#   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 flask import redirect, render_template, request, url_for

from drcr.models import AccountConfiguration, Amount, Posting, Transaction
from drcr.database import db
from drcr.plugins import render_plugin_template
from drcr.webapp import app, eofy_date

from .models import CGTAsset, CGTCostAdjustment
from .reports import tax_summary_report

from datetime import datetime
from math import copysign

@app.route('/tax/cgt-adjustments')
def cgt_adjustments():
	adjustments = db.select(CGTCostAdjustment).order_by(CGTCostAdjustment.dt.desc(), CGTCostAdjustment.account, CGTCostAdjustment.id.desc())
	if 'account' in request.args:
		adjustments = adjustments.where(CGTCostAdjustment.account == request.args['account'])
	if 'quantity' in request.args:
		adjustments = adjustments.where(CGTCostAdjustment.quantity == request.args['quantity'])
	if 'commodity' in request.args:
		adjustments = adjustments.where(CGTCostAdjustment.commodity == request.args['commodity'])
	if 'acquisition_date' in request.args:
		adjustments = adjustments.where(CGTCostAdjustment.acquisition_date == datetime.strptime(request.args['acquisition_date'], '%Y-%m-%d'))
	
	adjustments = db.session.scalars(adjustments).all()
	return render_plugin_template('austax', 'cgt_adjustments.html', cgt_adjustments=adjustments)

@app.route('/tax/cgt-adjustments/new', methods=['GET', 'POST'])
def cgt_adjustment_new():
	if request.method == 'GET':
		return render_plugin_template('austax', 'cgt_adjustments_edit.html', adjustment=None)
	
	asset = Amount.parse(request.form['asset'])
	adjustment = CGTCostAdjustment(
		quantity=asset.quantity,
		commodity=asset.commodity,
		account=request.form['account'],
		acquisition_date=datetime.strptime(request.form['acquisition_date'], '%Y-%m-%d'),
		dt=datetime.strptime(request.form['dt'], '%Y-%m-%d'),
		description=request.form['description'],
		cost_adjustment=Amount.parse(request.form['cost_adjustment']).quantity
	)
	db.session.add(adjustment)
	db.session.commit()
	
	return redirect(url_for('cgt_adjustments'))

@app.route('/tax/cgt-adjustments/edit', methods=['GET', 'POST'])
def cgt_adjustment_edit():
	if request.method == 'GET':
		return render_plugin_template('austax', 'cgt_adjustments_edit.html', adjustment=db.session.get(CGTCostAdjustment, request.args['id']))
	
	asset = Amount.parse(request.form['asset'])
	adjustment = db.session.get(CGTCostAdjustment, request.args['id'])
	adjustment.quantity = asset.quantity
	adjustment.commodity = asset.commodity
	adjustment.account = request.form['account']
	adjustment.acquisition_date = datetime.strptime(request.form['acquisition_date'], '%Y-%m-%d')
	adjustment.dt = datetime.strptime(request.form['dt'], '%Y-%m-%d')
	adjustment.description = request.form['description']
	adjustment.cost_adjustment = Amount.parse(request.form['cost_adjustment']).quantity
	
	db.session.add(adjustment)
	db.session.commit()
	
	return redirect(url_for('cgt_adjustments'))

@app.route('/tax/cgt-adjustments/multi-new', methods=['GET', 'POST'])
def cgt_adjustment_multinew():
	if request.method == 'GET':
		return render_plugin_template(
			'austax', 'cgt_adjustments_multinew.html',
			account=None,
			commodity=None,
			dt=None,
			description=None,
			cost_adjustment=None
		)
	
	# TODO: Preview mode?
	
	total_adjustment = Amount.parse(request.form['cost_adjustment']).quantity
	
	# Get all postings to the CGT asset account
	cgt_postings = db.session.scalars(
		db.select(Posting)
		.where(Posting.account == request.form['account'])
		.join(Posting.transaction)
		.order_by(Transaction.dt)
	).all()
	
	# Process postings to determine final balances
	assets = []
	
	for posting in cgt_postings:
		if '{' not in posting.commodity and posting.commodity != request.form['commodity']:
			continue
		if '{' in posting.commodity and posting.commodity[:posting.commodity.index('{')].strip() != request.form['commodity']:
			continue
		
		if posting.quantity >= 0:
			assets.append(CGTAsset(posting.quantity, posting.commodity, posting.account, posting.transaction.dt))
		elif posting.quantity < 0:
			asset = next((a for a in assets if a.commodity == posting.commodity and a.account == posting.account), None)
			
			if asset is None:
				raise Exception('Attempted credit {} without preceding debit balance'.quantity(posting.amount()))
			if asset.quantity + posting.quantity < 0:
				raise Exception('Attempted credit {} with insufficient debit balance {}'.quantity(posting.amount(), asset.amount()))
			
			if asset.quantity + posting.quantity != 0:
				raise NotImplementedError('Partial disposal of CGT asset not implemented')
			
			assets.remove(asset)
	
