package opamp

import (
	"context"

	"github.com/open-telemetry/opamp-go/protobufs"
	"github.com/open-telemetry/opamp-go/server"
	"github.com/open-telemetry/opamp-go/server/types"
	model "go.signoz.io/signoz/pkg/query-service/app/opamp/model"

	"go.uber.org/zap"
)

var opAmpServer *Server

type Server struct {
	server server.OpAMPServer
	agents *model.Agents

	agentConfigProvider AgentConfigProvider

	// cleanups to be run when stopping the server
	cleanups []func()
}

const capabilities = protobufs.ServerCapabilities_ServerCapabilities_AcceptsEffectiveConfig |
	protobufs.ServerCapabilities_ServerCapabilities_OffersRemoteConfig |
	protobufs.ServerCapabilities_ServerCapabilities_AcceptsStatus

func InitializeServer(
	agents *model.Agents, agentConfigProvider AgentConfigProvider,
) *Server {
	if agents == nil {
		agents = &model.AllAgents
	}

	opAmpServer = &Server{
		agents:              agents,
		agentConfigProvider: agentConfigProvider,
	}
	opAmpServer.server = server.New(zap.L().Sugar())
	return opAmpServer
}

func (srv *Server) Start(listener string) error {
	settings := server.StartSettings{
		Settings: server.Settings{
			Callbacks: server.CallbacksStruct{
				OnMessageFunc:         srv.OnMessage,
				OnConnectionCloseFunc: srv.onDisconnect,
			},
		},
		ListenEndpoint: listener,
	}

	unsubscribe := srv.agentConfigProvider.SubscribeToConfigUpdates(func() {
		err := srv.agents.RecommendLatestConfigToAll(srv.agentConfigProvider)
		if err != nil {
			zap.L().Error(
				"could not roll out latest config recommendation to connected agents", zap.Error(err),
			)
		}
	})
	srv.cleanups = append(srv.cleanups, unsubscribe)

	return srv.server.Start(settings)
}

func (srv *Server) Stop() {
	for _, cleanup := range srv.cleanups {
		defer cleanup()
	}

	srv.server.Stop(context.Background())
}

func (srv *Server) onDisconnect(conn types.Connection) {
	srv.agents.RemoveConnection(conn)
}

func (srv *Server) OnMessage(conn types.Connection, msg *protobufs.AgentToServer) *protobufs.ServerToAgent {
	agentID := msg.InstanceUid

	agent, created, err := srv.agents.FindOrCreateAgent(agentID, conn)
	if err != nil {
		zap.L().Error("Failed to find or create agent", zap.String("agentID", agentID), zap.Error(err))
		// TODO: handle error
	}

	if created {
		agent.CanLB = model.ExtractLbFlag(msg.AgentDescription)
		zap.L().Debug(
			"New agent added", zap.Bool("canLb", agent.CanLB),
			zap.String("ID", agent.ID),
			zap.Any("status", agent.CurrentStatus),
		)
	}

	response := &protobufs.ServerToAgent{
		InstanceUid:  agentID,
		Capabilities: uint64(capabilities),
	}

	agent.UpdateStatus(msg, response, srv.agentConfigProvider)

	return response
}

// global var methods to support singleton pattern. we want to discourage
// allow multiple servers in one installation
func Ready() bool {
	if opAmpServer == nil {
		return false
	}
	if opAmpServer.agents.Count() == 0 {
		zap.L().Warn("no agents available, all agent config requests will be rejected")
		return false
	}
	return true
}

func Subscribe(agentId string, hash string, f model.OnChangeCallback) {
	model.ListenToConfigUpdate(agentId, hash, f)
}