's charges\n"
            for person, _amount in available_charges:
                if person == msg.sender or _amount >= 0:
                    continue

                to_move = int(_amount * proportion)
                to_move_euro = to_euro(to_move)
                _, modification = self._transfer(msg.sender, car, person,
                                                 to_move)
                modifications += modification

                output += f'Transfer {to_move_euro} from {person} to {msg.sender}\n'

            output += "New Balances:\n"
            output += self.create_summary(msg.sender) + "\n"
            output += self.create_summary(car)

            self.may_record_change(
                msg.sender, Change(msg.args, modifications, msg.timestamp))

            return {'msg': output}

        return {'err': f'unknown car subcommand "{msg.args[1]}".'}

    def parse_tank_bill(self, _drives: list[str], fuel_charge: int,
                        service_charge: int):
        """Parse and distribute the tank bill across all passangers"""
        passengers: dict[str, dict[str, int]] = {}
        distance = 0.
        drives = [d.split(' ') for d in _drives]

        for drive in drives:
            try:
                drive_distance = int(drive[0])
            except (IndexError, ValueError):
                return None, "Lines have to start with the driven distance!"

            # calculate overall distance
            distance += drive_distance

            # collect distances per passenger
            drive_passengers = self.expand_aliases(drive[1:])
            for passenger in drive_passengers:
                passengers.setdefault(passenger, {
                    "distance": 0,
                    "cost": 0,
                    "service_charge": 0
                })["distance"] += drive_distance

        # calculate cost per kilometer
        if distance <= 0:
            return None, "Driven distance must be greater than 0!"

        c_km = fuel_charge / distance

        for drive in drives:
            drive_distance = int(drive[0])
            drive_passengers = self.expand_aliases(drive[1:])
            # calculate cost per drive split among passengers
            c_d = int(c_km * drive_distance / (len(drive_passengers)))
            sc_d = int(service_charge * drive_distance /
                       (len(drive_passengers)))
            for passenger in drive_passengers:
                passengers[passenger]["cost"] += c_d
                passengers[passenger]["service_charge"] += sc_d

        return passengers, None

    def tanken(self, msg: MessageContext) -> dict[str, str]:
        """Split a tank across all passengers"""
        if len(msg.args) < 2:
            return {
                'err':
                f'not in form "{msg.args[0]} amount [person] [car] [info]"'
            }
        try:
            amount = to_cent(msg.args[1])
        except (ValueError, TypeError):
            return {'err': 'amount must be a number'}

        # find recipient
        if len(msg.args) > 2 and msg.args[2] in self.name2num:
            recipient = msg.args[2]
        elif msg.sender:
            recipient = msg.sender
        else:
            return {'err': 'recipient unknown'}

        # find car
        car = None
        if len(msg.args) > 2 and msg.args[2] in self.available_cars:
            car = msg.args[2]
        elif len(msg.args) > 3 and msg.args[3] in self.available_cars:
            car = msg.args[3]

        service_charge = self.available_cars.get(car, 0)

        parts, err = self.parse_tank_bill(msg.body[1:], amount, service_charge)
        if err:
            return {'err': err}

        assert parts

        output = ""
        modifications: list[Modification] = []
        for pname, values in parts.items():
            output += f'{pname}: {values["distance"]}km = fuel: {to_euro(values["cost"])}, service charge: {to_euro(values["service_charge"])}\n'
            # record service charges
            if pname not in self.name2num:
                output += f'{pname} not known.'
            if car:
                person_to_charge = pname
                if pname not in self.name2num:
                    person_to_charge = recipient
                    output += f" {recipient} held accountable for service charge."

                modification = self.record(car, person_to_charge,
                                           values["service_charge"])
                if modification:
                    modifications.append(modification)

