Add PayloadCMS type definitions, Prettier config, and PNPM lockfile

src/__tests__/test-provider.test.ts

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+import type { TestProviderConfig} from '../types';
+
+import { TestPaymentProvider } from '../providers/test/provider'
+import { PaymentStatus } from '../types'
+
+describe('TestPaymentProvider', () => {
+  let provider: TestPaymentProvider
+  let config: TestProviderConfig
+
+  beforeEach(() => {
+    config = {
+      autoComplete: true,
+      defaultDelay: 0,
+      enabled: true,
+    }
+    provider = new TestPaymentProvider(config)
+  })
+
+  afterEach(() => {
+    provider.clearStoredData()
+  })
+
+  describe('createPayment', () => {
+    it('should create a payment with succeeded status when autoComplete is true', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+        description: 'Test payment',
+      })
+
+      expect(payment).toMatchObject({
+        amount: 2000,
+        currency: 'USD',
+        description: 'Test payment',
+        provider: 'test',
+        status: 'succeeded',
+      })
+      expect(payment.id).toBeDefined()
+      expect(payment.createdAt).toBeDefined()
+      expect(payment.updatedAt).toBeDefined()
+      expect(payment.providerData?.testMode).toBe(true)
+    })
+
+    it('should create a payment with pending status when autoComplete is false', async () => {
+      config.autoComplete = false
+      provider = new TestPaymentProvider(config)
+
+      const payment = await provider.createPayment({
+        amount: 1500,
+        currency: 'EUR',
+      })
+
+      expect(payment).toMatchObject({
+        amount: 1500,
+        currency: 'EUR',
+        status: 'pending',
+      })
+    })
+
+    it('should create a failed payment when simulateFailure is true', async () => {
+      const payment = await provider.createPayment({
+        amount: 1000,
+        currency: 'USD',
+        metadata: {
+          test: { simulateFailure: true },
+        },
+      })
+
+      expect(payment.status).toBe('failed')
+      expect(payment.providerData?.simulatedFailure).toBe(true)
+    })
+
+    it('should apply delay when specified', async () => {
+      const startTime = Date.now()
+      
+      await provider.createPayment({
+        amount: 1000,
+        currency: 'USD',
+        metadata: {
+          test: { delayMs: 100 },
+        },
+      })
+
+      const endTime = Date.now()
+      expect(endTime - startTime).toBeGreaterThanOrEqual(100)
+    })
+
+    it('should store payment data', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      const stored = provider.getStoredPayment(payment.id)
+      expect(stored).toEqual(payment)
+    })
+  })
+
+  describe('retrievePayment', () => {
+    it('should retrieve an existing payment', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      const retrieved = await provider.retrievePayment(payment.id)
+      expect(retrieved).toEqual(payment)
+    })
+
+    it('should throw error for non-existent payment', async () => {
+      await expect(provider.retrievePayment('non-existent')).rejects.toThrow(
+        'Payment non-existent not found'
+      )
+    })
+  })
+
+  describe('cancelPayment', () => {
+    it('should cancel a pending payment', async () => {
+      config.autoComplete = false
+      provider = new TestPaymentProvider(config)
+
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      const canceled = await provider.cancelPayment(payment.id)
+      expect(canceled.status).toBe('canceled')
+      expect(canceled.updatedAt).not.toBe(payment.updatedAt)
+    })
+
+    it('should not cancel a succeeded payment', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      await expect(provider.cancelPayment(payment.id)).rejects.toThrow(
+        'Cannot cancel a succeeded payment'
+      )
+    })
+
+    it('should throw error for non-existent payment', async () => {
+      await expect(provider.cancelPayment('non-existent')).rejects.toThrow(
+        'Payment non-existent not found'
+      )
+    })
+  })
+
+  describe('refundPayment', () => {
+    it('should create a full refund for succeeded payment', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      const refund = await provider.refundPayment(payment.id)
+      
+      expect(refund).toMatchObject({
+        amount: 2000,
+        currency: 'USD',
+        paymentId: payment.id,
+        status: 'succeeded',
+      })
+      expect(refund.id).toBeDefined()
+      expect(refund.createdAt).toBeDefined()
+
+      // Check payment status is updated
+      const updatedPayment = await provider.retrievePayment(payment.id)
+      expect(updatedPayment.status).toBe('refunded')
+    })
+
+    it('should create a partial refund', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      const refund = await provider.refundPayment(payment.id, 1000)
+      
+      expect(refund.amount).toBe(1000)
+      
+      // Check payment status is updated to partially_refunded
+      const updatedPayment = await provider.retrievePayment(payment.id)
+      expect(updatedPayment.status).toBe('partially_refunded')
+    })
+
+    it('should not refund a non-succeeded payment', async () => {
+      config.autoComplete = false
+      provider = new TestPaymentProvider(config)
+
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      await expect(provider.refundPayment(payment.id)).rejects.toThrow(
+        'Can only refund succeeded payments'
+      )
+    })
+
+    it('should not refund more than payment amount', async () => {
+      const payment = await provider.createPayment({
+        amount: 2000,
+        currency: 'USD',
+      })
+
+      await expect(provider.refundPayment(payment.id, 3000)).rejects.toThrow(
+        'Refund amount cannot exceed payment amount'
+      )
+    })
+  })
+
+  describe('handleWebhook', () => {
+    it('should handle webhook event', async () => {
+      const mockRequest = {
+        text: () => Promise.resolve(JSON.stringify({
+          type: 'payment.succeeded',
+          data: { paymentId: 'test_pay_123' }
+        }))
+      } as Request
+
+      const event = await provider.handleWebhook(mockRequest)
+
+      expect(event).toMatchObject({
+        type: 'payment.succeeded',
+        data: { paymentId: 'test_pay_123' },
+        provider: 'test',
+        verified: true,
+      })
+      expect(event.id).toBeDefined()
+    })
+
+    it('should throw error for invalid JSON', async () => {
+      const mockRequest = {
+        text: () => Promise.resolve('invalid json')
+      } as Request
+
+      await expect(provider.handleWebhook(mockRequest)).rejects.toThrow(
+        'Invalid JSON in webhook body'
+      )
+    })
+
+    it('should throw error when provider is disabled', async () => {
+      config.enabled = false
+      provider = new TestPaymentProvider(config)
+
+      const mockRequest = {
+        text: () => Promise.resolve('{}')
+      } as Request
+
+      await expect(provider.handleWebhook(mockRequest)).rejects.toThrow(
+        'Test provider is not enabled'
+      )
+    })
+  })
+
+  describe('data management', () => {
+    it('should clear all stored data', async () => {
+      await provider.createPayment({ amount: 1000, currency: 'USD' })
+      
+      expect(provider.getAllPayments()).toHaveLength(1)
+      
+      provider.clearStoredData()
+      
+      expect(provider.getAllPayments()).toHaveLength(0)
+      expect(provider.getAllRefunds()).toHaveLength(0)
+    })
+
+    it('should return all payments and refunds', async () => {
+      const payment1 = await provider.createPayment({ amount: 1000, currency: 'USD' })
+      const payment2 = await provider.createPayment({ amount: 2000, currency: 'EUR' })
+      const refund = await provider.refundPayment(payment1.id)
+
+      const payments = provider.getAllPayments()
+      const refunds = provider.getAllRefunds()
+
+      expect(payments).toHaveLength(2)
+      expect(refunds).toHaveLength(1)
+      expect(refunds[0]).toEqual(refund)
+    })
+  })
+})

