Clarify backend data pipeline naming concepts (importers, processors, materializers, calculators, and syncers) (#2255)

* Rename MarketDataSyncer to MarketDataImporter

* Materializers

* Importers

* More reference replacements

app/models/holding/materializer.rb

@@ -0,0 +1,60 @@
+# "Materializes" holdings (similar to a DB materialized view, but done at the app level)
+# into a series of records we can easily query and join with other data.
+class Holding::Materializer
+  def initialize(account, strategy:)
+    @account = account
+    @strategy = strategy
+  end
+
+  def materialize_holdings
+    calculate_holdings
+
+    Rails.logger.info("Persisting #{@holdings.size} holdings")
+    persist_holdings
+
+    if strategy == :forward
+      purge_stale_holdings
+    end
+
+    @holdings
+  end
+
+  private
+    attr_reader :account, :strategy
+
+    def calculate_holdings
+      @holdings = calculator.calculate
+    end
+
+    def persist_holdings
+      current_time = Time.now
+
+      account.holdings.upsert_all(
+        @holdings.map { |h| h.attributes
+               .slice("date", "currency", "qty", "price", "amount", "security_id")
+               .merge("account_id" => account.id, "updated_at" => current_time) },
+        unique_by: %i[account_id security_id date currency]
+      )
+    end
+
+    def purge_stale_holdings
+      portfolio_security_ids = account.entries.trades.map { |entry| entry.entryable.security_id }.uniq
+
+      # If there are no securities in the portfolio, delete all holdings
+      if portfolio_security_ids.empty?
+        Rails.logger.info("Clearing all holdings (no securities)")
+        account.holdings.delete_all
+      else
+        deleted_count = account.holdings.delete_by("date < ? OR security_id NOT IN (?)", account.start_date, portfolio_security_ids)
+        Rails.logger.info("Purged #{deleted_count} stale holdings") if deleted_count > 0
+      end
+    end
+
+    def calculator
+      if strategy == :reverse
+        Holding::ReverseCalculator.new(account)
+      else
+        Holding::ForwardCalculator.new(account)
+      end
+    end
+end