// Package service provides shared business logic for both
// the IRC wire protocol and HTTP/JSON transports.
package service

import (
	"context"
	"crypto/subtle"
	"encoding/json"
	"fmt"
	"log/slog"
	"strings"

	"git.eeqj.de/sneak/neoirc/internal/broker"
	"git.eeqj.de/sneak/neoirc/internal/config"
	"git.eeqj.de/sneak/neoirc/internal/db"
	"git.eeqj.de/sneak/neoirc/internal/logger"
	"git.eeqj.de/sneak/neoirc/pkg/irc"
	"go.uber.org/fx"
)

// Params defines the dependencies for creating a Service.
type Params struct {
	fx.In

	Logger   *logger.Logger
	Config   *config.Config
	Database *db.Database
	Broker   *broker.Broker
}

// Service provides shared business logic for IRC commands.
type Service struct {
	DB     *db.Database
	Broker *broker.Broker
	Config *config.Config
	Log    *slog.Logger
}

// New creates a new Service.
func New(params Params) *Service {
	return &Service{
		DB:     params.Database,
		Broker: params.Broker,
		Config: params.Config,
		Log:    params.Logger.Get(),
	}
}

// IRCError represents an IRC protocol-level error with a
// numeric code that both transports can map to responses.
type IRCError struct {
	Code    irc.IRCMessageType
	Params  []string
	Message string
}

func (e *IRCError) Error() string { return e.Message }

// JoinResult contains the outcome of a channel join.
type JoinResult struct {
	ChannelID int64
	IsCreator bool
}

// DirectMsgResult contains the outcome of a direct message.
type DirectMsgResult struct {
	UUID    string
	AwayMsg string
}

// FanOut inserts a message and enqueues it to all given
// session IDs, notifying each via the broker.
func (s *Service) FanOut(
	ctx context.Context,
	command, from, to string,
	params, body, meta json.RawMessage,
	sessionIDs []int64,
) (int64, string, error) {
	dbID, msgUUID, err := s.DB.InsertMessage(
		ctx, command, from, to, params, body, meta,
	)
	if err != nil {
		return 0, "", fmt.Errorf("insert message: %w", err)
	}

	for _, sid := range sessionIDs {
		_ = s.DB.EnqueueToSession(ctx, sid, dbID)
		s.Broker.Notify(sid)
	}

	return dbID, msgUUID, nil
}

// excludeSession returns a copy of ids without the given
// session.
func excludeSession(
	ids []int64,
	exclude int64,
) []int64 {
	out := make([]int64, 0, len(ids))

	for _, id := range ids {
		if id != exclude {
			out = append(out, id)
		}
	}

	return out
}

// SendChannelMessage validates membership and moderation,
// then fans out a message to all channel members except
// the sender. Returns the database row ID, message UUID,
// and any error. The dbID lets callers enqueue the same
// message to the sender when echo is needed (HTTP
// transport).
func (s *Service) SendChannelMessage(
	ctx context.Context,
	sessionID int64,
	nick, command, channel string,
	body, meta json.RawMessage,
) (int64, string, error) {
	chID, err := s.DB.GetChannelByName(ctx, channel)
	if err != nil {
		return 0, "", &IRCError{
			irc.ErrNoSuchChannel,
			[]string{channel},
			"No such channel",
		}
	}

	isMember, _ := s.DB.IsChannelMember(
		ctx, chID, sessionID,
	)
	if !isMember {
		return 0, "", &IRCError{
			irc.ErrCannotSendToChan,
			[]string{channel},
			"Cannot send to channel",
		}
	}

	moderated, _ := s.DB.IsChannelModerated(ctx, chID)
	if moderated {
		isOp, _ := s.DB.IsChannelOperator(
			ctx, chID, sessionID,
		)
		isVoiced, _ := s.DB.IsChannelVoiced(
			ctx, chID, sessionID,
		)