src/collections/customers.ts

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+import type { CollectionConfig } from 'payload'
+
+import type { 
+  AccessArgs,
+  CollectionAfterChangeHook,
+  CollectionBeforeChangeHook,
+  CustomerData,
+  CustomerDocument
+} from '../types/payload'
+
+export function createCustomersCollection(slug: string = 'customers'): CollectionConfig {
+  return {
+    slug,
+    access: {
+      create: ({ req: { user } }: AccessArgs) => !!user,
+      delete: ({ req: { user } }: AccessArgs) => !!user,
+      read: ({ req: { user } }: AccessArgs) => !!user,
+      update: ({ req: { user } }: AccessArgs) => !!user,
+    },
+    admin: {
+      defaultColumns: ['email', 'name', 'createdAt'],
+      group: 'Billing',
+      useAsTitle: 'email',
+    },
+    fields: [
+      {
+        name: 'email',
+        type: 'email',
+        admin: {
+          description: 'Customer email address',
+        },
+        index: true,
+        unique: true,
+      },
+      {
+        name: 'name',
+        type: 'text',
+        admin: {
+          description: 'Customer full name',
+        },
+      },
+      {
+        name: 'phone',
+        type: 'text',
+        admin: {
+          description: 'Customer phone number',
+        },
+      },
+      {
+        name: 'address',
+        type: 'group',
+        fields: [
+          {
+            name: 'line1',
+            type: 'text',
+            label: 'Address Line 1',
+          },
+          {
+            name: 'line2',
+            type: 'text',
+            label: 'Address Line 2',
+          },
+          {
+            name: 'city',
+            type: 'text',
+            label: 'City',
+          },
+          {
+            name: 'state',
+            type: 'text',
+            label: 'State/Province',
+          },
+          {
+            name: 'postal_code',
+            type: 'text',
+            label: 'Postal Code',
+          },
+          {
+            name: 'country',
+            type: 'text',
+            admin: {
+              description: 'ISO 3166-1 alpha-2 country code',
+            },
+            label: 'Country',
+            maxLength: 2,
+          },
+        ],
+      },
+      {
+        name: 'providerIds',
+        type: 'json',
+        admin: {
+          description: 'Customer IDs from payment providers',
+          readOnly: true,
+        },
+      },
+      {
+        name: 'metadata',
+        type: 'json',
+        admin: {
+          description: 'Additional customer metadata',
+        },
+      },
+      {
+        name: 'payments',
+        type: 'relationship',
+        admin: {
+          description: 'Customer payments',
+          readOnly: true,
+        },
+        hasMany: true,
+        relationTo: 'payments',
+      },
+      {
+        name: 'invoices',
+        type: 'relationship',
+        admin: {
+          description: 'Customer invoices',
+          readOnly: true,
+        },
+        hasMany: true,
+        relationTo: 'invoices',
+      },
+    ],
+    hooks: {
+      afterChange: [
+        ({ doc, operation, req }: CollectionAfterChangeHook<CustomerDocument>) => {
+          if (operation === 'create') {
+            req.payload.logger.info(`Customer created: ${doc.id} (${doc.email})`)
+          }
+        },
+      ],
+      beforeChange: [
+        ({ data, operation }: CollectionBeforeChangeHook<CustomerData>) => {
+          if (operation === 'create' || operation === 'update') {
+            // Normalize country code
+            if (data.address?.country) {
+              data.address.country = data.address.country.toUpperCase()
+              if (!/^[A-Z]{2}$/.test(data.address.country)) {
+                throw new Error('Country must be a 2-letter ISO code')
+              }
+            }
+          }
+        },
+      ],
+    },
+    timestamps: true,
+  }
+}

src/collections/index.ts

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+export { createCustomersCollection } from './customers'
+export { createInvoicesCollection } from './invoices'
+export { createPaymentsCollection } from './payments'
+export { createRefundsCollection } from './refunds'

src/collections/invoices.ts

@@ -0,0 +1,248 @@
+import type { CollectionConfig } from 'payload'
+
+import type { 
+  AccessArgs,
+  CollectionAfterChangeHook,
+  CollectionBeforeChangeHook,
+  CollectionBeforeValidateHook,
+  InvoiceData,
+  InvoiceDocument,
+  InvoiceItemData
+} from '../types/payload'
+
+export function createInvoicesCollection(slug: string = 'invoices'): CollectionConfig {
+  return {
+    slug,
+    access: {
+      create: ({ req: { user } }: AccessArgs) => !!user,
+      delete: ({ req: { user } }: AccessArgs) => !!user,
+      read: ({ req: { user } }: AccessArgs) => !!user,
+      update: ({ req: { user } }: AccessArgs) => !!user,
+    },
+    admin: {
+      defaultColumns: ['number', 'customer', 'status', 'amount', 'currency', 'dueDate'],
+      group: 'Billing',
+      useAsTitle: 'number',
+    },
+    fields: [
+      {
+        name: 'number',
+        type: 'text',
+        admin: {
+          description: 'Invoice number (e.g., INV-001)',
+        },
+        index: true,
+        required: true,
+        unique: true,
+      },
+      {
+        name: 'customer',
+        type: 'relationship',
+        admin: {
+          position: 'sidebar',
+        },
+        relationTo: 'customers',
+        required: true,
+      },
+      {
+        name: 'status',
+        type: 'select',
+        admin: {
+          position: 'sidebar',
+        },
+        defaultValue: 'draft',
+        options: [
+          { label: 'Draft', value: 'draft' },
+          { label: 'Open', value: 'open' },
+          { label: 'Paid', value: 'paid' },
+          { label: 'Void', value: 'void' },
+          { label: 'Uncollectible', value: 'uncollectible' },
+        ],
+        required: true,
+      },
+      {
+        name: 'currency',
+        type: 'text',
+        admin: {
+          description: 'ISO 4217 currency code (e.g., USD, EUR)',
+        },
+        defaultValue: 'USD',
+        maxLength: 3,
+        required: true,
+      },
+      {
+        name: 'items',
+        type: 'array',
+        admin: {
+          // Custom row labeling can be added here when needed
+        },
+        fields: [
+          {
+            name: 'description',
+            type: 'text',
+            admin: {
+              width: '40%',
+            },
+            required: true,
+          },
+          {
+            name: 'quantity',
+            type: 'number',
+            admin: {
+              width: '15%',
+            },
+            defaultValue: 1,
+            min: 1,
+            required: true,
+          },
+          {
+            name: 'unitAmount',
+            type: 'number',
+            admin: {
+              description: 'Amount in cents',
+              width: '20%',
+            },
+            min: 0,
+            required: true,
+          },
+          {
+            name: 'totalAmount',
+            type: 'number',
+            admin: {
+              description: 'Calculated: quantity × unitAmount',
+              readOnly: true,
+              width: '20%',
+            },
+          },
+        ],
+        minRows: 1,
+        required: true,
+      },
+      {
+        name: 'subtotal',
+        type: 'number',
+        admin: {
+          description: 'Sum of all line items',
+          readOnly: true,
+        },
+      },
+      {
+        name: 'taxAmount',
+        type: 'number',
+        admin: {
+          description: 'Tax amount in cents',
+        },
+        defaultValue: 0,
+      },
+      {
+        name: 'amount',
+        type: 'number',
+        admin: {
+          description: 'Total amount (subtotal + tax)',
+          readOnly: true,
+        },
+      },
+      {
+        name: 'dueDate',
+        type: 'date',
+        admin: {
+          date: {
+            pickerAppearance: 'dayOnly',
+          },
+        },
+      },
+      {
+        name: 'paidAt',
+        type: 'date',
+        admin: {
+          condition: (data: InvoiceData) => data.status === 'paid',
+          readOnly: true,
+        },
+      },
+      {
+        name: 'payment',
+        type: 'relationship',
+        admin: {
+          condition: (data: InvoiceData) => data.status === 'paid',
+          position: 'sidebar',
+        },
+        relationTo: 'payments',
+      },
+      {
+        name: 'notes',
+        type: 'textarea',
+        admin: {
+          description: 'Internal notes',
+        },
+      },
+      {
+        name: 'metadata',
+        type: 'json',
+        admin: {
+          description: 'Additional invoice metadata',
+        },
+      },
+    ],
+    hooks: {
+      afterChange: [
+        ({ doc, operation, req }: CollectionAfterChangeHook<InvoiceDocument>) => {
+          if (operation === 'create') {
+            req.payload.logger.info(`Invoice created: ${doc.number}`)
+          }
+        },
+      ],
+      beforeChange: [
+        ({ data, operation }: CollectionBeforeChangeHook<InvoiceData>) => {
+          if (operation === 'create') {
+            // Generate invoice number if not provided
+            if (!data.number) {
+              const timestamp = Date.now()
+              data.number = `INV-${timestamp}`
+            }
+
+            // Validate currency format
+            if (data.currency) {
+              data.currency = data.currency.toUpperCase()
+              if (!/^[A-Z]{3}$/.test(data.currency)) {
+                throw new Error('Currency must be a 3-letter ISO code')
+              }
+            }
+
+            // Set due date if not provided (30 days from now)
+            if (!data.dueDate) {
+              const dueDate = new Date()
+              dueDate.setDate(dueDate.getDate() + 30)
+              data.dueDate = dueDate.toISOString()
+            }
+          }
+
+          // Set paid date when status changes to paid
+          if (data.status === 'paid' && !data.paidAt) {
+            data.paidAt = new Date().toISOString()
+          }
+        },
+      ],
+      beforeValidate: [
+        ({ data }: CollectionBeforeValidateHook<InvoiceData>) => {
+          if (data && data.items && Array.isArray(data.items)) {
+            // Calculate totals for each line item
+            data.items = data.items.map((item: InvoiceItemData) => ({
+              ...item,
+              totalAmount: (item.quantity || 0) * (item.unitAmount || 0),
+            }))
+
+            // Calculate subtotal
+            data.subtotal = data.items.reduce(
+              (sum: number, item: InvoiceItemData) => sum + (item.totalAmount || 0),
+              0
+            )
+
+            // Calculate total amount
+            data.amount = (data.subtotal || 0) + (data.taxAmount || 0)
+          }
+        },
+      ],
+    },
+    timestamps: true,
+  }
+}

