Stock imports (#1363)

* Initial pass

* Marketstack data provider

* Marketstack data provider

* Refactor a bit

app/models/provider/marketstack.rb

@@ -0,0 +1,119 @@
+class Provider::Marketstack
+  include Retryable
+
+  def initialize(api_key)
+    @api_key = api_key
+  end
+
+  def fetch_security_prices(ticker:, start_date:, end_date:)
+    prices = paginate("#{base_url}/eod", {
+      symbols: ticker,
+      date_from: start_date.to_s,
+      date_to: end_date.to_s
+    }) do |body|
+      body.dig("data").map do |price|
+        {
+          date: price["date"],
+          price: price["close"]&.to_f,
+          currency: "USD"
+        }
+      end
+    end
+
+    SecurityPriceResponse.new(
+      prices: prices,
+      success?: true,
+      raw_response: prices.to_json
+    )
+  rescue StandardError => error
+    SecurityPriceResponse.new(
+      success?: false,
+      error: error,
+      raw_response: error
+    )
+  end
+
+  def fetch_tickers(exchange_mic: nil)
+    url = exchange_mic ? "#{base_url}/tickers?exchange=#{exchange_mic}" : "#{base_url}/tickers"
+    tickers = paginate(url) do |body|
+      body.dig("data").map do |ticker|
+        {
+          name: ticker["name"],
+          symbol: ticker["symbol"],
+          exchange: exchange_mic || ticker.dig("stock_exchange", "mic"),
+          country_code: ticker.dig("stock_exchange", "country_code")
+        }
+      end
+    end
+
+    TickerResponse.new(
+      tickers: tickers,
+      success?: true,
+      raw_response: tickers.to_json
+    )
+  rescue StandardError => error
+    TickerResponse.new(
+      success?: false,
+      error: error,
+      raw_response: error
+    )
+  end
+
+  private
+
+    attr_reader :api_key
+
+    SecurityPriceResponse = Struct.new(:prices, :success?, :error, :raw_response, keyword_init: true)
+    TickerResponse = Struct.new(:tickers, :success?, :error, :raw_response, keyword_init: true)
+
+    def base_url
+      "https://api.marketstack.com/v1"
+    end
+
+    def client
+      @client ||= Faraday.new(url: base_url) do |faraday|
+        faraday.params["access_key"] = api_key
+      end
+    end
+
+    def build_error(response)
+      Provider::Base::ProviderError.new(<<~ERROR)
+        Failed to fetch data from #{self.class}
+          Status: #{response.status}
+          Body: #{response.body.inspect}
+      ERROR
+    end
+
+    def fetch_page(url, page, params = {})
+      client.get(url) do |req|
+        params.each { |k, v| req.params[k.to_s] = v.to_s }
+        req.params["offset"] = (page - 1) * 100 # Marketstack uses offset-based pagination
+        req.params["limit"] = 10000 # Maximum allowed by Marketstack
+      end
+    end
+
+    def paginate(url, params = {})
+      results = []
+      page = 1
+      total_results = Float::INFINITY
+
+      while results.length < total_results
+        response = fetch_page(url, page, params)
+
+        if response.success?
+          body = JSON.parse(response.body)
+          page_results = yield(body)
+          results.concat(page_results)
+
+          total_results = body.dig("pagination", "total")
+          page += 1
+        else
+          raise build_error(response)
+        end
+
+        break if results.length >= total_results
+      end
+
+      results
+    end
+end