#   DrCr: Web-based double-entry bookkeeping framework
#   Copyright (C) 2022–2024  Lee Yingtong Li (RunasSudo)
#
#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU Affero General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program 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 Affero General Public License for more details.
#
#   You should have received a copy of the GNU Affero General Public License
#   along with this program.  If not, see <https://www.gnu.org/licenses/>.

from markupsafe import Markup

from . import AMOUNT_DPS
from .database import db

import functools
from itertools import groupby

class Transaction(db.Model):
	__tablename__ = 'transactions'
	
	id = db.Column(db.Integer, primary_key=True)
	
	dt = db.Column(db.DateTime)
	description = db.Column(db.String)
	
	postings = db.relationship('Posting', back_populates='transaction', cascade='all, delete-orphan')
	
	def __init__(self, dt=None, description=None, postings=None):
		self.dt = dt
		self.description = description
		self.postings = postings or []
	
	def assert_valid(self):
		"""Assert that debits equal credits"""
		
		total_dr = 0
		total_cr = 0
		
		for posting in self.postings:
			amount_cost = posting.amount().as_cost().quantity
			if amount_cost > 0:
				total_dr += amount_cost
			elif amount_cost < 0:
				total_cr -= amount_cost
		
		if total_dr != total_cr:
			raise AssertionError('Transaction debits ({}) and credits ({}) do not balance'.format(total_dr, total_cr))

class Posting(db.Model):
	__tablename__ = 'postings'
	
	id = db.Column(db.Integer, primary_key=True)
	transaction_id = db.Column(db.Integer, db.ForeignKey('transactions.id'))
	
	description = db.Column(db.String)
	account = db.Column(db.String)
	quantity = db.Column(db.Integer)
	commodity = db.Column(db.String)
	
	# Running balance of the account in units of reporting_commodity
	# Only takes into consideration Transactions stored in database, not API-generated ones
	running_balance = db.Column(db.Integer)
	
	transaction = db.relationship('Transaction', back_populates='postings')
	
	def __init__(self, description=None, account=None, quantity=None, commodity=None, running_balance=None):
		self.description = description
		self.account = account
		self.quantity = quantity
		self.commodity = commodity
		self.running_balance = running_balance
	
	def amount(self):
		return Amount(self.quantity, self.commodity)

def queue_invalidate_running_balances(account, dt_from):
	"""
	Invalidate running_balances for Postings in the specified account, from the given date onwards
	
	NOTE: Does not call db.session.commit()
	"""
	
	for posting in db.session.scalars(db.select(Posting).join(Posting.transaction).where((Transaction.dt >= dt_from) & (Posting.account == account))).all():
		posting.running_balance = None

class Amount:
	__slots__ = ['quantity', 'commodity']
	
	def __init__(self, quantity, commodity):
		self.quantity = quantity
		self.commodity = commodity
	
	@classmethod
	def parse(self, amount_str):
		if ' ' not in amount_str:
			# Default commodity
			quantity = round(float(amount_str) * (10**AMOUNT_DPS))
			return Amount(quantity, reporting_commodity())
		
		quantity_str = amount_str[:amount_str.index(' ')]
		quantity = round(float(quantity_str) * (10**AMOUNT_DPS))
		
		commodity = amount_str[amount_str.index(' ')+1:]
		return Amount(quantity, commodity)
	
	def __repr__(self):
		return '<{}: {}>'.format(self.__class__.__name__, self.format('force'))
	
	def __abs__(self):
		return Amount(abs(self.quantity), self.commodity)
	
	def __neg__(self):
		return Amount(-self.quantity, self.commodity)
	
	def __add__(self, other):
		if self.commodity != other.commodity:
			raise ValueError('Cannot add incompatible commodities {} and {}'.format(self.commodity, other.commodity))
		return Amount(self.quantity + other.quantity, self.commodity)
	
	def __sub__(self, other):
		return self + (-other)
	
	def clone(self):
		return Amount(self.quantity, self.commodity)
	
	def format(self, commodity='non_reporting'):
		if commodity not in ('non_reporting', 'force', 'hide'):
			raise ValueError('Invalid commodity reporting option')
		
		if (self.commodity == reporting_commodity() and commodity in ('non_reporting', 'force')) or commodity == 'hide':
			return Markup('{:,.{dps}f}'.format(self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS).replace(',', '&#x202F;'))
		elif len(self.commodity) == 1:
			return Markup('{0}{1:,.{dps}f}'.format(self.commodity, self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS).replace(',', '&#x202F;'))
		else:
			return Markup('{1:,.{dps}f} {0}'.format(self.commodity, self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS).replace(',', '&#x202F;'))
	