src/collections/payments.ts

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+import type { CollectionConfig } from 'payload'
+
+import type { 
+  AccessArgs,
+  CollectionAfterChangeHook,
+  CollectionBeforeChangeHook,
+  PaymentData,
+  PaymentDocument
+} from '../types/payload'
+
+export function createPaymentsCollection(slug: string = 'payments'): CollectionConfig {
+  return {
+    slug,
+    access: {
+      create: ({ req: { user } }: AccessArgs) => !!user,
+      delete: ({ req: { user } }: AccessArgs) => !!user,
+      read: ({ req: { user } }: AccessArgs) => !!user,
+      update: ({ req: { user } }: AccessArgs) => !!user,
+    },
+    admin: {
+      defaultColumns: ['id', 'provider', 'status', 'amount', 'currency', 'createdAt'],
+      group: 'Billing',
+      useAsTitle: 'id',
+    },
+    fields: [
+      {
+        name: 'provider',
+        type: 'select',
+        admin: {
+          position: 'sidebar',
+        },
+        options: [
+          { label: 'Stripe', value: 'stripe' },
+          { label: 'Mollie', value: 'mollie' },
+          { label: 'Test', value: 'test' },
+        ],
+        required: true,
+      },
+      {
+        name: 'providerId',
+        type: 'text',
+        admin: {
+          description: 'The payment ID from the payment provider',
+        },
+        label: 'Provider Payment ID',
+        required: true,
+        unique: true,
+      },
+      {
+        name: 'status',
+        type: 'select',
+        admin: {
+          position: 'sidebar',
+        },
+        options: [
+          { label: 'Pending', value: 'pending' },
+          { label: 'Processing', value: 'processing' },
+          { label: 'Succeeded', value: 'succeeded' },
+          { label: 'Failed', value: 'failed' },
+          { label: 'Canceled', value: 'canceled' },
+          { label: 'Refunded', value: 'refunded' },
+          { label: 'Partially Refunded', value: 'partially_refunded' },
+        ],
+        required: true,
+      },
+      {
+        name: 'amount',
+        type: 'number',
+        admin: {
+          description: 'Amount in cents (e.g., 2000 = $20.00)',
+        },
+        min: 1,
+        required: true,
+      },
+      {
+        name: 'currency',
+        type: 'text',
+        admin: {
+          description: 'ISO 4217 currency code (e.g., USD, EUR)',
+        },
+        maxLength: 3,
+        required: true,
+      },
+      {
+        name: 'description',
+        type: 'text',
+        admin: {
+          description: 'Payment description',
+        },
+      },
+      {
+        name: 'customer',
+        type: 'relationship',
+        admin: {
+          position: 'sidebar',
+        },
+        relationTo: 'customers',
+      },
+      {
+        name: 'invoice',
+        type: 'relationship',
+        admin: {
+          position: 'sidebar',
+        },
+        relationTo: 'invoices',
+      },
+      {
+        name: 'metadata',
+        type: 'json',
+        admin: {
+          description: 'Additional metadata for the payment',
+        },
+      },
+      {
+        name: 'providerData',
+        type: 'json',
+        admin: {
+          description: 'Raw data from the payment provider',
+          readOnly: true,
+        },
+      },
+      {
+        name: 'refunds',
+        type: 'relationship',
+        admin: {
+          position: 'sidebar',
+          readOnly: true,
+        },
+        hasMany: true,
+        relationTo: 'refunds',
+      },
+    ],
+    hooks: {
+      afterChange: [
+        ({ doc, operation, req }: CollectionAfterChangeHook<PaymentDocument>) => {
+          if (operation === 'create') {
+            req.payload.logger.info(`Payment created: ${doc.id} (${doc.provider})`)
+          }
+        },
+      ],
+      beforeChange: [
+        ({ data, operation }: CollectionBeforeChangeHook<PaymentData>) => {
+          if (operation === 'create') {
+            // Validate amount format
+            if (data.amount && !Number.isInteger(data.amount)) {
+              throw new Error('Amount must be an integer (in cents)')
+            }
+            
+            // Validate currency format
+            if (data.currency) {
+              data.currency = data.currency.toUpperCase()
+              if (!/^[A-Z]{3}$/.test(data.currency)) {
+                throw new Error('Currency must be a 3-letter ISO code')
+              }
+            }
+          }
+        },
+      ],
+    },
+    timestamps: true,
+  }
+}

src/collections/refunds.ts

@@ -0,0 +1,163 @@
+import type { CollectionConfig } from 'payload'
+
+import type { 
+  AccessArgs,
+  CollectionAfterChangeHook,
+  CollectionBeforeChangeHook,
+  RefundData,
+  RefundDocument
+} from '../types/payload'
+
+export function createRefundsCollection(slug: string = 'refunds'): CollectionConfig {
+  return {
+    slug,
+    access: {
+      create: ({ req: { user } }: AccessArgs) => !!user,
+      delete: ({ req: { user } }: AccessArgs) => !!user,
+      read: ({ req: { user } }: AccessArgs) => !!user,
+      update: ({ req: { user } }: AccessArgs) => !!user,
+    },
+    admin: {
+      defaultColumns: ['id', 'payment', 'amount', 'currency', 'status', 'createdAt'],
+      group: 'Billing',
+      useAsTitle: 'id',
+    },
+    fields: [
+      {
+        name: 'providerId',
+        type: 'text',
+        admin: {
+          description: 'The refund ID from the payment provider',
+        },
+        label: 'Provider Refund ID',
+        required: true,
+        unique: true,
+      },
+      {
+        name: 'payment',
+        type: 'relationship',
+        admin: {
+          position: 'sidebar',
+        },
+        relationTo: 'payments',
+        required: true,
+      },
+      {
+        name: 'status',
+        type: 'select',
+        admin: {
+          position: 'sidebar',
+        },
+        options: [
+          { label: 'Pending', value: 'pending' },
+          { label: 'Processing', value: 'processing' },
+          { label: 'Succeeded', value: 'succeeded' },
+          { label: 'Failed', value: 'failed' },
+          { label: 'Canceled', value: 'canceled' },
+        ],
+        required: true,
+      },
+      {
+        name: 'amount',
+        type: 'number',
+        admin: {
+          description: 'Refund amount in cents',
+        },
+        min: 1,
+        required: true,
+      },
+      {
+        name: 'currency',
+        type: 'text',
+        admin: {
+          description: 'ISO 4217 currency code (e.g., USD, EUR)',
+        },
+        maxLength: 3,
+        required: true,
+      },
+      {
+        name: 'reason',
+        type: 'select',
+        admin: {
+          description: 'Reason for the refund',
+        },
+        options: [
+          { label: 'Duplicate', value: 'duplicate' },
+          { label: 'Fraudulent', value: 'fraudulent' },
+          { label: 'Requested by Customer', value: 'requested_by_customer' },
+          { label: 'Other', value: 'other' },
+        ],
+      },
+      {
+        name: 'description',
+        type: 'textarea',
+        admin: {
+          description: 'Additional details about the refund',
+        },
+      },
+      {
+        name: 'metadata',
+        type: 'json',
+        admin: {
+          description: 'Additional refund metadata',
+        },
+      },
+      {
+        name: 'providerData',
+        type: 'json',
+        admin: {
+          description: 'Raw data from the payment provider',
+          readOnly: true,
+        },
+      },
+    ],
+    hooks: {
+      afterChange: [
+        async ({ doc, operation, req }: CollectionAfterChangeHook<RefundDocument>) => {
+          if (operation === 'create') {
+            req.payload.logger.info(`Refund created: ${doc.id} for payment: ${doc.payment}`)
+            
+            // Update the related payment's refund relationship
+            try {
+              const payment = await req.payload.findByID({
+                id: typeof doc.payment === 'string' ? doc.payment : doc.payment.id,
+                collection: 'payments',
+              })
+              
+              const refundIds = Array.isArray(payment.refunds) ? payment.refunds : []
+              
+              await req.payload.update({
+                id: typeof doc.payment === 'string' ? doc.payment : doc.payment.id,
+                collection: 'payments',
+                data: {
+                  refunds: [...refundIds, doc.id],
+                },
+              })
+            } catch (error) {
+              req.payload.logger.error(`Failed to update payment refunds: ${error}`)
+            }
+          }
+        },
+      ],
+      beforeChange: [
+        ({ data, operation }: CollectionBeforeChangeHook<RefundData>) => {
+          if (operation === 'create') {
+            // Validate amount format
+            if (data.amount && !Number.isInteger(data.amount)) {
+              throw new Error('Amount must be an integer (in cents)')
+            }
+            
+            // Validate currency format
+            if (data.currency) {
+              data.currency = data.currency.toUpperCase()
+              if (!/^[A-Z]{3}$/.test(data.currency)) {
+                throw new Error('Currency must be a 3-letter ISO code')
+              }
+            }
+          }
+        },
+      ],
+    },
+    timestamps: true,
+  }
+}

