// gomuks - A terminal Matrix client written in Go.
// Copyright (C) 2020 Tulir Asokan
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package rooms

import (
	"compress/gzip"
	"encoding/gob"
	"encoding/json"
	"fmt"
	"os"
	"time"

	sync "github.com/sasha-s/go-deadlock"

	"maunium.net/go/mautrix"
	"maunium.net/go/mautrix/event"
	"maunium.net/go/mautrix/id"

	"maunium.net/go/gomuks/debug"
)

func init() {
	gob.Register(map[string]interface{}{})
	gob.Register([]interface{}{})
}

type RoomNameSource int

const (
	UnknownRoomName RoomNameSource = iota
	MemberRoomName
	CanonicalAliasRoomName
	ExplicitRoomName
)

// RoomTag is a tag given to a specific room.
type RoomTag struct {
	// The name of the tag.
	Tag string
	// The order of the tag.
	Order json.Number
}

type UnreadMessage struct {
	EventID   id.EventID
	Counted   bool
	Highlight bool
}

type Member struct {
	event.MemberEventContent

	// The user who sent the membership event
	Sender id.UserID `json:"-"`
}

// Room represents a single Matrix room.
type Room struct {
	// The room ID.
	ID id.RoomID

	// Whether or not the user has left the room.
	HasLeft bool
	// Whether or not the room is encrypted.
	Encrypted bool

	// The first batch of events that has been fetched for this room.
	// Used for fetching additional history.
	PrevBatch string
	// The last_batch field from the most recent sync. Used for fetching member lists.
	LastPrevBatch string
	// The MXID of the user whose session this room was created for.
	SessionUserID id.UserID
	SessionMember *Member

	// The number of unread messages that were notified about.
	UnreadMessages   []UnreadMessage
	unreadCountCache *int
	highlightCache   *bool
	lastMarkedRead   id.EventID
	// Whether or not this room is marked as a direct chat.
	IsDirect bool

	// List of tags given to this room.
	RawTags []RoomTag
	// Timestamp of previously received actual message.
	LastReceivedMessage time.Time

	// The lazy loading summary for this room.
	Summary mautrix.LazyLoadSummary
	// Whether or not the members for this room have been fetched from the server.
	MembersFetched bool
	// Room state cache.
	state map[event.Type]map[string]*event.Event
	// MXID -> Member cache calculated from membership events.
	memberCache   map[id.UserID]*Member
	exMemberCache map[id.UserID]*Member
	// The first two non-SessionUserID members in the room. Calculated at
	// the same time as memberCache.
	firstMemberCache  *Member
	secondMemberCache *Member
	// The name of the room. Calculated from the state event name,
	// canonical_alias or alias or the member cache.
	NameCache string
	// The event type from which the name cache was calculated from.
	nameCacheSource RoomNameSource
	// The topic of the room. Directly fetched from the m.room.topic state event.
	topicCache string
	// The canonical alias of the room. Directly fetched from the m.room.canonical_alias state event.
	CanonicalAliasCache id.RoomAlias
	// Whether or not the room has been tombstoned.
	replacedCache bool
	// The room ID that replaced this room.
	replacedByCache *id.RoomID

	// Path for state store file.
	path string
	// Room cache object
	cache *RoomCache
	// Lock for state and other room stuff.
	lock sync.RWMutex
	// Pre/post un/load hooks
	preUnload  func() bool
	preLoad    func() bool
	postUnload func()
	postLoad   func()
	// Whether or not the room state has changed
	changed bool

	// Room state cache linked list.
	prev  *Room
	next  *Room
	touch int64
}

func debugPrintError(fn func() error, message string) {
	if err := fn(); err != nil {
		debug.Printf("%s: %v", message, err)
	}
}

func (room *Room) Loaded() bool {
	return room.state != nil
}

func (room *Room) Load() {
	room.cache.TouchNode(room)
	if room.Loaded() {
		return
	}
	if room.preLoad != nil && !room.preLoad() {
		return
	}
	room.lock.Lock()
	room.load()
	room.lock.Unlock()
	if room.postLoad != nil {
		room.postLoad()
	}
}

