// Package event is the platform's shared event vocabulary: one envelope shape
// (Event) and a small set of Type constants for the event meanings that
// genuinely cross module boundaries. It imports only the stdlib — never an app
// module, never a transport library — so every module can depend on it.
//
// Discipline: a Type constant earns its place only when a real producer emits it
// AND it is meaningful to another module. We do not pre-declare aspirational
// types. See docs/platform-event-messaging-sketch.md.
package event

import (
	"context"
	"encoding/json"
	"time"
)

// Type is the semantic event kind — the cross-module contract. A module may use
// its own private kinds internally; only meanings that cross a boundary belong
// here.
type Type string

const (
	// Editorial (graph-cms). Emitted by the CMS outbound bridge on content-graph
	// mutations. In-repo consumers are TBD (external generators today); this is
	// the first envelope producer, so the constants exist where they are emitted.
	ContentCreated Type = "content.created"
	ContentUpdated Type = "content.updated"
	ContentDeleted Type = "content.deleted"

	// Catalog (finder). These meanings already cross modules today — finder
	// writer → reader and → backoffice (MountFinderListener) — but still travel
	// as finder's legacy ChangeTopic strings on the wire. The constants document
	// the shared vocabulary; the wire migration onto the envelope is a later step.
	CatalogItemChanged      Type = "catalog.item_changed"      // legacy: finder "item_added"
	CatalogSnapshotReady    Type = "catalog.snapshot_ready"    // legacy: finder "snapshot_ready"
	CatalogSettingsChanged  Type = "catalog.settings_changed"  // legacy: finder "settings_change"
	CatalogFacetChanged     Type = "catalog.facet_changed"     // legacy: finder "facet_change"
	CatalogAccessoryChanged Type = "catalog.accessory_changed" // legacy: finder "accessory_change"
	// CatalogProjectionPublished carries the commerce-facing catalog Projection
	// (platform/catalog) — producer maps raw items → Projection once, consumers
	// (cart / checkout / order / UCP) read the typed shape. Distinct from
	// CatalogItemChanged (raw bodies, consumed by inventory/backoffice): a
	// product index emits BOTH; a non-product index emits neither projection.
	// Payload is a []catalog.ProjectionUpdate batch (upserts + deletes per SKU).
	CatalogProjectionPublished Type = "catalog.projection_published"
	CatalogSortOverride        Type = "catalog.sort_override"       // finder-internal: per-session/group/popularity overrides
	CatalogFieldSortOverride   Type = "catalog.field_sort_override" // finder-internal: live field ordering overrides

	// Inventory (go-redis-inventory core, emitted by the cart-inventory service).
	// A coarse stock-level crossing (none/low/high) for one SKU+location —
	// never a quantity. Exact stock is a synchronous query against the inventory
	// service; only level crossings cross a module boundary. Payload is an
	// inventory.LevelChanged (platform/inventory). First consumer: finder stock
	// overlay (display hints). See docs/inventory-shape.md.
	InventoryLevelChanged Type = "inventory.level_changed"

	// Commerce (order). Emitted by the order service saga after an order is
	// placed-and-paid (a durable outbox event). The authoritative "a sale
	// happened" fact — multiple modules react independently (inventory commits
	// stock, fulfillment allocates) without checkout coupling to any of them.
	// Payload is an order.Created (platform/order). See docs/inventory-shape.md
	// and docs/fulfillment-stance.md.
	OrderCreated Type = "order.created"

	// Analytics (tracking). Replaces the integer enum 0–6 that finder and
	// slask-tracking use on the `tracking` topic today. Producer: slask-finder
	// (pkg/tracking/rabbit-tracking.go). Consumer: slask-tracking
	// (pkg/events/rabbit-tracking.go).
	TrackSession     Type = "track.session"    // 0 — session start
	TrackSearch      Type = "track.search"     // 1 — search query
	TrackClick       Type = "track.click"      // 2 — item click / product view
	TrackCart        Type = "track.cart"       // 3,4 — add to / remove from cart
	TrackImpression  Type = "track.impression" // 5 — impression
	TrackAction      Type = "track.action"     // 6 — custom action (wishlist, etc.)
	TrackPageView    Type = "track.page_view"
	TrackPageEngaged Type = "track.page_engaged"
	TrackPageAction  Type = "track.page_action"
	TrackExperiment  Type = "track.experiment"
	// TrackPurchase — cut 23. Post-checkout funnel closure; emitted by
	// event_handlers.go::TrackPurchase on a purchase request. Replaces
	// 5 hand-written `pevent.Type("track.purchase")` literals with this
	// typed constant.
	TrackPurchase Type = "track.purchase"
	// TrackPromotionView / TrackPromotionClick — storefront promotion
	// attribution. Producer: the storefront promotion-badge islands, PLP
	// promo badges, bundle picker and cart bundle upsell (lib/track.ts
	// beacons → POST /api/track/promotion). Consumer: slask-tracking
	// (pkg/view PromoStats) — per-promotion view/click counters for the
	// promotions admin. Payload is the wire PromotionEvent (promotion id,
	// action, placement, optional item id). These ride the browser beacon
	// path only (no AMQP producer today), so they stay out of the
	// `track.*` RabbitMQ routing pattern by construction.
	TrackPromotionView  Type = "track.promotion_view"
	TrackPromotionClick Type = "track.promotion_click"
	// TrackEvent — free-form named storefront event (custom analytics
	// signals the storefront wires ad hoc: open_cart, plp_sort_change,
	// plp_filter_change, …). Producer: lib/track.ts trackEvent() beacons /
	// the data-track attribute island (POST /api/track/event). Consumer:
	// slask-tracking (pkg/view CustomEvent → pkg/customstats) — per-name
	// counters for the tracking read surface. Payload is the wire
	// CustomEvent (name + flat string props). Browser-beacon path only,
	// like the promotion pair.
	TrackEvent Type = "track.event"

