package store

import (
	"encoding/json"
	"errors"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"
)

var ErrNotFound = errors.New("not found")

type Role string

const (
	RoleUser      Role = "user"
	RoleModerator Role = "moderator"
	RoleAdmin     Role = "admin"
)

type AccessRule string

const (
	AccessEveryone   AccessRule = "everyone"
	AccessMembers    AccessRule = "members"
	AccessModerators AccessRule = "moderators"
	AccessAdmins     AccessRule = "admins"
)

type Room struct {
	ID          int64      `json:"id"`
	Name        string     `json:"name"`
	Description string     `json:"description"`
	ReadAccess  AccessRule `json:"read_access"`
	WriteAccess AccessRule `json:"write_access"`
	Members     []string   `json:"members"`
	CreatedAt   time.Time  `json:"created_at"`
}

type Message struct {
	ID        int64     `json:"id"`
	RoomID    int64     `json:"room_id"`
	Username  string    `json:"username"`
	Body      string    `json:"body"`
	CreatedAt time.Time `json:"created_at"`
}

type User struct {
	Username  string    `json:"username"`
	Subject   string    `json:"sub,omitempty"`
	Email     string    `json:"email,omitempty"`
	Role      Role      `json:"role"`
	CreatedAt time.Time `json:"created_at"`
	LastSeen  time.Time `json:"last_seen"`
}

type Store struct {
	mu            sync.RWMutex
	path          string
	nextRoomID    int64
	nextMessageID int64
	rooms         []Room
	messages      []Message
	users         []User
}

type diskData struct {
	NextRoomID    int64     `json:"next_room_id"`
	NextMessageID int64     `json:"next_message_id"`
	Rooms         []Room    `json:"rooms"`
	Messages      []Message `json:"messages"`
	Users         []User    `json:"users"`
}

func Open(path string) (*Store, error) {
	s := &Store{path: path, nextRoomID: 1, nextMessageID: 1}
	if err := s.load(); err != nil {
		return nil, err
	}
	if len(s.rooms) == 0 {
		now := time.Now().UTC()
		s.rooms = []Room{
			{ID: s.nextRoomID, Name: "Lobby", Description: "Allgemeiner Chat für alle", ReadAccess: AccessEveryone, WriteAccess: AccessEveryone, CreatedAt: now},
			{ID: s.nextRoomID + 1, Name: "Go", Description: "Golang, Backend und Deployment", ReadAccess: AccessEveryone, WriteAccess: AccessEveryone, CreatedAt: now},
			{ID: s.nextRoomID + 2, Name: "Random", Description: "Alles, was sonst nirgends passt", ReadAccess: AccessEveryone, WriteAccess: AccessEveryone, CreatedAt: now},
		}
		s.nextRoomID += 3
		if err := s.saveLocked(); err != nil {
			return nil, err
		}
	}
	return s, nil
}

func (s *Store) Close() error { return nil }

func (s *Store) load() error {
	b, err := os.ReadFile(s.path)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return err
	}
	var d diskData
	if err := json.Unmarshal(b, &d); err != nil {
		return err
	}
	s.nextRoomID = maxInt64(d.NextRoomID, 1)
	s.nextMessageID = maxInt64(d.NextMessageID, 1)
	s.rooms = d.Rooms
	s.messages = d.Messages
	s.users = d.Users
	for i := range s.rooms {
		s.rooms[i].ReadAccess = normalizeAccess(s.rooms[i].ReadAccess)
		s.rooms[i].WriteAccess = normalizeAccess(s.rooms[i].WriteAccess)
		s.rooms[i].Members = normalizeMembers(s.rooms[i].Members)
	}
	for i := range s.users {
		s.users[i].Role = normalizeRole(s.users[i].Role)
	}
	return nil
}

func (s *Store) saveLocked() error {
	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil && filepath.Dir(s.path) != "." {
		return err
	}
	d := diskData{NextRoomID: s.nextRoomID, NextMessageID: s.nextMessageID, Rooms: s.rooms, Messages: s.messages, Users: s.users}
	b, err := json.MarshalIndent(d, "", "  ")
	if err != nil {
		return err
	}
	tmp := s.path + ".tmp"
	if err := os.WriteFile(tmp, b, 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, s.path)
}

