package handlers

import (
	"context"
	"encoding/binary"
	"encoding/json"
	"github.com/jsiebens/ionscale/internal/config"
	"github.com/jsiebens/ionscale/internal/core"
	"github.com/jsiebens/ionscale/internal/domain"
	"github.com/jsiebens/ionscale/internal/mapping"
	"github.com/klauspost/compress/zstd"
	"github.com/labstack/echo/v4"
	"net/http"
	"slices"
	"sync"
	"tailscale.com/smallzstd"
	"tailscale.com/tailcfg"
	"tailscale.com/types/key"
	"tailscale.com/util/dnsname"
	"time"
)

func NewPollNetMapHandler(
	machineKey key.MachinePublic,
	sessionManager core.PollMapSessionManager,
	repository domain.Repository) *PollNetMapHandler {

	handler := &PollNetMapHandler{
		machineKey:     machineKey,
		sessionManager: sessionManager,
		repository:     repository,
	}

	return handler
}

type PollNetMapHandler struct {
	machineKey     key.MachinePublic
	repository     domain.Repository
	sessionManager core.PollMapSessionManager
}

func (h *PollNetMapHandler) PollNetMap(c echo.Context) error {
	ctx := c.Request().Context()

	req := &tailcfg.MapRequest{}
	if err := c.Bind(req); err != nil {
		return logError(err)
	}

	if req.Version < SupportedCapabilityVersion {
		return UnsupportedClientVersionError
	}

	machineKey := h.machineKey.String()
	nodeKey := req.NodeKey.String()

	var m *domain.Machine
	m, err := h.repository.GetMachineByKeys(ctx, machineKey, nodeKey)
	if err != nil {
		return logError(err)
	}

	if m == nil {
		return echo.NewHTTPError(http.StatusNotFound)
	}

	return h.handlePollNetMap(c, m, req)
}

func (h *PollNetMapHandler) handlePollNetMap(c echo.Context, m *domain.Machine, mapRequest *tailcfg.MapRequest) error {
	ctx := c.Request().Context()

	now := time.Now().UTC()
	tailnetID := m.TailnetID
	machineID := m.ID

	mapper := mapping.NewPollNetMapper(mapRequest, m.ID, h.repository, h.sessionManager)

	response, err := h.createMapResponse(mapper, false, mapRequest.Compress)
	if err != nil {
		return logError(err)
	}

	if !mapRequest.Stream {
		if !slices.Equal(m.HostInfo.RoutableIPs, mapRequest.Hostinfo.RoutableIPs) {
			m.AutoAllowIPs = m.Tailnet.ACLPolicy.Get().FindAutoApprovedIPs(mapRequest.Hostinfo.RoutableIPs, m.Tags, &m.User)
		}

		m.HostInfo = domain.HostInfo(*mapRequest.Hostinfo)
		m.DiscoKey = mapRequest.DiscoKey.String()
		m.Endpoints = mapRequest.Endpoints
		m.LastSeen = &now

		sanitizeHostname := dnsname.SanitizeHostname(m.HostInfo.Hostname)
		if m.UseOSHostname && m.Name != sanitizeHostname {
			nameIdx, err := h.repository.GetNextMachineNameIndex(ctx, m.TailnetID, sanitizeHostname)
			if err != nil {
				return logError(err)
			}
			m.Name = sanitizeHostname
			m.NameIdx = nameIdx
		}

		if err := h.repository.SaveMachine(ctx, m); err != nil {
			return logError(err)
		}

		h.sessionManager.NotifyAll(tailnetID)

		return c.JSONBlob(http.StatusOK, response)
	}

	updateChan := make(chan *core.Ping, 20)
	h.sessionManager.Register(m.TailnetID, m.ID, updateChan)

	// Listen to connection close
	notify := ctx.Done()

	keepAliveResponse, err := h.createKeepAliveResponse(mapRequest)
	if err != nil {
		return logError(err)
	}

	c.Response().WriteHeader(http.StatusOK)

	if _, err := c.Response().Write(response); err != nil {
		return logError(err)
	}
	c.Response().Flush()

	connectedDevices.WithLabelValues(m.Tailnet.Name).Inc()

	keepAliveTicker := time.NewTicker(config.KeepAliveInterval())
	syncTicker := time.NewTicker(5 * time.Second)

	defer func() {
		connectedDevices.WithLabelValues(m.Tailnet.Name).Dec()
		h.sessionManager.Deregister(m.TailnetID, m.ID, updateChan)
		keepAliveTicker.Stop()
		syncTicker.Stop()
		_ = h.repository.SetMachineLastSeen(ctx, machineID)
	}()

	var shouldUpdate bool = false

	for {
		select {
		case _, ok := <-updateChan:
			if !ok {
				return nil
			}
			shouldUpdate = true
		case <-keepAliveTicker.C:
			if mapRequest.KeepAlive {
				if _, err := c.Response().Write(keepAliveResponse); err != nil {
					return logError(err)
				}
				_ = h.repository.SetMachineLastSeen(ctx, machineID)
				c.Response().Flush()
			}
		case <-syncTicker.C:
			if shouldUpdate {
				machine, err := h.repository.GetMachine(ctx, machineID)
				if err != nil {
					return logError(err)
				}
				if machine == nil {
					return nil
				}

				var payload []byte
				var payloadErr error

				payload, payloadErr = h.createMapResponse(mapper, true, mapRequest.Compress)

				if payloadErr != nil {
					return payloadErr
				}

				if _, err := c.Response().Write(payload); err != nil {
					return logError(err)
				}
				c.Response().Flush()

				shouldUpdate = false
			}
		case <-notify:
			return nil
		}
	}
}

func (h *PollNetMapHandler) createKeepAliveResponse(request *tailcfg.MapRequest) ([]byte, error) {
	mapResponse := &tailcfg.MapResponse{
		KeepAlive: true,
	}

	return h.marshalResponse(request.Compress, mapResponse)
}

func (h *PollNetMapHandler) createMapResponse(m *mapping.PollNetMapper, delta bool, compress string) ([]byte, error) {
	response, err := m.CreateMapResponse(context.Background(), delta)
	if err != nil {
		return nil, err
	}
	return h.marshalResponse(compress, response)
}

func (h *PollNetMapHandler) marshalResponse(compress string, v interface{}) ([]byte, error) {
	var payload []byte

	marshalled, err := json.Marshal(v)
	if err != nil {
		return nil, err
	}

	if compress == "zstd" {
		payload = zstdEncode(marshalled)
	} else {
		payload = marshalled
	}

	data := make([]byte, 4)
	binary.LittleEndian.PutUint32(data, uint32(len(payload)))
	data = append(data, payload...)

	return data, nil
}

func zstdEncode(in []byte) []byte {
	encoder := zstdEncoderPool.Get().(*zstd.Encoder)
	out := encoder.EncodeAll(in, nil)
	_ = encoder.Close()
	zstdEncoderPool.Put(encoder)
	return out
}

var zstdEncoderPool = &sync.Pool{
	New: func() any {
		encoder, err := smallzstd.NewEncoder(nil, zstd.WithEncoderLevel(zstd.SpeedFastest))
		if err != nil {
			panic(err)
		}
		return encoder
	},
}