package server

import (
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/dgraph-io/badger/v3"
	"github.com/google/uuid"
	"github.com/gorilla/mux"
	"github.com/sirupsen/logrus"

	"github.com/kalzu/kvs/types"
)

// healthHandler returns server health status
func (s *Server) healthHandler(w http.ResponseWriter, r *http.Request) {
	mode := s.getMode()
	memberCount := len(s.getMembers())

	health := map[string]interface{}{
		"status":       "ok",
		"mode":         mode,
		"member_count": memberCount,
		"node_id":      s.config.NodeID,
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(health)
}

// getKVHandler retrieves a key-value pair
func (s *Server) getKVHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	path := vars["path"]

	var storedValue types.StoredValue
	err := s.db.View(func(txn *badger.Txn) error {
		item, err := txn.Get([]byte(path))
		if err != nil {
			return err
		}

		return item.Value(func(val []byte) error {
			return json.Unmarshal(val, &storedValue)
		})
	})

	if err == badger.ErrKeyNotFound {
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}
	if err != nil {
		s.logger.WithError(err).WithField("path", path).Error("Failed to get value")
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(storedValue)
}

// putKVHandler stores a key-value pair
func (s *Server) putKVHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	path := vars["path"]

	mode := s.getMode()
	if mode == "syncing" {
		http.Error(w, "Service Unavailable", http.StatusServiceUnavailable)
		return
	}

	if mode == "read-only" && !s.isClusterMember(r.RemoteAddr) {
		http.Error(w, "Forbidden", http.StatusForbidden)
		return
	}

	var data json.RawMessage
	if err := json.NewDecoder(r.Body).Decode(&data); err != nil {
		http.Error(w, "Bad Request", http.StatusBadRequest)
		return
	}

	now := time.Now().UnixMilli()
	newUUID := uuid.New().String()

	storedValue := types.StoredValue{
		UUID:      newUUID,
		Timestamp: now,
		Data:      data,
	}

	valueBytes, err := json.Marshal(storedValue)
	if err != nil {
		s.logger.WithError(err).Error("Failed to marshal stored value")
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}

	var isUpdate bool
	err = s.db.Update(func(txn *badger.Txn) error {
		// Check if key exists
		_, err := txn.Get([]byte(path))
		isUpdate = (err == nil)

		// Store main data
		if err := txn.Set([]byte(path), valueBytes); err != nil {
			return err
		}

		// Store timestamp index
		indexKey := fmt.Sprintf("_ts:%020d:%s", now, path)
		return txn.Set([]byte(indexKey), []byte(newUUID))
	})

	if err != nil {
		s.logger.WithError(err).WithField("path", path).Error("Failed to store value")
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}

	response := types.PutResponse{
		UUID:      newUUID,
		Timestamp: now,
	}

	status := http.StatusCreated
	if isUpdate {
		status = http.StatusOK
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(response)

	s.logger.WithFields(logrus.Fields{
		"path":      path,
		"uuid":      newUUID,
		"timestamp": now,
		"is_update": isUpdate,
	}).Info("Value stored")
}

// deleteKVHandler removes a key-value pair
func (s *Server) deleteKVHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	path := vars["path"]

	mode := s.getMode()
	if mode == "syncing" {
		http.Error(w, "Service Unavailable", http.StatusServiceUnavailable)
		return
	}

	if mode == "read-only" && !s.isClusterMember(r.RemoteAddr) {
		http.Error(w, "Forbidden", http.StatusForbidden)
		return
	}

	var found bool
	err := s.db.Update(func(txn *badger.Txn) error {
		// Check if key exists and get timestamp for index cleanup
		item, err := txn.Get([]byte(path))
		if err == badger.ErrKeyNotFound {
			return nil
		}
		if err != nil {
			return err
		}
		found = true

		var storedValue types.StoredValue
		err = item.Value(func(val []byte) error {
			return json.Unmarshal(val, &storedValue)
		})
		if err != nil {
			return err
		}

		// Delete main data
		if err := txn.Delete([]byte(path)); err != nil {
			return err
		}

		// Delete timestamp index
		indexKey := fmt.Sprintf("_ts:%020d:%s", storedValue.Timestamp, path)
		return txn.Delete([]byte(indexKey))
	})

	if err != nil {
		s.logger.WithError(err).WithField("path", path).Error("Failed to delete value")
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}

	if !found {
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}

	w.WriteHeader(http.StatusNoContent)

	s.logger.WithField("path", path).Info("Value deleted")
}

// isClusterMember checks if request is from a cluster member
func (s *Server) isClusterMember(remoteAddr string) bool {
	host, _, err := net.SplitHostPort(remoteAddr)
	if err != nil {
		return false
	}

	members := s.gossipService.GetMembers()
	for _, member := range members {
		memberHost, _, err := net.SplitHostPort(member.Address)
		if err == nil && memberHost == host {
			return true
		}
	}

	return false
}

// getMembersHandler returns current cluster members
func (s *Server) getMembersHandler(w http.ResponseWriter, r *http.Request) {
	members := s.getMembers()

