package router

import "io"
import "log"
import "net"
import "sync"
import "bufio"
import "net/url"
import "net/http"
import "hnakra/protocol"

type activeRequest struct {
	service     *Service
	body        chan []byte
	requestBody io.ReadCloser
	header      http.Header
	status      int
	url         *url.URL

	res         http.ResponseWriter
	wroteHeader bool
	headerMutex sync.Mutex
}

func (request *activeRequest) ensureHeader () {
	request.headerMutex.Lock()
	defer request.headerMutex.Unlock()
	if request.wroteHeader { return }

	for key, values := range request.header {
		for _, value := range values  {
			request.res.Header().Add(key, value)
		}
	}
	request.res.WriteHeader(request.status)
	request.wroteHeader = true
}

type Service struct {
	router *Router
	scheme, host, path string

	user, name, description string

	idFactory    *protocol.IDFactory
	requests     map[protocol.ID] *activeRequest
	requestsLock sync.RWMutex
	
	conn           net.Conn
	connLock       sync.Mutex
	connReadWriter *bufio.ReadWriter
	connErr        error
}

func (router *Router) newService (conn net.Conn) (service *Service) {
	service = &Service {
		idFactory: protocol.NewRouterIDFactory(),
		router:    router,
		conn:      conn,
		requests:  make(map[protocol.ID] *activeRequest),
		connReadWriter: bufio.NewReadWriter (
			bufio.NewReader(conn),
			bufio.NewWriter(conn)),
	}
	go service.work()
	return
}

func (service *Service) OverRequests (callback func (protocol.ID, *url.URL) bool) {
	service.requestsLock.RLock()
	defer service.requestsLock.RUnlock()
	for id, request := range service.requests {
		if !callback(id, request.url) { break }
	}
}

func (service *Service) User () string {
	return service.user
}

func (service *Service) Name () string {
	return service.name
}

func (service *Service) Description () string {
	return service.description
}

func (service *Service) Pattern () (user, name, description string) {
	return service.user, service.name, service.description
}

func (service *Service) Close () error {
	return service.conn.Close()
}

func (service *Service) Shutdown () error {
	// TODO: wait for all requests to finish
	return service.conn.Close()
}

func (service *Service) ServeHTTP (res http.ResponseWriter, req *http.Request) {
	// if we are only accepting https requests and we recieve an http one,
	// redirect to the https version
	if req.TLS == nil && service.scheme == "https" {
		newURL := req.URL
		newURL.Scheme = service.scheme
		http.Redirect(res, req, newURL.String(), http.StatusPermanentRedirect)
		return
	}

	// create a new request
	request, id := service.generateActiveRequest(res, req)
	defer service.freeRequest(id)
	
	// ask the service to fulfill it
	err := service.send(protocol.MessageHTTPRequest {
		ID:      id,
		Address: req.RemoteAddr,
		Method:  req.Method,
		URL:     req.URL.String(),
		Header:  protocol.Map(req.Header),
	})
	if err != nil {
		http.Error (
			res, "connection to service closed abruptly: " +
			err.Error(), http.StatusBadGateway)
		return
	}
	
	// read in the body chunk bu chunk from the channel, and finalize the
	// request when the channel is closed
	for chunk := range request.body {
		request.ensureHeader()
		res.Write(chunk)
	}

	// if we have stopped serving the page prematurely due to an error,
	// inform the user (if possible)
	if service.connErr != nil && !request.wroteHeader {
		http.Error (
			res, "connection to service closed abruptly: " +
			service.connErr.Error(), http.StatusBadGateway)
		return
	}
}

func (service *Service) generateActiveRequest (
	res http.ResponseWriter,
	req *http.Request,
) (
	*activeRequest,
	protocol.ID,
) {
	service.requestsLock.Lock()
	defer service.requestsLock.Unlock()

	id := service.idFactory.Next()
	request := &activeRequest {
		service: service,
		body:        make(chan []byte),
		header:      make(http.Header),
		status:      http.StatusOK,
		url:         req.URL,
		requestBody: req.Body,
		res:         res,
	}
	service.requests[id] = request
	return request, id
}

func (service *Service) freeRequest (id protocol.ID) {
	service.requestsLock.Lock()
	defer service.requestsLock.Unlock()
	delete(service.requests, id)
	service.idFactory.Free(id)
}

func (service *Service) work () {
	defer log.Println("X=- connection to", service.conn.RemoteAddr(), "closed")
	unhandle, ok := service.authenticate()
	if !ok { return }

	// dismantle service when we exit
	defer func () {
		unhandle()
		service.conn.Close()
		
		closedRequest := false
		service.requestsLock.Lock()
		for _, request := range service.requests {
			closedRequest = true
			close(request.body)
		}
		service.requestsLock.Unlock()
		
		if service.connErr != nil && closedRequest {
			log.Println("!!! service connection error:", service.connErr)
		}
	} ()

	// respond to requests
	for {
		message, err := protocol.ReadMessage(service.connReadWriter)
		if err != nil {
			service.connErr = err
			return
		}
		
		switch message.(type) {
		// set the header and status code of the request. when the first
		// body chunk is sent or the body is ended without any chunks
		// being sent, the serving goroutine will send the header data.
		case protocol.MessageHTTPResponse:
			response := message.(protocol.MessageHTTPResponse)
			service.requestsLock.RLock()
			if _, ok := service.requests[response.ID]; ok {
				service.requests[response.ID].header = http.Header(response.Header)
				service.requests[response.ID].status = int(response.Status)
				service.requests[response.ID].ensureHeader()
			}
			service.requestsLock.RUnlock()

