Events

The Event[P] type

type Event[P any] struct {
	Name   EventName `json:"name"`
	Params P         `json:"params,omitempty"`
}

func NewEvent[P any](name EventName, params P) Event[P]

Helpers on Event[P]:

Method	Description
AnyEvent()	Project to Event[any] for protocol-level encoding.
Decode(out)	Decode this event into another shape via mapstructure.
DecodeParams(out)	Decode only .Params.
EncodeParams(in)	Encode an arbitrary value into this event's .Params.

Predefined GA4 event names

pkg/sesamy/eventname.go defines 44 constants for GA4 automatically collected, enhanced-measurement, and recommended events. Examples:

ad_impression, add_payment_info, add_shipping_info, add_to_cart, add_to_wishlist,
begin_checkout, campaign_details, click, close_convert_lead, close_unconvert_lead,
disqualify_lead, earn_virtual_money, exception, file_download, first_visit,
form_start, form_submit, generate_lead, join_group, level_end, level_start,
level_up, login, logout, page_view, post_score, purchase, qualify_lead, refund,
remove_from_cart, screen_view, scroll, search, select_content, select_item,
select_promotion, share, sign_up, spend_virtual_currency, tutorial_begin,
tutorial_complete, unlock_achievement, user_engagement, video_complete,
video_progress, video_start, view_cart, view_item, view_item_list, view_promotion,
view_search_results

Use them as the first argument to NewEvent:

e := sesamy.NewEvent(sesamy.EventNamePurchase, params)

Custom event names are fine too — EventName is just a string:

const MyEvent sesamy.EventName = "my_custom_event"

Custom typed params

Define a struct and use the generic:

type PurchaseParams struct {
	TransactionID string  `json:"transaction_id"`
	Value         float64 `json:"value"`
	Currency      string  `json:"currency"`
}

ev := sesamy.NewEvent(sesamy.EventNamePurchase, PurchaseParams{
	TransactionID: "T-123",
	Value:         42,
	Currency:      "EUR",
})

// To transport: project to any-params:
any := ev.AnyEvent()

Provider-defined events

Providers ship their own typed events that wrap sesamy.Event[P]:

• Emarsys — EmarsysCart, EmarsysCategory, EmarsysPurchase, EmarsysView.
• Tracify — conversion-tracking events.

See reference/providers.

Decoding inbound events

A common pattern: react to specific event names with typed params.

func handle(l *zap.Logger, r *http.Request, e *sesamy.Event[any]) error {
	switch e.Name {
	case sesamy.EventNamePurchase:
		var p PurchaseParams
		if err := e.DecodeParams(&p); err != nil {
			return err
		}
		// do something with typed p
	}
	return nil
}

Plug into the middleware chain via gtaghttp.MiddlewareEventHandler or mpv2http.MiddlewareEventHandler — see server-side Collect.