            # recipient paid the fuel -> don't charge them
            if pname == recipient:
                continue

            if pname in self.name2num:
                modification = self.record(recipient, pname, values["cost"])
                if modification:
                    modifications.append(modification)
            else:
                output += " Please collect fuel cost manually\n"

        if msg.sender:
            self.may_record_change(
                msg.sender, Change(msg.args, modifications, msg.timestamp))

        output += "New Balance:\n"
        output += self.create_summary(recipient)
        if car:
            output += "\nCar "
            output += self.create_summary(car)
        return {'msg': output}

    def fuck(self, msg: MessageContext) -> dict[str, str]:
        """Rewind past changes"""
        if not msg.sender:
            return {'err': 'you must register first'}

        name = msg.sender

        nchanges = len(self.changes[name])
        if nchanges == 0:
            return {'msg': 'Nothing to rewind'}

        change_to_rewind = -1
        if len(msg.args) >= 2:
            try:
                change_to_rewind = int(msg.args[1]) - 1
            except ValueError:
                return {'err': 'change to rewind must be a number'}

            if change_to_rewind > nchanges:
                return {
                    'err': 'change to rewind is bigger than there are changes'
                }

        # pop last item
        change = self.changes[name].pop(change_to_rewind)

        output = name + ": sorry I fucked up!\nRewinding:\n"
        output += ' '.join(change.cmd) + "\n"
        for mod in change.modifications:
            output += f'{self.reverse(mod).out_string()}\n'

        for cmd_args in change.rewind_cmds:
            ret = self.cmds[cmd_args[0]](MessageContext(
                msg.sender_number, msg.sender, cmd_args, [''.join(cmd_args)],
                msg.timestamp))
            if 'err' in ret:
                output += "ERROR: " + ret['err']
            else:
                output += ret['msg']

        return {'msg': output}

    def list_changes(self, msg: MessageContext) -> dict[str, str]:
        """List changes made by the sender"""
        if not msg.sender:
            return {'err': 'you must register first'}

        changes_to_list = 5
        if len(msg.args) >= 2:
            try:
                changes_to_list = int(msg.args[1])
            except ValueError:
                return {
                    'err': 'the amount of changes to list must be a number'
                }

        nchanges = len(self.changes[msg.sender])
        if nchanges == 0:
            return {'msg': 'Nothing to list'}

        first_to_list = max(nchanges - changes_to_list, 0)

        if len(msg.args) == 3:
            try:
                first_to_list = int(msg.args[2]) - 1
            except ValueError:
                return {'err': 'the first change to list must be a number'}

            if first_to_list > nchanges:
                return {
                    'err':
                    'the first change to list is bigger than there are changes'
                }

        out = ""
        i = 0
        for i, change in enumerate(self.changes[msg.sender]):
            if i < first_to_list:
                continue

            if i >= first_to_list + changes_to_list:
                # i is used to track how many changes we listed
                # This change will not be listed so decrement i before extiting the loop.
                i -= 1
                break

            out += f'Change {i + 1}:\n'
            out += f'\t{" ".join(change.cmd)}\n'
            for mod in change.modifications:
                out += f'\t{mod.in_string()}\n'

        # prepend message header because we want to know how much changes we actually listed
        out = f'Changes from {msg.sender} {first_to_list + 1}-{i + 1}\n' + out

        return {'msg': out}

    def export_state(self, msg: MessageContext) -> dict[str, str]:
        """Send the state file as attachment"""
        if not msg.sender:
            return {'err': 'you must register first'}

        out = f'State from {datetime.now().date().isoformat()}'
        return {'msg': out, 'attachment': self.state_path}

    def schedule(self, msg: MessageContext) -> dict[str, str]:
        """Schedule a command for periodic execution"""
        if not msg.sender:
            return {'err': 'you must register first'}

        if len(msg.args) < 3:
            return {'err': f'not in form "{msg.args[0]} name cmd"'}

        name = msg.args[1]
        cmd = msg.args[2:]

        if not cmd[0] in self.cmds:
            return {
                'err':
                f'the command "{name}" can not be registered because "{cmd[0]}" is unknown'
            }
        initial_commad_msg = MessageContext(msg.sender_number, msg.sender, cmd,
                                            [], msg.timestamp)

        if name in self.scheduled_cmds:
            return {
                'err': f'there is already a scheduled command named "{name}"'
            }

