package caddyhugo

import (
	"fmt"
	"log"
	"net/http"
	"time"

	"git.stephensearles.com/stephen/acedoc"
	"github.com/gorilla/websocket"
)

// DeltaConn identifies the methods used in the original websocket implementation.
type DeltaConn interface {
	ReadJSON(v interface{}) error
	WriteJSON(v interface{}) error
}

func (ch *CaddyHugo) ObserveLTime(ltime uint64) uint64 {
	ch.mtx.Lock()

	if ch.ltime < ltime {
		ch.ltime = ltime
	}

	ch.mtx.Unlock()
	return ch.LTime()
}

func (ch *CaddyHugo) LTime() uint64 {
	ch.mtx.Lock()
	defer ch.mtx.Unlock()
	ch.ltime++
	return ch.ltime
}

func (ch *CaddyHugo) ShouldApply(ltime uint64) bool {
	lowest := ch.LowestPendingConfirmation()
	for _, c := range ch.Confirming() {
		if lowest == 0 || c < lowest {
			lowest = c
		}
	}

	if ltime < lowest {
		return false
	}

	ch.mtx.Lock()
	defer ch.mtx.Unlock()

	if _, ok := ch.confirmingToClient[ltime]; ok {
		return false
	}

	return true
}

func (ch *CaddyHugo) ConfirmLTime(ltime uint64) {
	ch.mtx.Lock()
	defer ch.mtx.Unlock()
	ch.confirmingToClient[ltime] = struct{}{}
}

func (ch *CaddyHugo) Confirming() []uint64 {
	var times []uint64

	ch.mtx.Lock()
	defer ch.mtx.Unlock()

	for ltime := range ch.confirmingToClient {
		times = append(times, ltime)
	}
	return times
}

func (ch *CaddyHugo) LowestPendingConfirmation() uint64 {
	var lowest uint64
	for _, c := range ch.Confirming() {
		if lowest == 0 || c < lowest {
			lowest = c
		}
	}
	return lowest
}

func (ch *CaddyHugo) ClearConfirmed(lowestPending uint64) {
	ch.mtx.Lock()
	defer ch.mtx.Unlock()

	for ltime := range ch.confirmingToClient {
		if ltime < lowestPending {
			delete(ch.confirmingToClient, ltime)
		}
	}
}

func (ch *CaddyHugo) DeltaWebsocket(w http.ResponseWriter, r *http.Request) (int, error) {
	var upgrader = websocket.Upgrader{
		ReadBufferSize:  1024,
		WriteBufferSize: 1024,
	}

	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		fmt.Println(err)
		return http.StatusBadRequest, err
	}

	conn.SetReadDeadline(time.Time{})

	doc, err := ch.editSession(docNameFromEditRequest(r))
	if err != nil {
		fmt.Println(err)
		return http.StatusBadRequest, err
	}

	return ch.handleDeltaConn(conn, doc)
}

func (ch *CaddyHugo) Message(deltas ...acedoc.Delta) Message {
	return Message{
		Deltas:        deltas,
		LTime:         ch.LTime(),
		Confirmed:     ch.Confirming(),
		LowestPending: ch.LowestPendingConfirmation(),
	}
}

func (ch *CaddyHugo) handleDeltaConn(conn DeltaConn, doc *editSession) (int, error) {
	const idlePing = 15 * time.Second
	const idlePingShort = 1 * time.Millisecond

	errCh := make(chan error)
	doneCh := make(chan struct{})
	defer func() {
		close(doneCh)
		close(errCh)
		for err := range errCh {
			log.Println(err)
		}
	}()

	timer := time.NewTimer(idlePing)
	resetTimer := func(d time.Duration) {
		if !timer.Stop() {
			select {
			case <-timer.C:
			default:
			}
		}
		timer.Reset(d)
	}

	wroteMessagesCh := make(chan Message, 2)

	client := doc.doc.Client(acedoc.DeltaHandlerFunc(func(ds []acedoc.Delta) error {
		m := ch.Message(ds...)
		wroteMessagesCh <- m
		return conn.WriteJSON(m)
	}))

	ch.mtx.Lock()
	doc.clients++
	ch.mtx.Unlock()

	defer func() {
		ch.mtx.Lock()
		client.Close()
		doc.clients--
		ch.mtx.Unlock()
	}()

	readMessagesCh := make(chan Message, 2)
	go func() {
		for {
			var message Message

			err := conn.ReadJSON(&message)
			if err != nil {
				errCh <- fmt.Errorf("error reading message from client conn: %v", err)
				return
			}
			ch.ObserveLTime(message.LTime)

			if len(message.Deltas) == 0 {
				time.Sleep(10 * time.Microsecond)
				continue
			}

			if !ch.ShouldApply(message.LTime) {
				continue
			}

			err = client.PushDeltas(message.Deltas...)
			if err != nil {
				errCh <- fmt.Errorf("error pushing deltas into document: %v", err)
				return
			}

			ch.ConfirmLTime(message.LTime)
			ch.ClearConfirmed(message.LowestPending)

			select {
			case readMessagesCh <- message:
			case <-doneCh:
				return
			}

		}
	}()

	for {
		select {
		case err := <-errCh:
			fmt.Println("error handling websocket connection:", err)
			return 500, err
		default:
		}

		select {
		case <-timer.C:
			conn.WriteJSON(ch.Message())
			resetTimer(idlePing)
		case <-readMessagesCh:
			resetTimer(idlePingShort)
		case <-wroteMessagesCh:
			resetTimer(idlePing)
		case <-doneCh:
			return 200, nil
		}
	}
}

type Message struct {
	Deltas        []acedoc.Delta `json:"deltas"`
	LTime         uint64         `json:"ltime"`
	Confirmed     []uint64       `json:"confirmed"`
	LowestPending uint64         `json:"lowestPending"`
}