package daemon

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"net/http"
	"time"

	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"

	"github.com/zrepl/zrepl/daemon/job"
	"github.com/zrepl/zrepl/daemon/nethelpers"
	"github.com/zrepl/zrepl/logger"
	"github.com/zrepl/zrepl/version"
	"github.com/zrepl/zrepl/zfs"
)

type controlJob struct {
	sockaddr *net.UnixAddr
	jobs     *jobs
}

func newControlJob(sockpath string, jobs *jobs) (j *controlJob, err error) {
	j = &controlJob{jobs: jobs}

	j.sockaddr, err = net.ResolveUnixAddr("unix", sockpath)
	if err != nil {
		err = errors.Wrap(err, "cannot resolve unix address")
		return
	}

	return
}

func (j *controlJob) Name() string { return jobNameControl }

func (j *controlJob) Status() *job.Status { return &job.Status{Type: job.TypeInternal} }

func (j *controlJob) OwnedDatasetSubtreeRoot() (p *zfs.DatasetPath, ok bool) { return nil, false }

var promControl struct {
	requestBegin    *prometheus.CounterVec
	requestFinished *prometheus.HistogramVec
}

func (j *controlJob) RegisterMetrics(registerer prometheus.Registerer) {
	promControl.requestBegin = prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: "zrepl",
		Subsystem: "control",
		Name:      "request_begin",
		Help:      "number of request we started to handle",
	}, []string{"endpoint"})

	promControl.requestFinished = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: "zrepl",
		Subsystem: "control",
		Name:      "request_finished",
		Help:      "time it took a request to finih",
		Buckets:   []float64{1e-6, 10e-6, 100e-6, 500e-6, 1e-3, 10e-3, 100e-3, 200e-3, 400e-3, 800e-3, 1, 10, 20},
	}, []string{"endpoint"})
	registerer.MustRegister(promControl.requestBegin)
	registerer.MustRegister(promControl.requestFinished)
}

const (
	ControlJobEndpointPProf   string = "/debug/pprof"
	ControlJobEndpointVersion string = "/version"
	ControlJobEndpointStatus  string = "/status"
	ControlJobEndpointSignal  string = "/signal"
)

func (j *controlJob) Run(ctx context.Context) {

	log := job.GetLogger(ctx)
	defer log.Info("control job finished")

	l, err := nethelpers.ListenUnixPrivate(j.sockaddr)
	if err != nil {
		log.WithError(err).Error("error listening")
		return
	}

	pprofServer := NewPProfServer(ctx)

	mux := http.NewServeMux()
	mux.Handle(ControlJobEndpointPProf,
		requestLogger{log: log, handler: jsonRequestResponder{log, func(decoder jsonDecoder) (interface{}, error) {
			var msg PprofServerControlMsg
			err := decoder(&msg)
			if err != nil {
				return nil, errors.Errorf("decode failed")
			}
			pprofServer.Control(msg)
			return struct{}{}, nil
		}}})

	mux.Handle(ControlJobEndpointVersion,
		requestLogger{log: log, handler: jsonResponder{log, func() (interface{}, error) {
			return version.NewZreplVersionInformation(), nil
		}}})

	mux.Handle(ControlJobEndpointStatus,
		// don't log requests to status endpoint, too spammy
		jsonResponder{log, func() (interface{}, error) {
			s := j.jobs.status()
			return s, nil
		}})

	mux.Handle(ControlJobEndpointSignal,
		requestLogger{log: log, handler: jsonRequestResponder{log, func(decoder jsonDecoder) (interface{}, error) {
			type reqT struct {
				Name string
				Op   string
			}
			var req reqT
			if decoder(&req) != nil {
				return nil, errors.Errorf("decode failed")
			}

			var err error
			switch req.Op {
			case "wakeup":
				err = j.jobs.wakeup(req.Name)
			case "reset":
				err = j.jobs.reset(req.Name)
			default:
				err = fmt.Errorf("operation %q is invalid", req.Op)
			}

			return struct{}{}, err
		}}})
	server := http.Server{
		Handler: mux,
		// control socket is local, 1s timeout should be more than sufficient, even on a loaded system
		WriteTimeout: 1 * time.Second,
		ReadTimeout:  1 * time.Second,
	}

outer:
	for {

		served := make(chan error)
		go func() {
			served <- server.Serve(l)
			close(served)
		}()

		select {
		case <-ctx.Done():
			log.WithError(ctx.Err()).Info("context done")
			err := server.Shutdown(context.Background())
			if err != nil {
				log.WithError(err).Error("cannot shutdown server")
			}
			break outer
		case err = <-served:
			if err != nil {
				log.WithError(err).Error("error serving")
				break outer
			}
		}

	}

}

type jsonResponder struct {
	log      Logger
	producer func() (interface{}, error)
}

func (j jsonResponder) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	logIoErr := func(err error) {
		if err != nil {
			j.log.WithError(err).Error("control handler io error")
		}
	}
	res, err := j.producer()
	if err != nil {
		j.log.WithError(err).Error("control handler error")
		w.WriteHeader(http.StatusInternalServerError)
		_, err = io.WriteString(w, err.Error())
		logIoErr(err)
		return
	}
	var buf bytes.Buffer
	err = json.NewEncoder(&buf).Encode(res)
	if err != nil {
		j.log.WithError(err).Error("control handler json marshal error")
		w.WriteHeader(http.StatusInternalServerError)
		_, err = io.WriteString(w, err.Error())
	} else {
		_, err = io.Copy(w, &buf)
	}
	logIoErr(err)
}

type jsonDecoder = func(interface{}) error

type jsonRequestResponder struct {
	log      Logger
	producer func(decoder jsonDecoder) (interface{}, error)
}

func (j jsonRequestResponder) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	logIoErr := func(err error) {
		if err != nil {
			j.log.WithError(err).Error("control handler io error")
		}
	}

	var decodeError error
	decoder := func(i interface{}) error {
		err := json.NewDecoder(r.Body).Decode(&i)
		decodeError = err
		return err
	}
	res, producerErr := j.producer(decoder)

	//If we had a decode error ignore output of producer and return error
	if decodeError != nil {
		w.WriteHeader(http.StatusBadRequest)
		_, err := io.WriteString(w, decodeError.Error())
		logIoErr(err)
		return
	}
	if producerErr != nil {
		j.log.WithError(producerErr).Error("control handler error")
		w.WriteHeader(http.StatusInternalServerError)
		_, err := io.WriteString(w, producerErr.Error())
		logIoErr(err)
		return
	}

	var buf bytes.Buffer
	encodeErr := json.NewEncoder(&buf).Encode(res)
	if encodeErr != nil {
		j.log.WithError(producerErr).Error("control handler json marhsal error")
		w.WriteHeader(http.StatusInternalServerError)
		_, err := io.WriteString(w, encodeErr.Error())
		logIoErr(err)
	} else {
		_, err := io.Copy(w, &buf)
		logIoErr(err)
	}
}

type requestLogger struct {
	log         logger.Logger
	handler     http.Handler
	handlerFunc http.HandlerFunc
}

func (l requestLogger) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	log := l.log.WithField("method", r.Method).WithField("url", r.URL)
	log.Debug("start")
	promControl.requestBegin.WithLabelValues(r.URL.Path).Inc()
	defer prometheus.NewTimer(promControl.requestFinished.WithLabelValues(r.URL.Path)).ObserveDuration()
	if l.handlerFunc != nil {
		l.handlerFunc(w, r)
	} else if l.handler != nil {
		l.handler.ServeHTTP(w, r)
	} else {
		log.Error("no handler or handlerFunc configured")
	}
	log.Debug("finish")
}