// Copyright 2026 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

// Package sessiontag carries a per-page-load identifier from the
// originating HTTP request down to the service- and model-layer SSE
// publishers. The publishers echo the tag back inside event payloads so
// the originating browser tab can suppress its own event after it has
// already applied the optimistic update locally.
//
// It is deliberately tiny and dependency-free so any feature that emits
// Server-Sent Events (project boards, milestones, ...) can share one
// context key without importing one another.
package sessiontag

import "context"

// sessionTagCtxKey is the context key under which the X-Session-Tag
// value from the originating HTTP request is stashed.
type sessionTagCtxKey struct{}

// WithSessionTag returns ctx decorated with the provided session tag.
// Web/API middleware reads the X-Session-Tag header and calls this so
// service- and model-layer publishers can pull the tag back out.
func WithSessionTag(ctx context.Context, tag string) context.Context {
	if tag == "" {
		return ctx
	}
	return context.WithValue(ctx, sessionTagCtxKey{}, tag)
}

// SessionTagFromContext returns the session tag previously stored via
// WithSessionTag, or "" when none was set.
func SessionTagFromContext(ctx context.Context) string {
	if v, ok := ctx.Value(sessionTagCtxKey{}).(string); ok {
		return v
	}
	return ""
}