austax: Implement helper utility to distribute CGT cost adjustment across multiple assets

austax/models.py

@@ -30,7 +30,7 @@ class CGTAsset(Amount):
 		self.cost_adjustments = []
 	
 	def __repr__(self):
-		return '<{}: {} [{:%Y-%m-%d}]>'.format(self.__class__.__name__, self.format(True), self.acquisition_date)
+		return '<{}: {} [{:%Y-%m-%d}]>'.format(self.__class__.__name__, self.format('force'), self.acquisition_date)
 	
 	def commodity_name(self):
 		return self.commodity[:self.commodity.index('{')].strip()

austax/templates/cgt_adjustments.html

@@ -23,6 +23,7 @@
 	
 	<div class="mb-2">
 		<a href="/tax/cgt-adjustments/new" class="btn btn-primary"><i class="bi bi-plus-lg"></i> New CGT adjustment</a>
+		<a href="/tax/cgt-adjustments/multi-new" class="btn btn-outline-primary"><i class="bi bi-plus-lg"></i> Multiple CGT adjustments</a>
 	</div>
 	
 	<table class="table">

austax/templates/cgt_adjustments_multinew.html

@@ -0,0 +1,69 @@
+{#  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/>.
+#}
+
+{% extends 'base.html' %}
+{% block title %}Multiple CGT adjustments{% endblock %}
+
+{% block content %}
+	<h1 class="h2 my-4">Multiple CGT adjustments</h1>
+	
+	<form method="POST">
+		<h2 class="h3">CGT assets</h2>
+		
+		<div class="row mb-2">
+			<label class="col-sm-2 col-form-label">Account</label>
+			<div class="col-sm-10">
+				<input type="text" class="form-control" name="account" value="{{ account or '' }}">
+			</div>
+		</div>
+		<div class="row mb-2">
+			<label class="col-sm-2 col-form-label">Commodity</label>
+			<div class="col-sm-10">
+				<input type="text" class="form-control" name="commodity" value="{{ commodity or '' }}">
+			</div>
+		</div>
+		
+		<div class="alert alert-info" role="alert">
+			The total cost adjustment will be distributed proportionally across all matching CGT assets.
+		</div>
+		
+		<h2 class="h3 mt-4">CGT adjustment</h2>
+		
+		<div class="row mb-2">
+			<label class="col-sm-2 col-form-label">Adjustment date</label>
+			<div class="col-sm-10">
+				<input type="date" class="form-control" name="dt" value="{{ dt or '' }}">
+			</div>
+		</div>
+		<div class="row mb-2">
+			<label class="col-sm-2 col-form-label">Description</label>
+			<div class="col-sm-10">
+				<input type="text" class="form-control" name="description" value="{{ description or '' }}">
+			</div>
+		</div>
+		<div class="row mb-4">
+			<label class="col-sm-2 col-form-label">Total cost adjustment</label>
+			<div class="col-sm-10">
+				<input type="number" class="form-control" name="cost_adjustment" step="0.01" value="{{ cost_adjustment or '' }}">
+			</div>
+		</div>
+		
+		<div class="text-end">
+			<button type="submit" class="btn btn-primary">Save</button>
+		</div>
+	</form>
+{% endblock %}

austax/views.py

@@ -25,10 +25,11 @@ from .models import CGTAsset, CGTCostAdjustment
 from .reports import eofy_date, tax_summary_report
 
 from datetime import datetime
+from math import copysign
 
 @app.route('/tax/cgt-adjustments')
 def cgt_adjustments():
-	adjustments = db.session.scalars(db.select(CGTCostAdjustment)).all()
+	adjustments = db.session.scalars(db.select(CGTCostAdjustment).order_by(CGTCostAdjustment.dt, CGTCostAdjustment.account)).all()
 	return render_plugin_template('austax', 'cgt_adjustments.html', cgt_adjustments=adjustments)
 
 @app.route('/tax/cgt-adjustments/new', methods=['GET', 'POST'])
@@ -71,6 +72,92 @@ def cgt_adjustment_edit():
 	
 	return redirect('/tax/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 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('/tax/cgt-adjustments')
+
 @app.route('/tax/cgt-assets')
 def cgt_assets():
 	# Find all CGT asset accounts