func (s *Store) EnsureUser(username, subject, email string, adminMatchers []string) (User, error) {
	username = strings.TrimSpace(username)
	email = strings.TrimSpace(email)
	subject = strings.TrimSpace(subject)
	if username == "" {
		return User{}, errors.New("empty username")
	}
	now := time.Now().UTC()
	s.mu.Lock()
	defer s.mu.Unlock()
	for i := range s.users {
		if sameIdentity(s.users[i], username, subject, email) {
			s.users[i].Username = username
			s.users[i].Subject = firstNonEmpty(s.users[i].Subject, subject)
			s.users[i].Email = firstNonEmpty(s.users[i].Email, email)
			if isAdminMatch(username, subject, email, adminMatchers) {
				s.users[i].Role = RoleAdmin
			}
			s.users[i].LastSeen = now
			if err := s.saveLocked(); err != nil {
				return User{}, err
			}
			return s.users[i], nil
		}
	}
	role := RoleUser
	if len(s.users) == 0 || isAdminMatch(username, subject, email, adminMatchers) {
		role = RoleAdmin
	}
	u := User{Username: username, Subject: subject, Email: email, Role: role, CreatedAt: now, LastSeen: now}
	s.users = append(s.users, u)
	if err := s.saveLocked(); err != nil {
		return User{}, err
	}
	return u, nil
}

func (s *Store) Users() ([]User, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	users := append([]User(nil), s.users...)
	sort.Slice(users, func(i, j int) bool { return strings.ToLower(users[i].Username) < strings.ToLower(users[j].Username) })
	return users, nil
}

func (s *Store) SetUserRole(username string, role Role) error {
	role = normalizeRole(role)
	s.mu.Lock()
	defer s.mu.Unlock()
	for i := range s.users {
		if strings.EqualFold(s.users[i].Username, username) {
			s.users[i].Role = role
			return s.saveLocked()
		}
	}
	return ErrNotFound
}

func (s *Store) Rooms() ([]Room, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	rooms := append([]Room(nil), s.rooms...)
	sort.Slice(rooms, func(i, j int) bool { return strings.ToLower(rooms[i].Name) < strings.ToLower(rooms[j].Name) })
	return rooms, nil
}

func (s *Store) VisibleRooms(user User) ([]Room, error) {
	rooms, err := s.Rooms()
	if err != nil {
		return nil, err
	}
	out := make([]Room, 0, len(rooms))
	for _, r := range rooms {
		if CanAccessRoom(user, r, true) {
			out = append(out, r)
		}
	}
	return out, nil
}

func (s *Store) CreateRoom(name, description string, readAccess, writeAccess AccessRule, members []string) (Room, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for _, r := range s.rooms {
		if strings.EqualFold(r.Name, name) {
			return Room{}, errors.New("room exists")
		}
	}
	r := Room{ID: s.nextRoomID, Name: name, Description: description, ReadAccess: normalizeAccess(readAccess), WriteAccess: normalizeAccess(writeAccess), Members: normalizeMembers(members), CreatedAt: time.Now().UTC()}
	s.nextRoomID++
	s.rooms = append(s.rooms, r)
	if err := s.saveLocked(); err != nil {
		return Room{}, err
	}
	return r, nil
}

func (s *Store) Room(id int64) (Room, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	for _, r := range s.rooms {
		if r.ID == id {
			return r, nil
		}
	}
	return Room{}, ErrNotFound
}

func (s *Store) UpdateRoomPermissions(id int64, readAccess, writeAccess AccessRule, members []string) (Room, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for i := range s.rooms {
		if s.rooms[i].ID == id {
			s.rooms[i].ReadAccess = normalizeAccess(readAccess)
			s.rooms[i].WriteAccess = normalizeAccess(writeAccess)
			s.rooms[i].Members = normalizeMembers(members)
			if err := s.saveLocked(); err != nil {
				return Room{}, err
			}
			return s.rooms[i], nil
		}
	}
	return Room{}, ErrNotFound
}