	def format_accounting(self, link=None):
		if self.quantity >= 0:
			text = '{:,.{dps}f}'.format(self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS).replace(',', '&#x202F;')
			space = '&nbsp;'
		else:
			text = '({:,.{dps}f})'.format(-self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS).replace(',', '&#x202F;')
			space = ''
		
		if link is None:
			return Markup(text + space)
		else:
			return Markup('<a href="{}" class="hover:text-blue-700 hover:underline">{}</a>{}'.format(link, text, space))
	
	def quantity_string(self):
		if self.commodity == reporting_commodity():
			return '{:.{dps}f}'.format(self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS)
		elif len(self.commodity) == 1:
			return '{0}{1:.{dps}f}'.format(self.commodity, self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS)
		else:
			return '{1:.{dps}f} {0}'.format(self.commodity, self.quantity / (10**AMOUNT_DPS), dps=AMOUNT_DPS)
	
	def as_cost(self):
		"""Convert commodity to reporting currency in cost basis"""
		
		if self.commodity == reporting_commodity():
			return self
		
		# TODO: Refactor this
		
		if '{{' in self.commodity:
			cost = float(self.commodity[self.commodity.index('{{')+2:self.commodity.index('}}')])
			if self.quantity < 0:
				cost = -cost
			return Amount(round(cost * (10**AMOUNT_DPS)), reporting_commodity())
		elif '{' in self.commodity:
			cost = float(self.commodity[self.commodity.index('{')+1:self.commodity.index('}')])
			return Amount(round(cost * self.quantity), reporting_commodity())  # FIXME: Custom reporting currency
		else:
			raise Exception('No cost base for commodity {}'.format(self.commodity))

class Balance:
	"""A collection of Amount's"""
	
	def __init__(self):
		self.amounts = []
	
	def clone(self):
		balance = Balance()
		balance.amounts = [a.clone() for a in self.amounts]
		return balance
	
	def add(self, rhs):
		amount = next((a for a in self.amounts if a.commodity == rhs.commodity), None)
		if amount is None:
			self.amounts.append(rhs)
		else:
			amount.quantity += rhs.quantity
	
	def clean(self):
		"""Remove zero amounts"""
		self.amounts = [a for a in self.amounts if a.quantity != 0]

class TrialBalancer:
	"""
	Applies transactions to generate a trial balance
	"""
	
	def __init__(self):
		self.accounts = {}
	
	@classmethod
	def from_cached(cls, start_date=None, end_date=None):
		"""Obtain a TrialBalancer based on the cached running_balance"""
		
		# First, recompute any running_balance if required
		stale_accounts = db.session.scalars('SELECT DISTINCT account FROM postings WHERE running_balance IS NULL').all()
		if stale_accounts:
			# Get all relevant Postings in database in correct order
			# FIXME: Recompute balances only from the last non-stale balance to be more efficient
			postings = db.session.scalars(db.select(Posting).join(Posting.transaction).where(Posting.account.in_(stale_accounts)).order_by(Transaction.dt, Transaction.id)).all()
			
			accounts = {}
			
			for posting in postings:
				if posting.account not in accounts:
					accounts[posting.account] = Amount(0, reporting_commodity())
				
				# FIXME: Handle commodities better (ensure compatible commodities)
				accounts[posting.account].quantity += posting.amount().as_cost().quantity
				
				posting.running_balance = accounts[posting.account].quantity
			
			db.session.commit()
		
		if start_date is not None:
			result_start_date = cls()
			
			# First SELECT the last applicable dt by account
			# Then, among the transactions with that dt, SELECT the last applicable transaction_id
			# Then extract the running_balance for each account at that transaction_id
			running_balances = db.session.execute('''
				SELECT p3.account, running_balance FROM
				(
					SELECT p1.account, max(p2.transaction_id) AS max_tid FROM
					(
						SELECT account, max(dt) AS max_dt FROM postings JOIN transactions ON postings.transaction_id = transactions.id WHERE dt < :start_date GROUP BY account
					) p1
					JOIN postings p2 ON p1.account = p2.account AND p1.max_dt = transactions.dt JOIN transactions ON p2.transaction_id = transactions.id GROUP BY p2.account
				) p3
				JOIN postings p4 ON p3.account = p4.account AND p3.max_tid = p4.transaction_id
			''', {'start_date': start_date})
			