        # Test the command
        saved_dry_run = self.enable_dry_run()
        ret = self.cmds[cmd[0]](initial_commad_msg)
        self.restore_dry_run(saved_dry_run)

        if 'err' in ret:
            return {
                'err':
                f'the command "{name}" failed with "{ret["err"]}" and will not be recorded'
            }

        scheduled_cmd = {
            "schedule": msg.args[0][1:],
            "last_time": None,
            "sender": msg.sender,
            "cmd": cmd
        }

        self.scheduled_cmds[name] = scheduled_cmd
        output = f'Recorded the {msg.args[0][1:]} command "{" ".join(cmd)}" as "{name}"\n'
        output += f'Running {scheduled_cmd["schedule"]} command {name} for {msg.sender} initially\n'

        previous_change_count = len(self.changes[msg.sender])
        ret = self.cmds[cmd[0]](initial_commad_msg)
        if 'err' in ret:
            output += 'ERROR: ' + ret['err']
        else:
            output += ret['msg']

        # The executed command did not create a new Change
        # -> create a dummy change to cancel the scheduled command
        if previous_change_count == len(self.changes[msg.sender]):
            self.changes[msg.sender].append(Change(cmd, [], msg.timestamp))
        self.changes[msg.sender][-1].rewind_cmds.append(["cancel", name])

        now = datetime.now().date()
        scheduled_cmd["last_time"] = now.isoformat()

        return {'msg': output}

    def cancel(self, msg: MessageContext) -> dict[str, str]:
        """Cancel a previously scheduled command"""
        cmd_name = msg.args[1]
        if not cmd_name in self.scheduled_cmds:
            return {'err': f'"{cmd_name}" is not a scheduled command'}
        cmd = self.scheduled_cmds[cmd_name]

        if not cmd["sender"] == msg.sender:
            return {'err': 'only the original creator can cancel this command'}

        del self.scheduled_cmds[cmd_name]
        return {'msg': f'Cancelled the {cmd["schedule"]} cmd "{cmd_name}"'}

    @classmethod
    def thanks(cls, msg: MessageContext) -> dict[str, str]:
        """Thank geldschieberbot for its loyal service"""
        sender_name = msg.sender or msg.sender_number
        out = f'You are welcome. It is a pleasure to work with you, {sender_name}.'
        nick = None if len(msg.args) == 1 else msg.args[1]
        if nick:
            out = f"{out}\nBut don't call me {nick}."

        return {'msg': out}

    def alias(self, msg: MessageContext) -> dict[str, str]:
        """List or create aliases"""

        if len(msg.args) == 1:
            out = ''
            for alias, users in self.aliases.items():
                out += f'\n\t{alias}: {" ".join(users)}'
            return {'msg': f'Aliases:\n\tall: {" ".join(self.name2num)}{out}'}

        if len(msg.args) == 2:
            return {'err': 'Not a valid alias command'}

        if msg.args[1] == 'remove':
            alias = msg.args[2]
            if alias not in self.aliases:
                return {'err': f'Alias "{alias}" not registered'}

            del self.aliases[alias]
            return {'msg': f'Alias "{alias}" removed'}

        # create a new alias
        alias = msg.args[1]
        if alias in self.aliases or alias == 'all':
            return {'err': f'Alias "{alias}" is already registered'}

        if alias in self.name2num:
            return {'err': f'A user "{alias}" is already registered'}

        try:
            to_cent(alias)
            return {'err': 'Pure numerical aliases are not allowed'}
        except (ValueError, TypeError):
            pass

        users = msg.args[2:]
        for user in users:
            if user not in self.name2num:
                return {'err': f'User {user} is not registered'}

        self.aliases[alias] = users
        return {'msg': f'New alias "{alias}" registered'}

    def __init__(self, state_path, group_id, dry_run=False):
        """Create a new Geldschieberbot"""
        self.state_path = state_path
        self.group_id = group_id

        self.dry_run = dry_run  # Run without changing the stored state
        self.record_changes = True  # Should changes be recorded

        self.load_state()

        # Command dispatch table
        self.cmds = {
            'reg': self.register,
            'register': self.register,
            'alias': self.alias,
            'sum': self.summary,
            'summary': self.summary,
            'balance': self.summary,
            'full-sum': self.full_summary,
            'full-summary': self.full_summary,
            'ls': self.list_users,
            'list': self.list_users,
            'split': self.split,
            'teil': self.split,
            'schieb': self.transaction,
            'gib': self.transaction,
            'zieh': self.transaction,
            'nimm': self.transaction,
            'help': self.usage,
            'usage': self.usage,
            'transfer': self.transfer,
            'cars': self.cars,
            'tanken': self.tanken,
            'fuck': self.fuck,
            'rewind': self.fuck,
            'undo': self.fuck,
            'list-changes': self.list_changes,
            'export-state': self.export_state,
            'weekly': self.schedule,
            'monthly': self.schedule,
            'yearly': self.schedule,
            'cancel': self.cancel,
            'thanks': self.thanks,
        }

