Typed stripe event generator

event_gen.go

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"html/template"
	"io/ioutil"
	"os"
	"sort"
)

const (
	templateStr = `// Code generated by go generate; DO NOT EDIT.
// generated from template in generate/events.go
package quote

import (
	"encoding/json"

	"github.com/stripe/stripe-go"
)

type Event struct {
	ObjectSet              bool
	Event                  stripe.Event
	{{ range $t := .Types }}{{ $t }}  *stripe.{{ $t }}
	{{ end }}
}

func (e *Event) UnmarshalJSON(data []byte) error {
	if err := json.Unmarshal(data, &e.Event); err != nil {
		return err
	}
	switch e.Event.Type { {{ range $key, $types := .Data }}
	case "{{ $key }}":
		{{ $len := len $types }}{{ if eq $len 1 }}{{ range $field := $types }}
		if err := json.Unmarshal([]byte(e.Event.Data.Raw), e.{{ $field }}); err != nil {
			return err
		}
		e.ObjectSet = true{{ end }} {{ else }}
		var err error{{ range $field := $types }}
		err = json.Unmarshal([]byte(e.Event.Data.Raw), e.{{ $field }})
		// correct type {{ $field }}, return early
		if err == nil {
			e.ObjectSet = true
			return nil
		}{{ end }} {{ end }} {{ end }}
	}
	return nil
}

func (e Event) MarshalJSON() ([]byte, error) {
	type mEvent struct {
		stripe.Event
		Object interface{} ` + "`json:" + `"object"` + "`" + `
	}
	me := mEvent{
		Event: e.Event,
	}
	{{ range $_, $types := .Data }}
	{{ range $field := $types }}
	if e.{{ $field }} != nil {
		me.Object = e.{{ $field }}
		return json.Marshal(me)
	}{{ end }} {{ end }}
	// fallback to default -> marshal raw stripe event
	return json.Marshal(me.Event)
}
`
)

type templateVars struct {
	Data  map[string][]string
	Types []string
}

func main() {
	var (
		inPath, out string
	)
	flag.StringVar(&inPath, "input", "./events.json", "input file to generate code from")
	flag.StringVar(&out, "output", "", "output file")
	flag.Parse()

	jsonStr, err := ioutil.ReadFile(inPath)
	if err != nil {
		fmt.Sprintf("Error reading file: %+v\n", err)
		os.Exit(1)
	}

	vars := templateVars{}
	if err := json.Unmarshal(jsonStr, &vars.Data); err != nil {
		fmt.Sprintf("Error unmarshalling file contents: %+v\n", err)
		os.Exit(1)
	}

	stripeTypes := map[string]struct{}{}
	for _, types := range vars.Data {
		for _, t := range types {
			if _, ok := stripeTypes[t]; !ok {
				stripeTypes[t] = struct{}{}
				vars.Types = append(vars.Types, t)
			}
		}
	}
	sort.Strings(vars.Types)

	to := os.Stdout
	if out != "" {
		f, err := os.Create(out)
		if err != nil {
			fmt.Sprintf("Could not create file %s: %+v\n", out, err)
			os.Exit(1)
		}
		defer f.Close()
		to = f
	}
	t := template.Must(template.New("quote").Parse(templateStr))
	t.Execute(to, vars)
}

