// Command behavision-agent is the Go half of the edge install: it supervises
// the Python recognition engine and moves its events to the server.
//
// Modes:
//
//	run      supervise the engine and drain the spool (what the tray runs)
//	status   one-shot health report, for support and for the installer
//	paths    where this agent thinks state lives
//
// The tray and the Wails UI wrap this; none of the logic below assumes a
// window exists, so `run` works headless over SSH or from a scheduled task.
package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"strings"
	"syscall"
	"time"

	"github.com/loyaly/behavision-agent/pkg/bridge"
	"github.com/loyaly/behavision-agent/pkg/cameras"
	"github.com/loyaly/behavision-agent/pkg/config"
	"github.com/loyaly/behavision-agent/pkg/engine"
	"github.com/loyaly/behavision-agent/pkg/enrol"
	"github.com/loyaly/behavision-agent/pkg/mqtt"
	"github.com/loyaly/behavision-agent/pkg/paths"
	"github.com/loyaly/behavision-agent/pkg/spool"
)

var version = "dev"

func main() {
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, `behavision-agent %s

usage: %s <command>

  run              supervise the engine and report to head office (default)
  claim <code>     link this PC to a shop, using an installation code
  status           what this PC is and whether it is claimed
  paths            where this install reads and writes
`, version, filepath.Base(os.Args[0]))
	}
	flag.Parse()

	mode := "run"
	if flag.NArg() > 0 {
		mode = flag.Arg(0)
	}
	var err error
	switch mode {
	case "run":
		err = cmdRun()
	case "status":
		err = cmdStatus()
	case "claim":
		err = cmdClaim(flag.Args()[1:])
	case "paths":
		err = cmdPaths()
	default:
		flag.Usage()
		os.Exit(2)
	}
	if err != nil {
		log.Fatalf("behavision-agent: %v", err)
	}
}

// cmdClaim is the headless half of onboarding.
//
// The desktop app has had a Setup screen for this; a back-office PC with no
// window had nothing at all, so the only way to claim one was to hand-edit
// agent.json - which is the state that screen was built to end.
func cmdClaim(args []string) error {
	if len(args) == 0 {
		return fmt.Errorf("usage: behavision-agent claim <installation code>\n" +
			"Ask whoever manages your shops for one - they can create it from\n" +
			"the Behavision platform, under the shop.")
	}
	// Joined rather than requiring quotes: the code is printed in groups for
	// reading aloud, and an operator pasting it will paste the spaces too.
	code := strings.Join(args, "")

	if err := paths.EnsureState(); err != nil {
		return err
	}
	cfg, err := config.Load(paths.AgentConfig())
	if err != nil {
		return err
	}
	base := cfg.CloudBase
	if v := os.Getenv("BEHAVISION_CLOUD"); v != "" {
		base = v
	}
	if base == "" {
		base = "https://mcp.loyaly.ai"
	}

	b, err := enrol.Claim(context.Background(), base, code)
	if err != nil {
		return err
	}

	// The slugs, not the uuids: the topic prefix is <client>.<site> and the
	// broker's ACL is written against exactly that username.
	cfg.ClientID = b.ClientSlug
	cfg.SiteID = b.SiteSlug
	cfg.SiteName = b.SiteName
	cfg.BrokerURL = b.MQTTURL
	cfg.BrokerUsername = b.MQTTUser
	cfg.BrokerPassword = b.MQTTPass
	cfg.AgentToken = b.AgentToken
	cfg.CloudBase = base
	// A PC that was running on its own and has now been linked is no longer
	// standalone.
	cfg.Standalone = false
	if err := cfg.Save(paths.AgentConfig()); err != nil {
		// Reported, never swallowed: a claim that is not on disk works until
		// the next restart and then silently is not claimed any more, which
		// looks exactly like a wrong code.
		return fmt.Errorf("could not save the settings: %w", err)
	}

	fmt.Printf("linked to %s (%s.%s)\n", b.SiteName, b.ClientSlug, b.SiteSlug)
	fmt.Printf("settings written to %s\n", paths.AgentConfig())
	fmt.Println("restart the agent for it to take effect.")
	return nil
}

func cmdPaths() error {
	return json.NewEncoder(os.Stdout).Encode(map[string]string{
		"version":      version,
		"install_root": paths.InstallRoot(),
		"state_root":   paths.StateRoot(),
		"agent_config": paths.AgentConfig(),
		"spool":        paths.SpoolDir(),
		"engine_log":   paths.EngineLog(),
	})
}