src/exports/client.tsx

@@ -0,0 +1,68 @@
+/**
+ * Client-side components and utilities for the billing plugin
+ * These components run in the browser and have access to React hooks and client-side APIs
+ */
+
+'use client'
+
+import React from 'react'
+
+// Example client component that could be used in the admin dashboard
+export const BillingDashboardWidget: React.FC = () => {
+  return (
+    <div className="billing-dashboard-widget">
+      <h3>Billing Overview</h3>
+      <p>Payment statistics and recent transactions will be displayed here.</p>
+    </div>
+  )
+}
+
+// Client-side utilities
+export const formatCurrency = (amount: number, currency: string) => {
+  return new Intl.NumberFormat('en-US', {
+    currency: currency.toUpperCase(),
+    style: 'currency',
+  }).format(amount / 100)
+}
+
+export const getPaymentStatusColor = (status: string) => {
+  switch (status) {
+    case 'canceled':
+      return 'gray'
+    case 'failed':
+      return 'red'
+    case 'pending':
+      return 'yellow'
+    case 'succeeded':
+      return 'green'
+    default:
+      return 'blue'
+  }
+}
+
+// Example of a client component for payment status display
+export const PaymentStatusBadge: React.FC<{ status: string }> = ({ status }) => {
+  const color = getPaymentStatusColor(status)
+  
+  return (
+    <span 
+      className={`payment-status-badge payment-status-${status}`}
+      style={{ 
+        backgroundColor: color,
+        borderRadius: '4px',
+        color: 'white',
+        fontSize: '12px',
+        padding: '2px 8px'
+      }}
+    >
+      {status.toUpperCase()}
+    </span>
+  )
+}
+
+export default {
+  BillingDashboardWidget,
+  formatCurrency,
+  getPaymentStatusColor,
+  PaymentStatusBadge,
+}

src/exports/rsc.tsx

@@ -0,0 +1,146 @@
+/**
+ * React Server Components (RSC) and server-side utilities for the billing plugin
+ * These components run on the server and can access server-side APIs and databases
+ */
+
+import React from 'react'
+
+// Server component that can fetch data during server-side rendering
+interface BillingServerStatsProps {
+  payloadInstance?: unknown
+}
+
+export const BillingServerStats: React.FC<BillingServerStatsProps> = async ({ 
+  payloadInstance 
+}) => {
+  // In a real implementation, this would fetch data from the database
+  // const stats = await payloadInstance?.find({
+  //   collection: 'payments',
+  //   limit: 0,
+  //   depth: 0
+  // })
+
+  return (
+    <div className="billing-server-stats">
+      <h3>Payment Statistics</h3>
+      <div className="stats-grid">
+        <div className="stat-item">
+          <span className="stat-label">Total Payments</span>
+          <span className="stat-value">-</span>
+        </div>
+        <div className="stat-item">
+          <span className="stat-label">Successful</span>
+          <span className="stat-value">-</span>
+        </div>
+        <div className="stat-item">
+          <span className="stat-label">Pending</span>
+          <span className="stat-value">-</span>
+        </div>
+        <div className="stat-item">
+          <span className="stat-label">Failed</span>
+          <span className="stat-value">-</span>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+// Server-side utility functions
+export const generateInvoiceNumber = () => {
+  const timestamp = Date.now()
+  const random = Math.random().toString(36).substring(2, 8).toUpperCase()
+  return `INV-${timestamp}-${random}`
+}
+
+export const calculateInvoiceTotal = (items: Array<{
+  quantity: number
+  unitAmount: number
+}>, taxRate: number = 0) => {
+  const subtotal = items.reduce((sum, item) => sum + (item.quantity * item.unitAmount), 0)
+  const taxAmount = Math.round(subtotal * taxRate)
+  return {
+    subtotal,
+    taxAmount,
+    total: subtotal + taxAmount
+  }
+}
+
+// Server component for displaying invoice details
+interface InvoiceDetailsProps {
+  invoice?: {
+    amount: number
+    currency: string
+    customer?: {
+      email?: string
+      name?: string
+    }
+    dueDate?: string
+    items?: Array<{
+      description: string
+      quantity: number
+      totalAmount: number
+      unitAmount: number
+    }>
+    number: string
+    status: string
+  }
+  readonly?: boolean
+}
+
+export const InvoiceDetails: React.FC<InvoiceDetailsProps> = ({ invoice, readonly = false }) => {
+  if (!invoice) {
+    return <div>No invoice data available</div>
+  }
+
+  return (
+    <div className="invoice-details">
+      <div className="invoice-header">
+        <h3>Invoice {invoice.number}</h3>
+        <span className={`status-badge status-${invoice.status}`}>
+          {invoice.status}
+        </span>
+      </div>
+      
+      <div className="invoice-content">
+        <div className="invoice-meta">
+          <p><strong>Customer:</strong> {invoice.customer?.name || invoice.customer?.email}</p>
+          <p><strong>Due Date:</strong> {invoice.dueDate ? new Date(invoice.dueDate).toLocaleDateString() : 'N/A'}</p>
+          <p><strong>Amount:</strong> {invoice.currency} {(invoice.amount / 100).toFixed(2)}</p>
+        </div>
+
+        {invoice.items && invoice.items.length > 0 && (
+          <div className="invoice-items">
+            <h4>Items</h4>
+            <table className="items-table">
+              <thead>
+                <tr>
+                  <th>Description</th>
+                  <th>Quantity</th>
+                  <th>Unit Amount</th>
+                  <th>Total</th>
+                </tr>
+              </thead>
+              <tbody>
+                {invoice.items.map((item, index) => (
+                  <tr key={index}>
+                    <td>{item.description}</td>
+                    <td>{item.quantity}</td>
+                    <td>{invoice.currency} {(item.unitAmount / 100).toFixed(2)}</td>
+                    <td>{invoice.currency} {(item.totalAmount / 100).toFixed(2)}</td>
+                  </tr>
+                ))}
+              </tbody>
+            </table>
+          </div>
+        )}
+      </div>
+    </div>
+  )
+}
+
+export default {
+  BillingServerStats,
+  calculateInvoiceTotal,
+  generateInvoiceNumber,
+  InvoiceDetails,
+}

