package db

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"time"

	"github.com/google/uuid"
)

func generateToken() string {
	b := make([]byte, 32)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)
}

// IRCMessage is the IRC envelope format for all messages.
type IRCMessage struct {
	ID      string          `json:"id"`
	Command string          `json:"command"`
	From    string          `json:"from,omitempty"`
	To      string          `json:"to,omitempty"`
	Body    json.RawMessage `json:"body,omitempty"`
	TS      string          `json:"ts"`
	Meta    json.RawMessage `json:"meta,omitempty"`
	// Internal DB fields (not in JSON)
	DBID int64 `json:"-"`
}

// ChannelInfo is a lightweight channel representation.
type ChannelInfo struct {
	ID    int64  `json:"id"`
	Name  string `json:"name"`
	Topic string `json:"topic"`
}

// MemberInfo represents a channel member.
type MemberInfo struct {
	ID       int64     `json:"id"`
	Nick     string    `json:"nick"`
	LastSeen time.Time `json:"lastSeen"`
}

// CreateUser registers a new user with the given nick.
func (s *Database) CreateUser(ctx context.Context, nick string) (int64, string, error) {
	token := generateToken()
	now := time.Now()
	res, err := s.db.ExecContext(ctx,
		"INSERT INTO users (nick, token, created_at, last_seen) VALUES (?, ?, ?, ?)",
		nick, token, now, now)
	if err != nil {
		return 0, "", fmt.Errorf("create user: %w", err)
	}
	id, _ := res.LastInsertId()
	return id, token, nil
}

// GetUserByToken returns user id and nick for a given auth token.
func (s *Database) GetUserByToken(ctx context.Context, token string) (int64, string, error) {
	var id int64
	var nick string
	err := s.db.QueryRowContext(ctx, "SELECT id, nick FROM users WHERE token = ?", token).Scan(&id, &nick)
	if err != nil {
		return 0, "", err
	}
	_, _ = s.db.ExecContext(ctx, "UPDATE users SET last_seen = ? WHERE id = ?", time.Now(), id)
	return id, nick, nil
}

// GetUserByNick returns user id for a given nick.
func (s *Database) GetUserByNick(ctx context.Context, nick string) (int64, error) {
	var id int64
	err := s.db.QueryRowContext(ctx, "SELECT id FROM users WHERE nick = ?", nick).Scan(&id)
	return id, err
}

// GetOrCreateChannel returns the channel id, creating it if needed.
func (s *Database) GetOrCreateChannel(ctx context.Context, name string) (int64, error) {
	var id int64
	err := s.db.QueryRowContext(ctx, "SELECT id FROM channels WHERE name = ?", name).Scan(&id)
	if err == nil {
		return id, nil
	}
	now := time.Now()
	res, err := s.db.ExecContext(ctx,
		"INSERT INTO channels (name, created_at, updated_at) VALUES (?, ?, ?)",
		name, now, now)
	if err != nil {
		return 0, fmt.Errorf("create channel: %w", err)
	}
	id, _ = res.LastInsertId()
	return id, nil
}

// JoinChannel adds a user to a channel.
func (s *Database) JoinChannel(ctx context.Context, channelID, userID int64) error {
	_, err := s.db.ExecContext(ctx,
		"INSERT OR IGNORE INTO channel_members (channel_id, user_id, joined_at) VALUES (?, ?, ?)",
		channelID, userID, time.Now())
	return err
}

// PartChannel removes a user from a channel.
func (s *Database) PartChannel(ctx context.Context, channelID, userID int64) error {
	_, err := s.db.ExecContext(ctx,
		"DELETE FROM channel_members WHERE channel_id = ? AND user_id = ?",
		channelID, userID)
	return err
}

// DeleteChannelIfEmpty deletes a channel if it has no members.
func (s *Database) DeleteChannelIfEmpty(ctx context.Context, channelID int64) error {
	_, err := s.db.ExecContext(ctx,
		`DELETE FROM channels WHERE id = ? AND NOT EXISTS
		 (SELECT 1 FROM channel_members WHERE channel_id = ?)`,
		channelID, channelID)
	return err
}

