// fleet-agent — the on-host steady-state control-plane client (telemetry v1).
//
// Runs in the booted system as a systemd service. It dials the fleet-manager over
// mTLS using the host's reused TPM identity (private key stays in the TPM), opens
// the long-lived FleetAgent.Session bidi stream, sends a Hello then periodic
// HealthSnapshots, and — in this telemetry-only build — LOGS but does NOT act on
// the DesiredState/Command messages the manager pushes back. The receive path is
// wired now so the reconcile actuators (kiosk URL, reboot, drain) can be added in a
// follow-up without a protocol change.
//
// No inbound host port: the host always dials out (works behind the OPNsense L3
// hop from the authenticated host VLAN to the mgmt plane). A dropped stream is
// retried with jittered backoff; the manager treats stream loss as "offline".
package main

import (
	"context"
	"log"
	"math/rand"
	"os"
	"os/signal"
	"strconv"
	"strings"
	"syscall"
	"time"

	fleetpb "fleet-agent/proto"

	"github.com/google/go-tpm/tpm2"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
	"google.golang.org/grpc/keepalive"
)

type config struct {
	manager    string // manager host:port (DNS name — fleet-generic, invariant #1 safe)
	serverName string // TLS SNI / hostname to verify (defaults to manager host)
	caFile     string // fleet CA bundle: verifies the manager's server cert
	tpmPath    string
	handle     tpm2.TPMHandle
	nvIndex    tpm2.TPMHandle
	interval   time.Duration
	hostapiURL string
	kioskEnv   string // path to /etc/kiosk/kiosk.env (source of KIOSK_URL)
}

func main() {
	log.SetFlags(0)
	log.SetPrefix("fleet-agent: ")
	cfg := loadConfig()

	id, err := loadTPMIdentity(cfg.tpmPath, cfg.handle, cfg.nvIndex)
	if err != nil {
		log.Fatalf("TPM identity: %v", err)
	}
	defer id.Close()
	log.Printf("identity: cert serial %x (CN=%q) — dialing %s",
		id.cert.Leaf.SerialNumber, id.cert.Leaf.Subject.CommonName, cfg.manager)

	tlsCfg, err := clientTLS(id, cfg.caFile, cfg.serverName)
	if err != nil {
		log.Fatalf("client TLS: %v", err)
	}
	cc, err := grpc.NewClient(cfg.manager,
		grpc.WithTransportCredentials(credentials.NewTLS(tlsCfg)),
		grpc.WithKeepaliveParams(keepalive.ClientParameters{
			Time:                20 * time.Second, // >= server MinTime (10s)
			Timeout:             10 * time.Second,
			PermitWithoutStream: true,
		}),
	)
	if err != nil {
		log.Fatalf("grpc client: %v", err)
	}
	defer cc.Close()
	client := fleetpb.NewFleetAgentClient(cc)

	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

	p := &prober{hostapiURL: cfg.hostapiURL}
	backoff := time.Second
	for ctx.Err() == nil {
		start := time.Now()
		if err := runSession(ctx, client, cfg, p); err != nil && ctx.Err() == nil {
			log.Printf("session ended: %v", err)
		}
		if ctx.Err() != nil {
			break
		}
		// Reset backoff after a session that stayed up a while; otherwise grow it
		// (capped) with jitter to avoid reconnect storms across the fleet.
		if time.Since(start) > 30*time.Second {
			backoff = time.Second
		}
		sleep := min(backoff+time.Duration(rand.Int63n(int64(backoff+1))), 30*time.Second)
		log.Printf("reconnecting in %s", sleep.Round(time.Millisecond))
		select {
		case <-ctx.Done():
		case <-time.After(sleep):
		}
		if backoff < 15*time.Second {
			backoff *= 2
		}
	}
	log.Printf("shutting down")
}

// runSession opens one Session stream, sends Hello + periodic snapshots, and logs
// any ManagerDown. It returns when the stream fails or ctx is cancelled.
func runSession(ctx context.Context, client fleetpb.FleetAgentClient, cfg config, p *prober) error {
	sctx, cancel := context.WithCancel(ctx)
	defer cancel()

	stream, err := client.Session(sctx)
	if err != nil {
		return err
	}

	// Hello first — what we're running, so the manager reconciles version drift.
	facts := fetchFacts(sctx, cfg.hostapiURL)
	if err := stream.Send(&fleetpb.AgentUp{Msg: &fleetpb.AgentUp_Hello{Hello: buildHello(facts, readKioskURL(cfg.kioskEnv))}}); err != nil {
		return err
	}
	log.Printf("connected to %s — streaming health every %s", cfg.manager, cfg.interval)

