First sketch of budgeting module

app/models/transfer_matcher.rb

@@ -0,0 +1,36 @@
+class TransferMatcher
+  attr_reader :family
+
+  def initialize(family)
+    @family = family
+  end
+
+  def match!(transaction_entries)
+    ActiveRecord::Base.transaction do
+      transaction_entries.each do |entry|
+        entry.entryable.update!(category_id: transfer_category.id)
+      end
+
+      create_transfers(transaction_entries)
+    end
+  end
+
+  private
+    def create_transfers(entries)
+      matches = entries.to_a.combination(2).select do |entry1, entry2|
+        entry1.amount == -entry2.amount &&
+        entry1.account_id != entry2.account_id &&
+        (entry1.date - entry2.date).abs <= 4
+      end
+
+      matches.each do |match|
+        Account::Transfer.create!(entries: match)
+      end
+    end
+
+    def transfer_category
+      @transfer_category ||= family.categories.find_or_create_by!(classification: "transfer") do |category|
+        category.name = "Transfer"
+      end
+    end
+end