[PM 18701]Optional payment modal after signup (#6014)

* Add endpoint to swap plan frequency

* Add endpoint to swap plan frequency

* Resolve pr comments

Signed-off-by: Cy Okeke <cokeke@bitwarden.com>

* Refactor the code

Signed-off-by: Cy Okeke <cokeke@bitwarden.com>

* Refactor for  thr update change frequency

* Add Automatic modal opening

* catch for organization paying with PayPal

---------

Signed-off-by: Cy Okeke <cokeke@bitwarden.com>

src/Core/Billing/Constants/StripeConstants.cs

@@ -118,4 +118,11 @@ public static class StripeConstants
         public const string Deferred = "deferred";
         public const string Immediately = "immediately";
     }
+
+    public static class MissingPaymentMethodBehaviorOptions
+    {
+        public const string CreateInvoice = "create_invoice";
+        public const string Cancel = "cancel";
+        public const string Pause = "pause";
+    }
 }

src/Core/Billing/Organizations/Services/IOrganizationBillingService.cs

@@ -1,4 +1,5 @@
 using Bit.Core.AdminConsole.Entities;
+using Bit.Core.Billing.Enums;
 using Bit.Core.Billing.Models;
 using Bit.Core.Billing.Organizations.Models;
 using Bit.Core.Billing.Tax.Models;
@@ -44,4 +45,15 @@ public interface IOrganizationBillingService
         Organization organization,
         TokenizedPaymentSource tokenizedPaymentSource,
         TaxInformation taxInformation);
+
+    /// <summary>
+    /// Updates the subscription with new plan frequencies and changes the collection method to charge_automatically if a valid payment method exists.
+    /// Validates that the customer has a payment method attached before switching to automatic charging.
+    /// Handles both Password Manager and Secrets Manager subscription items separately to ensure billing interval compatibility.
+    /// </summary>
+    /// <param name="organization">The Organization whose subscription to update.</param>
+    /// <param name="newPlanType">The Stripe price/plan for the new Password Manager and secrets manager.</param>
+    /// <exception cref="ArgumentNullException">Thrown when the <paramref name="organization"/> is <see langword="null"/>.</exception>
+    /// <exception cref="BillingException">Thrown when no payment method is found for the customer, no plan IDs are provided, or subscription update fails.</exception>
+    Task UpdateSubscriptionPlanFrequency(Organization organization, PlanType newPlanType);
 }

src/Core/Billing/Organizations/Services/OrganizationBillingService.cs

@@ -145,6 +145,55 @@ public class OrganizationBillingService(
         {
             await subscriberService.UpdatePaymentSource(organization, tokenizedPaymentSource);
             await subscriberService.UpdateTaxInformation(organization, taxInformation);
+            await UpdateMissingPaymentMethodBehaviourAsync(organization);
+        }
+    }
+
+    public async Task UpdateSubscriptionPlanFrequency(
+        Organization organization, PlanType newPlanType)
+    {
+        ArgumentNullException.ThrowIfNull(organization);
+
+        var subscription = await subscriberService.GetSubscriptionOrThrow(organization);
+        var subscriptionItems = subscription.Items.Data;
+
+        var newPlan = await pricingClient.GetPlanOrThrow(newPlanType);
+        var oldPlan = await pricingClient.GetPlanOrThrow(organization.PlanType);
+
+        // Build the subscription update options
+        var subscriptionItemOptions = new List<SubscriptionItemOptions>();
+        foreach (var item in subscriptionItems)
+        {
+            var subscriptionItemOption = new SubscriptionItemOptions
+            {
+                Id = item.Id,
+                Quantity = item.Quantity,
+                Price = item.Price.Id == oldPlan.SecretsManager.StripeSeatPlanId ? newPlan.SecretsManager.StripeSeatPlanId : newPlan.PasswordManager.StripeSeatPlanId
+            };
+
+            subscriptionItemOptions.Add(subscriptionItemOption);
+        }
+        var updateOptions = new SubscriptionUpdateOptions
+        {
+            Items = subscriptionItemOptions,
+            ProrationBehavior = StripeConstants.ProrationBehavior.CreateProrations
+        };
+
+        try
+        {
+            // Update the subscription in Stripe
+            await stripeAdapter.SubscriptionUpdateAsync(subscription.Id, updateOptions);
+            organization.PlanType = newPlan.Type;
+            await organizationRepository.ReplaceAsync(organization);
+        }
+        catch (StripeException stripeException)
+        {
+            logger.LogError(stripeException, "Failed to update subscription plan for subscriber ({SubscriberID}): {Error}",
+                organization.Id, stripeException.Message);
+
+            throw new BillingException(
+                message: "An error occurred while updating the subscription plan",
+                innerException: stripeException);
         }
     }
 
@@ -545,5 +594,24 @@ public class OrganizationBillingService(
         return subscriptionProductIds.Intersect(couponAppliesTo ?? []).Any();
     }
 
+    private async Task UpdateMissingPaymentMethodBehaviourAsync(Organization organization)
+    {
+        var subscription = await subscriberService.GetSubscriptionOrThrow(organization);
+        if (subscription.TrialSettings?.EndBehavior?.MissingPaymentMethod == StripeConstants.MissingPaymentMethodBehaviorOptions.Cancel)
+        {
+            var options = new SubscriptionUpdateOptions
+            {
+                TrialSettings = new SubscriptionTrialSettingsOptions
+                {
+                    EndBehavior = new SubscriptionTrialSettingsEndBehaviorOptions
+                    {
+                        MissingPaymentMethod = StripeConstants.MissingPaymentMethodBehaviorOptions.CreateInvoice
+                    }
+                }
+            };
+            await stripeAdapter.SubscriptionUpdateAsync(organization.GatewaySubscriptionId, options);
+        }
+    }
+
     #endregion
 }