func (room *Room) load() {
	if room.Loaded() {
		return
	}
	debug.Print("Loading state for room", room.ID, "from disk")
	room.state = make(map[event.Type]map[string]*event.Event)
	file, err := os.OpenFile(room.path, os.O_RDONLY, 0600)
	if err != nil {
		if !os.IsNotExist(err) {
			debug.Print("Failed to open room state file for reading:", err)
		} else {
			debug.Print("Room state file for", room.ID, "does not exist")
		}
		return
	}
	defer debugPrintError(file.Close, "Failed to close room state file after reading")
	cmpReader, err := gzip.NewReader(file)
	if err != nil {
		debug.Print("Failed to open room state gzip reader:", err)
		return
	}
	defer debugPrintError(cmpReader.Close, "Failed to close room state gzip reader")
	dec := gob.NewDecoder(cmpReader)
	if err = dec.Decode(&room.state); err != nil {
		debug.Print("Failed to decode room state:", err)
	}
	room.changed = false
}

func (room *Room) Touch() {
	room.cache.TouchNode(room)
}

func (room *Room) Unload() bool {
	if room.preUnload != nil && !room.preUnload() {
		return false
	}
	debug.Print("Unloading", room.ID)
	room.Save()
	room.state = nil
	room.memberCache = nil
	room.exMemberCache = nil
	room.firstMemberCache = nil
	room.secondMemberCache = nil
	if room.postUnload != nil {
		room.postUnload()
	}
	return true
}

func (room *Room) SetPreUnload(fn func() bool) {
	room.preUnload = fn
}

func (room *Room) SetPreLoad(fn func() bool) {
	room.preLoad = fn
}

func (room *Room) SetPostUnload(fn func()) {
	room.postUnload = fn
}

func (room *Room) SetPostLoad(fn func()) {
	room.postLoad = fn
}

func (room *Room) Save() {
	if !room.Loaded() {
		debug.Print("Failed to save room", room.ID, "state: room not loaded")
		return
	}
	if !room.changed {
		debug.Print("Not saving", room.ID, "as state hasn't changed")
		return
	}
	debug.Print("Saving state for room", room.ID, "to disk")
	file, err := os.OpenFile(room.path, os.O_WRONLY|os.O_CREATE, 0600)
	if err != nil {
		debug.Print("Failed to open room state file for writing:", err)
		return
	}
	defer debugPrintError(file.Close, "Failed to close room state file after writing")
	cmpWriter := gzip.NewWriter(file)
	defer debugPrintError(cmpWriter.Close, "Failed to close room state gzip writer")
	enc := gob.NewEncoder(cmpWriter)
	room.lock.RLock()
	defer room.lock.RUnlock()
	if err := enc.Encode(&room.state); err != nil {
		debug.Print("Failed to encode room state:", err)
	}
}

// MarkRead clears the new message statuses on this room.
func (room *Room) MarkRead(eventID id.EventID) bool {
	room.lock.Lock()
	defer room.lock.Unlock()
	if room.lastMarkedRead == eventID {
		return false
	}
	room.lastMarkedRead = eventID
	readToIndex := -1
	for index, unreadMessage := range room.UnreadMessages {
		if unreadMessage.EventID == eventID {
			readToIndex = index
		}
	}
	if readToIndex >= 0 {
		room.UnreadMessages = room.UnreadMessages[readToIndex+1:]
		room.highlightCache = nil
		room.unreadCountCache = nil
	}
	return true
}

func (room *Room) UnreadCount() int {
	room.lock.Lock()
	defer room.lock.Unlock()
	if room.unreadCountCache == nil {
		room.unreadCountCache = new(int)
		for _, unreadMessage := range room.UnreadMessages {
			if unreadMessage.Counted {
				*room.unreadCountCache++
			}
		}
	}
	return *room.unreadCountCache
}

func (room *Room) Highlighted() bool {
	room.lock.Lock()
	defer room.lock.Unlock()
	if room.highlightCache == nil {
		room.highlightCache = new(bool)
		for _, unreadMessage := range room.UnreadMessages {
			if unreadMessage.Highlight {
				*room.highlightCache = true
				break
			}
		}
	}
	return *room.highlightCache
}