events.json

{
  "account.updated": [
    "Account"
  ],
  "account.application.authorized": [
    "Application"
  ],
  "account.application.deauthorized": [
    "Application"
  ],
  "account.external_account.created": [
    "Card",
    "BankAccount"
  ],
  "account.external_account.deleted": [
    "Card",
    "BankAccount"
  ],
  "account.external_account.updated": [
    "Card",
    "BankAccount"
  ],
  "application_fee.created": [
    "ApplicationFee"
  ],
  "application_fee.refunded": [
    "ApplicationFee"
  ],
  "application_fee.refund.updated": [
    "FeeRefund"
  ],
  "balance.available": [
    "Balance"
  ],
  "charge.captured": [
    "Charge"
  ],
  "charge.expired": [
    "Charge"
  ],
  "charge.failed": [
    "Charge"
  ],
  "charge.pending": [
    "Charge"
  ],
  "charge.refunded": [
    "Charge"
  ],
  "charge.succeeded": [
    "Charge"
  ],
  "charge.updated": [
    "Charge"
  ],
  "charge.dispute.closed": [
    "Dispute"
  ],
  "charge.dispute.created": [
    "Dispute"
  ],
  "charge.dispute.funds_reinstated": [
    "Dispute"
  ],
  "charge.dispute.funds_withdrawn": [
    "Dispute"
  ],
  "charge.dispute.updated": [
    "Dispute"
  ],
  "charge.refund.updated": [
    "Refund"
  ],
  "coupon.created": [
    "Coupon"
  ],
  "coupon.deleted": [
    "Coupon"
  ],
  "coupon.updated": [
    "Coupon"
  ],
  "customer.created": [
    "Customer"
  ],
  "customer.deleted": [
    "Customer"
  ],
  "customer.updated": [
    "Customer"
  ],
  "customer.discount.created": [
    "Discount"
  ],
  "customer.discount.deleted": [
    "Discount"
  ],
  "customer.discount.updated": [
    "Discount"
  ],
  "customer.source.created": [
    "Card"
  ],
  "customer.source.deleted": [
    "Card"
  ],
  "customer.source.expiring": [
    "Card"
  ],
  "customer.source.updated": [
    "Card"
  ],
  "customer.subscription.created": [
    "Subscription"
  ],
  "customer.subscription.deleted": [
    "Subscription"
  ],
  "customer.subscription.trial_will_end": [
    "Subscription"
  ],
  "customer.subscription.updated": [
    "Subscription"
  ],
  "file.created": [
    "File"
  ],
  "invoice.created": [
    "Invoice"
  ],
  "invoice.deleted": [
    "Invoice"
  ],
  "invoice.finalized": [
    "Invoice"
  ],
  "invoice.marked_uncollectible": [
    "Invoice"
  ],
  "invoice.payment_failed": [
    "Invoice"
  ],
  "invoice.payment_succeeded": [
    "Invoice"
  ],
  "invoice.sent": [
    "Invoice"
  ],
  "invoice.upcoming": [
    "Invoice"
  ],
  "invoice.updated": [
    "Invoice"
  ],
  "invoice.voided": [
    "Invoice"
  ],
  "invoiceitem.created": [
    "InvoiceItem"
  ],
  "invoiceitem.deleted": [
    "InvoiceItem"
  ],
  "invoiceitem.updated": [
    "InvoiceItem"
  ],
  "issuing_authorization.created": [
    "IssuingAuthorization"
  ],
  "issuing_authorization.request": [
    "IssuingAuthorization"
  ],
  "issuing_authorization.updated": [
    "IssuingAuthorization"
  ],
  "issuing_card.created": [
    "IssuingCard"
  ],
  "issuing_card.updated": [
    "IssuingCard"
  ],
  "issuing_cardholder.created": [
    "IssuingCardholder"
  ],
  "issuing_cardholder.updated": [
    "IssuingCardholder"
  ],
  "issuing_dispute.created": [
    "IssuingDispute"
  ],
  "issuing_dispute.updated": [
    "IssuingDispute"
  ],
  "issuing_transaction.created": [
    "IssuingTransaction"
  ],
  "issuing_transaction.updated": [
    "IssuingTransaction"
  ],
  "order.created": [
    "Order"
  ],
  "order.payment_failed": [
    "Order"
  ],
  "order.payment_succeeded": [
    "Order"
  ],
  "order.updated": [
    "Order"
  ],
  "order_return.created": [
    "OrderReturn"
  ],
  "payment_intent.amount_capturable_updated": [
    "PaymentIntent"
  ],
  "payment_intent.created": [
    "PaymentIntent"
  ],
  "payment_intent.payment_failed": [
    "PaymentIntent"
  ],
  "payment_intent.requires_capture": [
    "PaymentIntent"
  ],
  "payment_intent.succeeded": [
    "PaymentIntent"
  ],
  "payout.canceled": [
    "Payout"
  ],
  "payout.created": [
    "Payout"
  ],
  "payout.failed": [
    "Payout"
  ],
  "payout.paid": [
    "Payout"
  ],
  "payout.updated": [
    "Payout"
  ],
  "plan.created": [
    "Plan"
  ],
  "plan.deleted": [
    "Plan"
  ],
  "plan.updated": [
    "Plan"
  ],
  "product.created": [
    "Product"
  ],
  "product.deleted": [
    "Product"
  ],
  "product.updated": [
    "Product"
  ],
  "recipient.created": [
    "Recipient"
  ],
  "recipient.deleted": [
    "Recipient"
  ],
  "recipient.updated": [
    "Recipient"
  ],
  "reporting.report_run.failed": [
    "ReportRun"
  ],
  "reporting.report_run.succeeded": [
    "ReportRun"
  ],
  "reporting.report_type.updated": [
    "ReportType"
  ],
  "review.closed": [
    "Review"
  ],
  "review.opened": [
    "Review"
  ],
  "sigma.scheduled_query_run.created": [
    "SigmaScheduledQueryRun"
  ],
  "sku.created": [
    "SKU"
  ],
  "sku.deleted": [
    "SKU"
  ],
  "sku.updated": [
    "SKU"
  ],
  "source.canceled": [
    "Source"
  ],
  "source.chargeable": [
    "Source"
  ],
  "source.failed": [
    "Source"
  ],
  "source.mandate_notification": [
    "Source"
  ],
  "source.refund_attributes_required": [
    "Source"
  ],
  "source.transaction.created": [
    "SourceTransaction"
  ],
  "source.transaction.updated": [
    "SourceTransaction"
  ],
  "topup.canceled": [
    "Topup"
  ],
  "topup.created": [
    "Topup"
  ],
  "topup.failed": [
    "Topup"
  ],
  "topup.reversed": [
    "Topup"
  ],
  "topup.succeeded": [
    "Topup"
  ],
  "transfer.created": [
    "Transfer"
  ],
  "transfer.reversed": [
    "Transfer"
  ],
  "transfer.updated": [
    "Transfer"
  ]
}