		// send the body chunk along the body channel to the goroutine
		// serving the request.
		case protocol.MessageHTTPBodySegment:
			segment := message.(protocol.MessageHTTPBodySegment)
			service.requestsLock.RLock()
			if _, ok := service.requests[segment.ID]; ok {
				service.requests[segment.ID].body <- segment.Data
			} else {
				log.Println("!!! service sent segment for nonexistent request", segment.ID)
			}
			service.requestsLock.RUnlock()

		// close the body channel and remove the request from the list,
		// signaling to the goroutine serving the request that the body
		// has been read entirely.
		case protocol.MessageHTTPBodyEnd:
			end := message.(protocol.MessageHTTPBodyEnd)
			service.requestsLock.Lock()
			if _, ok := service.requests[end.ID]; ok {
				close(service.requests[end.ID].body)
				service.requests[end.ID].body = nil
			} else {
				log.Println("!!! service ended nonexistent request", end.ID)
			}
			service.requestsLock.Unlock()

		// the client wants the reqeust body
		case protocol.MessageHTTPBodyRequest:
			id := message.(protocol.MessageHTTPBodyRequest).ID
			service.requestsLock.RLock()
			if request, ok := service.requests[id]; ok {
				body := request.requestBody
				request.requestBody = nil

				if body == nil {
					// TODO: send an error to the service bc this
					// means either the implementation of
					// http.Request is broken or the service has
					// requested the body twice.
				} else {
					go service.sendRequestBody(body, id)
				}
			} else {
				log.Println("!!! service requested body for nonexistent request", id)
			}
			service.requestsLock.RUnlock()

		// a message from the client.
		case protocol.MessageStatus:
			status := message.(protocol.MessageStatus)
			log.Println("(i)", service.name, "says:", status.Status)
			
		default:
			log.Println("ERR service sent unknown type code")
			service.Close()
		}
	}
}

func (service *Service) sendRequestBody (body io.ReadCloser, id protocol.ID) {
	// FIXME: is this a good max buffer size? maybe make it configurable
	buffer := [2048]byte { }
	for {
		n, err := body.Read(buffer[:])

		if n > 0 {
			if service.send(protocol.MessageHTTPBodySegment {
				ID:   id,
				Data: buffer[:n],
			}) != nil { return }
		}
		
		if err != nil {
			if err != io.EOF {
				// TODO: send the service an error
			}
			break
		}
	}
	service.send(protocol.MessageHTTPBodyEnd { ID: id })
}

func (service *Service) authenticate () (func(), bool) {
	// get login details
	message, err := protocol.ReadMessage(service.connReadWriter)
	if err != nil {
		service.Close()
		return nil, false
	}
	login, ok := message.(protocol.MessageLogin)
	if !ok {
		log.Println (
			"ERR", service.conn.RemoteAddr(),
			"sent wrong type code, expected",
			protocol.TypeLogin)
		service.send(protocol.MessageStatus {
			Status: protocol.StatusBadMessageType,
		})
		service.Close()
		return nil, false
	}

	// create pattern
	service.scheme = login.Scheme
	service.host   = login.Host
	service.path   = login.Path
	if service.scheme == "" { service.scheme = "https://" }
	if service.host   == "" { service.host   = "@"        }
	if service.path   == "" { service.path   = "/"        }

	// validate credentials
	status := service.router.Validate (
		login.User, login.Key,
		service.scheme, service.host, service.path)
	service.send(protocol.MessageStatus { Status: status })
	if status == protocol.StatusOk {
		service.user        = login.User
		service.name        = login.Name
		service.description = login.Description
		
		log.Println (
			"-->", service.conn.RemoteAddr(),
			"logged in as", login.User, "on",
			FormatPattern(service.scheme, service.host, service.path))
	} else {
		log.Println (
			"ERR", service.conn.RemoteAddr(),
			"failed login as", login.User, "on",
			FormatPattern(service.scheme, service.host, service.path))
		service.conn.Close()
		return nil, false	
	}

	// mount service on the mux.
	var unhandle func ()
	muxPattern := service.host + service.path 
	switch service.scheme {
	case "http", "https":
		err = service.router.HTTPMux().Handle(muxPattern, service)
		unhandle = func () {
			service.router.HTTPMux().Unhandle(muxPattern)
		}
	default:
		err = protocol.StatusBadMount
	}
	if err != nil {
		log.Println (
			"ERR", service.name,
			"sent bad mount pattern:",
			FormatPattern(service.scheme, service.host, service.path))
		service.send(protocol.MessageStatus {
			Status: protocol.StatusBadMount,
		})
		service.Close()
		return nil, false
	}

	// list the service in the router
	service.router.list(service)
	return func () {
		unhandle()
		service.router.unlist(service)
	}, true
}

func (service *Service) send (message protocol.Message) (err error) {
	service.connLock.Lock()
	defer service.connLock.Unlock()
	err = message.Send(service.connReadWriter)
	if err != nil { return }
	return service.connReadWriter.Flush()
}