func (room *Room) HasNewMessages() bool {
	return len(room.UnreadMessages) > 0
}

func (room *Room) AddUnread(eventID id.EventID, counted, highlight bool) {
	room.lock.Lock()
	defer room.lock.Unlock()
	room.UnreadMessages = append(room.UnreadMessages, UnreadMessage{
		EventID:   eventID,
		Counted:   counted,
		Highlight: highlight,
	})
	if counted {
		if room.unreadCountCache == nil {
			room.unreadCountCache = new(int)
		}
		*room.unreadCountCache++
	}
	if highlight {
		if room.highlightCache == nil {
			room.highlightCache = new(bool)
		}
		*room.highlightCache = true
	}
}

var (
	tagDirect  = RoomTag{"net.maunium.gomuks.fake.direct", "0.5"}
	tagInvite  = RoomTag{"net.maunium.gomuks.fake.invite", "0.5"}
	tagDefault = RoomTag{"", "0.5"}
	tagLeave   = RoomTag{"net.maunium.gomuks.fake.leave", "0.5"}
)

func (room *Room) Tags() []RoomTag {
	room.lock.RLock()
	defer room.lock.RUnlock()
	if len(room.RawTags) == 0 {
		if room.IsDirect {
			return []RoomTag{tagDirect}
		} else if room.SessionMember != nil && room.SessionMember.Membership == event.MembershipInvite {
			return []RoomTag{tagInvite}
		} else if room.SessionMember != nil && room.SessionMember.Membership != event.MembershipJoin {
			return []RoomTag{tagLeave}
		}
		return []RoomTag{tagDefault}
	}
	return room.RawTags
}

func (room *Room) UpdateSummary(summary mautrix.LazyLoadSummary) {
	if summary.JoinedMemberCount != nil {
		room.Summary.JoinedMemberCount = summary.JoinedMemberCount
	}
	if summary.InvitedMemberCount != nil {
		room.Summary.InvitedMemberCount = summary.InvitedMemberCount
	}
	if summary.Heroes != nil {
		room.Summary.Heroes = summary.Heroes
	}
	if room.nameCacheSource <= MemberRoomName {
		room.NameCache = ""
	}
}

// UpdateState updates the room's current state with the given Event. This will clobber events based
// on the type/state_key combination.
func (room *Room) UpdateState(evt *event.Event) {
	if evt.StateKey == nil {
		panic("Tried to UpdateState() event with no state key.")
	}
	room.Load()
	room.lock.Lock()
	defer room.lock.Unlock()
	room.changed = true
	_, exists := room.state[evt.Type]
	if !exists {
		room.state[evt.Type] = make(map[string]*event.Event)
	}
	switch content := evt.Content.Parsed.(type) {
	case *event.RoomNameEventContent:
		room.NameCache = content.Name
		room.nameCacheSource = ExplicitRoomName
	case *event.CanonicalAliasEventContent:
		if room.nameCacheSource <= CanonicalAliasRoomName {
			room.NameCache = string(content.Alias)
			room.nameCacheSource = CanonicalAliasRoomName
		}
		room.CanonicalAliasCache = content.Alias
	case *event.MemberEventContent:
		if room.nameCacheSource <= MemberRoomName {
			room.NameCache = ""
		}
		room.updateMemberState(id.UserID(evt.GetStateKey()), evt.Sender, content)
	case *event.TopicEventContent:
		room.topicCache = content.Topic
	case *event.EncryptionEventContent:
		if content.Algorithm == id.AlgorithmMegolmV1 {
			room.Encrypted = true
		}
	}

	if evt.Type != event.StateMember {
		debug.Printf("Updating state %s#%s for %s", evt.Type.String(), evt.GetStateKey(), room.ID)
	}

	room.state[evt.Type][*evt.StateKey] = evt
}

func (room *Room) updateMemberState(userID, sender id.UserID, content *event.MemberEventContent) {
	if userID == room.SessionUserID {
		debug.Print("Updating session user state:", content)
		room.SessionMember = room.eventToMember(userID, sender, content)
	}
	if room.memberCache != nil {
		member := room.eventToMember(userID, sender, content)
		if member.Membership.IsInviteOrJoin() {
			existingMember, ok := room.memberCache[userID]
			if ok {
				*existingMember = *member
			} else {
				delete(room.exMemberCache, userID)
				room.memberCache[userID] = member
				room.updateNthMemberCache(userID, member)
			}
		} else {
			existingExMember, ok := room.exMemberCache[userID]
			if ok {
				*existingExMember = *member
			} else {
				delete(room.memberCache, userID)
				room.exMemberCache[userID] = member
			}
		}
	}
}

