package db

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

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

// CreateUser registers a new user with the given nick and returns the user with token.
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
	}
	// Update last_seen
	_, _ = 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
}

// 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
}

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

// 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
}

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

// MessageInfo represents a chat message.
type MessageInfo struct {
	ID        int64     `json:"id"`
	Channel   string    `json:"channel,omitempty"`
	Nick      string    `json:"nick"`
	Content   string    `json:"content"`
	IsDM      bool      `json:"isDm,omitempty"`
	DMTarget  string    `json:"dmTarget,omitempty"`
	CreatedAt time.Time `json:"createdAt"`
}

// GetMessages returns messages for a channel, optionally after a given ID.
func (s *Database) GetMessages(ctx context.Context, channelID int64, afterID int64, limit int) ([]MessageInfo, error) {
	if limit <= 0 {
		limit = 50
	}
	rows, err := s.db.QueryContext(ctx,
		`SELECT m.id, c.name, u.nick, m.content, m.created_at
		 FROM messages m
		 INNER JOIN users u ON u.id = m.user_id
		 INNER JOIN channels c ON c.id = m.channel_id
		 WHERE m.channel_id = ? AND m.is_dm = 0 AND m.id > ?
		 ORDER BY m.id ASC LIMIT ?`, channelID, afterID, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var msgs []MessageInfo
	for rows.Next() {
		var m MessageInfo
		if err := rows.Scan(&m.ID, &m.Channel, &m.Nick, &m.Content, &m.CreatedAt); err != nil {
			return nil, err
		}
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []MessageInfo{}
	}
	return msgs, nil
}

// SendMessage inserts a channel message.
func (s *Database) SendMessage(ctx context.Context, channelID, userID int64, content string) (int64, error) {
	res, err := s.db.ExecContext(ctx,
		"INSERT INTO messages (channel_id, user_id, content, is_dm, created_at) VALUES (?, ?, ?, 0, ?)",
		channelID, userID, content, time.Now())
	if err != nil {
		return 0, err
	}
	return res.LastInsertId()
}

// SendDM inserts a direct message.
func (s *Database) SendDM(ctx context.Context, fromID, toID int64, content string) (int64, error) {
	res, err := s.db.ExecContext(ctx,
		"INSERT INTO messages (user_id, content, is_dm, dm_target_id, created_at) VALUES (?, ?, 1, ?, ?)",
		fromID, content, toID, time.Now())
	if err != nil {
		return 0, err
	}
	return res.LastInsertId()
}

// GetDMs returns direct messages between two users after a given ID.
func (s *Database) GetDMs(ctx context.Context, userA, userB int64, afterID int64, limit int) ([]MessageInfo, error) {
	if limit <= 0 {
		limit = 50
	}
	rows, err := s.db.QueryContext(ctx,
		`SELECT m.id, u.nick, m.content, t.nick, m.created_at
		 FROM messages m
		 INNER JOIN users u ON u.id = m.user_id
		 INNER JOIN users t ON t.id = m.dm_target_id
		 WHERE m.is_dm = 1 AND m.id > ?
		 AND ((m.user_id = ? AND m.dm_target_id = ?) OR (m.user_id = ? AND m.dm_target_id = ?))
		 ORDER BY m.id ASC LIMIT ?`, afterID, userA, userB, userB, userA, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var msgs []MessageInfo
	for rows.Next() {
		var m MessageInfo
		if err := rows.Scan(&m.ID, &m.Nick, &m.Content, &m.DMTarget, &m.CreatedAt); err != nil {
			return nil, err
		}
		m.IsDM = true
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []MessageInfo{}
	}
	return msgs, nil
}