	// Receive loop: v1 LOGS desired-state/commands, does not act on them.
	go func() {
		for {
			down, err := stream.Recv()
			if err != nil {
				cancel()
				return
			}
			logDown(down)
		}
	}()

	// Send one snapshot immediately, then on the interval.
	t := time.NewTicker(cfg.interval)
	defer t.Stop()
	if err := stream.Send(&fleetpb.AgentUp{Msg: &fleetpb.AgentUp_Snapshot{Snapshot: p.snapshot(sctx)}}); err != nil {
		return err
	}
	for {
		select {
		case <-sctx.Done():
			return sctx.Err()
		case <-t.C:
			if err := stream.Send(&fleetpb.AgentUp{Msg: &fleetpb.AgentUp_Snapshot{Snapshot: p.snapshot(sctx)}}); err != nil {
				return err
			}
		}
	}
}

// logDown records a manager->host message. TELEMETRY-ONLY v1: received, logged,
// NOT applied. The reconcile actuators land in a follow-up (see docs/TODO.md #14).
func logDown(down *fleetpb.ManagerDown) {
	switch m := down.GetMsg().(type) {
	case *fleetpb.ManagerDown_Desired:
		d := m.Desired
		log.Printf("desired-state (NOT applied — telemetry-only): target_version=%q kiosk_url=%q reboot_at=%d drain=%v",
			d.GetTargetVersion(), d.GetKioskUrl(), d.GetRebootAtUnix(), d.GetDrain())
	case *fleetpb.ManagerDown_Command:
		log.Printf("command (NOT applied — telemetry-only): id=%s kind=%s", m.Command.GetCommandId(), m.Command.GetKind())
	}
}

// ---- config ----------------------------------------------------------------

func loadConfig() config {
	manager := env("FLEET_AGENT_MANAGER", "diskless-server.bitasylum.org:9600")
	cfg := config{
		manager:    manager,
		serverName: env("FLEET_AGENT_SERVER_NAME", hostOf(manager)),
		caFile:     env("FLEET_AGENT_CA", "/etc/dot1x/radius-ca.pem"),
		tpmPath:    env("FLEET_AGENT_TPM", "/dev/tpmrm0"),
		handle:     mustHandle(env("FLEET_AGENT_HANDLE", "0x81000100")),
		nvIndex:    mustHandle(env("FLEET_AGENT_NVINDEX", "0x01800100")),
		interval:   envDuration("FLEET_AGENT_INTERVAL", 30*time.Second),
		hostapiURL: env("FLEET_AGENT_HOSTAPI", "http://127.0.0.1:9099/v1/host"),
		kioskEnv:   env("FLEET_AGENT_KIOSK_ENV", "/etc/kiosk/kiosk.env"),
	}
	return cfg
}

func env(k, def string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return def
}

func envDuration(k string, def time.Duration) time.Duration {
	if v := os.Getenv(k); v != "" {
		if d, err := time.ParseDuration(v); err == nil {
			return d
		}
		log.Printf("bad %s=%q — using %s", k, v, def)
	}
	return def
}

// hostOf strips the :port from a host:port, leaving the DNS name for TLS
// verification. Handles bare hosts and IPv6 in brackets conservatively.
func hostOf(hostport string) string {
	if i := strings.LastIndex(hostport, ":"); i > strings.LastIndex(hostport, "]") {
		return strings.Trim(hostport[:i], "[]")
	}
	return strings.Trim(hostport, "[]")
}

func mustHandle(s string) tpm2.TPMHandle {
	h, err := parseHandle(s)
	if err != nil {
		log.Fatalf("bad TPM handle/index %q: %v", s, err)
	}
	return h
}

// parseHandle parses a 0x-prefixed (or bare) hex TPM handle/NV index.
func parseHandle(s string) (tpm2.TPMHandle, error) {
	v, err := strconv.ParseUint(strings.TrimPrefix(strings.ToLower(s), "0x"), 16, 32)
	if err != nil {
		return 0, err
	}
	return tpm2.TPMHandle(v), nil
}

// readKioskURL extracts KIOSK_URL from the kiosk env file (KEY=VALUE lines).
// Best-effort: "" if the file is absent (the manager still gets a Hello).
func readKioskURL(path string) string {
	b, err := os.ReadFile(path)
	if err != nil {
		return ""
	}
	for line := range strings.SplitSeq(string(b), "\n") {
		line = strings.TrimSpace(line)
		if v, ok := strings.CutPrefix(line, "KIOSK_URL="); ok {
			return strings.Trim(strings.TrimSpace(v), `"'`)
		}
	}
	return ""
}