// GetStateEvent returns the state event for the given type/state_key combo, or nil.
func (room *Room) GetStateEvent(eventType event.Type, stateKey string) *event.Event {
	room.Load()
	room.lock.RLock()
	defer room.lock.RUnlock()
	stateEventMap, _ := room.state[eventType]
	evt, _ := stateEventMap[stateKey]
	return evt
}

// getStateEvents returns the state events for the given type.
func (room *Room) getStateEvents(eventType event.Type) map[string]*event.Event {
	stateEventMap, _ := room.state[eventType]
	return stateEventMap
}

// GetTopic returns the topic of the room.
func (room *Room) GetTopic() string {
	if len(room.topicCache) == 0 {
		topicEvt := room.GetStateEvent(event.StateTopic, "")
		if topicEvt != nil {
			room.topicCache = topicEvt.Content.AsTopic().Topic
		}
	}
	return room.topicCache
}

func (room *Room) GetCanonicalAlias() id.RoomAlias {
	if len(room.CanonicalAliasCache) == 0 {
		canonicalAliasEvt := room.GetStateEvent(event.StateCanonicalAlias, "")
		if canonicalAliasEvt != nil {
			room.CanonicalAliasCache = canonicalAliasEvt.Content.AsCanonicalAlias().Alias
		} else {
			room.CanonicalAliasCache = "-"
		}
	}
	if room.CanonicalAliasCache == "-" {
		return ""
	}
	return room.CanonicalAliasCache
}

// updateNameFromNameEvent updates the room display name to be the name set in the name event.
func (room *Room) updateNameFromNameEvent() {
	nameEvt := room.GetStateEvent(event.StateRoomName, "")
	if nameEvt != nil {
		room.NameCache = nameEvt.Content.AsRoomName().Name
	}
}

// updateNameFromMembers updates the room display name based on the members in this room.
//
// The room name depends on the number of users:
//  Less than two users -> "Empty room"
//  Exactly two users   -> The display name of the other user.
//  More than two users -> The display name of one of the other users, followed
//                         by "and X others", where X is the number of users
//                         excluding the local user and the named user.
func (room *Room) updateNameFromMembers() {
	members := room.GetMembers()
	if len(members) <= 1 {
		room.NameCache = "Empty room"
	} else if room.firstMemberCache == nil {
		room.NameCache = "Room"
	} else if len(members) == 2 {
		room.NameCache = room.firstMemberCache.Displayname
	} else if len(members) == 3 && room.secondMemberCache != nil {
		room.NameCache = fmt.Sprintf("%s and %s", room.firstMemberCache.Displayname, room.secondMemberCache.Displayname)
	} else {
		members := room.firstMemberCache.Displayname
		count := len(members) - 2
		if room.secondMemberCache != nil {
			members += ", " + room.secondMemberCache.Displayname
			count--
		}
		room.NameCache = fmt.Sprintf("%s and %d others", members, count)
	}
}

// updateNameCache updates the room display name based on the room state in the order
// specified in spec section 11.2.2.5.
func (room *Room) updateNameCache() {
	if len(room.NameCache) == 0 {
		room.updateNameFromNameEvent()
		room.nameCacheSource = ExplicitRoomName
	}
	if len(room.NameCache) == 0 {
		room.NameCache = string(room.GetCanonicalAlias())
		room.nameCacheSource = CanonicalAliasRoomName
	}
	if len(room.NameCache) == 0 {
		room.updateNameFromMembers()
		room.nameCacheSource = MemberRoomName
	}
}

