Handle missing weekend stock prices in sync process (#1242)

* Don't append missing prices if already known

* Add failing test

* Handle weekend stock prices

* Fix tests and gapfill logic

app/models/gapfiller.rb

@@ -0,0 +1,44 @@
+class Gapfiller
+  attr_reader :series
+
+  def initialize(series, start_date:, end_date:, cache:)
+    @series = series
+    @date_range = start_date..end_date
+    @cache = cache
+  end
+
+  def run
+    gapfilled_records = []
+
+    date_range.each do |date|
+      record = series.find { |r| r.date == date }
+
+      if should_gapfill?(date, record)
+        prev_record = gapfilled_records.find { |r| r.date == date - 1.day }
+
+        if prev_record
+          new_record = create_gapfilled_record(prev_record, date)
+          gapfilled_records << new_record
+        end
+      else
+        gapfilled_records << record if record
+      end
+    end
+
+    gapfilled_records
+  end
+
+  private
+    attr_reader :date_range, :cache
+
+    def should_gapfill?(date, record)
+      date.on_weekend? && record.nil?
+    end
+
+    def create_gapfilled_record(prev_record, date)
+      new_record = prev_record.class.new(prev_record.attributes.except("id", "created_at", "updated_at"))
+      new_record.date = date
+      new_record.save! if cache
+      new_record
+    end
+end