	// Newsletter campaign attribution (review 3.8). Producer: the order
	// service's MailerSend webhook receiver (cmd/order/newsletter-webhook.go)
	// when MailerSend reports an open / click for a newsletter send. Consumer:
	// slask-tracking (pkg/events/rabbit-tracking.go) — feeds per-send
	// open/click rates for the backoffice delivery log. Payload is an
	// event.CampaignEvent. Wire routing keys `track.campaign_open` /
	// `track.campaign_click` ride the existing `track.*` pattern on the
	// catalog exchange.
	TrackCampaignOpen  Type = "track.campaign_open"
	TrackCampaignClick Type = "track.campaign_click"

	// Wishlist attribution (W6d of docs/plan-wishlist-favorites.md).
	// Producers: profile service (share-page read) and cart service
	// (list→cart conversion). Consumer: slask-tracking
	// (pkg/events/rabbit-tracking.go) — feeds the saved-together
	// co-occurrence group. Payload is an event.WishlistEvent — product
	// ids only, never owner identity (C5 pseudonymity). Wire routing
	// keys are `track.wishlist_viewed` / `track.wishlist_to_cart` so
	// they ride the existing `track.*` pattern on the catalog exchange.
	WishlistViewed Type = "wishlist.viewed"  // public share-page read
	WishlistToCart Type = "wishlist.to_cart" // list → cart conversion

	// Wishlist mutation outbox (W6 hardening of docs/plan-wishlist-favorites.md).
	// Producers: profile service (owner-scoped wishlist mutations, emitted
	// from the UCP handlers on successful applies) and cart service (cart→list
	// conversion). No in-repo consumer yet — these are the durable domain
	// facts that future consumers bind to (price-drop / back-in-stock
	// notifications, merchandising analytics, GDPR audit). Wire routing keys
	// mirror the Type (`wishlist.created`, `wishlist.item_added`, …,
	// `cart.to_wishlist`) on the catalog exchange. Unlike the tracking
	// attribution pair above, these ride their own routing keys — NOT the
	// `track.*` pattern — so slask-tracking's existing `track.*` binding
	// does not pick them up. Payload: event.WishlistMutationEvent (profile)
	// / event.CartToWishlistEvent (cart). See docs/amqp-topics.md.
	WishlistCreated     Type = "wishlist.created"    // explicit user-created list (not the implicit default materialisation)
	WishlistItemAdded   Type = "wishlist.item_added" // one per SKU added (single-add and batch paths)
	WishlistItemRemoved Type = "wishlist.item_removed"
	WishlistShared      Type = "wishlist.shared"  // share (re)generated — token itself never leaves the service
	CartToWishlist      Type = "cart.to_wishlist" // cart → list conversion (cart service)
)

// CampaignEvent is the payload for the newsletter campaign attribution
// events (TrackCampaignOpen / TrackCampaignClick). Deliberately pseudonymous
// (C5): it carries the send id (the `newsletter:{sendID}` MailerSend tag
// parsed from the webhook) and a sha256 hex hash of the recipient email,
// never the address itself. At is unix seconds (MailerSend's created_at;
// falls back to arrival time when absent).
//
// URL is the link that was clicked (TrackCampaignClick only): the webhook
// receiver stamps the MailerSend click URL so slask-tracking can aggregate
// top-clicked links per send. Empty for opens and for clicks whose payload
// carried no URL.
type CampaignEvent struct {
	SendID    string `json:"sendId"`
	EmailHash string `json:"emailHash"`
	At        int64  `json:"at,omitempty"`
	URL       string `json:"url,omitempty"`
}

