package proxy

import (
	"encoding/base64"
	"time"

	"github.com/centrifugal/centrifugo/v6/internal/config"
	"github.com/centrifugal/centrifugo/v6/internal/configtypes"
	"github.com/centrifugal/centrifugo/v6/internal/metrics"
	"github.com/centrifugal/centrifugo/v6/internal/proxyproto"

	"github.com/centrifugal/centrifuge"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/rs/zerolog/log"
)

// PublishHandlerConfig ...
type PublishHandlerConfig struct {
	Proxies map[string]PublishProxy
}

// PublishHandler ...
type PublishHandler struct {
	config    PublishHandlerConfig
	summary   map[string]prometheus.Observer
	histogram map[string]prometheus.Observer
	errors    map[string]prometheus.Counter
	inflight  map[string]prometheus.Gauge
}

// NewPublishHandler ...
func NewPublishHandler(c PublishHandlerConfig) *PublishHandler {
	h := &PublishHandler{
		config: c,
	}
	summary := map[string]prometheus.Observer{}
	histogram := map[string]prometheus.Observer{}
	errors := map[string]prometheus.Counter{}
	inflight := map[string]prometheus.Gauge{}
	for name, p := range c.Proxies {
		summary[name] = metrics.ProxyCallDurationSummary.WithLabelValues(p.Protocol(), "publish", name)
		histogram[name] = metrics.ProxyCallDurationHistogram.WithLabelValues(p.Protocol(), "publish", name)
		errors[name] = metrics.ProxyCallErrorCount.WithLabelValues(p.Protocol(), "publish", name)
		inflight[name] = metrics.ProxyCallInflightRequests.WithLabelValues(p.Protocol(), "publish", name)
	}
	h.summary = summary
	h.histogram = histogram
	h.errors = errors
	h.inflight = inflight
	return h
}

// PublishHandlerFunc ...
type PublishHandlerFunc func(Client, centrifuge.PublishEvent, configtypes.ChannelOptions, PerCallData) (centrifuge.PublishReply, error)

// Handle Publish.
func (h *PublishHandler) Handle(node *centrifuge.Node) PublishHandlerFunc {
	return func(client Client, e centrifuge.PublishEvent, chOpts configtypes.ChannelOptions, pcd PerCallData) (centrifuge.PublishReply, error) {
		started := time.Now()

		var p PublishProxy
		var summary prometheus.Observer
		var histogram prometheus.Observer
		var errors prometheus.Counter

		proxyEnabled := chOpts.PublishProxyEnabled
		proxyName := chOpts.PublishProxyName
		if !proxyEnabled {
			log.Info().Str("channel", e.Channel).Msg("publish proxy not enabled for a channel")
			return centrifuge.PublishReply{}, centrifuge.ErrorNotAvailable
		}
		p = h.config.Proxies[proxyName]
		summary = h.summary[proxyName]
		histogram = h.histogram[proxyName]
		errors = h.errors[proxyName]
		inflight := h.inflight[proxyName]
		inflight.Inc()
		defer inflight.Dec()

		req := &proxyproto.PublishRequest{
			Client:    client.ID(),
			Protocol:  string(client.Transport().Protocol()),
			Transport: client.Transport().Name(),
			Encoding:  getEncoding(p.UseBase64()),

			User:    client.UserID(),
			Channel: e.Channel,
		}
		if p.IncludeMeta() && pcd.Meta != nil {
			req.Meta = proxyproto.Raw(pcd.Meta)
		}
		if !p.UseBase64() {
			req.Data = e.Data
		} else {
			req.B64Data = base64.StdEncoding.EncodeToString(e.Data)
		}

		publishRep, err := p.ProxyPublish(client.Context(), req)
		duration := time.Since(started).Seconds()
		if err != nil {
			select {
			case <-client.Context().Done():
				// Client connection already closed.
				return centrifuge.PublishReply{}, centrifuge.DisconnectConnectionClosed
			default:
			}
			summary.Observe(duration)
			histogram.Observe(duration)
			errors.Inc()
			log.Error().Err(err).Str("client", client.ID()).Str("channel", e.Channel).Msg("error proxying publish")
			return centrifuge.PublishReply{}, err
		}
		summary.Observe(duration)
		histogram.Observe(duration)

		if publishRep.Disconnect != nil {
			return centrifuge.PublishReply{}, proxyproto.DisconnectFromProto(publishRep.Disconnect)
		}
		if publishRep.Error != nil {
			return centrifuge.PublishReply{}, proxyproto.ErrorFromProto(publishRep.Error)
		}

		historySize := chOpts.HistorySize
		historyTTL := chOpts.HistoryTTL
		historyMetaTTL := chOpts.HistoryMetaTTL

		data := e.Data
		var tags map[string]string
		var idempotencyKey string
		var useDelta bool
		var version uint64
		var versionEpoch string
		if publishRep.Result != nil {
			if publishRep.Result.Data != nil {
				data = publishRep.Result.Data
			} else if publishRep.Result.B64Data != "" {
				decodedData, err := base64.StdEncoding.DecodeString(publishRep.Result.B64Data)
				if err != nil {
					log.Error().Err(err).Str("client", client.ID()).Msg("error decoding base64 data")
					return centrifuge.PublishReply{}, centrifuge.ErrorInternal
				}
				data = decodedData
			}

			if publishRep.Result.SkipHistory {
				historySize = 0
				historyTTL = 0
			}

			tags = publishRep.Result.Tags
			idempotencyKey = publishRep.Result.IdempotencyKey
			useDelta = publishRep.Result.Delta
			version = publishRep.Result.Version
			versionEpoch = publishRep.Result.VersionEpoch
		}

		// The proxy may replace the data client sent, so validate the final data
		// against the channel format – same policy as for the client-supplied one.
		if err := config.ValidatePublicationData(data, chOpts.PublicationDataFormat); err != nil {
			log.Info().Err(err).Str("channel", e.Channel).Str("client", client.ID()).Msg("publish proxy data validation failed")
			return centrifuge.PublishReply{}, centrifuge.ErrorBadRequest
		}

		result, err := node.Publish(
			e.Channel, data,
			centrifuge.WithClientInfo(e.ClientInfo),
			centrifuge.WithHistory(historySize, historyTTL.ToDuration(), historyMetaTTL.ToDuration()),
			centrifuge.WithTags(tags),
			centrifuge.WithIdempotencyKey(idempotencyKey),
			centrifuge.WithDelta(useDelta),
			centrifuge.WithVersion(version, versionEpoch),
		)
		return centrifuge.PublishReply{Result: &result}, err
	}
}