			for running_balance in running_balances.all():
				result_start_date.accounts[running_balance.account] = Amount(running_balance.running_balance, reporting_commodity())
		
		if end_date is None:
			result = cls()
			
			running_balances = db.session.execute('''
				SELECT p3.account, running_balance FROM
				(
					SELECT p1.account, max(p2.transaction_id) AS max_tid FROM
					(
						SELECT account, max(dt) AS max_dt FROM postings JOIN transactions ON postings.transaction_id = transactions.id GROUP BY account
					) p1
					JOIN postings p2 ON p1.account = p2.account AND p1.max_dt = transactions.dt JOIN transactions ON p2.transaction_id = transactions.id GROUP BY p2.account
				) p3
				JOIN postings p4 ON p3.account = p4.account AND p3.max_tid = p4.transaction_id
			''')
			
			for running_balance in running_balances.all():
				result.accounts[running_balance.account] = Amount(running_balance.running_balance, reporting_commodity())
		
		if end_date is not None:
			result = cls()
			
			running_balances = db.session.execute('''
				SELECT p3.account, running_balance FROM
				(
					SELECT p1.account, max(p2.transaction_id) AS max_tid FROM
					(
						SELECT account, max(dt) AS max_dt FROM postings JOIN transactions ON postings.transaction_id = transactions.id WHERE dt <= :end_date GROUP BY account
					) p1
					JOIN postings p2 ON p1.account = p2.account AND p1.max_dt = transactions.dt JOIN transactions ON p2.transaction_id = transactions.id GROUP BY p2.account
				) p3
				JOIN postings p4 ON p3.account = p4.account AND p3.max_tid = p4.transaction_id
			''', {'end_date': end_date})
			
			for running_balance in running_balances.all():
				result.accounts[running_balance.account] = Amount(running_balance.running_balance, reporting_commodity())
		
		# Subtract balances at start_date from balances at end_date if required
		if start_date is not None:
			for k in result.accounts.keys():
				# If k not in result_start_date, then the balance at start_date was necessarily 0 and subtraction is not required
				if k in result_start_date.accounts:
					result.accounts[k].quantity -= result_start_date.accounts[k].quantity
		
		return result
	
	def apply_transactions(self, transactions):
		for transaction in transactions:
			for posting in transaction.postings:
				if posting.account not in self.accounts:
					self.accounts[posting.account] = Amount(0, reporting_commodity())
				
				# FIXME: Handle commodities better (ensure compatible commodities)
				self.accounts[posting.account].quantity += posting.amount().as_cost().quantity
	
	def transfer_balance(self, source_account, destination_account, description=None):
		"""Transfer the balance of the source account to the destination account"""
		
		# TODO: Keep a record of internal transactions?
		
		if source_account == destination_account:
			# Don't do anything in this case!!
			return
		
		if source_account not in self.accounts:
			return
		
		if destination_account not in self.accounts:
			self.accounts[destination_account] = Amount(0, reporting_commodity())
		
		# FIXME: Handle commodities
		self.accounts[destination_account].quantity += self.accounts[source_account].quantity
		del self.accounts[source_account]

class AccountConfiguration(db.Model):
	__tablename__ = 'account_configurations'
	
	id = db.Column(db.Integer, primary_key=True)
	
	account = db.Column(db.String)
	kind = db.Column(db.String)
	data = db.Column(db.JSON)
	
	@staticmethod
	def get_all():
		account_configurations = db.session.execute(db.select(AccountConfiguration).order_by(AccountConfiguration.account)).scalars()
		account_configurations = {v: list(g) for v, g in groupby(account_configurations, lambda c: c.account)}
		
		return account_configurations
	
	@staticmethod
	def get_all_kinds():
		account_configurations = AccountConfiguration.get_all()
		kinds = {k: [vv.kind for vv in v] for k, v in account_configurations.items()}
		
		return kinds

# ----------------
# Metadata helpers

class Metadata(db.Model):
	__tablename__ = 'metadata'
	
	id = db.Column(db.Integer, primary_key=True)
	
	key = db.Column(db.String)
	value = db.Column(db.String)
	
	@staticmethod
	def get(key):
		return Metadata.query.filter_by(key=key).one().value

@functools.cache  # Very poor performance if result is not cached!
def reporting_commodity():
	"""Get the native reporting commodity"""
	
	return Metadata.get('reporting_commodity')