// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>

package main

import (
	"context"
	"flag"
	"fmt"
	"log/slog"
	"net"
	"net/http"
	"os"
	"os/signal"
	"syscall"

	grpcprom "github.com/grpc-ecosystem/go-grpc-middleware/providers/prometheus"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"google.golang.org/grpc"
	"google.golang.org/grpc/reflection"

	buildinfo "git.ipng.ch/ipng/vpp-maglev/cmd"
	"git.ipng.ch/ipng/vpp-maglev/internal/checker"
	"git.ipng.ch/ipng/vpp-maglev/internal/config"
	"git.ipng.ch/ipng/vpp-maglev/internal/grpcapi"
	"git.ipng.ch/ipng/vpp-maglev/internal/metrics"
	"git.ipng.ch/ipng/vpp-maglev/internal/vpp"
)

func main() {
	if err := run(); err != nil {
		slog.Error("startup-fatal", "err", err)
		os.Exit(1)
	}
}

func run() error {
	// ---- flags / env --------------------------------------------------------
	printVersion := flag.Bool("version", false, "print version and exit")
	checkOnly := flag.Bool("check", false, "check config file and exit (0=ok, 1=parse error, 2=semantic error)")
	enableReflection := flag.Bool("reflection", true, "enable gRPC server reflection (for grpcurl)")
	configPath := stringFlag("config", "/etc/vpp-maglev/maglev.yaml", "MAGLEV_CONFIG", "path to maglev.yaml")
	grpcAddr := stringFlag("grpc-addr", ":9090", "MAGLEV_GRPC_ADDR", "gRPC listen address")
	metricsAddr := stringFlag("metrics-addr", ":9091", "MAGLEV_METRICS_ADDR", "Prometheus /metrics listen address (empty to disable)")
	vppAPIAddr := stringFlag("vpp-api-addr", "/run/vpp/api.sock", "MAGLEV_VPP_API_ADDR", "VPP binary API socket path (empty to disable)")
	vppStatsAddr := stringFlag("vpp-stats-addr", "/run/vpp/stats.sock", "MAGLEV_VPP_STATS_ADDR", "VPP stats socket path")
	logLevel := stringFlag("log-level", "info", "MAGLEV_LOG_LEVEL", "log level (debug|info|warn|error)")
	flag.Parse()

	if *printVersion {
		fmt.Printf("maglevd %s (commit %s, built %s)\n",
			buildinfo.Version(), buildinfo.Commit(), buildinfo.Date())
		return nil
	}

	if *checkOnly {
		_, result := config.Check(*configPath)
		if result.OK() {
			fmt.Printf("config ok: %s\n", *configPath)
			return nil
		}
		if result.ParseError != "" {
			fmt.Fprintf(os.Stderr, "parse error: %s\n", result.ParseError)
			os.Exit(1)
		}
		fmt.Fprintf(os.Stderr, "semantic error: %s\n", result.SemanticError)
		os.Exit(2)
	}

	// ---- logging ------------------------------------------------------------
	var level slog.Level
	if err := level.UnmarshalText([]byte(*logLevel)); err != nil {
		return fmt.Errorf("invalid log level %q: %w", *logLevel, err)
	}
	jsonHandler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: level})
	logBroadcaster := grpcapi.NewLogBroadcaster(jsonHandler)
	slog.SetDefault(slog.New(logBroadcaster))
	slog.Info("starting", "version", buildinfo.Version(), "commit", buildinfo.Commit(), "date", buildinfo.Date())

	// ---- config -------------------------------------------------------------
	cfg, err := config.Load(*configPath)
	if err != nil {
		return fmt.Errorf("load config: %w", err)
	}
	slog.Info("config-loaded", "path", *configPath, "frontends", len(cfg.Frontends))

	// ---- checker ------------------------------------------------------------
	chkr := checker.New(cfg)

	ctx, rootCancel := context.WithCancel(context.Background())
	defer rootCancel()

	go func() {
		if err := chkr.Run(ctx); err != nil {
			slog.Error("checker-exited", "err", err)
		}
	}()

	// ---- VPP connection -----------------------------------------------------
	var vppClient *vpp.Client
	if *vppAPIAddr != "" {
		vppClient = vpp.New(*vppAPIAddr, *vppStatsAddr)
		vppClient.SetStateSource(chkr)
		go vppClient.Run(ctx)
		// The reconciler subscribes to checker events and pushes per-VIP
		// syncs into VPP on every backend state transition. This is the
		// single place where transitions translate into dataplane changes.
		reconciler := vpp.NewReconciler(vppClient, chkr, chkr)
		go reconciler.Run(ctx)
	}

	// ---- gRPC server --------------------------------------------------------
	// Server-side metrics for every RPC: call counters, in-flight gauges,
	// and handler-latency histograms, labelled by method and gRPC code.
	// Provided by go-grpc-middleware's prometheus adapter; the metric
	// families are emitted on the /metrics endpoint alongside ours.
	grpcMetrics := grpcprom.NewServerMetrics(
		grpcprom.WithServerHandlingTimeHistogram(),
	)
	lis, err := net.Listen("tcp", *grpcAddr)
	if err != nil {
		return fmt.Errorf("listen %s: %w", *grpcAddr, err)
	}
	srv := grpc.NewServer(
		grpc.UnaryInterceptor(grpcMetrics.UnaryServerInterceptor()),
		grpc.StreamInterceptor(grpcMetrics.StreamServerInterceptor()),
	)
	maglevServer := grpcapi.NewServer(ctx, chkr, logBroadcaster, *configPath, vppClient)
	grpcapi.RegisterMaglevServer(srv, maglevServer)
	if *enableReflection {
		reflection.Register(srv)
	}
	// Pre-register every method with 0 so the metric shows up on first
	// scrape even before any RPC has been received.
	grpcMetrics.InitializeMetrics(srv)
	slog.Info("grpc-listening", "addr", *grpcAddr, "reflection", *enableReflection)

	go func() {
		if err := srv.Serve(lis); err != nil {
			slog.Error("grpc-serve-error", "err", err)
		}
	}()

	// ---- Prometheus metrics -------------------------------------------------
	if *metricsAddr != "" {
		reg := prometheus.DefaultRegisterer
		// vppClient may be nil when VPP integration is disabled; the
		// collector handles that by skipping the vpp_* gauges.
		var vppSrc metrics.VPPSource
		if vppClient != nil {
			vppSrc = vppClient
		}
		metrics.Register(reg, chkr, vppSrc)
		reg.MustRegister(grpcMetrics)

		mux := http.NewServeMux()
		mux.Handle("/metrics", promhttp.Handler())
		slog.Info("metrics-listening", "addr", *metricsAddr)
		go func() {
			if err := http.ListenAndServe(*metricsAddr, mux); err != nil && err != http.ErrServerClosed {
				slog.Error("metrics-serve-error", "err", err)
			}
		}()
	}

	// ---- signal handling ----------------------------------------------------
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGHUP, syscall.SIGTERM, syscall.SIGINT)

	for sig := range sigCh {
		switch sig {
		case syscall.SIGHUP:
			maglevServer.TriggerReload()

		case syscall.SIGTERM, syscall.SIGINT:
			slog.Info("shutdown", "signal", sig)
			rootCancel()
			srv.GracefulStop()
			return nil
		}
	}
	return nil
}

// stringFlag declares a flag that falls back to an environment variable.
func stringFlag(name, defaultVal, envKey, usage string) *string {
	val := defaultVal
	if v := os.Getenv(envKey); v != "" {
		val = v
	}
	return flag.String(name, val, fmt.Sprintf("%s (env: %s)", usage, envKey))
}