src/index.ts

@@ -0,0 +1,132 @@
+import type { Config } from 'payload'
+
+import type { BillingPluginConfig } from './types'
+
+import { createCustomersCollection } from './collections/customers'
+import { createInvoicesCollection } from './collections/invoices'
+import { createPaymentsCollection } from './collections/payments'
+import { createRefundsCollection } from './collections/refunds'
+import { providerRegistry } from './providers/base/provider'
+import { TestPaymentProvider } from './providers/test/provider'
+
+export * from './providers/base/provider'
+export * from './providers/test/provider'
+export * from './types'
+
+export const billingPlugin = (pluginConfig: BillingPluginConfig = {}) => (config: Config): Config => {
+  if (pluginConfig.disabled) {
+    return config
+  }
+
+  // Initialize collections
+  if (!config.collections) {
+    config.collections = []
+  }
+
+  config.collections.push(
+    createPaymentsCollection(pluginConfig.collections?.payments || 'payments'),
+    createCustomersCollection(pluginConfig.collections?.customers || 'customers'),
+    createInvoicesCollection(pluginConfig.collections?.invoices || 'invoices'),
+    createRefundsCollection(pluginConfig.collections?.refunds || 'refunds'),
+  )
+
+  // Initialize endpoints
+  if (!config.endpoints) {
+    config.endpoints = []
+  }
+
+  config.endpoints?.push(
+    // Webhook endpoints
+    {
+      handler: async (req) => {
+        try {
+          const provider = providerRegistry.get(req.routeParams?.provider as string)
+          if (!provider) {
+            return Response.json({ error: 'Provider not found' }, { status: 404 })
+          }
+
+          const signature = req.headers.get('stripe-signature') || 
+                          req.headers.get('x-mollie-signature')
+
+          const event = await provider.handleWebhook(req as unknown as Request, signature || '')
+          
+          // TODO: Process webhook event and update database
+          
+          return Response.json({ eventId: event.id, received: true })
+        } catch (error) {
+          console.error('[BILLING] Webhook error:', error)
+          return Response.json({ error: 'Webhook processing failed' }, { status: 400 })
+        }
+      },
+      method: 'post',
+      path: '/billing/webhooks/:provider'
+    },
+    // Health check endpoint
+    {
+      handler: async () => {
+        const providers = providerRegistry.getAll().map(p => ({
+          name: p.name,
+          status: 'active'
+        }))
+        
+        return Response.json({
+          providers,
+          status: 'ok',
+          version: '0.1.0'
+        })
+      },
+      method: 'get',
+      path: '/billing/health'
+    }
+  )
+
+  // Initialize providers and onInit hook
+  const incomingOnInit = config.onInit
+
+  config.onInit = async (payload) => {
+    // Execute any existing onInit functions first
+    if (incomingOnInit) {
+      await incomingOnInit(payload)
+    }
+
+    // Initialize payment providers
+    initializeProviders(pluginConfig)
+    
+    // Log initialization
+    console.log('[BILLING] Plugin initialized with providers:', 
+      providerRegistry.getAll().map(p => p.name).join(', ')
+    )
+  }
+
+  return config
+}
+
+function initializeProviders(config: BillingPluginConfig) {
+  // Initialize test provider if enabled
+  if (config.providers?.test?.enabled) {
+    const testProvider = new TestPaymentProvider(config.providers.test)
+    providerRegistry.register(testProvider)
+  }
+
+  // TODO: Initialize Stripe provider
+  // TODO: Initialize Mollie provider
+}
+
+// Utility function to get payment provider
+export function getPaymentProvider(name: string) {
+  const provider = providerRegistry.get(name)
+  if (!provider) {
+    throw new Error(`Payment provider '${name}' not found`)
+  }
+  return provider
+}
+
+// Utility function to list available providers
+export function getAvailableProviders() {
+  return providerRegistry.getAll().map(p => ({
+    name: p.name,
+    // Add provider-specific info here
+  }))
+}
+
+export default billingPlugin

src/providers/base/provider.ts

@@ -0,0 +1,63 @@
+import type { CreatePaymentOptions, Payment, PaymentProvider, Refund, WebhookEvent } from '../../types'
+
+export abstract class BasePaymentProvider implements PaymentProvider {
+  abstract name: string
+
+  protected formatAmount(amount: number, currency: string): number {
+    this.validateAmount(amount)
+    this.validateCurrency(currency)
+    return amount
+  }
+  protected log(level: 'error' | 'info' | 'warn', message: string, data?: Record<string, unknown>): void {
+    const logData = {
+      message,
+      provider: this.name,
+      ...data,
+    }
+    
+    console[level](`[${this.name.toUpperCase()}]`, logData)
+  }
+  protected validateAmount(amount: number): void {
+    if (amount <= 0 || !Number.isInteger(amount)) {
+      throw new Error('Amount must be a positive integer in cents')
+    }
+  }
+  protected validateCurrency(currency: string): void {
+    if (!currency || currency.length !== 3) {
+      throw new Error('Currency must be a valid 3-letter ISO currency code')
+    }
+  }
+  abstract cancelPayment(id: string): Promise<Payment>
+
+  abstract createPayment(options: CreatePaymentOptions): Promise<Payment>
+
+  abstract handleWebhook(request: Request, signature?: string): Promise<WebhookEvent>
+
+  abstract refundPayment(id: string, amount?: number): Promise<Refund>
+
+  abstract retrievePayment(id: string): Promise<Payment>
+}
+
+export function createProviderRegistry() {
+  const providers = new Map<string, PaymentProvider>()
+
+  return {
+    register(provider: PaymentProvider): void {
+      providers.set(provider.name, provider)
+    },
+
+    get(name: string): PaymentProvider | undefined {
+      return providers.get(name)
+    },
+
+    getAll(): PaymentProvider[] {
+      return Array.from(providers.values())
+    },
+
+    has(name: string): boolean {
+      return providers.has(name)
+    }
+  }
+}
+
+export const providerRegistry = createProviderRegistry()

src/providers/test/provider.ts

@@ -0,0 +1,225 @@
+import type { 
+  CreatePaymentOptions, 
+  Payment, 
+  PaymentStatus, 
+  Refund, 
+  TestProviderConfig,
+  WebhookEvent
+} from '../../types';
+
+import { 
+  RefundStatus
+} from '../../types'
+import { BasePaymentProvider } from '../base/provider'
+
+interface TestPaymentData {
+  delayMs?: number
+  failAfterMs?: number
+  simulateFailure?: boolean
+}
+
+export class TestPaymentProvider extends BasePaymentProvider {
+  private config: TestProviderConfig
+  private payments = new Map<string, Payment>()
+  private refunds = new Map<string, Refund>()
+  name = 'test'
+
+  constructor(config: TestProviderConfig) {
+    super()
+    this.config = config
+  }
+
+  private sleep(ms: number): Promise<void> {
+    return new Promise(resolve => setTimeout(resolve, ms))
+  }
+
+  async cancelPayment(id: string): Promise<Payment> {
+    const payment = this.payments.get(id)
+    if (!payment) {
+      throw new Error(`Payment ${id} not found`)
+    }
+
+    if (payment.status === 'succeeded') {
+      throw new Error('Cannot cancel a succeeded payment')
+    }
+
+    const canceledPayment = {
+      ...payment,
+      status: 'canceled' as PaymentStatus,
+      updatedAt: new Date().toISOString()
+    }
+
+    this.payments.set(id, canceledPayment)
+    
+    this.log('info', 'Payment canceled', { paymentId: id })
+    
+    return canceledPayment
+  }
+
+  clearStoredData(): void {
+    this.payments.clear()
+    this.refunds.clear()
+    this.log('info', 'Test data cleared')
+  }
+
+  async createPayment(options: CreatePaymentOptions): Promise<Payment> {
+    const testData = options.metadata?.test as TestPaymentData || {}
+    const delay = testData.delayMs ?? this.config.defaultDelay ?? 0
+    
+    if (delay > 0) {
+      await this.sleep(delay)
+    }
+
+    const shouldFail = testData.simulateFailure ?? 
+      (this.config.simulateFailures && Math.random() < (this.config.failureRate ?? 0.1))
+
+    const paymentId = `test_pay_${Date.now()}_${Math.random().toString(36).substring(7)}`
+    
+    const payment: Payment = {
+      id: paymentId,
+      amount: options.amount,
+      createdAt: new Date().toISOString(),
+      currency: options.currency,
+      customer: options.customer,
+      description: options.description,
+      metadata: options.metadata,
+      provider: this.name,
+      providerData: {
+        autoCompleted: this.config.autoComplete,
+        delayApplied: delay,
+        simulatedFailure: shouldFail,
+        testMode: true
+      },
+      status: shouldFail ? 'failed' : (this.config.autoComplete ? 'succeeded' : 'pending'),
+      updatedAt: new Date().toISOString()
+    }
+
+    this.payments.set(paymentId, payment)
+    
+    this.log('info', 'Payment created', {
+      amount: options.amount,
+      currency: options.currency,
+      paymentId,
+      status: payment.status
+    })
+
+    // Simulate async status updates if configured
+    if (testData.failAfterMs && !shouldFail) {
+      setTimeout(() => {
+        const updatedPayment = { ...payment, status: 'failed' as PaymentStatus, updatedAt: new Date().toISOString() }
+        this.payments.set(paymentId, updatedPayment)
+        this.log('info', 'Payment failed after delay', { paymentId })
+      }, testData.failAfterMs)
+    }
+
+    return payment
+  }
+
+  getAllPayments(): Payment[] {
+    return Array.from(this.payments.values())
+  }
+
+  getAllRefunds(): Refund[] {
+    return Array.from(this.refunds.values())
+  }
+
+  // Test-specific methods
+  getStoredPayment(id: string): Payment | undefined {
+    return this.payments.get(id)
+  }
+
+  getStoredRefund(id: string): Refund | undefined {
+    return this.refunds.get(id)
+  }
+
+  async handleWebhook(request: Request, signature?: string): Promise<WebhookEvent> {
+    if (!this.config.enabled) {
+      throw new Error('Test provider is not enabled')
+    }
+
+    // For test provider, we'll simulate webhook events
+    const body = await request.text()
+    let eventData: Record<string, unknown>
+
+    try {
+      eventData = JSON.parse(body)
+    } catch (error) {
+      throw new Error('Invalid JSON in webhook body')
+    }
+
+    const event: WebhookEvent = {
+      id: `test_evt_${Date.now()}_${Math.random().toString(36).substring(7)}`,
+      type: (eventData.type as string) || 'payment.status_changed',
+      data: eventData,
+      provider: this.name,
+      verified: true // Test provider always considers webhooks verified
+    }
+
+    this.log('info', 'Webhook received', {
+      type: event.type,
+      dataKeys: Object.keys(event.data),
+      eventId: event.id
+    })
+
+    return event
+  }
+
+  async refundPayment(id: string, amount?: number): Promise<Refund> {
+    const payment = this.payments.get(id)
+    if (!payment) {
+      throw new Error(`Payment ${id} not found`)
+    }
+
+    if (payment.status !== 'succeeded') {
+      throw new Error('Can only refund succeeded payments')
+    }
+
+    const refundAmount = amount ?? payment.amount
+    if (refundAmount > payment.amount) {
+      throw new Error('Refund amount cannot exceed payment amount')
+    }
+
+    const refundId = `test_ref_${Date.now()}_${Math.random().toString(36).substring(7)}`
+    
+    const refund: Refund = {
+      id: refundId,
+      amount: refundAmount,
+      createdAt: new Date().toISOString(),
+      currency: payment.currency,
+      paymentId: id,
+      providerData: {
+        autoCompleted: this.config.autoComplete,
+        testMode: true
+      },
+      status: this.config.autoComplete ? 'succeeded' : 'pending'
+    }
+
+    this.refunds.set(refundId, refund)
+
+    // Update payment status
+    const newPaymentStatus: PaymentStatus = refundAmount === payment.amount ? 'refunded' : 'partially_refunded'
+    const updatedPayment = {
+      ...payment,
+      status: newPaymentStatus,
+      updatedAt: new Date().toISOString()
+    }
+    this.payments.set(id, updatedPayment)
+
+    this.log('info', 'Refund created', {
+      amount: refundAmount,
+      paymentId: id,
+      refundId,
+      status: refund.status
+    })
+
+    return refund
+  }
+
+  async retrievePayment(id: string): Promise<Payment> {
+    const payment = this.payments.get(id)
+    if (!payment) {
+      throw new Error(`Payment ${id} not found`)
+    }
+    return payment
+  }
+}