func cmdStatus() error {
	cfg, err := config.Load(paths.AgentConfig())
	if err != nil {
		return err
	}
	// The engine invents its own Basic credential when none is configured,
	// which is the default. Reading it here is what stops every call the agent
	// makes to the engine coming back 401 on a stock install.
	cfg = cfg.WithEngineCredentials(paths.APICredentials())
	q, err := spool.Open(paths.SpoolDir(), cfg.SpoolMax)
	if err != nil {
		return err
	}
	sup := engine.New(engine.Options{
		Command:   func(context.Context) *exec.Cmd { return nil },
		HealthURL: strings.TrimRight(cfg.APIBase, "/") + "/api/health",
		StatsURL:  strings.TrimRight(cfg.APIBase, "/") + "/api/stats",
		User:      cfg.APIUser, Password: cfg.APIPassword,
	})
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	out := map[string]any{
		"version":           version,
		"configured":        cfg.Configured(),
		"secrets_protected": config.SecretsProtected(),
		"queued":            q.Len(),
		"dropped":           q.Dropped(),
	}
	if h, err := sup.Health(ctx); err != nil {
		out["engine"] = map[string]any{"reachable": false, "error": err.Error()}
	} else {
		out["engine"] = h
	}
	enc := json.NewEncoder(os.Stdout)
	enc.SetIndent("", "  ")
	return enc.Encode(out)
}

func cmdRun() error {
	logger := log.New(os.Stdout, "", log.LstdFlags|log.LUTC)
	if err := paths.EnsureState(); err != nil {
		return err
	}
	cfg, err := config.Load(paths.AgentConfig())
	if err != nil {
		return err
	}
	// The engine invents its own Basic credential when none is configured,
	// which is the default. Reading it here is what stops every call the agent
	// makes to the engine coming back 401 on a stock install.
	cfg = cfg.WithEngineCredentials(paths.APICredentials())
	// Opened before the engine starts: detections arriving in the first second
	// must have somewhere to land.
	q, err := spool.Open(paths.SpoolDir(), cfg.SpoolMax)
	if err != nil {
		return fmt.Errorf("spool: %w", err)
	}
	logFile, err := engine.LogFile(paths.EngineLog())
	if err != nil {
		return err
	}
	defer logFile.Close()

	exe := cfg.EngineExe
	if !filepath.IsAbs(exe) {
		// Resolved against the install root, not the working directory: a
		// service or a shortcut can start us anywhere.
		exe = filepath.Join(paths.InstallRoot(), exe)
	}
	// hookURL is read when the engine is LAUNCHED, not when the supervisor is
	// built, because the bridge has not picked its port yet and because a
	// restarted engine has to be told again.
	var hookURL string
	sup := engine.New(engine.Options{
		Command: func(ctx context.Context) *exec.Cmd {
			cmd := exec.CommandContext(ctx, exe, cfg.EngineArgs...)
			// How the engine learns where to send detections. The engine's
			// config already reads `events.webhook_url: ${BEHAVISION_WEBHOOK_URL}`
			// and python-dotenv does not override a variable the process
			// already has, so this needs no new endpoint and no fixed port.
			//
			// Without it the engine recognised people and the bridge received
			// nothing - the URL was returned, logged and even exposed on the
			// desktop's status object, and never actually given to the engine.
			// A claimed shop PC published heartbeats and zero visits.
			cmd.Env = engine.ChildEnv(hookURL)
			return cmd
		},
		LogWriter: logFile,
		HealthURL: strings.TrimRight(cfg.APIBase, "/") + "/api/health",
		StatsURL:  strings.TrimRight(cfg.APIBase, "/") + "/api/stats",
		User:      cfg.APIUser, Password: cfg.APIPassword,
	})

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

	// The bridge always runs, claimed or not: a PC that is set up before its
	// tenant credentials arrive must still record the footfall it sees, and
	// the spool is what holds it until the broker is configured.
	// Created before the bridge and handed over unconditionally. On a PC that
	// is not claimed yet there is no pump reading it, which costs nothing: the
	// waker's single slot fills once and every later ring is dropped.
	waker := mqtt.NewWaker()
	br := &bridge.Bridge{
		Queue:       q,
		Wake:        waker.Wake,
		Embeddings:  bridge.NewEngineEmbeddings(cfg.APIBase, cfg.APIUser, cfg.APIPassword),
		TopicPrefix: topicPrefix(cfg),
		Log:         logger,
		// Uploads face images through a URL the server mints, so this PC never
		// holds bucket credentials. Harmless when the engine writes no images
		// or the PC is not claimed: Upload reports "images off" and the visit
		// queues without a photo.
		Uploader: &bridge.SpacesUploader{
			BaseURL: cfg.CloudBase, Token: cfg.AgentToken,
		},
	}
	// Cameras, kept in step with head office. Runs whether or not this PC is
	// claimed: unclaimed it simply logs that it has no credentials yet, and the
	// engine carries on with the cameras already in its own store.
	uploader := &bridge.SpacesUploader{BaseURL: cfg.CloudBase, Token: cfg.AgentToken}
	cloud := cameras.NewCloudClient(cfg.CloudBase, cfg.AgentToken)
	cloud.Upload = uploader.UploadBytes
	eng := cameras.NewEngineClient(cfg.APIBase, cfg.APIUser, cfg.APIPassword)
	go cameras.New(eng, cloud, logger).Run(ctx)
	// The live relay, which uploads nothing until somebody at head office is
	// actually watching a camera.
	go cameras.NewLive(eng, cloud, logger).Run(ctx)