// PollMessages returns all new messages (channel + DM) for a user after a given ID.
func (s *Database) PollMessages(ctx context.Context, userID int64, afterID int64, limit int) ([]MessageInfo, error) {
	if limit <= 0 {
		limit = 100
	}
	rows, err := s.db.QueryContext(ctx,
		`SELECT m.id, COALESCE(c.name, ''), u.nick, m.content, m.is_dm, COALESCE(t.nick, ''), m.created_at
		 FROM messages m
		 INNER JOIN users u ON u.id = m.user_id
		 LEFT JOIN channels c ON c.id = m.channel_id
		 LEFT JOIN users t ON t.id = m.dm_target_id
		 WHERE m.id > ? AND (
		   (m.is_dm = 0 AND m.channel_id IN (SELECT channel_id FROM channel_members WHERE user_id = ?))
		   OR (m.is_dm = 1 AND (m.user_id = ? OR m.dm_target_id = ?))
		 )
		 ORDER BY m.id ASC LIMIT ?`, afterID, userID, userID, userID, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var msgs []MessageInfo
	for rows.Next() {
		var m MessageInfo
		var isDM int
		if err := rows.Scan(&m.ID, &m.Channel, &m.Nick, &m.Content, &isDM, &m.DMTarget, &m.CreatedAt); err != nil {
			return nil, err
		}
		m.IsDM = isDM == 1
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []MessageInfo{}
	}
	return msgs, nil
}

// GetMessagesBefore returns channel messages before a given ID (for history scrollback).
func (s *Database) GetMessagesBefore(ctx context.Context, channelID int64, beforeID int64, limit int) ([]MessageInfo, error) {
	if limit <= 0 {
		limit = 50
	}
	var query string
	var args []any
	if beforeID > 0 {
		query = `SELECT m.id, c.name, u.nick, m.content, m.created_at
			FROM messages m
			INNER JOIN users u ON u.id = m.user_id
			INNER JOIN channels c ON c.id = m.channel_id
			WHERE m.channel_id = ? AND m.is_dm = 0 AND m.id < ?
			ORDER BY m.id DESC LIMIT ?`
		args = []any{channelID, beforeID, limit}
	} else {
		query = `SELECT m.id, c.name, u.nick, m.content, m.created_at
			FROM messages m
			INNER JOIN users u ON u.id = m.user_id
			INNER JOIN channels c ON c.id = m.channel_id
			WHERE m.channel_id = ? AND m.is_dm = 0
			ORDER BY m.id DESC LIMIT ?`
		args = []any{channelID, limit}
	}
	rows, err := s.db.QueryContext(ctx, query, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var msgs []MessageInfo
	for rows.Next() {
		var m MessageInfo
		if err := rows.Scan(&m.ID, &m.Channel, &m.Nick, &m.Content, &m.CreatedAt); err != nil {
			return nil, err
		}
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []MessageInfo{}
	}
	// 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
}

// GetDMsBefore returns DMs between two users before a given ID (for history scrollback).
func (s *Database) GetDMsBefore(ctx context.Context, userA, userB int64, beforeID int64, limit int) ([]MessageInfo, error) {
	if limit <= 0 {
		limit = 50
	}
	var query string
	var args []any
	if beforeID > 0 {
		query = `SELECT m.id, u.nick, m.content, t.nick, m.created_at
			FROM messages m
			INNER JOIN users u ON u.id = m.user_id
			INNER JOIN users t ON t.id = m.dm_target_id
			WHERE m.is_dm = 1 AND m.id < ?
			AND ((m.user_id = ? AND m.dm_target_id = ?) OR (m.user_id = ? AND m.dm_target_id = ?))
			ORDER BY m.id DESC LIMIT ?`
		args = []any{beforeID, userA, userB, userB, userA, limit}
	} else {
		query = `SELECT m.id, u.nick, m.content, t.nick, m.created_at
			FROM messages m
			INNER JOIN users u ON u.id = m.user_id
			INNER JOIN users t ON t.id = m.dm_target_id
			WHERE m.is_dm = 1
			AND ((m.user_id = ? AND m.dm_target_id = ?) OR (m.user_id = ? AND m.dm_target_id = ?))
			ORDER BY m.id DESC LIMIT ?`
		args = []any{userA, userB, userB, userA, limit}
	}
	rows, err := s.db.QueryContext(ctx, query, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var msgs []MessageInfo
	for rows.Next() {
		var m MessageInfo
		if err := rows.Scan(&m.ID, &m.Nick, &m.Content, &m.DMTarget, &m.CreatedAt); err != nil {
			return nil, err
		}
		m.IsDM = true
		msgs = append(msgs, m)
	}
	if msgs == nil {
		msgs = []MessageInfo{}
	}
	// 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, _ int64, topic string) error {
	_, err := s.db.ExecContext(ctx,
		"UPDATE channels SET topic = ? WHERE name = ?", topic, channelName)
	return err
}

// GetServerName returns the server name (unused, config provides this).
func (s *Database) GetServerName() string {
	return ""
}

// 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
}