/*
Real-time Online/Offline Charging System (OCS) for Telecom & ISP environments
Copyright (C) ITsysCOM GmbH

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>
*/

package agents

import (
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/cgrates/birpc"
	"github.com/cgrates/birpc/context"
	"github.com/cgrates/cgrates/engine"
	"github.com/cgrates/kamevapi"

	"github.com/cgrates/cgrates/config"
	"github.com/cgrates/cgrates/sessions"
	"github.com/cgrates/cgrates/utils"
)

var (
	kamAuthReqRegexp       = regexp.MustCompile(CGR_AUTH_REQUEST)
	kamCallStartRegexp     = regexp.MustCompile(CGR_CALL_START)
	kamCallEndRegexp       = regexp.MustCompile(CGR_CALL_END)
	kamDlgListRegexp       = regexp.MustCompile(CGR_DLG_LIST)
	kamProcessMessageRegex = regexp.MustCompile(CGR_PROCESS_MESSAGE)
	kamProcessCDRRegex     = regexp.MustCompile(CGR_PROCESS_CDR)
)

func NewKamailioAgent(kaCfg *config.KamAgentCfg,
	connMgr *engine.ConnManager, timezone string) (*KamailioAgent, error) {
	ka := &KamailioAgent{
		cfg:              kaCfg,
		connMgr:          connMgr,
		timezone:         timezone,
		conns:            make([]*kamevapi.KamEvapi, len(kaCfg.EvapiConns)),
		activeSessionIDs: make(chan []*sessions.SessionID),
	}
	srv, err := birpc.NewServiceWithMethodsRename(ka, utils.AgentV1, true, func(oldFn string) (newFn string) {
		return strings.TrimPrefix(oldFn, "V1")
	})
	if err != nil {
		return nil, err
	}
	ka.ctx = context.WithClient(context.TODO(), srv)
	return ka, nil
}

type KamailioAgent struct {
	cfg              *config.KamAgentCfg
	connMgr          *engine.ConnManager
	timezone         string
	conns            []*kamevapi.KamEvapi
	activeSessionIDs chan []*sessions.SessionID
	ctx              *context.Context
}

func (self *KamailioAgent) Connect() (err error) {
	eventHandlers := map[*regexp.Regexp][]func([]byte, int){
		kamAuthReqRegexp:       {self.onCgrAuth},
		kamCallStartRegexp:     {self.onCallStart},
		kamCallEndRegexp:       {self.onCallEnd},
		kamDlgListRegexp:       {self.onDlgList},
		kamProcessMessageRegex: {self.onCgrProcessMessage},
		kamProcessCDRRegex:     {self.onCgrProcessCDR},
	}
	var reply string
	// make a call kamailio_agent -> sessions_conns to create an active client needed for syncSessions when restoring sessions, since prior clients are lost when engine shuts down
	if err := self.connMgr.Call(self.ctx, self.cfg.SessionSConns, utils.SessionSv1Ping, &utils.CGREvent{}, &reply); err != nil {
		return err
	}
	errChan := make(chan error)
	for connIdx, connCfg := range self.cfg.EvapiConns {
		if self.conns[connIdx], err = kamevapi.NewKamEvapi(connCfg.Address, connIdx, connCfg.Reconnects, connCfg.MaxReconnectInterval,
			utils.FibDuration, eventHandlers, utils.Logger); err != nil {
			return
		}
		go func(conn *kamevapi.KamEvapi) { // Start reading in own goroutine, return on error
			if err := conn.ReadEvents(); err != nil {
				errChan <- err
			}
		}(self.conns[connIdx])
	}
	err = <-errChan // Will keep the Connect locked until the first error in one of the connections
	return
}

func (self *KamailioAgent) Shutdown() (err error) {
	for conIndx, conn := range self.conns {
		if conn == nil {
			break
		}
		if err = conn.Disconnect(); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> can't disconnect connection at index %v because: %s",
				utils.KamailioAgent, conIndx, err))
			continue
		}
	}
	return
}

