#   DrCr: Web-based double-entry bookkeeping framework
#   Copyright (C) 2022–2023  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 flask import url_for

from .models import AccountConfiguration, Amount, TrialBalancer
from .webapp import all_transactions, eofy_date, sofy_date

from datetime import datetime, timedelta

class Report:
	def __init__(self, title=None, entries=None):
		self.title = title
		self.entries = entries or []
	
	def calculate(self):
		"""Calculate all subtotals, etc."""
		
		for entry in self.entries:
			entry.calculate(self)
	
	def by_id(self, id):
		# TODO: Make more efficient?
		
		for entry in self.entries:
			if entry.id == id:
				return entry
			if isinstance(entry, Section):
				result = entry.by_id(id)
				if result is not None:
					return result
		
		return None

class Section:
	def __init__(self, title=None, entries=None, *, id=None):
		self.title = title
		self.entries = entries or []
		self.id = id
	
	def calculate(self, parent):
		for entry in self.entries:
			entry.calculate(self)
	
	def by_id(self, id):
		# TODO: Make more efficient?
		
		for entry in self.entries:
			if entry.id == id:
				return entry
			if isinstance(entry, Section):
				result = entry.by_id(id)
				if result is not None:
					return result
		
		return None

class Entry:
	def __init__(self, text=None, amount=None, *, id=None, link=None, heading=False, bordered=False):
		self.text = text
		self.amount = amount
		self.id = id
		self.link = link
		self.heading = heading
		self.bordered = bordered
	
	def calculate(self, parent):
		pass

class Subtotal:
	def __init__(self, text=None, *, id=None, visible=True, bordered=False, floor=0):
		self.text = text
		self.id = id
		self.visible = visible
		self.bordered = bordered
		self.floor = floor
		
		self.amount = None
	
	def calculate(self, parent):
		amount = sum(e.amount.quantity for e in parent.entries if isinstance(e, Entry))
		if self.floor:
			amount = (amount // self.floor) * self.floor
		
		self.amount = Amount(amount, '$')

class Calculated(Entry):
	def __init__(self, text=None, calc=None, **kwargs):
		super().__init__(text=text, **kwargs)
		self.calc = calc
		
		self.amount = None
	
	def calculate(self, parent):
		self.amount = self.calc(parent)

class Spacer:
	id = None
	
	def calculate(self, parent):
		pass

def validate_accounts(accounts, account_configurations):
	for account in accounts:
		n = sum(1 for c in account_configurations.get(account, []) if c in ('drcr.asset', 'drcr.liability', 'drcr.equity', 'drcr.income', 'drcr.expense'))
		if n != 1:
			raise Exception('Account "{}" mapped to {} account types (expected 1)'.format(account, n))

def entries_for_kind(account_configurations, accounts, kind, neg=False, floor=0):
	entries = []
	for account_name, amount in accounts.items():
		if kind in account_configurations.get(account_name, []) and amount.quantity != 0:
			if neg:
				amount = -amount
			if floor:
				amount.quantity = (amount.quantity // floor) * floor
			entries.append(Entry(text=account_name, amount=amount, link=url_for('account_transactions', account=account_name)))
	return entries

def balance_sheet_report():
	# Get trial balance
	balancer = TrialBalancer()
	balancer.apply_transactions(all_transactions())
	
	accounts = dict(sorted(balancer.accounts.items()))
	
	# Get account configurations
	account_configurations = AccountConfiguration.get_all_kinds()
	validate_accounts(accounts, account_configurations)
	
	day_before_sofy = sofy_date()
	day_before_sofy -= timedelta(days=1)
	
	report = Report(
		title='Balance sheet',
		entries=[
			Section(
				title='Assets',
				entries=entries_for_kind(account_configurations, accounts, 'drcr.asset') + [Subtotal('Total assets', bordered=True)]
			),
			Spacer(),
			Section(
				title='Liabilities',
				entries=entries_for_kind(account_configurations, accounts, 'drcr.liability', True) + [Subtotal('Total liabilities', bordered=True)]
			),
			Spacer(),
			Section(
				title='Equity',
				entries=entries_for_kind(account_configurations, accounts, 'drcr.equity', True) + [
					Calculated(
						'Current year surplus (deficit)',
						lambda _: income_statement_report().by_id('net_surplus').amount,
						link=url_for('income_statement')
					),
					Calculated(
						'Accumulated surplus (deficit)',
						lambda _: income_statement_report(start_date=datetime.min, end_date=day_before_sofy).by_id('net_surplus').amount
					),
					Subtotal('Total equity', bordered=True)
				]
			),
		]
	)
	report.calculate()
	
	return report

def income_statement_report(start_date=None, end_date=None):
	if start_date is None:
		start_date = sofy_date()
	if end_date is None:
		end_date = eofy_date()
	
	# Get trial balance
	balancer = TrialBalancer()
	balancer.apply_transactions(all_transactions(start_date=start_date, end_date=end_date))
	
	accounts = dict(sorted(balancer.accounts.items()))
	
	# Get account configurations
	account_configurations = AccountConfiguration.get_all_kinds()
	validate_accounts(accounts, account_configurations)
	
	report = Report(
		title='Income statement',
		entries=[
			Section(
				title='Income',
				entries=entries_for_kind(account_configurations, accounts, 'drcr.income', True) + [Subtotal('Total income', id='total_income', bordered=True)]
			),
			Spacer(),
			Section(
				title='Expenses',
				entries=entries_for_kind(account_configurations, accounts, 'drcr.expense') + [Subtotal('Total expenses', id='total_expenses', bordered=True)]
			),
			Spacer(),
			Calculated(
				'Net surplus (deficit)',
				lambda r: r.by_id('total_income').amount - r.by_id('total_expenses').amount,
				id='net_surplus',
				heading=True,
				bordered=True
			)
		]
	)
	report.calculate()
	
	return report