src/types/index.ts

@@ -0,0 +1,224 @@
+import type { Config } from 'payload'
+
+// Base payment provider interface
+export interface PaymentProvider {
+  cancelPayment(id: string): Promise<Payment>
+  createPayment(options: CreatePaymentOptions): Promise<Payment>
+  handleWebhook(request: Request, signature?: string): Promise<WebhookEvent>
+  name: string
+  refundPayment(id: string, amount?: number): Promise<Refund>
+  retrievePayment(id: string): Promise<Payment>
+}
+
+// Payment types
+export interface CreatePaymentOptions {
+  amount: number
+  cancelUrl?: string
+  currency: string
+  customer?: string
+  description?: string
+  metadata?: Record<string, unknown>
+  returnUrl?: string
+}
+
+export interface Payment {
+  amount: number
+  createdAt: string
+  currency: string
+  customer?: string
+  description?: string
+  id: string
+  metadata?: Record<string, unknown>
+  provider: string
+  providerData?: Record<string, unknown>
+  status: PaymentStatus
+  updatedAt: string
+}
+
+export interface Refund {
+  amount: number
+  createdAt: string
+  currency: string
+  id: string
+  paymentId: string
+  providerData?: Record<string, unknown>
+  reason?: string
+  status: RefundStatus
+}
+
+export interface WebhookEvent {
+  data: Record<string, unknown>
+  id: string
+  provider: string
+  type: string
+  verified: boolean
+}
+
+// Status enums
+export type PaymentStatus = 
+  | 'canceled'
+  | 'failed'
+  | 'partially_refunded'
+  | 'pending'
+  | 'processing'
+  | 'refunded'
+  | 'succeeded'
+
+export type RefundStatus =
+  | 'canceled'
+  | 'failed'
+  | 'pending'
+  | 'processing'
+  | 'succeeded'
+
+// Provider configurations
+export interface StripeConfig {
+  apiVersion?: string
+  publishableKey: string
+  secretKey: string
+  webhookEndpointSecret: string
+}
+
+export interface MollieConfig {
+  apiKey: string
+  testMode?: boolean
+  webhookUrl: string
+}
+
+export interface TestProviderConfig {
+  autoComplete?: boolean
+  defaultDelay?: number
+  enabled: boolean
+  failureRate?: number
+  simulateFailures?: boolean
+}
+
+// Plugin configuration
+export interface BillingPluginConfig {
+  admin?: {
+    customComponents?: boolean
+    dashboard?: boolean
+  }
+  collections?: {
+    customers?: string
+    invoices?: string
+    payments?: string
+    refunds?: string
+  }
+  disabled?: boolean
+  providers?: {
+    mollie?: MollieConfig
+    stripe?: StripeConfig
+    test?: TestProviderConfig
+  }
+  webhooks?: {
+    basePath?: string
+    cors?: boolean
+  }
+}
+
+// Collection types
+export interface PaymentRecord {
+  amount: number
+  createdAt: string
+  currency: string
+  customer?: string
+  description?: string
+  id: string
+  metadata?: Record<string, unknown>
+  provider: string
+  providerData?: Record<string, unknown>
+  providerId: string
+  status: PaymentStatus
+  updatedAt: string
+}
+
+export interface CustomerRecord {
+  address?: {
+    city?: string
+    country?: string
+    line1?: string
+    line2?: string
+    postal_code?: string
+    state?: string
+  }
+  createdAt: string
+  email?: string
+  id: string
+  metadata?: Record<string, unknown>
+  name?: string
+  phone?: string
+  providerIds?: Record<string, string>
+  updatedAt: string
+}
+
+export interface InvoiceRecord {
+  amount: number
+  createdAt: string
+  currency: string
+  customer?: string
+  dueDate?: string
+  id: string
+  items: InvoiceItem[]
+  metadata?: Record<string, unknown>
+  number: string
+  paidAt?: string
+  status: InvoiceStatus
+  updatedAt: string
+}
+
+export interface InvoiceItem {
+  description: string
+  quantity: number
+  totalAmount: number
+  unitAmount: number
+}
+
+export type InvoiceStatus = 
+  | 'draft'
+  | 'open' 
+  | 'paid'
+  | 'uncollectible'
+  | 'void'
+
+// Plugin type
+export interface BillingPluginOptions extends BillingPluginConfig {
+  disabled?: boolean
+}
+
+// Error types
+export class BillingError extends Error {
+  constructor(
+    message: string,
+    public code: string,
+    public provider?: string,
+    public details?: Record<string, unknown>
+  ) {
+    super(message)
+    this.name = 'BillingError'
+  }
+}
+
+export class PaymentProviderError extends BillingError {
+  constructor(
+    message: string,
+    provider: string,
+    code?: string,
+    details?: Record<string, unknown>
+  ) {
+    super(message, code || 'PROVIDER_ERROR', provider, details)
+    this.name = 'PaymentProviderError'
+  }
+}
+
+export class WebhookError extends BillingError {
+  constructor(
+    message: string,
+    provider: string,
+    code?: string,
+    details?: Record<string, unknown>
+  ) {
+    super(message, code || 'WEBHOOK_ERROR', provider, details)
+    this.name = 'WebhookError'
+  }
+}

