function account_series_map(accounts, tabulation)
	map = {}

	for i=1,100 do -- we're not messing with accounts more than 100 levels deep
		all_handled = true
		for id, acct in pairs(accounts) do
			if not map[id] then
				all_handled = false
				if not acct.parent then
					map[id] = tabulation:series(acct.name)
				elseif map[acct.parent.accountid] then
					map[id] = map[acct.parent.accountid]:series(acct.name)
				end
			end
		end
		if all_handled then
			return map
		end
	end

	error("Accounts nested (at least) 100 levels deep")
end

function generate()
	year = date.now().year
	account_type = account.Expense

	accounts = get_accounts()
	r = tabulation.new(12)
	r:title(year .. " Monthly Expenses")
	series_map = account_series_map(accounts, r)

	for month=1,12 do
		begin_date = date.new(year, month, 1)
		end_date = date.new(year, month+1, 1)

		r:label(month, tostring(begin_date))

		for id, acct in pairs(accounts) do
			series = series_map[id]
			if acct.type == account_type then
				balance = acct:balance(begin_date, end_date)
				series:value(month, balance.amount)
			end
		end
	end

	return r
end