		if !isOp && !isVoiced {
			return 0, "", &IRCError{
				irc.ErrCannotSendToChan,
				[]string{channel},
				"Cannot send to channel (+m)",
			}
		}
	}

	memberIDs, _ := s.DB.GetChannelMemberIDs(ctx, chID)
	recipients := excludeSession(memberIDs, sessionID)

	dbID, uuid, fanErr := s.FanOut(
		ctx, command, nick, channel,
		nil, body, meta, recipients,
	)
	if fanErr != nil {
		return 0, "", fanErr
	}

	return dbID, uuid, nil
}

// SendDirectMessage validates the target and sends a
// direct message, returning the message UUID and any away
// message set on the target.
func (s *Service) SendDirectMessage(
	ctx context.Context,
	sessionID int64,
	nick, command, target string,
	body, meta json.RawMessage,
) (*DirectMsgResult, error) {
	targetSID, err := s.DB.GetSessionByNick(ctx, target)
	if err != nil {
		return nil, &IRCError{
			irc.ErrNoSuchNick,
			[]string{target},
			"No such nick",
		}
	}

	away, _ := s.DB.GetAway(ctx, targetSID)

	recipients := []int64{targetSID}
	if targetSID != sessionID {
		recipients = append(recipients, sessionID)
	}

	_, uuid, fanErr := s.FanOut(
		ctx, command, nick, target,
		nil, body, meta, recipients,
	)
	if fanErr != nil {
		return nil, fanErr
	}

	return &DirectMsgResult{UUID: uuid, AwayMsg: away}, nil
}

// JoinChannel creates or joins a channel, making the
// first joiner the operator. Fans out the JOIN to all
// channel members.
func (s *Service) JoinChannel(
	ctx context.Context,
	sessionID int64,
	nick, channel string,
) (*JoinResult, error) {
	chID, err := s.DB.GetOrCreateChannel(ctx, channel)
	if err != nil {
		return nil, fmt.Errorf("get/create channel: %w", err)
	}

	memberCount, countErr := s.DB.CountChannelMembers(
		ctx, chID,
	)
	isCreator := countErr == nil && memberCount == 0

	if isCreator {
		err = s.DB.JoinChannelAsOperator(
			ctx, chID, sessionID,
		)
	} else {
		err = s.DB.JoinChannel(ctx, chID, sessionID)
	}

	if err != nil {
		return nil, fmt.Errorf("join channel: %w", err)
	}

	memberIDs, _ := s.DB.GetChannelMemberIDs(ctx, chID)
	body, _ := json.Marshal([]string{channel}) //nolint:errchkjson

	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
		ctx, irc.CmdJoin, nick, channel,
		nil, body, nil, memberIDs,
	)

	return &JoinResult{
		ChannelID: chID,
		IsCreator: isCreator,
	}, nil
}

// PartChannel validates membership, broadcasts PART to
// remaining members, removes the user, and cleans up empty
// channels.
func (s *Service) PartChannel(
	ctx context.Context,
	sessionID int64,
	nick, channel, reason string,
) error {
	chID, err := s.DB.GetChannelByName(ctx, channel)
	if err != nil {
		return &IRCError{
			irc.ErrNoSuchChannel,
			[]string{channel},
			"No such channel",
		}
	}

	isMember, _ := s.DB.IsChannelMember(
		ctx, chID, sessionID,
	)
	if !isMember {
		return &IRCError{
			irc.ErrNotOnChannel,
			[]string{channel},
			"You're not on that channel",
		}
	}

	memberIDs, _ := s.DB.GetChannelMemberIDs(ctx, chID)
	recipients := excludeSession(memberIDs, sessionID)
	body, _ := json.Marshal([]string{reason}) //nolint:errchkjson

