// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1

package internal

import (
	"fmt"
	"net"
	"time"

	"github.com/armon/go-metrics"

	agentmiddleware "github.com/hashicorp/consul/agent/grpc-middleware"

	middleware "github.com/grpc-ecosystem/go-grpc-middleware"
	recovery "github.com/grpc-ecosystem/go-grpc-middleware/recovery"
	"google.golang.org/grpc"
	"google.golang.org/grpc/keepalive"

	"github.com/hashicorp/consul/agent/consul/rate"
)

var (
	metricsLabels = []metrics.Label{{
		Name:  "server_type",
		Value: "internal",
	}}
)

// NewHandler returns a gRPC server that accepts connections from Handle(conn).
func NewHandler(logger Logger, addr net.Addr, metricsObj *metrics.Metrics, rateLimiter rate.RequestLimitsHandler) *Handler {
	if metricsObj == nil {
		metricsObj = metrics.Default()
	}

	// We don't need to pass tls.Config to the server since it's multiplexed
	// behind the RPC listener, which already has TLS configured.
	recoveryOpts := agentmiddleware.PanicHandlerMiddlewareOpts(logger)

	opts := []grpc.ServerOption{
		grpc.InTapHandle(agentmiddleware.ServerRateLimiterMiddleware(rateLimiter, agentmiddleware.NewPanicHandler(logger), logger)),
		grpc.StatsHandler(agentmiddleware.NewStatsHandler(metricsObj, metricsLabels)),
		middleware.WithUnaryServerChain(
			// Add middlware interceptors to recover in case of panics.
			recovery.UnaryServerInterceptor(recoveryOpts...),
		),
		middleware.WithStreamServerChain(
			// Add middlware interceptors to recover in case of panics.
			recovery.StreamServerInterceptor(recoveryOpts...),
			agentmiddleware.NewActiveStreamCounter(metricsObj, metricsLabels).Intercept,
		),
		grpc.KeepaliveEnforcementPolicy(keepalive.EnforcementPolicy{
			MinTime: 15 * time.Second,
		}),
	}

	// We don't need to pass tls.Config to the server since it's multiplexed
	// behind the RPC listener, which already has TLS configured.
	srv := grpc.NewServer(opts...)

	return &Handler{srv: srv, listener: NewListener(addr)}
}

// Handler implements a handler for the rpc server listener, and the
// agent.Component interface for managing the lifecycle of the grpc.Server.
type Handler struct {
	srv      *grpc.Server
	listener *Listener
}

// Handle the connection by sending it to a channel for the grpc.Server to receive.
func (h *Handler) Handle(conn net.Conn) {
	h.listener.conns <- conn
}

func (h *Handler) Run() error {
	return h.srv.Serve(h.listener)
}

// Implements the grpc.ServiceRegistrar interface to allow registering services
// with the Handler.
func (h *Handler) RegisterService(svc *grpc.ServiceDesc, impl any) {
	h.srv.RegisterService(svc, impl)
}

func (h *Handler) Shutdown() error {
	h.srv.Stop()
	return nil
}

// NoOpHandler implements the same methods as Handler, but performs no handling.
// It may be used in place of Handler to disable the grpc server.
type NoOpHandler struct {
	Logger Logger
}

type Logger interface {
	Error(string, ...interface{})
	Warn(string, ...interface{})
}

func (h NoOpHandler) Handle(conn net.Conn) {
	h.Logger.Error("gRPC conn opened but gRPC RPC is disabled, closing",
		"conn", logConn(conn))
	_ = conn.Close()
}

func (h NoOpHandler) Run() error {
	return nil
}

func (h NoOpHandler) Shutdown() error {
	return nil
}

// logConn is a local copy of github.com/hashicorp/memberlist.LogConn, to avoid
// a large dependency for a minor formatting function.
// logConn is used to keep log formatting consistent.
func logConn(conn net.Conn) string {
	if conn == nil {
		return "from=<unknown address>"
	}
	addr := conn.RemoteAddr()
	if addr == nil {
		return "from=<unknown address>"
	}

	return fmt.Sprintf("from=%s", addr.String())
}