Stock imports (#1363)

* Initial pass

* Marketstack data provider

* Marketstack data provider

* Refactor a bit

app/models/security/importer.rb

@@ -0,0 +1,27 @@
+class Security::Importer
+  def initialize(provider, stock_exchange = nil)
+    @provider = provider
+    @stock_exchange = stock_exchange
+  end
+
+  def import
+    securities = @provider.fetch_tickers(exchange_mic: @stock_exchange)&.tickers
+
+    stock_exchanges = StockExchange.where(mic: securities.map { |s| s[:exchange] }).index_by(&:mic)
+    existing_securities = Security.where(ticker: securities.map { |s| s[:symbol] }, stock_exchange_id: stock_exchanges.values.map(&:id)).pluck(:ticker, :stock_exchange_id).to_set
+
+    securities_to_create = securities.map do |security|
+      stock_exchange_id = stock_exchanges[security[:exchange]]&.id
+      next if existing_securities.include?([ security[:symbol], stock_exchange_id ])
+
+      {
+        name: security[:name],
+        ticker: security[:symbol],
+        stock_exchange_id: stock_exchange_id,
+        country_code: security[:country_code]
+      }
+    end.compact
+
+    Security.insert_all(securities_to_create) unless securities_to_create.empty?
+  end
+end