Implement voucher per event and for all events of an organizer: apply voucher in billing setting

[HungNgien]

Add a field to input invoice voucher for organizers

This PR resolves #382

Summary by Sourcery

Add support for invoice vouchers in billing settings. Apply voucher discounts to organizer or event-specific invoices.

New Features:

• Introduce invoice vouchers to provide discounts on ticket fees.

Tests:

• Update tests to cover new voucher functionality.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request implements the ability for organizers to apply voucher codes to their monthly invoices. It introduces a new "Invoice Voucher" field in the organizer billing settings. The backend logic now calculates the total amount due, applies any valid voucher, and updates the billing invoice accordingly. The voucher application logic considers voucher limitations, such as organizer restrictions and event-specific usage.

Sequence diagram for monthly billing collection with voucher application

sequenceDiagram
    participant System
    participant Event
    participant BillingInvoice
    participant InvoiceVoucher

    System->>Event: collect_billing_invoice()
    Event->>BillingInvoice: Check existing invoice
    alt No existing invoice
        Event->>Event: Calculate total amount
        Event->>InvoiceVoucher: Check voucher validity
        alt Valid voucher
            InvoiceVoucher-->>Event: Apply voucher discount
        end
        Event->>BillingInvoice: Create new invoice with discount
        BillingInvoice-->>System: Return billing response
        alt Voucher applied
            System->>InvoiceVoucher: Increment redeemed count
        end
    end

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Entity relationship diagram for billing and voucher system

erDiagram
    ORGANIZER ||--o{ EVENT : has
    ORGANIZER ||--o| ORGANIZER_BILLING : has
    ORGANIZER_BILLING ||--o| INVOICE_VOUCHER : uses
    EVENT ||--o{ BILLING_INVOICE : generates
    BILLING_INVOICE }|--|| INVOICE_VOUCHER : applies

    BILLING_INVOICE {
        decimal amount
        decimal ticket_fee
        decimal final_ticket_fee
        decimal voucher_discount
        date monthly_bill
    }

    INVOICE_VOUCHER {
        string code
        decimal value
        string price_mode
    }

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Class diagram for billing and voucher models

classDiagram
    class BillingInvoice {
        +Decimal amount
        +String currency
        +Decimal ticket_fee
        +Decimal final_ticket_fee
        +Decimal voucher_discount
        +Date monthly_bill
        +save()
    }

    class OrganizerBillingModel {
        +InvoiceVoucher invoice_voucher
        +String stripe_customer_id
        +save()
    }

    class InvoiceVoucher {
        +calculate_price()
        +is_active()
    }

    OrganizerBillingModel --> InvoiceVoucher
    BillingInvoice --> OrganizerBillingModel

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File-Level Changes

Change	Details	Files
Added a new Invoice Voucher field to the organizer billing settings form.	Added a new field to the organizer billing settings form to input and validate invoice voucher codes. Updated the organizer billing settings template to include the new Invoice Voucher field. Added validation to ensure the entered voucher code is valid, active, and applicable to the organizer. If a valid voucher is provided, it's saved with the organizer's billing information.	src/pretix/control/forms/organizer_forms/organizer_form.py src/pretix/control/templates/pretixcontrol/organizers/billing.html
Implemented voucher application logic in billing calculation.	Added logic to collect_billing_invoice to apply invoice vouchers and calculate discounts. Added calculate_price method to the InvoiceVoucher model to calculate the discounted price based on the voucher's settings. Updated the generate_invoice_pdf function to display the voucher discount and final ticket fee on the invoice. Added final_ticket_fee and voucher_discount fields to the BillingInvoice model to store the discounted fee and the discount amount. Added invoice_voucher field to the OrganizerBillingModel to store the applied voucher. Added pydantic dependency for schema definitions. Created a database migration to add the new fields to the BillingInvoice and OrganizerBillingModel models. Created a CollectBillingResponse schema to structure the response of the billing collection process.	src/pretix/eventyay_common/tasks.py src/pretix/base/models/vouchers.py src/pretix/eventyay_common/billing_invoice.py src/pretix/base/models/billing.py src/pretix/base/models/organizer.py pyproject.toml src/pretix/base/migrations/0007_billinginvoice_final_ticket_fee_and_more.py src/pretix/eventyay_common/schemas/billing.py
Updated billing-related tasks and functions to use the final ticket fee after voucher application.	Modified monthly_billing_collect to handle voucher application and update redeemed voucher count. Updated process_auto_billing_charge to use the final_ticket_fee when charging organizers. Updated retry_failed_payment and check_billing_status_for_warning to consider final_ticket_fee instead of the original ticket_fee. Updated calculate_ticket_fee to return the original ticket fee, the final ticket fee after voucher application, and the voucher discount amount.	src/pretix/eventyay_common/tasks.py

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#382	Implement voucher functionality for a single event	✅
#382	Implement voucher functionality for all events of an organizer	✅

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[sourcery-ai]

Hey @HungNgien - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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