	// Before the engine starts, so the engine can be launched already knowing
	// where to post its detections.
	//
	// A PC set up to run on its own is the one case where it should not: it
	// has nothing to report to and, unlike an unclaimed one, never will, so
	// queuing would write up to SpoolMax visits - each carrying a face
	// template, which is biometric personal data - into a queue nothing is
	// going to drain. Recognition and the cameras are unaffected; they belong
	// to the engine, not the pump.
	if cfg.Standalone && !cfg.Configured() {
		logger.Print("standalone: recognition runs locally, nothing is reported")
	} else {
		url, stopBridge, err := br.Listen(ctx)
		if err != nil {
			return fmt.Errorf("event bridge: %w", err)
		}
		defer stopBridge()
		hookURL = url
		logger.Printf("event bridge listening on %s", hookURL)
	}

	logger.Printf("starting engine: %s %s", exe, strings.Join(cfg.EngineArgs, " "))
	sup.Start()

	if cfg.Configured() {
		logger.Printf("tenant %s / site %s; broker %s",
			cfg.ClientID, cfg.SiteID, cfg.BrokerURL)
		client, err := mqtt.NewClient(mqtt.ClientOptions{
			BrokerURL: cfg.BrokerURL,
			ClientID:  "behavision-" + cfg.ClientID + "-" + cfg.SiteID,
			Username:  cfg.BrokerUsername, Password: cfg.BrokerPassword,
			CAFile: cfg.BrokerCAFile, Log: logger,
		})
		if err != nil {
			// Not fatal. Events keep accumulating on disk and go out when the
			// link returns - which is the entire point of the spool.
			logger.Printf("broker unavailable, queuing locally: %v", err)
		} else {
			defer client.Close()
			pump := &mqtt.Pump{
				Queue: q, Publisher: client, Log: logger,
				Wake:           waker.C(),
				HeartbeatTopic: topicPrefix(cfg) + "/heartbeat",
				HeartbeatPayload: func() []byte {
					return heartbeat(q, sup)
				},
			}
			go pump.Run(ctx)
			logger.Print("broker pump running")
		}
	} else {
		logger.Print("not claimed by a tenant yet - recording locally only")
	}

	<-ctx.Done()
	logger.Print("stopping engine")
	sup.Stop()
	return nil
}

// topicPrefix is the site's MQTT namespace. The broker enforces
// `pattern write bv/%u/...`, so this must equal the credential's username or
// every publish is refused.
func topicPrefix(cfg config.Config) string {
	if cfg.ClientID == "" || cfg.SiteID == "" {
		return ""
	}
	return "bv/" + cfg.ClientID + "." + cfg.SiteID
}

// heartbeat says the site is alive and what shape it is in.
//
// `dropped` matters most: non-zero means this site's queue overflowed and it
// genuinely lost footfall the customer paid for. Reporting it is the only way
// that becomes visible rather than being inferred from a dip in a graph.
func heartbeat(q *spool.Spool, sup *engine.Supervisor) []byte {
	hb := map[string]any{
		"sent_at":       time.Now().UTC().Format(time.RFC3339),
		"agent_version": version,
		"queued":        q.Len(),
		"dropped":       q.Dropped(),
	}
	if sup != nil {
		state, _ := sup.State()
		hb["engine_state"] = string(state)
		hctx, cancel := context.WithTimeout(context.Background(), 4*time.Second)
		defer cancel()
		if h, err := sup.Health(hctx); err == nil {
			hb["recognition_model"] = h.RecognitionModel
			hb["cameras"] = h.Cameras
		}
		// The share of faces this site's cameras saw and discarded before they
		// could become visits. It is the difference between "a quiet week" and
		// "the camera is pointed at the ceiling", which are the same row of
		// numbers on a footfall report without it. Measured on the Office1
		// camera it was 0.727.
		if st, err := sup.Stats(hctx); err == nil {
			if worst, ok := st.WorstBelowGate(); ok {
				hb["fraction_below_gate"] = worst
			}
		}
	}
	b, _ := json.Marshal(hb)
	return b
}