First basic code for currency exchange rate routines.

app/Services/Currency/ExchangeRateInterface.php

@@ -0,0 +1,38 @@
+<?php
+/**
+ * ExchangeRateInterface.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\Services\Currency;
+
+
+use Carbon\Carbon;
+use FireflyIII\Models\CurrencyExchangeRate;
+use FireflyIII\Models\TransactionCurrency;
+use FireflyIII\User;
+
+interface ExchangeRateInterface
+{
+    /**
+     * @param TransactionCurrency $fromCurrency
+     * @param TransactionCurrency $toCurrency
+     * @param Carbon              $date
+     *
+     * @return CurrencyExchangeRate
+     */
+    public function getRate(TransactionCurrency $fromCurrency, TransactionCurrency $toCurrency, Carbon $date): CurrencyExchangeRate;
+
+    /**
+     * @param User $user
+     *
+     * @return mixed
+     */
+    public function setUser(User $user);
+
+}

app/Services/Currency/FixerIO.php

@@ -0,0 +1,69 @@
+<?php
+/**
+ * FixerIO.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\Services\Currency;
+
+
+use Carbon\Carbon;
+use FireflyIII\Models\CurrencyExchangeRate;
+use FireflyIII\Models\TransactionCurrency;
+use FireflyIII\User;
+use Log;
+use Requests;
+
+/**
+ * Class FixerIO
+ *
+ * @package FireflyIII\Services\Currency
+ */
+class FixerIO implements ExchangeRateInterface
+{
+    /** @var  User */
+    protected $user;
+
+    public function getRate(TransactionCurrency $fromCurrency, TransactionCurrency $toCurrency, Carbon $date): CurrencyExchangeRate
+    {
+        $uri     = sprintf('https://api.fixer.io/%s?base=%s&symbols=%s', $date->format('Y-m-d'), $fromCurrency->code, $toCurrency->code);
+        $result  = Requests::get($uri);
+        $rate    = 1.0;
+        $content = null;
+        if ($result->status_code !== 200) {
+            Log::error(sprintf('Something went wrong. Received error code %d and body "%s" from FixerIO.', $result->status_code, $result->body));
+        }
+        // get rate from body:
+        if ($result->status_code === 200) {
+            $content = json_decode($result->body, true);
+        }
+        if (!is_null($content)) {
+            $code = $toCurrency->code;
+            $rate = isset($content['rates'][$code]) ? $content['rates'][$code] : '1';
+        }
+
+        // create new currency exchange rate object:
+        $exchangeRate = new CurrencyExchangeRate;
+        $exchangeRate->user()->associate($this->user);
+        $exchangeRate->fromCurrency()->associate($fromCurrency);
+        $exchangeRate->toCurrency()->associate($toCurrency);
+        $exchangeRate->date = $date;
+        $exchangeRate->rate = $rate;
+        $exchangeRate->save();
+
+        return $exchangeRate;
+    }
+
+    /**
+     * @param User $user
+     */
+    public function setUser(User $user)
+    {
+        $this->user = $user;
+    }
+}