package adapter

import (
	"bytes"
	"context"
	"encoding/json"
	"net/http"
	"time"
)

// HTTPTelemetry POSTs to the control plane, per docs/adapter-contract.md.
// It must never carry subscriber identity or post body text; callers control
// that by what they put in fields.
type HTTPTelemetry struct {
	ControlURL string
	hc         *http.Client
}

// NewHTTPTelemetry builds a telemetry emitter posting to
// <controlURL>/control/v1/telemetry.
func NewHTTPTelemetry(controlURL string) *HTTPTelemetry {
	return &HTTPTelemetry{ControlURL: controlURL, hc: &http.Client{Timeout: 10 * time.Second}}
}

func (t *HTTPTelemetry) Emit(ctx context.Context, event string, fields map[string]any) {
	if t.ControlURL == "" {
		return
	}
	payload := map[string]any{"event": event, "fields": fields}
	body, err := json.Marshal(payload)
	if err != nil {
		return
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, t.ControlURL+"/control/v1/telemetry", bytes.NewReader(body))
	if err != nil {
		return
	}
	req.Header.Set("Content-Type", "application/json")
	// Best-effort: a dropped telemetry event must never fail the publication
	// it describes.
	resp, err := t.hc.Do(req)
	if err != nil {
		return
	}
	_ = resp.Body.Close()
}