// GetTitle returns the display name of the room.
//
// The display name is returned from the cache.
// If the cache is empty, it is updated first.
func (room *Room) GetTitle() string {
	room.updateNameCache()
	return room.NameCache
}

func (room *Room) IsReplaced() bool {
	if room.replacedByCache == nil {
		evt := room.GetStateEvent(event.StateTombstone, "")
		var replacement id.RoomID
		if evt != nil {
			content, ok := evt.Content.Parsed.(*event.TombstoneEventContent)
			if ok {
				replacement = content.ReplacementRoom
			}
		}
		room.replacedCache = evt != nil
		room.replacedByCache = &replacement
	}
	return room.replacedCache
}

func (room *Room) ReplacedBy() id.RoomID {
	if room.replacedByCache == nil {
		room.IsReplaced()
	}
	return *room.replacedByCache
}

func (room *Room) eventToMember(userID, sender id.UserID, member *event.MemberEventContent) *Member {
	if len(member.Displayname) == 0 {
		member.Displayname = string(userID)
	}
	return &Member{
		MemberEventContent: *member,
		Sender:             sender,
	}
}

func (room *Room) updateNthMemberCache(userID id.UserID, member *Member) {
	if userID != room.SessionUserID {
		if room.firstMemberCache == nil {
			room.firstMemberCache = member
		} else if room.secondMemberCache == nil {
			room.secondMemberCache = member
		}
	}
}

// createMemberCache caches all member events into a easily processable MXID -> *Member map.
func (room *Room) createMemberCache() map[id.UserID]*Member {
	if len(room.memberCache) > 0 {
		return room.memberCache
	}
	cache := make(map[id.UserID]*Member)
	exCache := make(map[id.UserID]*Member)
	room.lock.RLock()
	memberEvents := room.getStateEvents(event.StateMember)
	room.firstMemberCache = nil
	room.secondMemberCache = nil
	if memberEvents != nil {
		for userIDStr, evt := range memberEvents {
			userID := id.UserID(userIDStr)
			member := room.eventToMember(userID, evt.Sender, evt.Content.AsMember())
			if member.Membership.IsInviteOrJoin() {
				cache[userID] = member
				room.updateNthMemberCache(userID, member)
			} else {
				exCache[userID] = member
			}
			if userID == room.SessionUserID {
				room.SessionMember = member
			}
		}
	}
	if len(room.Summary.Heroes) > 1 {
		room.firstMemberCache, _ = cache[room.Summary.Heroes[0]]
	}
	if len(room.Summary.Heroes) > 2 {
		room.secondMemberCache, _ = cache[room.Summary.Heroes[1]]
	}
	room.lock.RUnlock()
	room.lock.Lock()
	room.memberCache = cache
	room.exMemberCache = exCache
	room.lock.Unlock()
	return cache
}

// GetMembers returns the members in this room.
//
// The members are returned from the cache.
// If the cache is empty, it is updated first.
func (room *Room) GetMembers() map[id.UserID]*Member {
	room.Load()
	room.createMemberCache()
	return room.memberCache
}

func (room *Room) GetMemberList() []id.UserID {
	members := room.GetMembers()
	memberList := make([]id.UserID, len(members))
	index := 0
	for userID, _ := range members {
		memberList[index] = userID
		index++
	}
	return memberList
}

// GetMember returns the member with the given MXID.
// If the member doesn't exist, nil is returned.
func (room *Room) GetMember(userID id.UserID) *Member {
	if userID == room.SessionUserID && room.SessionMember != nil {
		return room.SessionMember
	}
	room.Load()
	room.createMemberCache()
	room.lock.RLock()
	member, ok := room.memberCache[userID]
	if ok {
		room.lock.RUnlock()
		return member
	}
	exMember, ok := room.exMemberCache[userID]
	if ok {
		room.lock.RUnlock()
		return exMember
	}
	room.lock.RUnlock()
	return nil
}

func (room *Room) GetMemberCount() int {
	if room.memberCache == nil && room.Summary.JoinedMemberCount != nil {
		return *room.Summary.JoinedMemberCount
	}
	return len(room.GetMembers())
}

// GetSessionOwner returns the ID of the user whose session this room was created for.
func (room *Room) GetOwnDisplayname() string {
	member := room.GetMember(room.SessionUserID)
	if member != nil {
		return member.Displayname
	}
	return ""
}

// NewRoom creates a new Room with the given ID
func NewRoom(roomID id.RoomID, cache *RoomCache) *Room {
	return &Room{
		ID:    roomID,
		state: make(map[event.Type]map[string]*event.Event),
		path:  cache.roomPath(roomID),
		cache: cache,

		SessionUserID: cache.getOwner(),
	}
}