feat: Payment system with voucher cards.

feat: Design with inversion dependency injection architecture.
feat: Prettier http middleware.
feat: Re-write items categories with preferred accounts.

server/src/system/models/Subscriptions/Plan.js

@@ -0,0 +1,94 @@
+import { Model, mixin } from 'objection';
+import SystemModel from '@/system/models/SystemModel';
+import { PlanSubscription } from '..';
+
+export default class Plan extends mixin(SystemModel) {
+  /**
+   * Table name.
+   */
+  static get tableName() {
+    return 'subscription_plans';
+  }
+
+  /**
+   * Timestamps columns.
+   */
+  static get timestamps() {
+    return ['createdAt', 'updatedAt'];
+  }
+
+  /**
+   * Defined virtual attributes.
+   */
+  static get virtualAttributes() {
+    return ['isFree', 'hasTrial'];
+  }
+
+  /**
+   * Model modifiers.
+   */
+  static get modifiers() {
+    return {
+      getFeatureBySlug(builder, featureSlug) {
+        builder.where('slug', featureSlug);
+      },
+    };
+  }
+
+  /**
+   * Relationship mapping.
+   */
+  static get relationMappings() {
+    const PlanFeature = require('@/system/models/Subscriptions/PlanFeature');
+
+    return {
+      /**
+       * The plan may have many features.
+       */
+      features: {
+        relation: Model.BelongsToOneRelation,
+        modelClass: PlanFeature.default,
+        join: {
+          from: 'subscriptions_plans.id',
+          to: 'subscriptions_plan_features.planId',
+        },
+      },
+
+      /**
+       * The plan may have many subscriptions.
+       */
+      subscriptions: {
+        relation: Model.HasManyRelation,
+        modelClass: PlanSubscription.default,
+        join: {
+          from: 'subscription_plans.id',
+          to: 'subscription_plans.planId',
+        },
+      }
+    };
+  }
+
+  /**
+   * Check if plan is free.
+   * @return {boolean}
+   */
+  isFree() {
+    return this.price <= 0;
+  }
+
+  /**
+   * Check if plan is paid.
+   * @return {boolean}
+   */
+  isPaid() {
+    return !this.isFree();
+  }
+
+  /**
+   * Check if plan has trial.
+   * @return {boolean}
+   */
+  hasTrial() {
+    return this.trialPeriod && this.trialInterval;
+  }
+}