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(members)
}

// joinMemberHandler handles member join requests
func (s *Server) joinMemberHandler(w http.ResponseWriter, r *http.Request) {
	var req types.JoinRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Bad Request", http.StatusBadRequest)
		return
	}

	now := time.Now().UnixMilli()
	member := &types.Member{
		ID:              req.ID,
		Address:         req.Address,
		LastSeen:        now,
		JoinedTimestamp: req.JoinedTimestamp,
	}

	s.addMember(member)

	// Return current member list
	members := s.getMembers()
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(members)
}

// leaveMemberHandler handles member leave requests
func (s *Server) leaveMemberHandler(w http.ResponseWriter, r *http.Request) {
	var req types.LeaveRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Bad Request", http.StatusBadRequest)
		return
	}

	s.removeMember(req.ID)
	w.WriteHeader(http.StatusNoContent)
}

// pairsByTimeHandler handles queries for key-value pairs by timestamp
func (s *Server) pairsByTimeHandler(w http.ResponseWriter, r *http.Request) {
	var req types.PairsByTimeRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "Bad Request", http.StatusBadRequest)
		return
	}

	// Default limit to 15 as per spec
	if req.Limit <= 0 {
		req.Limit = 15
	}

	var pairs []types.PairsByTimeResponse

	err := s.db.View(func(txn *badger.Txn) error {
		opts := badger.DefaultIteratorOptions
		opts.PrefetchSize = req.Limit
		it := txn.NewIterator(opts)
		defer it.Close()

		prefix := []byte("_ts:")
		// The original logic for prefix filtering here was incomplete.
		// For Merkle tree sync, this handler is no longer used for core sync.
		// It remains as a client-facing API.
		
		for it.Seek(prefix); it.ValidForPrefix(prefix) && len(pairs) < req.Limit; it.Next() {
			item := it.Item()
			key := string(item.Key())

			// Parse timestamp index key: "_ts:{timestamp}:{path}"
			parts := strings.SplitN(key, ":", 3)
			if len(parts) != 3 {
				continue
			}

			timestamp, err := strconv.ParseInt(parts[1], 10, 64)
			if err != nil {
				continue
			}

			// Filter by timestamp range
			if req.StartTimestamp > 0 && timestamp < req.StartTimestamp {
				continue
			}
			if req.EndTimestamp > 0 && timestamp >= req.EndTimestamp {
				continue
			}

			path := parts[2]

			// Filter by prefix if specified
			if req.Prefix != "" && !strings.HasPrefix(path, req.Prefix) {
				continue
			}

			var uuid string
			err = item.Value(func(val []byte) error {
				uuid = string(val)
				return nil
			})
			if err != nil {
				continue
			}

			pairs = append(pairs, types.PairsByTimeResponse{
				Path:      path,
				UUID:      uuid,
				Timestamp: timestamp,
			})
		}

		return nil
	})

	if err != nil {
		s.logger.WithError(err).Error("Failed to query pairs by time")
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}

	if len(pairs) == 0 {
		w.WriteHeader(http.StatusNoContent)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(pairs)
}

// gossipHandler handles gossip protocol messages
func (s *Server) gossipHandler(w http.ResponseWriter, r *http.Request) {
	var remoteMemberList []types.Member
	if err := json.NewDecoder(r.Body).Decode(&remoteMemberList); err != nil {
		http.Error(w, "Bad Request", http.StatusBadRequest)
		return
	}

	// Merge the received member list using cluster service
	s.gossipService.MergeMemberList(remoteMemberList, s.config.NodeID)

	// Respond with our current member list
	localMembers := s.gossipService.GetMembers()
	gossipResponse := make([]types.Member, len(localMembers))
	for i, member := range localMembers {
		gossipResponse[i] = *member
	}

	// Add ourselves to the response
	selfMember := types.Member{
		ID:              s.config.NodeID,
		Address:         fmt.Sprintf("%s:%d", s.config.BindAddress, s.config.Port),
		LastSeen:        time.Now().UnixMilli(),
		JoinedTimestamp: s.getJoinedTimestamp(),
	}
	gossipResponse = append(gossipResponse, selfMember)

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(gossipResponse)

	s.logger.WithField("remote_members", len(remoteMemberList)).Debug("Processed gossip request")
}

// getBackupStatusHandler returns current backup status
func (s *Server) getBackupStatusHandler(w http.ResponseWriter, r *http.Request) {
	status := s.getBackupStatus()
	
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(status)
}