// ListChannels returns all channels the user has joined.
func (s *Database) ListChannels(ctx context.Context, userID int64) ([]ChannelInfo, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT c.id, c.name, c.topic FROM channels c
		 INNER JOIN channel_members cm ON cm.channel_id = c.id
		 WHERE cm.user_id = ? ORDER BY c.name`, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var channels []ChannelInfo
	for rows.Next() {
		var ch ChannelInfo
		if err := rows.Scan(&ch.ID, &ch.Name, &ch.Topic); err != nil {
			return nil, err
		}
		channels = append(channels, ch)
	}
	if channels == nil {
		channels = []ChannelInfo{}
	}
	return channels, nil
}

// ListAllChannels returns all channels.
func (s *Database) ListAllChannels(ctx context.Context) ([]ChannelInfo, error) {
	rows, err := s.db.QueryContext(ctx,
		"SELECT id, name, topic FROM channels ORDER BY name")
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var channels []ChannelInfo
	for rows.Next() {
		var ch ChannelInfo
		if err := rows.Scan(&ch.ID, &ch.Name, &ch.Topic); err != nil {
			return nil, err
		}
		channels = append(channels, ch)
	}
	if channels == nil {
		channels = []ChannelInfo{}
	}
	return channels, nil
}

// ChannelMembers returns all members of a channel.
func (s *Database) ChannelMembers(ctx context.Context, channelID int64) ([]MemberInfo, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT u.id, u.nick, u.last_seen FROM users u
		 INNER JOIN channel_members cm ON cm.user_id = u.id
		 WHERE cm.channel_id = ? ORDER BY u.nick`, channelID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var members []MemberInfo
	for rows.Next() {
		var m MemberInfo
		if err := rows.Scan(&m.ID, &m.Nick, &m.LastSeen); err != nil {
			return nil, err
		}
		members = append(members, m)
	}
	if members == nil {
		members = []MemberInfo{}
	}
	return members, nil
}

// GetChannelMemberIDs returns user IDs of all members in a channel.
func (s *Database) GetChannelMemberIDs(ctx context.Context, channelID int64) ([]int64, error) {
	rows, err := s.db.QueryContext(ctx,
		"SELECT user_id FROM channel_members WHERE channel_id = ?", channelID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var ids []int64
	for rows.Next() {
		var id int64
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		ids = append(ids, id)
	}
	return ids, nil
}

// GetUserChannelIDs returns channel IDs the user is a member of.
func (s *Database) GetUserChannelIDs(ctx context.Context, userID int64) ([]int64, error) {
	rows, err := s.db.QueryContext(ctx,
		"SELECT channel_id FROM channel_members WHERE user_id = ?", userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var ids []int64
	for rows.Next() {
		var id int64
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		ids = append(ids, id)
	}
	return ids, nil
}

// InsertMessage stores a message and returns its DB ID.
func (s *Database) InsertMessage(ctx context.Context, command, from, to string, body json.RawMessage, meta json.RawMessage) (int64, string, error) {
	msgUUID := uuid.New().String()
	now := time.Now().UTC()
	if body == nil {
		body = json.RawMessage("[]")
	}
	if meta == nil {
		meta = json.RawMessage("{}")
	}
	res, err := s.db.ExecContext(ctx,
		`INSERT INTO messages (uuid, command, msg_from, msg_to, body, meta, created_at)
		 VALUES (?, ?, ?, ?, ?, ?, ?)`,
		msgUUID, command, from, to, string(body), string(meta), now)
	if err != nil {
		return 0, "", err
	}
	id, _ := res.LastInsertId()
	return id, msgUUID, nil
}

// EnqueueMessage adds a message to a user's delivery queue.
func (s *Database) EnqueueMessage(ctx context.Context, userID, messageID int64) error {
	_, err := s.db.ExecContext(ctx,
		"INSERT OR IGNORE INTO client_queues (user_id, message_id, created_at) VALUES (?, ?, ?)",
		userID, messageID, time.Now())
	return err
}

