Revert "feat(server): deprecated the subscription module."

This reverts commit 3b79ac66ae.

packages/server/src/system/models/Subscriptions/Plan.ts

@@ -0,0 +1,82 @@
+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.
+   */
+  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 PlanSubscription = require('system/models/Subscriptions/PlanSubscription');
+
+    return {
+      /**
+       * The plan may have many subscriptions.
+       */
+      subscriptions: {
+        relation: Model.HasManyRelation,
+        modelClass: PlanSubscription.default,
+        join: {
+          from: 'subscription_plans.id',
+          to: 'subscription_plan_subscriptions.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;
+  }
+}