// onCgrAuth is called when new event of type CGR_AUTH_REQUEST is coming
func (ka *KamailioAgent) onCgrAuth(evData []byte, connIdx int) {
	if connIdx >= len(ka.conns) { // protection against index out of range panic
		err := fmt.Errorf("Index out of range[0,%v): %v ", len(ka.conns), connIdx)
		utils.Logger.Err(fmt.Sprintf("<%s> %s", utils.KamailioAgent, err.Error()))
		return
	}
	kev, err := NewKamEvent(evData, ka.cfg.EvapiConns[connIdx].Alias, ka.conns[connIdx].RemoteAddr().String())
	if err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> unmarshalling event data: %s, error: %s",
			utils.KamailioAgent, evData, err.Error()))
		return
	}
	if kev[utils.RequestType] == utils.MetaNone { // Do not process this request
		return
	}
	if kev.MissingParameter() {
		if kRply, err := kev.AsKamAuthReply(nil, nil, utils.ErrMandatoryIeMissing); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed building auth reply for event: %s, error: %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		} else if err = ka.conns[connIdx].Send(kRply.String()); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed sending auth reply for event: %s, error %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		}
		return
	}
	authArgs := kev.V1AuthorizeArgs()
	if authArgs == nil {
		utils.Logger.Err(fmt.Sprintf("<%s> event: %s cannot generate auth session arguments",
			utils.KamailioAgent, kev[utils.OriginID]))
		return
	}
	authArgs.CGREvent.Event[EvapiConnID] = connIdx // Attach the connection ID
	var authReply sessions.V1AuthorizeReply
	// take the error after calling SessionSv1.AuthorizeEvent
	// and send it as parameter to AsKamAuthReply
	err = ka.connMgr.Call(ka.ctx, ka.cfg.SessionSConns,
		utils.SessionSv1AuthorizeEvent,
		authArgs, &authReply)
	if kar, err := kev.AsKamAuthReply(authArgs, &authReply, err); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed building auth reply for event: %s, error: %s",
			utils.KamailioAgent, kev[utils.OriginID], err.Error()))
	} else if err = ka.conns[connIdx].Send(kar.String()); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed sending auth reply for event: %s, error: %s",
			utils.KamailioAgent, kev[utils.OriginID], err.Error()))
	}
}

func (ka *KamailioAgent) onCallStart(evData []byte, connIdx int) {
	if connIdx >= len(ka.conns) { // protection against index out of range panic
		err := fmt.Errorf("Index out of range[0,%v): %v ", len(ka.conns), connIdx)
		utils.Logger.Err(fmt.Sprintf("<%s> %s", utils.KamailioAgent, err.Error()))
		return
	}
	kev, err := NewKamEvent(evData, ka.cfg.EvapiConns[connIdx].Alias, ka.conns[connIdx].RemoteAddr().String())
	if err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> unmarshalling event: %s, error: %s",
			utils.KamailioAgent, evData, err.Error()))
		return
	}
	if kev[utils.RequestType] == utils.MetaNone { // Do not process this request
		return
	}
	if kev.MissingParameter() {
		ka.disconnectSession(connIdx,
			NewKamSessionDisconnect(kev[KamHashEntry], kev[KamHashID],
				utils.ErrMandatoryIeMissing.Error()))
		return
	}
	initSessionArgs := kev.V1InitSessionArgs()
	if initSessionArgs == nil {
		utils.Logger.Err(fmt.Sprintf("<%s> event: %s cannot generate init session arguments",
			utils.KamailioAgent, kev[utils.OriginID]))
		return
	}
	initSessionArgs.CGREvent.Event[EvapiConnID] = connIdx // Attach the connection ID so we can properly disconnect later

	var initReply sessions.V1InitSessionReply
	if err := ka.connMgr.Call(ka.ctx, ka.cfg.SessionSConns,
		utils.SessionSv1InitiateSession,
		initSessionArgs, &initReply); err != nil {
		utils.Logger.Err(
			fmt.Sprintf("<%s> could not process answer for event %s, error: %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		ka.disconnectSession(connIdx,
			NewKamSessionDisconnect(kev[KamHashEntry], kev[KamHashID],
				utils.ErrServerError.Error()))
		return
	}
}