// PollMessages returns queued messages for a user after a given queue ID.
func (s *Database) PollMessages(ctx context.Context, userID int64, afterQueueID int64, limit int) ([]IRCMessage, int64, error) {
	if limit <= 0 {
		limit = 100
	}
	rows, err := s.db.QueryContext(ctx,
		`SELECT cq.id, m.uuid, m.command, m.msg_from, m.msg_to, m.body, m.meta, m.created_at
		 FROM client_queues cq
		 INNER JOIN messages m ON m.id = cq.message_id
		 WHERE cq.user_id = ? AND cq.id > ?
		 ORDER BY cq.id ASC LIMIT ?`, userID, afterQueueID, limit)
	if err != nil {
		return nil, afterQueueID, err
	}
	defer rows.Close()

	var msgs []IRCMessage
	var lastQID int64
	for rows.Next() {
		var m IRCMessage
		var qID int64
		var body, meta string
		var ts time.Time
		if err := rows.Scan(&qID, &m.ID, &m.Command, &m.From, &m.To, &body, &meta, &ts); err != nil {
			return nil, afterQueueID, err
		}
		m.Body = json.RawMessage(body)
		m.Meta = json.RawMessage(meta)
		m.TS = ts.Format(time.RFC3339Nano)
		m.DBID = qID
		lastQID = qID
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []IRCMessage{}
	}
	if lastQID == 0 {
		lastQID = afterQueueID
	}
	return msgs, lastQID, nil
}

// GetHistory returns message history for a target (channel or DM nick pair).
func (s *Database) GetHistory(ctx context.Context, target string, beforeID int64, limit int) ([]IRCMessage, error) {
	if limit <= 0 {
		limit = 50
	}
	var query string
	var args []any
	if beforeID > 0 {
		query = `SELECT id, uuid, command, msg_from, msg_to, body, meta, created_at
			FROM messages WHERE msg_to = ? AND id < ? AND command = 'PRIVMSG'
			ORDER BY id DESC LIMIT ?`
		args = []any{target, beforeID, limit}
	} else {
		query = `SELECT id, uuid, command, msg_from, msg_to, body, meta, created_at
			FROM messages WHERE msg_to = ? AND command = 'PRIVMSG'
			ORDER BY id DESC LIMIT ?`
		args = []any{target, limit}
	}
	rows, err := s.db.QueryContext(ctx, query, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var msgs []IRCMessage
	for rows.Next() {
		var m IRCMessage
		var dbID int64
		var body, meta string
		var ts time.Time
		if err := rows.Scan(&dbID, &m.ID, &m.Command, &m.From, &m.To, &body, &meta, &ts); err != nil {
			return nil, err
		}
		m.Body = json.RawMessage(body)
		m.Meta = json.RawMessage(meta)
		m.TS = ts.Format(time.RFC3339Nano)
		m.DBID = dbID
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []IRCMessage{}
	}
	// Reverse to ascending order
	for i, j := 0, len(msgs)-1; i < j; i, j = i+1, j-1 {
		msgs[i], msgs[j] = msgs[j], msgs[i]
	}
	return msgs, nil
}

// ChangeNick updates a user's nickname.
func (s *Database) ChangeNick(ctx context.Context, userID int64, newNick string) error {
	_, err := s.db.ExecContext(ctx,
		"UPDATE users SET nick = ? WHERE id = ?", newNick, userID)
	return err
}

// SetTopic sets the topic for a channel.
func (s *Database) SetTopic(ctx context.Context, channelName string, topic string) error {
	_, err := s.db.ExecContext(ctx,
		"UPDATE channels SET topic = ?, updated_at = ? WHERE name = ?", topic, time.Now(), channelName)
	return err
}

// DeleteUser removes a user and all their data.
func (s *Database) DeleteUser(ctx context.Context, userID int64) error {
	_, err := s.db.ExecContext(ctx, "DELETE FROM users WHERE id = ?", userID)
	return err
}

// GetAllChannelMembershipsForUser returns (channelID, channelName) for all channels a user is in.
func (s *Database) GetAllChannelMembershipsForUser(ctx context.Context, userID int64) ([]ChannelInfo, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT c.id, c.name, c.topic FROM channels c
		 INNER JOIN channel_members cm ON cm.channel_id = c.id
		 WHERE cm.user_id = ?`, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var channels []ChannelInfo
	for rows.Next() {
		var ch ChannelInfo
		if err := rows.Scan(&ch.ID, &ch.Name, &ch.Topic); err != nil {
			return nil, err
		}
		channels = append(channels, ch)
	}
	return channels, nil
}