Add feature to split transaction into balanced pairs

Might be useful later for cash basis

ledger_pyreport/__init__.py

@@ -309,6 +309,7 @@ def transaction():
 	uuid = flask.request.args['uuid']
 	cash = flask.request.args.get('cash', False)
 	commodity = flask.request.args.get('commodity', False)
+	split = flask.request.args.get('split', False)
 	
 	# General ledger
 	l = ledger.raw_transactions_at_date(None)
@@ -320,15 +321,20 @@ def transaction():
 	
 	transaction = next((t for t in l.transactions if str(t.uuid) == uuid))
 	
+	if split:
+		postings = transaction.split(report_commodity)
+		transaction = Transaction(l, transaction.id, transaction.date, transaction.description, transaction.code, transaction.uuid)
+		transaction.postings = [p for r in postings for p in r]
+	
 	if commodity:
 		total_dr = sum((p.amount for p in transaction.postings if p.amount > 0), Balance()).clean()
 		total_cr = sum((p.amount for p in transaction.postings if p.amount < 0), Balance()).clean()
 		totals = itertools.zip_longest(total_dr.amounts, total_cr.amounts)
-		return flask.render_template('transaction_commodity.html', ledger=l, transaction=transaction, totals=totals, total_dr=total_dr.exchange(report_commodity, True), total_cr=total_cr.exchange(report_commodity, True), report_commodity=report_commodity, cash=cash, date=date, pstart=pstart)
+		return flask.render_template('transaction_commodity.html', ledger=l, transaction=transaction, totals=totals, total_dr=total_dr.exchange(report_commodity, True), total_cr=total_cr.exchange(report_commodity, True), report_commodity=report_commodity, cash=cash, split=split, date=date, pstart=pstart)
 	else:
 		total_dr = sum((p.amount for p in transaction.postings if p.amount > 0), Balance()).exchange(report_commodity, True)
 		total_cr = sum((p.amount for p in transaction.postings if p.amount < 0), Balance()).exchange(report_commodity, True)
-		return flask.render_template('transaction.html', ledger=l, transaction=transaction, total_dr=total_dr, total_cr=total_cr, report_commodity=report_commodity, cash=cash, date=date, pstart=pstart)
+		return flask.render_template('transaction.html', ledger=l, transaction=transaction, total_dr=total_dr, total_cr=total_cr, report_commodity=report_commodity, cash=cash, split=split, date=date, pstart=pstart)
 
 # Template filters
 

ledger_pyreport/jinja2/transaction.html

@@ -22,7 +22,8 @@
 
 {% block links %}
 	{{ super() }}
-	<li><a href="/transaction?{{ {'date': date.strftime('%Y-%m-%d'), 'pstart': pstart.strftime('%Y-%m-%d'), 'uuid': transaction.uuid, 'cash': 'on' if cash else '', 'commodity': 'on'}|urlencode }}">Show commodity detail</a></li>
+	<li><a href="/transaction?{{ {'date': date.strftime('%Y-%m-%d'), 'pstart': pstart.strftime('%Y-%m-%d'), 'uuid': transaction.uuid, 'cash': 'on' if cash else '', 'commodity': 'on', 'split': 'on' if split else ''}|urlencode }}">Show commodity detail</a></li>
+	{% if not split %}<li><a href="/transaction?{{ {'date': date.strftime('%Y-%m-%d'), 'pstart': pstart.strftime('%Y-%m-%d'), 'uuid': transaction.uuid, 'cash': 'on' if cash else '', 'split': 'on'}|urlencode }}">Balance postings</a></li>{% endif %}
 {% endblock %}
 
 {% block report %}

ledger_pyreport/jinja2/transaction_commodity.html

@@ -20,6 +20,11 @@
 
 {% block title %}{{ transaction.description }}{% endblock %}
 
+{% block links %}
+	{{ super() }}
+	{% if not split %}<li><a href="/transaction?{{ {'date': date.strftime('%Y-%m-%d'), 'pstart': pstart.strftime('%Y-%m-%d'), 'uuid': transaction.uuid, 'cash': 'on' if cash else '', 'commodity': 'on', 'split': 'on'}|urlencode }}">Balance postings</a></li>{% endif %}
+{% endblock %}
+
 {% block report %}
 	<h1 style="margin-bottom: 1em;">Transaction</h1>
 	

ledger_pyreport/model.py

@@ -20,6 +20,7 @@ from decimal import Decimal
 from enum import Enum
 import functools
 import itertools
+import math
 
 class Ledger:
 	def __init__(self, date):
@@ -104,6 +105,52 @@ class Transaction:
 			result.postings.append(posting)
 		
 		return result
+	
+	def split(self, report_commodity):
+		# Split postings into debit-credit pairs (cost price)
+		unbalanced_postings = [] # List of [posting, base amount in report commodity, amount to balance in report commodity]
+		result = [] # List of balanced pairs
+		
+		for posting in self.postings:
+			base_amount = posting.amount.exchange(report_commodity, True).amount # Used to apportion other commodities
+			amount_to_balance = base_amount
+			
+			# Try to balance against previously unbalanced postings
+			for unbalanced_posting in unbalanced_postings[:]:
+				if math.copysign(1, amount_to_balance) != math.copysign(1, unbalanced_posting[2]):
+					if abs(unbalanced_posting[2]) == abs(amount_to_balance):
+						# Just enough
+						unbalanced_postings.remove(unbalanced_posting)
+						result.append((
+							Posting(self, posting.account, Amount(amount_to_balance / base_amount * posting.amount.amount, posting.amount.commodity), posting.comment, posting.state),
+							Posting(self, unbalanced_posting[0].account, Amount(-amount_to_balance / unbalanced_posting[1] * unbalanced_posting[0].amount.amount, unbalanced_posting[0].amount.commodity), unbalanced_posting[0].comment, unbalanced_posting[0].state)
+						))
+						amount_to_balance = 0
+					elif abs(unbalanced_posting[2]) > abs(amount_to_balance):
+						# Excess - partial balancing of unbalanced posting
+						unbalanced_posting[2] += amount_to_balance
+						result.append((
+							Posting(self, posting.account, Amount(amount_to_balance / base_amount * posting.amount.amount, posting.amount.commodity), posting.comment, posting.state),
+							Posting(self, unbalanced_posting[0].account, Amount(-amount_to_balance / unbalanced_posting[1] * unbalanced_posting[0].amount.amount, unbalanced_posting[0].amount.commodity), unbalanced_posting[0].comment, unbalanced_posting[0].state)
+						))
+						amount_to_balance = 0
+					elif abs(unbalanced_posting[2]) < abs(amount_to_balance):
+						# Not enough - partial balancing of this posting
+						amount_to_balance += unbalanced_posting[2]
+						result.append((
+							Posting(self, posting.account, Amount(-unbalanced_posting[2] / base_amount * posting.amount.amount, posting.amount.commodity), posting.comment, posting.state),
+							Posting(self, unbalanced_posting[0].account, Amount(unbalanced_posting[2] / unbalanced_posting[1] * unbalanced_posting[0].amount.amount, unbalanced_posting[0].amount.commodity), unbalanced_posting[0].comment, unbalanced_posting[0].state)
+						))
+						unbalanced_posting[2] = 0
+			
+			if amount_to_balance:
+				# Unbalanced remainder - add it to the list
+				unbalanced_postings.append([posting, base_amount, amount_to_balance])
+		
+		if unbalanced_postings:
+			raise Exception('Unexpectedly imbalanced transaction')
+		
+		return result
 
 class Posting:
 	class State(Enum):