src/types/payload.ts

@@ -0,0 +1,148 @@
+/**
+ * PayloadCMS type definitions for hooks and handlers
+ */
+
+import type { PayloadRequest, User } from 'payload'
+
+// Collection hook types
+export interface CollectionBeforeChangeHook<T = Record<string, unknown>> {
+  data: T
+  operation: 'create' | 'delete' | 'update'
+  originalDoc?: T
+  req: PayloadRequest
+}
+
+export interface CollectionAfterChangeHook<T = Record<string, unknown>> {
+  doc: T
+  operation: 'create' | 'delete' | 'update'
+  previousDoc?: T
+  req: PayloadRequest
+}
+
+export interface CollectionBeforeValidateHook<T = Record<string, unknown>> {
+  data?: T
+  operation: 'create' | 'update'
+  originalDoc?: T
+  req: PayloadRequest
+}
+
+// Access control types
+export interface AccessArgs<T = unknown> {
+  data?: T
+  id?: number | string
+  req: {
+    payload: unknown
+    user: null | User
+  }
+}
+
+// Invoice item type for hooks
+export interface InvoiceItemData {
+  description: string
+  quantity: number
+  totalAmount?: number
+  unitAmount: number
+}
+
+// Invoice data type for hooks
+export interface InvoiceData {
+  amount?: number
+  currency?: string
+  customer?: string
+  dueDate?: string
+  items?: InvoiceItemData[]
+  metadata?: Record<string, unknown>
+  notes?: string
+  number?: string
+  paidAt?: string
+  payment?: string
+  status?: string
+  subtotal?: number
+  taxAmount?: number
+}
+
+// Payment data type for hooks
+export interface PaymentData {
+  amount?: number
+  currency?: string
+  customer?: string
+  description?: string
+  invoice?: string
+  metadata?: Record<string, unknown>
+  provider?: string
+  providerData?: Record<string, unknown>
+  providerId?: string
+  status?: string
+}
+
+// Customer data type for hooks
+export interface CustomerData {
+  address?: {
+    city?: string
+    country?: string
+    line1?: string
+    line2?: string
+    postal_code?: string
+    state?: string
+  }
+  email?: string
+  metadata?: Record<string, unknown>
+  name?: string
+  phone?: string
+  providerIds?: Record<string, string>
+}
+
+// Refund data type for hooks
+export interface RefundData {
+  amount?: number
+  currency?: string
+  description?: string
+  metadata?: Record<string, unknown>
+  payment?: { id: string } | string
+  providerData?: Record<string, unknown>
+  providerId?: string
+  reason?: string
+  status?: string
+}
+
+// Document types with required fields after creation
+export interface PaymentDocument extends PaymentData {
+  amount: number
+  createdAt: string
+  currency: string
+  id: string
+  provider: string
+  providerId: string
+  status: string
+  updatedAt: string
+}
+
+export interface CustomerDocument extends CustomerData {
+  createdAt: string
+  id: string
+  updatedAt: string
+}
+
+export interface InvoiceDocument extends InvoiceData {
+  amount: number
+  createdAt: string
+  currency: string
+  customer: string
+  id: string
+  items: InvoiceItemData[]
+  number: string
+  status: string
+  updatedAt: string
+}
+
+export interface RefundDocument extends RefundData {
+  amount: number
+  createdAt: string
+  currency: string
+  id: string
+  payment: { id: string } | string
+  providerId: string
+  refunds?: string[]
+  status: string
+  updatedAt: string
+}

src/utils/currency.ts

@@ -0,0 +1,130 @@
+/**
+ * Currency utility functions for payment processing
+ */
+
+// Common currency configurations
+export const CURRENCY_CONFIG = {
+  AUD: { name: 'Australian Dollar', decimals: 2, symbol: 'A$' },
+  CAD: { name: 'Canadian Dollar', decimals: 2, symbol: 'C$' },
+  CHF: { name: 'Swiss Franc', decimals: 2, symbol: 'Fr' },
+  DKK: { name: 'Danish Krone', decimals: 2, symbol: 'kr' },
+  EUR: { name: 'Euro', decimals: 2, symbol: '€' },
+  GBP: { name: 'British Pound', decimals: 2, symbol: '£' },
+  JPY: { name: 'Japanese Yen', decimals: 0, symbol: '¥' },
+  NOK: { name: 'Norwegian Krone', decimals: 2, symbol: 'kr' },
+  SEK: { name: 'Swedish Krona', decimals: 2, symbol: 'kr' },
+  USD: { name: 'US Dollar', decimals: 2, symbol: '$' },
+} as const
+
+export type SupportedCurrency = keyof typeof CURRENCY_CONFIG
+
+/**
+ * Validates if a currency code is supported
+ */
+export function isSupportedCurrency(currency: string): currency is SupportedCurrency {
+  return currency in CURRENCY_CONFIG
+}
+
+/**
+ * Validates currency format (3-letter ISO code)
+ */
+export function isValidCurrencyCode(currency: string): boolean {
+  return /^[A-Z]{3}$/.test(currency)
+}
+
+/**
+ * Converts amount from cents to major currency unit
+ */
+export function fromCents(amount: number, currency: string): number {
+  if (!isValidCurrencyCode(currency)) {
+    throw new Error(`Invalid currency code: ${currency}`)
+  }
+
+  const config = CURRENCY_CONFIG[currency as SupportedCurrency]
+  if (!config) {
+    // Default to 2 decimals for unknown currencies
+    return amount / 100
+  }
+
+  return config.decimals === 0 ? amount : amount / Math.pow(10, config.decimals)
+}
+
+/**
+ * Converts amount from major currency unit to cents
+ */
+export function toCents(amount: number, currency: string): number {
+  if (!isValidCurrencyCode(currency)) {
+    throw new Error(`Invalid currency code: ${currency}`)
+  }
+
+  const config = CURRENCY_CONFIG[currency as SupportedCurrency]
+  if (!config) {
+    // Default to 2 decimals for unknown currencies
+    return Math.round(amount * 100)
+  }
+
+  return config.decimals === 0 
+    ? Math.round(amount) 
+    : Math.round(amount * Math.pow(10, config.decimals))
+}
+
+/**
+ * Formats amount for display with currency symbol
+ */
+export function formatAmount(amount: number, currency: string, options?: {
+  showCode?: boolean
+  showSymbol?: boolean
+}): string {
+  const { showCode = false, showSymbol = true } = options || {}
+  
+  if (!isValidCurrencyCode(currency)) {
+    throw new Error(`Invalid currency code: ${currency}`)
+  }
+
+  const majorAmount = fromCents(amount, currency)
+  const config = CURRENCY_CONFIG[currency as SupportedCurrency]
+  
+  let formatted = majorAmount.toFixed(config?.decimals ?? 2)
+  
+  if (showSymbol && config?.symbol) {
+    formatted = `${config.symbol}${formatted}`
+  }
+  
+  if (showCode) {
+    formatted += ` ${currency}`
+  }
+  
+  return formatted
+}
+
+/**
+ * Gets currency information
+ */
+export function getCurrencyInfo(currency: string) {
+  if (!isValidCurrencyCode(currency)) {
+    throw new Error(`Invalid currency code: ${currency}`)
+  }
+
+  return CURRENCY_CONFIG[currency as SupportedCurrency] || {
+    name: currency,
+    decimals: 2,
+    symbol: currency
+  }
+}
+
+/**
+ * Validates amount is positive and properly formatted
+ */
+export function validateAmount(amount: number): void {
+  if (!Number.isFinite(amount)) {
+    throw new Error('Amount must be a finite number')
+  }
+  
+  if (amount <= 0) {
+    throw new Error('Amount must be positive')
+  }
+  
+  if (!Number.isInteger(amount)) {
+    throw new Error('Amount must be an integer (in cents)')
+  }
+}

src/utils/index.ts

@@ -0,0 +1,3 @@
+export * from './currency'
+export * from './logger'
+export * from './validation'

