Multi-Currency Part 2 (#543)

* Support all currencies, handle outside DB

* Remove currencies from seed

* Fix account balance namespace

* Set default currency on authentication

* Cache currency instances

* Implement multi-currency syncs with tests

* Series fallback, passing tests

* Fix conflicts

* Make value group concrete class that works with currency values

* Fix migration conflict

* Update tests to expect multi-currency results

* Update account list to use group method

* Namespace updates

* Fetch unknown exchange rates from API

* Fix date range bug

* Ensure demo data works without external API

* Enforce cascades only at DB level

app/models/exchange_rate.rb

@@ -1,16 +1,42 @@
 class ExchangeRate < ApplicationRecord
   validates :base_currency, :converted_currency, presence: true
 
-  def self.convert(from, to, amount)
-    return amount unless EXCHANGE_RATE_ENABLED
-
-    rate = ExchangeRate.find_by(base_currency: from, converted_currency: to)
-
-    # TODO: Handle the case where the rate is not found
-    if rate.nil?
-      amount # Silently handle the error by returning the original amount
-    else
+  class << self
+    def convert(from, to, amount)
+      rate = ExchangeRate.find_by(base_currency: from, converted_currency: to, date: Date.current)
+      return nil if rate.nil?
       amount * rate.rate
     end
+
+    def get_rate(from, to, date)
+      _from = Money::Currency.new(from)
+      _to = Money::Currency.new(to)
+      find_by! base_currency: _from.iso_code, converted_currency: _to.iso_code, date: date
+    rescue
+      logger.warn "Exchange rate not found for #{_from.iso_code} to #{_to.iso_code} on #{date}"
+      nil
+    end
+
+    def get_rate_series(from, to, date_range)
+      where(base_currency: from, converted_currency: to, date: date_range).order(:date)
+    end
+
+    # TODO: Replace with generic provider
+    # See https://github.com/maybe-finance/maybe/pull/556
+    def fetch_rate_from_provider(from, to, date)
+      response = Faraday.get("https://api.synthfinance.com/rates/historical") do |req|
+        req.headers["Authorization"] = "Bearer #{ENV["SYNTH_API_KEY"]}"
+        req.params["date"] = date.to_s
+        req.params["from"] = from
+        req.params["to"] = to
+      end
+
+      if response.success?
+        rates = JSON.parse(response.body)
+        rates.dig("data", "rates", to)
+      else
+        nil
+      end
+    end
   end
 end