	# Distribute total adjustment across matching assets
	total_quantity = sum(a.quantity for a in assets)
	cgt_adjustments = {}
	
	for asset in assets:
		cgt_adjustments[asset] = total_adjustment * asset.quantity / total_quantity
	
	# Round up as many as required to equal the total adjustment
	rounding_shortfall = abs(total_adjustment) - sum(int(abs(v)) for v in cgt_adjustments.values())
	largest_remainders = [(k, abs(v) - int(abs(v))) for k, v in cgt_adjustments.items()]
	largest_remainders.sort(key=lambda x: x[1], reverse=True)
	for asset, _ in largest_remainders[:rounding_shortfall]:
		adjustment = cgt_adjustments[asset]
		adjustment = copysign(int(abs(adjustment)) + 1, adjustment)
		cgt_adjustments[asset] = adjustment
	
	# Round others down
	for asset, adjustment in cgt_adjustments.items():
		cgt_adjustments[asset] = copysign(int(abs(adjustment)), adjustment)
	
	# Sanity check
	assert sum(v for v in cgt_adjustments.values()) == total_adjustment
	
	# Add adjustments
	for asset, adjustment in cgt_adjustments.items():
		adjustment = CGTCostAdjustment(
			quantity=asset.quantity,
			commodity=asset.commodity,
			account=asset.account,
			acquisition_date=asset.acquisition_date,
			dt=datetime.strptime(request.form['dt'], '%Y-%m-%d'),
			description=request.form['description'],
			cost_adjustment=adjustment
		)
		db.session.add(adjustment)
	
	db.session.commit()
	
	return redirect(url_for('cgt_adjustments'))

@app.route('/tax/cgt-assets')
def cgt_assets():
	# Find all CGT asset accounts
	cgt_accounts = []
	account_configurations = AccountConfiguration.get_all_kinds()
	for account_name, kinds in account_configurations.items():
		if 'austax.cgtasset' in kinds:
			cgt_accounts.append(account_name)
	
	# Get all postings to CGT asset accounts
	cgt_postings = db.session.scalars(
		db.select(Posting)
		.where(Posting.account.in_(cgt_accounts))
		.join(Posting.transaction)
		.order_by(Transaction.dt)
	).all()
	
	# Process postings to determine final balances
	assets = []
	
	for posting in cgt_postings:
		if posting.commodity == '$':
			# FIXME: Detect this better
			continue
		
		if posting.quantity >= 0:
			assets.append(CGTAsset(posting.quantity, posting.commodity, posting.account, posting.transaction.dt))
		elif posting.quantity < 0:
			asset = next((a for a in assets if a.commodity == posting.commodity and a.account == posting.account), None)
			
			if asset is None:
				raise Exception('Attempted credit {} without preceding debit balance'.format(posting.amount()))
			if asset.quantity + posting.quantity < 0:
				raise Exception('Attempted credit {} with insufficient debit balance {}'.format(posting.amount(), asset.amount()))
			
			if asset.quantity + posting.quantity != 0:
				raise NotImplementedError('Partial disposal of CGT asset not implemented')
			
			asset.disposal_date = posting.transaction.dt
			
			# Calculate disposal value by searching for matching asset postings
			asset.disposal_value = Amount(0, '$')
			for other_posting in posting.transaction.postings:
				if posting != other_posting and 'drcr.asset' in account_configurations.get(other_posting.account, []):
					asset.disposal_value.quantity += other_posting.amount().as_cost().quantity
	
	# Process CGT adjustments
	for cost_adjustment in db.session.scalars(db.select(CGTCostAdjustment)).all():
		asset = next((a for a in assets if a.quantity == cost_adjustment.quantity and a.commodity == cost_adjustment.commodity and a.account == cost_adjustment.account and a.acquisition_date == cost_adjustment.acquisition_date), None)
		
		if asset is None:
			raise Exception('No matching CGT asset for {}'.format(repr(cost_adjustment.asset())))
		
		asset.cost_adjustments.append(cost_adjustment)
	
	return render_plugin_template('austax', 'cgt_assets.html', assets=assets, eofy_date=eofy_date())

@app.route('/tax/summary')
def tax_summary():
	report = tax_summary_report()
	return render_template('report.html', report=report)