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        if not exc_type:
            self.save_state()

    def enable_dry_run(self) -> bool:
        """Enable dry run"""
        old_value = self.dry_run
        self.dry_run = True
        return old_value

    def restore_dry_run(self, old_value: bool):
        """Restore dry run setting to old value"""
        self.dry_run = old_value

    def disable_record_changes(self) -> bool:
        """Disable change recording and return previous value"""
        old_value = self.record_changes
        self.record_changes = False
        return old_value

    def restore_record_changes(self, old_value: bool):
        """Restore record change setting to old value"""
        self.record_changes = old_value

    def may_record_change(self, user: str, change: Change):
        """Record a change for a user if change recording is enabled"""
        if self.record_changes and not self.dry_run:
            self.changes[user].append(change)

    def handle(self, envelope: dict) -> list[Reply]:
        """Parse and respond to a message"""
        sender_number = envelope["source"]
        if not "dataMessage" in envelope or not envelope[
                "dataMessage"] or not envelope["dataMessage"]["message"]:
            return []

        message = envelope["dataMessage"]
        if message["groupInfo"] and message["groupInfo"][
                "groupId"] != self.group_id:
            return []

        body = [l.strip() for l in message["message"].lower().splitlines()]

        if len(body) == 0 or not body[0].startswith('!'):
            return []

        replies: list[Reply] = []

        args = body[0].split(' ')
        msg_context = MessageContext(sender_number,
                                     self.num2name.get(sender_number, None),
                                     args, body, message['timestamp'])
        cmd = args[0][1:]
        if cmd in self.cmds:
            ret = self.cmds[cmd](msg_context)
            if 'err' in ret:
                replies.append(Reply(f'ERROR: {ret["err"]}', None))
            else:
                if not 'msg' in ret:
                    print(ret)
                replies.append(Reply(ret['msg'], ret.get('attachment', None)))
        else:
            replies.append(
                Reply(
                    'ERROR: unknown cmd. Enter !help for a list of commands.',
                    None))

        self.save_state()
        return replies

    def run_scheduled_cmds(self) -> list[Reply]:
        """Progress the scheduled commands"""
        replies: list[Reply] = []
        self.record_changes = False

        now = datetime.now().date()
        week_delta = timedelta(days=7)
        for name, scheduled_cmd in self.scheduled_cmds.items():

            last_time, interval = scheduled_cmd["last_time"], scheduled_cmd[
                "schedule"]
            if hasattr(date, "fromisoformat"):
                last_time = date.fromisoformat(last_time)
            else:
                last_time = date(*map(int, last_time.split("-")))

            d = last_time
            while True:
                if interval == "yearly":
                    d = date(d.year + 1, d.month, d.day)
                elif interval == "monthly":
                    if d.day > 28:
                        d = date(d.year, d.month, 28)
                    if d.month == 12:
                        d = date(d.year + 1, 1, d.day)
                    else:
                        d = date(d.year, d.month + 1, d.day)
                else:
                    d = d + week_delta

                if d <= now:
                    cmd_args, runas = scheduled_cmd['cmd'], scheduled_cmd[
                        'sender']
                    runas_name = self.num2name.get(runas, runas)
                    out = f'Running {interval} command {name} for {runas_name} triggered on {d.isoformat()}'
                    # TODO: use d as timestamp
                    cmd_ctx = MessageContext(runas, runas_name, cmd_args, [],
                                             '')
                    ret = self.cmds[cmd_args[0]](cmd_ctx)

                    if 'err' in ret:
                        replies.append(
                            Reply(f'{out}\nERROR: {ret["err"]}', None))
                    else:
                        replies.append(
                            Reply(f'{out}\n{ret["msg"]}',
                                  ret.get('attachment', None)))

                    scheduled_cmd["last_time"] = d.isoformat()
                else:
                    break
        return replies