Implement logic to throttle emails

.env.example

@@ -48,3 +48,4 @@ POSTMARK_API_TOKEN=
 
 GOOGLE_MAPS_API_KEY=
 API_SECRET=superdoopersecrethere
+ERROR_EMAIL=

app/Utils/Traits/ThrottlesEmail.php

@@ -0,0 +1,76 @@
+<?php
+/**
+ * Invoice Ninja (https://invoiceninja.com)
+ *
+ * @link https://github.com/invoiceninja/invoiceninja source repository
+ *
+ * @copyright Copyright (c) 2019. Invoice Ninja LLC (https://invoiceninja.com)
+ *
+ * @license https://opensource.org/licenses/AAL
+ */
+
+namespace App\Utils\Traits;
+
+use App\Models\Company;
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\Mail;
+
+/**
+ * Class ThrottlesEmail
+ * @package App\Utils\Traits
+ */
+trait ThrottlesEmail
+{
+
+
+	public function getDailyEmailLimit(Company $company)
+	{
+		$limit = config('ninja.daily_email_limit');
+
+        $limit += $company->created_at->diffInMonths() * 100;
+
+        return min($limit, 5000);
+	}
+
+	public function isThrottled(Company $company)
+    {
+
+        $key = $company->company_key;
+
+        // http://stackoverflow.com/questions/1375501/how-do-i-throttle-my-sites-api-users
+        $day = 60 * 60 * 24;
+        $day_limit = $this->getDailyEmailLimit();
+        $day_throttle = Cache::get("email_day_throttle:{$key}", null);
+        $last_api_request = Cache::get("last_email_request:{$key}", 0);
+        $last_api_diff = time() - $last_api_request;
+
+        if (is_null($day_throttle)) {
+            $new_day_throttle = 0;
+        } else {
+            $new_day_throttle = $day_throttle - $last_api_diff;
+            $new_day_throttle = $new_day_throttle < 0 ? 0 : $new_day_throttle;
+            $new_day_throttle += $day / $day_limit;
+            $day_hits_remaining = floor(($day - $new_day_throttle) * $day_limit / $day);
+            $day_hits_remaining = $day_hits_remaining >= 0 ? $day_hits_remaining : 0;
+        }
+
+        Cache::put("email_day_throttle:{$key}", $new_day_throttle, 60);
+        Cache::put("last_email_request:{$key}", time(), 60);
+
+        if ($new_day_throttle > $day) {
+            $error_email = config('ninja.error_email');
+            if ($error_email && ! Cache::get("throttle_notified:{$key}")) {
+                Mail::raw('Account Throttle: ' . $company->company_key, function ($message) use ($error_email, $company) {
+                    $message->to($error_email)
+                            ->from(config('ninja.contact.email'))
+                            ->subject("Email throttle triggered for company " . $company->id);
+                });
+            }
+            Cache::put("throttle_notified:{$key}", true, 60 * 24);
+            
+            return true;
+        }
+
+        return false;
+    }
+}

config/ninja.php

@@ -15,6 +15,8 @@ return [
     'key_length' => 64,
     'date_format' => 'Y-m-d',
     'date_time_format' => 'Y-m-d H:i',
+    'daily_email_limit' => 300,
+    'error_email' => env('ERROR_EMAIL', ''),
 
     'environment' => env('NINJA_ENVIRONMENT', 'selfhost'), // 'hosted', 'development', 'selfhost', 'reseller'