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

package main

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

	"google.golang.org/grpc"

	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"
)

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")
	configPath := stringFlag("config", "/etc/maglev/frontend.yaml", "MAGLEV_CONFIG", "path to frontend.yaml")
	grpcAddr := stringFlag("grpc-addr", ":9090", "MAGLEV_GRPC_ADDR", "gRPC listen address")
	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
	}

	// ---- logging ------------------------------------------------------------
	var level slog.Level
	if err := level.UnmarshalText([]byte(*logLevel)); err != nil {
		return fmt.Errorf("invalid log level %q: %w", *logLevel, err)
	}
	slog.SetDefault(slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: level})))
	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)
		}
	}()

	// ---- gRPC server --------------------------------------------------------
	lis, err := net.Listen("tcp", *grpcAddr)
	if err != nil {
		return fmt.Errorf("listen %s: %w", *grpcAddr, err)
	}
	srv := grpc.NewServer()
	grpcapi.RegisterMaglevServer(srv, grpcapi.NewServer(ctx, chkr))
	slog.Info("grpc-listening", "addr", *grpcAddr)

	go func() {
		if err := srv.Serve(lis); err != nil {
			slog.Error("grpc-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:
			slog.Info("config-reload-start")
			newCfg, err := config.Load(*configPath)
			if err != nil {
				slog.Error("config-reload-error", "err", err)
				continue
			}
			if err := chkr.Reload(ctx, newCfg); err != nil {
				slog.Error("checker-reload-error", "err", err)
				continue
			}
			slog.Info("config-reload-done", "frontends", len(newCfg.Frontends))

		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))
}