	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
		ctx, irc.CmdPart, nick, channel,
		nil, body, nil, recipients,
	)

	s.DB.PartChannel(ctx, chID, sessionID) //nolint:errcheck,gosec
	s.DB.DeleteChannelIfEmpty(ctx, chID)   //nolint:errcheck,gosec

	return nil
}

// SetTopic validates membership and topic-lock, sets the
// topic, and broadcasts the change.
func (s *Service) SetTopic(
	ctx context.Context,
	sessionID int64,
	nick, channel, topic string,
) error {
	chID, err := s.DB.GetChannelByName(ctx, channel)
	if err != nil {
		return &IRCError{
			irc.ErrNoSuchChannel,
			[]string{channel},
			"No such channel",
		}
	}

	isMember, _ := s.DB.IsChannelMember(
		ctx, chID, sessionID,
	)
	if !isMember {
		return &IRCError{
			irc.ErrNotOnChannel,
			[]string{channel},
			"You're not on that channel",
		}
	}

	topicLocked, _ := s.DB.IsChannelTopicLocked(ctx, chID)
	if topicLocked {
		isOp, _ := s.DB.IsChannelOperator(
			ctx, chID, sessionID,
		)
		if !isOp {
			return &IRCError{
				irc.ErrChanOpPrivsNeeded,
				[]string{channel},
				"You're not channel operator",
			}
		}
	}

	if setErr := s.DB.SetTopic(
		ctx, channel, topic,
	); setErr != nil {
		return fmt.Errorf("set topic: %w", setErr)
	}

	_ = s.DB.SetTopicMeta(ctx, channel, topic, nick)

	memberIDs, _ := s.DB.GetChannelMemberIDs(ctx, chID)
	body, _ := json.Marshal([]string{topic}) //nolint:errchkjson

	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
		ctx, irc.CmdTopic, nick, channel,
		nil, body, nil, memberIDs,
	)

	return nil
}

// KickUser validates operator status and target
// membership, broadcasts the KICK, removes the target,
// and cleans up empty channels.
func (s *Service) KickUser(
	ctx context.Context,
	sessionID int64,
	nick, channel, targetNick, reason string,
) error {
	chID, err := s.DB.GetChannelByName(ctx, channel)
	if err != nil {
		return &IRCError{
			irc.ErrNoSuchChannel,
			[]string{channel},
			"No such channel",
		}
	}

	isOp, _ := s.DB.IsChannelOperator(
		ctx, chID, sessionID,
	)
	if !isOp {
		return &IRCError{
			irc.ErrChanOpPrivsNeeded,
			[]string{channel},
			"You're not channel operator",
		}
	}

	targetSID, err := s.DB.GetSessionByNick(
		ctx, targetNick,
	)
	if err != nil {
		return &IRCError{
			irc.ErrNoSuchNick,
			[]string{targetNick},
			"No such nick/channel",
		}
	}

	isMember, _ := s.DB.IsChannelMember(
		ctx, chID, targetSID,
	)
	if !isMember {
		return &IRCError{
			irc.ErrUserNotInChannel,
			[]string{targetNick, channel},
			"They aren't on that channel",
		}
	}

	memberIDs, _ := s.DB.GetChannelMemberIDs(ctx, chID)
	body, _ := json.Marshal([]string{reason}) //nolint:errchkjson
	params, _ := json.Marshal(                //nolint:errchkjson
		[]string{targetNick},
	)

	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
		ctx, irc.CmdKick, nick, channel,
		params, body, nil, memberIDs,
	)

	s.DB.PartChannel(ctx, chID, targetSID) //nolint:errcheck,gosec
	s.DB.DeleteChannelIfEmpty(ctx, chID)   //nolint:errcheck,gosec

	return nil
}

// ChangeNick changes a user's nickname and broadcasts the
// change to all users sharing channels.
func (s *Service) ChangeNick(
	ctx context.Context,
	sessionID int64,
	oldNick, newNick string,
) error {
	err := s.DB.ChangeNick(ctx, sessionID, newNick)
	if err != nil {
		if strings.Contains(err.Error(), "UNIQUE") ||
			db.IsUniqueConstraintError(err) {
			return &IRCError{
				irc.ErrNicknameInUse,
				[]string{newNick},
				"Nickname is already in use",
			}
		}