func (ka *KamailioAgent) onCallEnd(evData []byte, connIdx int) {
	if connIdx >= len(ka.conns) { // protection against index out of range panic
		err := fmt.Errorf("Index out of range[0,%v): %v ", len(ka.conns), connIdx)
		utils.Logger.Err(fmt.Sprintf("<%s> %s", utils.KamailioAgent, err.Error()))
		return
	}
	kev, err := NewKamEvent(evData, ka.cfg.EvapiConns[connIdx].Alias, ka.conns[connIdx].RemoteAddr().String())
	if err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> unmarshalling event: %s, error: %s",
			utils.KamailioAgent, evData, err.Error()))
		return
	}
	if kev[utils.RequestType] == utils.MetaNone { // Do not process this request
		return
	}
	if kev.MissingParameter() {
		utils.Logger.Err(fmt.Sprintf("<%s> mandatory IE missing out from event: %s",
			utils.KamailioAgent, kev[utils.OriginID]))
		return
	}
	tsArgs := kev.V1TerminateSessionArgs()
	if tsArgs == nil {
		utils.Logger.Err(fmt.Sprintf("<%s> event: %s cannot generate terminate session arguments",
			utils.KamailioAgent, kev[utils.OriginID]))
		return
	}
	var reply string
	tsArgs.CGREvent.Event[EvapiConnID] = connIdx // Attach the connection ID in case we need to create a session and disconnect it
	if err := ka.connMgr.Call(ka.ctx, ka.cfg.SessionSConns,
		utils.SessionSv1TerminateSession,
		tsArgs, &reply); err != nil {
		utils.Logger.Err(
			fmt.Sprintf("<%s> could not terminate session with event %s, error: %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		// no return here since we want CDR anyhow
	}
	if ka.cfg.CreateCdr || strings.Contains(kev[utils.CGRFlags], utils.MetaCDRs) {
		if err := ka.connMgr.Call(ka.ctx, ka.cfg.SessionSConns,
			utils.SessionSv1ProcessCDR,
			tsArgs.CGREvent, &reply); err != nil {
			utils.Logger.Err(fmt.Sprintf("%s> failed processing CGREvent: %s, error: %s",
				utils.KamailioAgent, utils.ToJSON(tsArgs.CGREvent), err.Error()))
		}
	}
}

func (ka *KamailioAgent) onDlgList(evData []byte, connIdx int) {
	kamDlgRpl, err := NewKamDlgReply(evData)
	if err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> unmarshalling event data: %s, error: %s",
			utils.KamailioAgent, evData, err.Error()))
		return
	}
	var sIDs []*sessions.SessionID
	for _, dlgInfo := range kamDlgRpl.Jsonrpl_body.Result {
		originHost := ka.conns[connIdx].RemoteAddr().String()
		originID := dlgInfo.CallId + ";" + dlgInfo.Caller.Tag
		for _, variable := range dlgInfo.Variables {
			if variable.CgrOriginHost != utils.EmptyString {
				originHost = variable.CgrOriginHost
			}
			if variable.CgrOriginID != utils.EmptyString {
				originID = variable.CgrOriginID
			}
		}
		sIDs = append(sIDs, &sessions.SessionID{
			OriginHost: originHost,
			OriginID:   originID,
		})
	}
	ka.activeSessionIDs <- sIDs
}

func (ka *KamailioAgent) onCgrProcessMessage(evData []byte, connIdx int) {
	if connIdx >= len(ka.conns) { // protection against index out of range panic
		err := fmt.Errorf("Index out of range[0,%v): %v ", len(ka.conns), connIdx)
		utils.Logger.Err(fmt.Sprintf("<%s> %s", utils.KamailioAgent, err.Error()))
		return
	}
	kev, err := NewKamEvent(evData, ka.cfg.EvapiConns[connIdx].Alias, ka.conns[connIdx].RemoteAddr().String())
	if err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> unmarshalling event data: %s, error: %s",
			utils.KamailioAgent, evData, err.Error()))
		return
	}

	if kev.MissingParameter() {
		if kRply, err := kev.AsKamProcessMessageReply(nil, nil, utils.ErrMandatoryIeMissing); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed building process session event reply for event: %s, error: %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		} else if err = ka.conns[connIdx].Send(kRply.String()); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed sending process session event reply for event: %s, error %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		}
		return
	}