func (s *Store) RecentMessages(roomID int64, limit int) ([]Message, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	var msgs []Message
	for _, m := range s.messages {
		if m.RoomID == roomID {
			msgs = append(msgs, m)
		}
	}
	sort.Slice(msgs, func(i, j int) bool {
		if msgs[i].CreatedAt.Equal(msgs[j].CreatedAt) {
			return msgs[i].ID < msgs[j].ID
		}
		return msgs[i].CreatedAt.Before(msgs[j].CreatedAt)
	})
	if limit > 0 && len(msgs) > limit {
		msgs = msgs[len(msgs)-limit:]
	}
	return append([]Message(nil), msgs...), nil
}

func (s *Store) AddMessage(roomID int64, username, body string) (Message, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	found := false
	for _, r := range s.rooms {
		if r.ID == roomID {
			found = true
			break
		}
	}
	if !found {
		return Message{}, ErrNotFound
	}
	m := Message{ID: s.nextMessageID, RoomID: roomID, Username: username, Body: body, CreatedAt: time.Now().UTC()}
	s.nextMessageID++
	s.messages = append(s.messages, m)
	if err := s.saveLocked(); err != nil {
		return Message{}, err
	}
	return m, nil
}

func (s *Store) CleanupMessagesOlderThan(cutoff time.Time) (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	kept := s.messages[:0]
	deleted := 0
	for _, m := range s.messages {
		if m.CreatedAt.Before(cutoff) {
			deleted++
			continue
		}
		kept = append(kept, m)
	}
	s.messages = kept
	if deleted == 0 {
		return 0, nil
	}
	return deleted, s.saveLocked()
}

func CanAccessRoom(user User, room Room, read bool) bool {
	if user.Role == RoleAdmin {
		return true
	}
	rule := room.WriteAccess
	if read {
		rule = room.ReadAccess
	}
	rule = normalizeAccess(rule)
	switch rule {
	case AccessEveryone:
		return true
	case AccessMembers:
		return isRoomMember(room, user.Username) || user.Role == RoleModerator
	case AccessModerators:
		return user.Role == RoleModerator || user.Role == RoleAdmin
	case AccessAdmins:
		return user.Role == RoleAdmin
	default:
		return false
	}
}

func isRoomMember(room Room, username string) bool {
	for _, m := range room.Members {
		if strings.EqualFold(strings.TrimSpace(m), strings.TrimSpace(username)) {
			return true
		}
	}
	return false
}

func normalizeRole(role Role) Role {
	switch Role(strings.ToLower(strings.TrimSpace(string(role)))) {
	case RoleAdmin:
		return RoleAdmin
	case RoleModerator:
		return RoleModerator
	default:
		return RoleUser
	}
}

func normalizeAccess(rule AccessRule) AccessRule {
	switch AccessRule(strings.ToLower(strings.TrimSpace(string(rule)))) {
	case AccessMembers:
		return AccessMembers
	case AccessModerators:
		return AccessModerators
	case AccessAdmins:
		return AccessAdmins
	default:
		return AccessEveryone
	}
}

func normalizeMembers(members []string) []string {
	seen := map[string]bool{}
	var out []string
	for _, m := range members {
		m = strings.TrimSpace(m)
		if m == "" {
			continue
		}
		key := strings.ToLower(m)
		if seen[key] {
			continue
		}
		seen[key] = true
		out = append(out, m)
	}
	sort.Strings(out)
	return out
}

func sameIdentity(u User, username, subject, email string) bool {
	if subject != "" && u.Subject != "" && subject == u.Subject {
		return true
	}
	if email != "" && u.Email != "" && strings.EqualFold(email, u.Email) {
		return true
	}
	return strings.EqualFold(u.Username, username)
}

func isAdminMatch(username, subject, email string, matchers []string) bool {
	for _, m := range matchers {
		m = strings.TrimSpace(strings.ToLower(m))
		if m == "" {
			continue
		}
		if strings.EqualFold(m, username) || strings.EqualFold(m, email) || m == strings.ToLower(subject) {
			return true
		}
	}
	return false
}

func firstNonEmpty(a, b string) string {
	if strings.TrimSpace(a) != "" {
		return a
	}
	return b
}

func maxInt64(a, b int64) int64 {
	if a > b {
		return a
	}
	return b
}