		return &IRCError{
			irc.ErrErroneusNickname,
			[]string{newNick},
			"Erroneous nickname",
		}
	}

	s.broadcastNickChange(ctx, sessionID, oldNick, newNick)

	return nil
}

// BroadcastQuit broadcasts a QUIT to all channel peers,
// parts all channels, and deletes the session. Uses the
// FanOut pattern: one message row fanned out to all unique
// peer sessions.
func (s *Service) BroadcastQuit(
	ctx context.Context,
	sessionID int64,
	nick, reason string,
) {
	channels, err := s.DB.GetSessionChannels(
		ctx, sessionID,
	)
	if err != nil {
		return
	}

	notified := make(map[int64]bool)

	for _, ch := range channels {
		memberIDs, memErr := s.DB.GetChannelMemberIDs(
			ctx, ch.ID,
		)
		if memErr != nil {
			continue
		}

		for _, mid := range memberIDs {
			if mid == sessionID || notified[mid] {
				continue
			}

			notified[mid] = true
		}
	}

	if len(notified) > 0 {
		recipients := make([]int64, 0, len(notified))
		for sid := range notified {
			recipients = append(recipients, sid)
		}

		body, _ := json.Marshal([]string{reason}) //nolint:errchkjson

		_, _, _ = s.FanOut(
			ctx, irc.CmdQuit, nick, "",
			nil, body, nil, recipients,
		)
	}

	for _, ch := range channels {
		s.DB.PartChannel(ctx, ch.ID, sessionID) //nolint:errcheck,gosec
		s.DB.DeleteChannelIfEmpty(ctx, ch.ID)   //nolint:errcheck,gosec
	}

	s.DB.DeleteSession(ctx, sessionID) //nolint:errcheck,gosec
}

// SetAway sets or clears the away message. Returns true
// if the message was cleared (empty string).
func (s *Service) SetAway(
	ctx context.Context,
	sessionID int64,
	message string,
) (bool, error) {
	err := s.DB.SetAway(ctx, sessionID, message)
	if err != nil {
		return false, fmt.Errorf("set away: %w", err)
	}

	return message == "", nil
}

// Oper validates operator credentials and grants oper
// status to the session.
func (s *Service) Oper(
	ctx context.Context,
	sessionID int64,
	name, password string,
) error {
	cfgName := s.Config.OperName
	cfgPassword := s.Config.OperPassword

	// Use constant-time comparison and return the same
	// error for all failures to prevent information
	// leakage about valid operator names.
	if cfgName == "" || cfgPassword == "" ||
		subtle.ConstantTimeCompare(
			[]byte(name), []byte(cfgName),
		) != 1 ||
		subtle.ConstantTimeCompare(
			[]byte(password), []byte(cfgPassword),
		) != 1 {
		return &IRCError{
			irc.ErrNoOperHost,
			nil,
			"No O-lines for your host",
		}
	}

	_ = s.DB.SetSessionOper(ctx, sessionID, true)

	return nil
}

// ValidateChannelOp checks that the session is a channel
// operator. Returns the channel ID.
func (s *Service) ValidateChannelOp(
	ctx context.Context,
	sessionID int64,
	channel string,
) (int64, error) {
	chID, err := s.DB.GetChannelByName(ctx, channel)
	if err != nil {
		return 0, &IRCError{
			irc.ErrNoSuchChannel,
			[]string{channel},
			"No such channel",
		}
	}

	isOp, _ := s.DB.IsChannelOperator(
		ctx, chID, sessionID,
	)
	if !isOp {
		return 0, &IRCError{
			irc.ErrChanOpPrivsNeeded,
			[]string{channel},
			"You're not channel operator",
		}
	}

