// The agent's wiring for the host half of the reverse channel (issue #53 / C6
// Step 3). The dial/serve/backoff machinery itself lives in
// internal/tunnelclient — a leaf package, so the edge's acceptance test can
// drive the SAME loop this agent runs (internal/host imports internal/edge,
// so the edge tests can never import this package). What is left here is the
// part that is genuinely agent-shaped: reading the env, and publishing the
// state the status heartbeat reports.
package host

import (
	"context"
	"log"
	"net/http"
	"os"
	"sync/atomic"

	"github.com/carlosframework/platform/internal/tunnelclient"
)

// tunnelStateVal is "" (disabled/never started), "connected", or
// "reconnecting" — read by statusLoop's heartbeat probe (probes must fail
// toward honest values; "" means the loop isn't running at all).
var tunnelStateVal atomic.Value

func tunnelState() string {
	if v, ok := tunnelStateVal.Load().(string); ok {
		return v
	}
	return ""
}

// tunnelLoop dials CARLOS_TUNNEL_URL and serves handler over the inverted
// conn, forever, with jittered capped backoff. Inert unless all three env
// vars are set — the same convention as every other optional agent loop.
func tunnelLoop(handler http.Handler) {
	rawURL := os.Getenv("CARLOS_TUNNEL_URL")
	token := os.Getenv("CARLOS_TUNNEL_TOKEN")
	name := os.Getenv("CARLOS_TUNNEL_NAME")
	if rawURL == "" || token == "" || name == "" {
		if rawURL != "" || token != "" || name != "" {
			log.Printf("agent: tunnel loop disabled: need all of CARLOS_TUNNEL_URL, CARLOS_TUNNEL_TOKEN, CARLOS_TUNNEL_NAME")
		}
		return
	}
	log.Printf("agent: tunnel loop armed (%s as %q)", rawURL, name)
	// context.Background(): the agent's tunnel runs for the life of the
	// process and is torn down with it. The ctx exists for callers that need
	// to stop the loop deterministically (the edge's e2e), not for this one.
	tunnelclient.Loop(context.Background(), tunnelclient.Config{
		URL:     rawURL,
		Name:    name,
		Token:   token,
		Handler: handler,
		OnState: func(s string) { tunnelStateVal.Store(s) },
		// The "agent: " prefix is what operators grep the journal for, so it
		// is preserved here rather than baked into the leaf package.
		Logf: func(format string, args ...any) { log.Printf("agent: "+format, args...) },
	})
}