First basic code for currency exchange rate routines.

app/Http/Controllers/Json/ExchangeController.php

@@ -0,0 +1,60 @@
+<?php
+/**
+ * ExchangeController.php
+ * Copyright (c) 2017 thegrumpydictator@gmail.com
+ * This software may be modified and distributed under the terms of the Creative Commons Attribution-ShareAlike 4.0 International License.
+ *
+ * See the LICENSE file for details.
+ */
+
+declare(strict_types=1);
+
+namespace FireflyIII\Http\Controllers\Json;
+
+
+use Carbon\Carbon;
+use FireflyIII\Http\Controllers\Controller;
+use FireflyIII\Models\TransactionCurrency;
+use FireflyIII\Repositories\Currency\CurrencyRepositoryInterface;
+use FireflyIII\Services\Currency\ExchangeRateInterface;
+use Illuminate\Http\Request;
+use Response;
+
+/**
+ * Class ExchangeController
+ *
+ * @package FireflyIII\Http\Controllers\Json
+ */
+class ExchangeController extends Controller
+{
+    /**
+     * @param Request             $request
+     * @param TransactionCurrency $fromCurrency
+     * @param TransactionCurrency $toCurrency
+     * @param Carbon              $date
+     */
+    public function getRate(Request $request, TransactionCurrency $fromCurrency, TransactionCurrency $toCurrency, Carbon $date)
+    {
+        /** @var CurrencyRepositoryInterface $repository */
+        $repository = app(CurrencyRepositoryInterface::class);
+        $rate       = $repository->getExchangeRate($fromCurrency, $toCurrency, $date);
+        $amount     = null;
+        if (is_null($rate->id)) {
+            $preferred = env('EXCHANGE_RATE_SERVICE', config('firefly.preferred_exchange_service'));
+            $class     = config('firefly.currency_exchange_services.' . $preferred);
+            /** @var ExchangeRateInterface $object */
+            $object = app($class);
+            $object->setUser(auth()->user());
+            $rate = $object->getRate($fromCurrency, $toCurrency, $date);
+        }
+        $return           = $rate->toArray();
+        $return['amount'] = null;
+        if (!is_null($request->get('amount'))) {
+            // assume amount is in "from" currency:
+            $return['amount'] = bcmul($request->get('amount'), $rate->rate);
+        }
+
+        return Response::json($return);
+    }
+
+}