	return chID, nil
}

// ApplyMemberMode applies +o/-o or +v/-v on a channel
// member after validating the target.
func (s *Service) ApplyMemberMode(
	ctx context.Context,
	chID int64,
	channel, targetNick string,
	mode rune,
	adding bool,
) error {
	targetSID, err := s.DB.GetSessionByNick(
		ctx, targetNick,
	)
	if err != nil {
		return &IRCError{
			irc.ErrNoSuchNick,
			[]string{targetNick},
			"No such nick/channel",
		}
	}

	isMember, _ := s.DB.IsChannelMember(
		ctx, chID, targetSID,
	)
	if !isMember {
		return &IRCError{
			irc.ErrUserNotInChannel,
			[]string{targetNick, channel},
			"They aren't on that channel",
		}
	}

	switch mode {
	case 'o':
		_ = s.DB.SetChannelMemberOperator(
			ctx, chID, targetSID, adding,
		)
	case 'v':
		_ = s.DB.SetChannelMemberVoiced(
			ctx, chID, targetSID, adding,
		)
	}

	return nil
}

// SetChannelFlag applies +m/-m or +t/-t on a channel.
func (s *Service) SetChannelFlag(
	ctx context.Context,
	chID int64,
	flag rune,
	setting bool,
) error {
	switch flag {
	case 'm':
		if err := s.DB.SetChannelModerated(
			ctx, chID, setting,
		); err != nil {
			return fmt.Errorf("set moderated: %w", err)
		}
	case 't':
		if err := s.DB.SetChannelTopicLocked(
			ctx, chID, setting,
		); err != nil {
			return fmt.Errorf("set topic locked: %w", err)
		}
	}

	return nil
}

// BroadcastMode fans out a MODE change to all channel
// members.
func (s *Service) BroadcastMode(
	ctx context.Context,
	nick, channel string,
	chID int64,
	modeText string,
) {
	memberIDs, _ := s.DB.GetChannelMemberIDs(ctx, chID)
	body, _ := json.Marshal([]string{modeText}) //nolint:errchkjson

	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
		ctx, irc.CmdMode, nick, channel,
		nil, body, nil, memberIDs,
	)
}

// QueryChannelMode returns the channel mode string.
func (s *Service) QueryChannelMode(
	ctx context.Context,
	chID int64,
) string {
	modes := "+"

	moderated, _ := s.DB.IsChannelModerated(ctx, chID)
	if moderated {
		modes += "m"
	}

	topicLocked, _ := s.DB.IsChannelTopicLocked(ctx, chID)
	if topicLocked {
		modes += "t"
	}

	return modes
}

// broadcastNickChange notifies channel peers of a nick
// change.
func (s *Service) broadcastNickChange(
	ctx context.Context,
	sessionID int64,
	oldNick, newNick string,
) {
	channels, err := s.DB.GetSessionChannels(
		ctx, sessionID,
	)
	if err != nil {
		return
	}

	body, _ := json.Marshal([]string{newNick}) //nolint:errchkjson
	notified := make(map[int64]bool)

	dbID, _, insErr := s.DB.InsertMessage(
		ctx, irc.CmdNick, oldNick, "",
		nil, body, nil,
	)
	if insErr != nil {
		return
	}

	// Notify the user themselves (for multi-client sync).
	_ = s.DB.EnqueueToSession(ctx, sessionID, dbID)
	s.Broker.Notify(sessionID)
	notified[sessionID] = true

	for _, ch := range channels {
		memberIDs, memErr := s.DB.GetChannelMemberIDs(
			ctx, ch.ID,
		)
		if memErr != nil {
			continue
		}

		for _, mid := range memberIDs {
			if notified[mid] {
				continue
			}

			notified[mid] = true

			_ = s.DB.EnqueueToSession(ctx, mid, dbID)
			s.Broker.Notify(mid)
		}
	}
}