src/utils/logger.ts

@@ -0,0 +1,113 @@
+/**
+ * Structured logging utilities for the billing plugin
+ */
+
+export type LogLevel = 'debug' | 'error' | 'info' | 'warn'
+
+export interface LogContext {
+  [key: string]: unknown
+  amount?: number
+  currency?: string
+  customerId?: string
+  invoiceId?: string
+  paymentId?: string
+  provider?: string
+  refundId?: string
+  webhookId?: string
+}
+
+export interface Logger {
+  debug(message: string, context?: LogContext): void
+  error(message: string, context?: LogContext): void
+  info(message: string, context?: LogContext): void
+  warn(message: string, context?: LogContext): void
+}
+
+/**
+ * Creates a structured logger with consistent formatting
+ */
+export function createLogger(namespace: string = 'BILLING'): Logger {
+  const log = (level: LogLevel, message: string, context: LogContext = {}) => {
+    const timestamp = new Date().toISOString()
+    const logData = {
+      level: level.toUpperCase(),
+      message,
+      namespace,
+      timestamp,
+      ...context,
+    }
+
+    // Use console methods based on log level
+    const consoleMethod = console[level] || console.log
+    consoleMethod(`[${namespace}] ${message}`, logData)
+  }
+
+  return {
+    debug: (message: string, context?: LogContext) => log('debug', message, context),
+    error: (message: string, context?: LogContext) => log('error', message, context),
+    info: (message: string, context?: LogContext) => log('info', message, context),
+    warn: (message: string, context?: LogContext) => log('warn', message, context),
+  }
+}
+
+/**
+ * Default logger instance for the plugin
+ */
+export const logger = createLogger('BILLING')
+
+/**
+ * Creates a provider-specific logger
+ */
+export function createProviderLogger(providerName: string): Logger {
+  return createLogger(`BILLING:${providerName.toUpperCase()}`)
+}
+
+/**
+ * Log payment operations with consistent structure
+ */
+export function logPaymentOperation(
+  operation: string,
+  paymentId: string,
+  provider: string,
+  context?: LogContext
+) {
+  logger.info(`Payment ${operation}`, {
+    operation,
+    paymentId,
+    provider,
+    ...context,
+  })
+}
+
+/**
+ * Log webhook events with consistent structure
+ */
+export function logWebhookEvent(
+  provider: string,
+  eventType: string,
+  webhookId: string,
+  context?: LogContext
+) {
+  logger.info(`Webhook received`, {
+    eventType,
+    provider,
+    webhookId,
+    ...context,
+  })
+}
+
+/**
+ * Log errors with consistent structure
+ */
+export function logError(
+  error: Error,
+  operation: string,
+  context?: LogContext
+) {
+  logger.error(`Operation failed: ${operation}`, {
+    error: error.message,
+    operation,
+    stack: error.stack,
+    ...context,
+  })
+}

src/utils/validation.ts

@@ -0,0 +1,181 @@
+/**
+ * Validation utilities for billing data
+ */
+
+import { z } from 'zod'
+
+import { isValidCurrencyCode } from './currency'
+
+/**
+ * Zod schema for payment creation options
+ */
+export const createPaymentSchema = z.object({
+  amount: z.number().int().positive('Amount must be positive').min(1, 'Amount must be at least 1 cent'),
+  cancelUrl: z.string().url('Invalid cancel URL').optional(),
+  currency: z.string().length(3, 'Currency must be 3 characters').regex(/^[A-Z]{3}$/, 'Currency must be uppercase'),
+  customer: z.string().optional(),
+  description: z.string().max(500, 'Description too long').optional(),
+  metadata: z.record(z.unknown()).optional(),
+  returnUrl: z.string().url('Invalid return URL').optional(),
+})
+
+/**
+ * Zod schema for customer data
+ */
+export const customerSchema = z.object({
+  name: z.string().max(100, 'Name too long').optional(),
+  address: z.object({
+    city: z.string().max(50).optional(),
+    country: z.string().length(2, 'Country must be 2 characters').regex(/^[A-Z]{2}$/, 'Country must be uppercase').optional(),
+    line1: z.string().max(100).optional(),
+    line2: z.string().max(100).optional(),
+    postal_code: z.string().max(20).optional(),
+    state: z.string().max(50).optional(),
+  }).optional(),
+  email: z.string().email('Invalid email address').optional(),
+  metadata: z.record(z.unknown()).optional(),
+  phone: z.string().max(20, 'Phone number too long').optional(),
+})
+
+/**
+ * Zod schema for invoice items
+ */
+export const invoiceItemSchema = z.object({
+  description: z.string().min(1, 'Description is required').max(200, 'Description too long'),
+  quantity: z.number().int().positive('Quantity must be positive'),
+  unitAmount: z.number().int().min(0, 'Unit amount must be non-negative'),
+})
+
+/**
+ * Zod schema for invoice creation
+ */
+export const invoiceSchema = z.object({
+  currency: z.string().length(3).regex(/^[A-Z]{3}$/),
+  customer: z.string().min(1, 'Customer is required'),
+  dueDate: z.string().datetime().optional(),
+  items: z.array(invoiceItemSchema).min(1, 'At least one item is required'),
+  metadata: z.record(z.unknown()).optional(),
+  notes: z.string().max(1000).optional(),
+  taxAmount: z.number().int().min(0).default(0),
+})
+
+/**
+ * Validates payment creation data
+ */
+export function validateCreatePayment(data: unknown) {
+  const result = createPaymentSchema.safeParse(data)
+  if (!result.success) {
+    throw new Error(`Invalid payment data: ${result.error.issues.map(i => i.message).join(', ')}`)
+  }
+  
+  // Additional currency validation
+  if (!isValidCurrencyCode(result.data.currency)) {
+    throw new Error(`Unsupported currency: ${result.data.currency}`)
+  }
+  
+  return result.data
+}
+
+/**
+ * Validates customer data
+ */
+export function validateCustomer(data: unknown) {
+  const result = customerSchema.safeParse(data)
+  if (!result.success) {
+    throw new Error(`Invalid customer data: ${result.error.issues.map(i => i.message).join(', ')}`)
+  }
+  return result.data
+}
+
+/**
+ * Validates invoice data
+ */
+export function validateInvoice(data: unknown) {
+  const result = invoiceSchema.safeParse(data)
+  if (!result.success) {
+    throw new Error(`Invalid invoice data: ${result.error.issues.map(i => i.message).join(', ')}`)
+  }
+  
+  // Additional currency validation
+  if (!isValidCurrencyCode(result.data.currency)) {
+    throw new Error(`Unsupported currency: ${result.data.currency}`)
+  }
+  
+  return result.data
+}
+
+/**
+ * Validates webhook signature format
+ */
+export function validateWebhookSignature(signature: string, provider: string): void {
+  if (!signature) {
+    throw new Error(`Missing webhook signature for ${provider}`)
+  }
+  
+  switch (provider) {
+    case 'mollie':
+      if (signature.length < 32) {
+        throw new Error('Invalid Mollie webhook signature length')
+      }
+      break
+    case 'stripe':
+      if (!signature.startsWith('t=')) {
+        throw new Error('Invalid Stripe webhook signature format')
+      }
+      break
+    case 'test':
+      // Test provider accepts any signature
+      break
+    default:
+      throw new Error(`Unknown provider: ${provider}`)
+  }
+}
+
+/**
+ * Validates payment provider name
+ */
+export function validateProviderName(provider: string): void {
+  const validProviders = ['stripe', 'mollie', 'test']
+  if (!validProviders.includes(provider)) {
+    throw new Error(`Invalid provider: ${provider}. Must be one of: ${validProviders.join(', ')}`)
+  }
+}
+
+/**
+ * Validates payment amount and currency combination
+ */
+export function validateAmountAndCurrency(amount: number, currency: string): void {
+  if (!Number.isInteger(amount) || amount <= 0) {
+    throw new Error('Amount must be a positive integer')
+  }
+  
+  if (!isValidCurrencyCode(currency)) {
+    throw new Error('Invalid currency code')
+  }
+  
+  // Validate minimum amounts for different currencies
+  const minimums: Record<string, number> = {
+    EUR: 50,  // €0.50
+    GBP: 30,  // £0.30
+    JPY: 50,  // ¥50
+    USD: 50,  // $0.50
+  }
+  
+  const minimum = minimums[currency] || 50
+  if (amount < minimum) {
+    throw new Error(`Amount too small for ${currency}. Minimum: ${minimum} cents`)
+  }
+}
+
+/**
+ * Validates refund amount against original payment
+ */
+export function validateRefundAmount(refundAmount: number, paymentAmount: number): void {
+  if (!Number.isInteger(refundAmount) || refundAmount <= 0) {
+    throw new Error('Refund amount must be a positive integer')
+  }
+  
+  if (refundAmount > paymentAmount) {
+    throw new Error('Refund amount cannot exceed original payment amount')
+  }
+}