add Value class; keep track of account balances over time

lib/gnucash.rb

@@ -1,6 +1,7 @@
 require "gnucash/account"
 require "gnucash/book"
 require "gnucash/transaction"
+require "gnucash/value"
 require "gnucash/version"
 
 module Gnucash

lib/gnucash/account.rb

@@ -38,6 +38,15 @@ module Gnucash
       @transactions.sort! do |a, b|
         a[:txn].date <=> b[:txn].date
       end
+      balance = Value.new(0)
+      @balances = @transactions.map do |txn_hash|
+        balance += txn_hash[:value]
+        [txn_hash[:txn].date, balance]
+      end
+    end
+
+    def current_balance
+      @balances.last[1] rescue Value.new(0)
     end
   end
 end

lib/gnucash/transaction.rb

@@ -10,13 +10,8 @@ module Gnucash
       @id = node.xpath('trn:id').text
       @date = node.xpath('trn:date-posted/ts:date').text.split(' ').first
       @splits = node.xpath('trn:splits/trn:split').map do |split_node|
-        value_str = split_node.xpath('split:value').text
-        value_parts = value_str.split('/')
-        unless value_parts.size == 2 and value_parts[1] == '100'
-          raise "Unexpected value format: #{value_str.inspect}"
-        end
+        value = Value.new(split_node.xpath('split:value').text)
         account_id = split_node.xpath('split:account').text
-        value = value_parts.first.to_i
         account = @book.find_account_by_id(account_id)
         unless account
           raise "Could not find account with ID #{account_id} for transaction #{@id}"

lib/gnucash/value.rb

@@ -0,0 +1,30 @@
+module Gnucash
+  class Value
+    attr_accessor :val
+    def initialize(val)
+      if val.is_a?(String)
+        if val =~ /^(-?\d+)\/100$/
+          @val = $1.to_i
+        else
+          raise "Unexpected value string: #{val.inspect}"
+        end
+      elsif val.is_a?(Fixnum)
+        @val = val
+      else
+        raise "Unexpected value type: #{val.class}"
+      end
+    end
+
+    def +(other)
+      Value.new(@val + other.val)
+    end
+
+    def -(other)
+      Value.new(@val - other.val)
+    end
+
+    def to_s
+      (@val / 100.0).round(2).to_s
+    end
+  end
+end