package server

import (
	"context"
	"encoding/json"
	"net/http"
	"regexp"
	"strings"
	"sync"

	"github.com/gorilla/mux"
	"github.com/sirupsen/logrus"
)

var tcpShieldPattern = regexp.MustCompile("///.*")

func init() {
	apiRoutes.Path("/routes").Methods("GET").
		Headers("Accept", "application/json").
		HandlerFunc(routesListHandler)
	apiRoutes.Path("/routes").Methods("POST").
		Headers("Content-Type", "application/json").
		HandlerFunc(routesCreateHandler)
	apiRoutes.Path("/defaultRoute").Methods("POST").
		Headers("Content-Type", "application/json").
		HandlerFunc(routesSetDefault)
	apiRoutes.Path("/routes/{serverAddress}").Methods("DELETE").HandlerFunc(routesDeleteHandler)
}

func routesListHandler(writer http.ResponseWriter, _ *http.Request) {
	mappings := Routes.GetMappings()
	bytes, err := json.Marshal(mappings)
	if err != nil {
		logrus.WithError(err).Error("Failed to marshal mappings")
		writer.WriteHeader(http.StatusInternalServerError)
		return
	}
	_, err = writer.Write(bytes)
	if err != nil {
		logrus.WithError(err).Error("Failed to write response")
	}
}

func routesDeleteHandler(writer http.ResponseWriter, request *http.Request) {
	serverAddress := mux.Vars(request)["serverAddress"]
	RoutesConfig.DeleteMapping(serverAddress)
	if serverAddress != "" {
		if Routes.DeleteMapping(serverAddress) {
			writer.WriteHeader(http.StatusOK)
		} else {
			writer.WriteHeader(http.StatusNotFound)
		}
	}
}

func routesCreateHandler(writer http.ResponseWriter, request *http.Request) {
	var definition = struct {
		ServerAddress string
		Backend       string
	}{}

	//goland:noinspection GoUnhandledErrorResult
	defer request.Body.Close()

	decoder := json.NewDecoder(request.Body)
	err := decoder.Decode(&definition)
	if err != nil {
		logrus.WithError(err).Error("Unable to get request body")
		writer.WriteHeader(http.StatusBadRequest)
		return
	}

	Routes.CreateMapping(definition.ServerAddress, definition.Backend, func(ctx context.Context) error { return nil })
	RoutesConfig.AddMapping(definition.ServerAddress, definition.Backend)
	writer.WriteHeader(http.StatusCreated)
}

func routesSetDefault(writer http.ResponseWriter, request *http.Request) {
	var body = struct {
		Backend string
	}{}

	//goland:noinspection GoUnhandledErrorResult
	defer request.Body.Close()

	decoder := json.NewDecoder(request.Body)
	err := decoder.Decode(&body)
	if err != nil {
		logrus.WithError(err).Error("Unable to parse request")
		writer.WriteHeader(http.StatusBadRequest)
		return
	}

	Routes.SetDefaultRoute(body.Backend)
	RoutesConfig.SetDefaultRoute(body.Backend)
	writer.WriteHeader(http.StatusOK)
}

type IRoutes interface {
	Reset()
	RegisterAll(mappings map[string]string)
	// FindBackendForServerAddress returns the host:port for the external server address, if registered.
	// Otherwise, an empty string is returned. Also returns the normalized version of the given serverAddress.
	// The 3rd value returned is an (optional) "waker" function which a caller must invoke to wake up serverAddress.
	FindBackendForServerAddress(ctx context.Context, serverAddress string) (string, string, func(ctx context.Context) error)
	GetMappings() map[string]string
	DeleteMapping(serverAddress string) bool
	CreateMapping(serverAddress string, backend string, waker func(ctx context.Context) error)
	SetDefaultRoute(backend string)
	SimplifySRV(srvEnabled bool)
}

var Routes = NewRoutes()

func NewRoutes() IRoutes {
	r := &routesImpl{
		mappings: make(map[string]mapping),
	}

	return r
}

func (r *routesImpl) RegisterAll(mappings map[string]string) {
	for k, v := range mappings {
		r.CreateMapping(k, v, func(ctx context.Context) error { return nil })
	}
}

type mapping struct {
	backend string
	waker   func(ctx context.Context) error
}

type routesImpl struct {
	sync.RWMutex
	mappings     map[string]mapping
	defaultRoute string
	simplifySRV  bool
}

func (r *routesImpl) Reset() {
	r.mappings = make(map[string]mapping)
}

func (r *routesImpl) SetDefaultRoute(backend string) {
	r.defaultRoute = backend

	logrus.WithFields(logrus.Fields{
		"backend": backend,
	}).Info("Using default route")
}

func (r *routesImpl) SimplifySRV(srvEnabled bool) {
	r.simplifySRV = srvEnabled
}

func (r *routesImpl) FindBackendForServerAddress(_ context.Context, serverAddress string) (string, string, func(ctx context.Context) error) {
	r.RLock()
	defer r.RUnlock()

	// Trim off Forge null-delimited address parts like \x00FML3\x00
	serverAddress = strings.Split(serverAddress, "\x00")[0]

	serverAddress = strings.ToLower(
		// trim the root zone indicator, see https://en.wikipedia.org/wiki/Fully_qualified_domain_name
		strings.TrimSuffix(serverAddress, "."))

	logrus.WithFields(logrus.Fields{
		"serverAddress": serverAddress,
	}).Debug("Finding backend for server address")

	if r.simplifySRV {
		parts := strings.Split(serverAddress, ".")
		tcpIndex := -1
		for i, part := range parts {
			if part == "_tcp" {
				tcpIndex = i
				break
			}
		}
		if tcpIndex != -1 {
			parts = parts[tcpIndex+1:]
		}

		serverAddress = strings.Join(parts, ".")
	}

	// Strip suffix of TCP Shield
	serverAddress = tcpShieldPattern.ReplaceAllString(serverAddress, "")

	if r.mappings != nil {
		if mapping, exists := r.mappings[serverAddress]; exists {
			return mapping.backend, serverAddress, mapping.waker
		}
	}
	return r.defaultRoute, serverAddress, nil
}

func (r *routesImpl) GetMappings() map[string]string {
	r.RLock()
	defer r.RUnlock()

	result := make(map[string]string, len(r.mappings))
	for k, v := range r.mappings {
		result[k] = v.backend
	}
	return result
}

func (r *routesImpl) DeleteMapping(serverAddress string) bool {
	r.Lock()
	defer r.Unlock()
	logrus.WithField("serverAddress", serverAddress).Info("Deleting route")

	if _, ok := r.mappings[serverAddress]; ok {
		delete(r.mappings, serverAddress)
		return true
	} else {
		return false
	}
}

func (r *routesImpl) CreateMapping(serverAddress string, backend string, waker func(ctx context.Context) error) {
	r.Lock()
	defer r.Unlock()

	serverAddress = strings.ToLower(serverAddress)

	logrus.WithFields(logrus.Fields{
		"serverAddress": serverAddress,
		"backend":       backend,
	}).Info("Created route mapping")
	r.mappings[serverAddress] = mapping{backend: backend, waker: waker}
}