	//in case that we don't receive cgr_flags from kamailio
	//we consider this as ping-pong event
	if _, has := kev[utils.CGRFlags]; !has {
		if err = ka.conns[connIdx].Send(kev.AsKamProcessMessageEmptyReply().String()); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed sending empty process message reply for event: %s, error %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		}
	}

	procEvArgs := kev.V1ProcessMessageArgs()
	if procEvArgs == nil {
		utils.Logger.Err(fmt.Sprintf("<%s> event: %s cannot generate process message session arguments",
			utils.KamailioAgent, kev[utils.OriginID]))
		return
	}
	procEvArgs.CGREvent.Event[EvapiConnID] = connIdx // Attach the connection ID

	var processReply sessions.V1ProcessMessageReply
	err = ka.connMgr.Call(ka.ctx, ka.cfg.SessionSConns,
		utils.SessionSv1ProcessMessage,
		procEvArgs, &processReply)
	// take the error after calling SessionSv1.ProcessMessage
	// and send it as parameter to AsKamProcessMessageReply
	if kar, err := kev.AsKamProcessMessageReply(procEvArgs, &processReply, err); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed building process session event reply for event: %s, error: %s",
			utils.KamailioAgent, kev[utils.OriginID], err.Error()))
	} else if err = ka.conns[connIdx].Send(kar.String()); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed sending auth reply for event: %s, error: %s",
			utils.KamailioAgent, kev[utils.OriginID], err.Error()))
	}
}

func (ka *KamailioAgent) onCgrProcessCDR(evData []byte, connIdx int) {
	if connIdx >= len(ka.conns) { // protection against index out of range panic
		err := fmt.Errorf("Index out of range[0,%v): %v ", len(ka.conns), connIdx)
		utils.Logger.Err(fmt.Sprintf("<%s> %s", utils.KamailioAgent, err.Error()))
		return
	}
	kev, err := NewKamEvent(evData, ka.cfg.EvapiConns[connIdx].Alias, ka.conns[connIdx].RemoteAddr().String())
	if err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> unmarshalling event data: %s, error: %s",
			utils.KamailioAgent, evData, err.Error()))
		return
	}

	if kev.MissingParameter() {
		if kRply, err := kev.AsKamProcessCDRReply(nil, nil, utils.ErrMandatoryIeMissing); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed building process session event reply for event: %s, error: %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		} else if err = ka.conns[connIdx].Send(kRply.String()); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed sending process session event reply for event: %s, error %s",
				utils.KamailioAgent, kev[utils.OriginID], err.Error()))
		}
		return
	}

	procCDRArgs := kev.V1ProcessCDRArgs()
	if procCDRArgs == nil {
		utils.Logger.Err(fmt.Sprintf("<%s> event: %s cannot generate process cdr session arguments",
			utils.KamailioAgent, kev[utils.OriginID]))
		return
	}
	procCDRArgs.Event[EvapiConnID] = connIdx // Attach the connection ID

	var processReply string
	err = ka.connMgr.Call(ka.ctx, ka.cfg.SessionSConns,
		utils.SessionSv1ProcessCDR,
		procCDRArgs, &processReply)
	// take the error after calling SessionSv1.ProcessCDR
	// and send it as parameter to AsKamProcessCDRReply
	if kar, err := kev.AsKamProcessCDRReply(procCDRArgs, &processReply, err); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed building process session event reply for event: %s, error: %s",
			utils.KamailioAgent, kev[utils.OriginID], err.Error()))
	} else if err = ka.conns[connIdx].Send(kar.String()); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed sending auth reply for event: %s, error: %s",
			utils.KamailioAgent, kev[utils.OriginID], err.Error()))
	}
}

func (self *KamailioAgent) disconnectSession(connIdx int, dscEv *KamSessionDisconnect) (err error) {
	if err = self.conns[connIdx].Send(dscEv.String()); err != nil {
		utils.Logger.Err(fmt.Sprintf("<%s> failed sending disconnect request: %s,  connection id: %v, error %s",
			utils.KamailioAgent, utils.ToJSON(dscEv), connIdx, err.Error()))
	}
	return
}