// WishlistEvent is the payload for the wishlist attribution events
// (WishlistViewed / WishlistToCart). Deliberately lean: list id + catalog
// item ids only — no owner id, no list name, no share token, so the
// pseudonymous tracking contract (C5) holds on the wire.
type WishlistEvent struct {
	ListId  uint32   `json:"listId"`
	ItemIds []uint32 `json:"itemIds"`
}

// WishlistMutationEvent is the payload for the wishlist mutation outbox
// events (WishlistCreated / WishlistItemAdded / WishlistItemRemoved /
// WishlistShared). Fields are optional per event:
//
//	wishlist.created      → ListId + Name
//	wishlist.item_added   → ListId + Sku + ItemId
//	wishlist.item_removed → ListId + Sku (+ ItemId when known)
//	wishlist.shared       → ListId + Name
//
// No owner identity, no share token (C5): a consumer can correlate by list
// id but never attribute a list to a customer from the event alone.
type WishlistMutationEvent struct {
	ListId uint32 `json:"listId"`
	Name   string `json:"name,omitempty"`
	Sku    string `json:"sku,omitempty"`
	ItemId uint32 `json:"itemId,omitempty"`
}

// CartToWishlistEvent is the payload for cart.to_wishlist (cart service).
// Carries the pseudonymised owner profile id (the cart's UserId — a
// customer-scoped opaque uint64 id, never an email/name) plus the list the
// lines landed in and the SKUs copied. Unlike the tracking pair, this is a
// domain outbox event on its own routing key; a future consumer (e.g.
// price-drop) needs the owner to address the customer.
type CartToWishlistEvent struct {
	OwnerId  uint64   `json:"ownerId"`
	ListId   uint32   `json:"listId"`
	ListName string   `json:"listName,omitempty"`
	Skus     []string `json:"skus,omitempty"`
}

// KnownTypes lists every event that has a declared Track* constant above.
// New pevent constants MUST also be added here so IsKnownType stays in
// sync. Used by HTTP handlers' forward-validation (e.g. SessionsPanel
// ?event_types= param, cut 25) so caller's typo's surface as a 400
// rather than silently dropping unknown tokens.
// KnownTypes is deliberately Track*-only: IsKnownType validates the
// user-facing `track.*` event-type query surface (SessionsPanel
// ?event_types= etc.). The wishlist attribution types (WishlistViewed /
// WishlistToCart) are consumed exclusively over AMQP and never appear in
// that HTTP param surface, so they stay out of this list (the drift-guard
// test enforces the Track* discipline).
var KnownTypes = []Type{
	TrackSession, TrackSearch, TrackClick, TrackCart, TrackPurchase,
	TrackImpression, TrackAction, TrackPageView, TrackPageEngaged,
	TrackPageAction, TrackExperiment,
	TrackPromotionView, TrackPromotionClick, TrackEvent,
	// Track* constants without a browser beacon: consumed over AMQP only,
	// but the drift-guard test requires every declared Track* constant to
	// appear here so the HTTP ?event_types= surface stays exhaustive.
	TrackCampaignOpen, TrackCampaignClick,
}

// IsKnownType reports whether s matches one of the declared Track*
// constants. Case-sensitive + exact-match. Callers MUST pass the canonical
// lowercase form (e.g. "track.search", NOT "Track.Search" or
// "TRACK.SEARCH"). Track* constants are declared lowercase in this file,
// and this function matches the literal string value of each constant.
// Callers should validate with this BEFORE casting untrusted input to Type.
func IsKnownType(s string) bool {
	for _, t := range KnownTypes {
		if string(t) == s {
			return true
		}
	}
	return false
}

// Event is the one envelope. Payload is per-Type, agreed between producer and
// consumer (json.RawMessage, not a god-struct). A nil Payload means "the subject
// changed; fetch the latest state."
type Event struct {
	ID      string            `json:"id"`                // unique; enables idempotent/at-least-once dedupe
	Type    Type              `json:"type"`              // the vocabulary
	Source  string            `json:"source"`            // module identifier ("graph-cms", "finder", ...)
	Subject string            `json:"subject"`           // the resource that changed (node id, sku, ...)
	Payload json.RawMessage   `json:"payload,omitempty"` // per-Type body, or nil
	Time    time.Time         `json:"time"`
	Meta    map[string]string `json:"meta,omitempty"` // trace id, causation, country, dataType, ...
}

// Handler consumes an event. Returning an error means "not handled" — durable
// transports may redeliver; fire-and-forget transports just log.
type Handler func(ctx context.Context, e Event) error