Migrate from Stripe Charges API to Stripe Checkout Sessions API

[li-xinwei]

Summary

• Migrate payment processing from the legacy Stripe Charges API (Stripe::Charge.create) and embedded Checkout.js to the modern Stripe Checkout Sessions API (Stripe::Checkout::Session.create)
• Redirect users to Stripe's hosted checkout page for a more secure payment experience with built-in support for SCA/3D Secure, Apple Pay, Google Pay, and other payment methods
• Send itemized ticket breakdown as line_items to Stripe instead of only the total cost, improving payment tracking and reconciliation on both the Stripe Dashboard and customer receipts
• Add stripe_session_id to the payments table for better payment tracking and session-based verification

Changes

Payment Model (app/models/payment.rb)

• Replaced purchase method (which used Stripe::Charge.create) with:
  • create_checkout_session — creates a Stripe Checkout Session with itemized line items and redirects to Stripe
  • complete_checkout — retrieves the session after redirect, verifies payment status, and records charge details
• Added build_line_items private method that maps each unpaid TicketPurchase to a Stripe line item with proper currency conversion
• Added unpaid_ticket_purchases helper method

Payments Controller (app/controllers/payments_controller.rb)

• create action now creates a Payment record and Stripe Checkout Session, then redirects to Stripe's hosted page
• Added success action — handles the return from Stripe after successful payment, verifies the session, marks tickets as paid, and handles registration
• Added cancel action — handles payment cancellation, redirects back to payment page
• Removed dependency on stripeToken/stripeEmail params (no longer needed with hosted checkout)

Routes (config/routes.rb)

• Added success and cancel collection routes under payments

Views

• Replaced legacy Stripe Checkout.js <script> tag with a standard form submit button that initiates the checkout flow
• Updated payment summary page messaging to indicate redirect to Stripe

Database

• Migration to add stripe_session_id (string, unique index) to payments table
• Updated db/schema.rb

Tests

• Updated spec/models/payment_spec.rb to test create_checkout_session and complete_checkout methods using RSpec mocks
• Updated spec/features/ticket_purchases_spec.rb to work with the new checkout flow

Test plan

• Verify that selecting tickets and clicking "Pay" creates a Stripe Checkout Session and redirects to Stripe
• Verify successful payment redirects back with confirmation and marks tickets as paid
• Verify cancelled payment redirects back to payment page with appropriate message
• Verify itemized ticket details appear correctly on the Stripe Checkout page
• Verify registration ticket flow still works (auto-registration after payment)
• Verify free ticket purchases are unaffected
• Verify currency conversion works correctly in checkout line items
• Run bundle exec rspec spec/models/payment_spec.rb
• Run bundle exec rspec spec/features/ticket_purchases_spec.rb

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