// Internal method to disconnect session in Kamailio
func (ka *KamailioAgent) V1DisconnectSession(ctx *context.Context, cgrEv utils.CGREvent, reply *string) (err error) {
	hEntry := utils.IfaceAsString(cgrEv.Event[KamHashEntry])
	hID := utils.IfaceAsString(cgrEv.Event[KamHashID])
	connIdxIface, has := cgrEv.Event[EvapiConnID]
	if !has {
		utils.Logger.Err(
			fmt.Sprintf("<%s> error: <%s:%s> when attempting to disconnect <%s:%s> and <%s:%s>",
				utils.KamailioAgent, utils.ErrNotFound.Error(), EvapiConnID,
				KamHashEntry, hEntry, KamHashID, hID))
		return
	}
	connIdx, err := utils.IfaceAsTInt64(connIdxIface)
	if err != nil {
		return err
	}
	if int(connIdx) >= len(ka.conns) { // protection against index out of range panic
		err = fmt.Errorf("Index out of range[0,%v): %v ", len(ka.conns), connIdx)
		utils.Logger.Err(fmt.Sprintf("<%s> %s", utils.KamailioAgent, err.Error()))
		return
	}
	if err = ka.disconnectSession(int(connIdx),
		NewKamSessionDisconnect(hEntry, hID,
			utils.ErrInsufficientCredit.Error())); err != nil {
		return
	}
	*reply = utils.OK
	return
}

// V1GetActiveSessionIDs returns a list of CGRIDs based on active sessions from agent
func (ka *KamailioAgent) V1GetActiveSessionIDs(ctx *context.Context, ignParam string, sessionIDs *[]*sessions.SessionID) (err error) {
	kamEv := utils.ToJSON(map[string]string{utils.Event: CGR_DLG_LIST})
	var sentDLG int
	for i, evapi := range ka.conns {
		if err := evapi.Send(kamEv); err != nil {
			utils.Logger.Err(fmt.Sprintf("<%s> failed sending event to connIdx<%v>, error %s",
				utils.KamailioAgent, i, err.Error()))
			continue
		}
		sentDLG++
	}
	if sentDLG == 0 {
		return
	}
	tm := time.NewTimer(config.CgrConfig().GeneralCfg().ReplyTimeout)
	for i := 0; i < sentDLG; i++ {
		select {
		case sIDs := <-ka.activeSessionIDs:
			*sessionIDs = append(*sessionIDs, sIDs...)
		case <-tm.C:
			return errors.New("timeout executing dialog list")
		}
	}
	if len(*sessionIDs) == 0 {
		return utils.ErrNoActiveSession
	}
	tm.Stop()
	return
}

// Reload recreates the connection buffers
// only used on reload
func (ka *KamailioAgent) Reload() {
	ka.conns = make([]*kamevapi.KamEvapi, len(ka.cfg.EvapiConns))
}

// V1AlterSession is used to implement the sessions.BiRPClient interface
func (*KamailioAgent) V1AlterSession(*context.Context, utils.CGREvent, *string) error {
	return utils.ErrNotImplemented
}

// V1DisconnectPeer is used to implement the sessions.BiRPClient interface
func (*KamailioAgent) V1DisconnectPeer(*context.Context, *utils.DPRArgs, *string) error {
	return utils.ErrNotImplemented
}

// V1WarnDisconnect is used to implement the sessions.BiRPClient interface
func (*KamailioAgent) V1WarnDisconnect(*context.Context, map[string]any, *string) error {
	return utils.ErrNotImplemented
}