import os
import sys
import psycopg2
from psycopg2 import sql
from psycopg2.extensions import ISOLATION_LEVEL_AUTOCOMMIT
import uuid
from datetime import datetime
import pytz
import pdb

tz = pytz.timezone('Europe/Madrid')

class Database():

    name = 'fediverse database library'

    def __init__(self, config_file=None, fediverse_db=None, fediverse_db_user=None, fediverse_db_user_password=None):

        self.config_file = "config/db_config.txt"
        self.fediverse_db = self.__get_parameter("fediverse_db", self.config_file)
        self.fediverse_db_user = self.__get_parameter("fediverse_db_user", self.config_file)
        self.fediverse_db_user_password = self.__get_parameter("fediverse_db_user_password", self.config_file)

        db_setup = self.__check_dbsetup(self)

        if not db_setup:

            self.fediverse_db = input("\nFediverse database name: ")
            self.fediverse_db_user = input("\nFediverse database user: ")
            self.fediverse_db_user_password = input("\nFediverse database user password: ")

            self.__createdb(self)  
            self.__create_config(self)
            self.__write_config(self)

    def write_server(self, server, federated_with, now):

        now = datetime.now()

        insert_sql = "INSERT INTO world(server, federated_with, updated_at, saved_at, checked) VALUES(%s,%s,%s,%s,%s) ON CONFLICT DO NOTHING"

        conn = None

        try:

            conn = psycopg2.connect(database = self.fediverse_db, user = self.fediverse_db_user, password = self.fediverse_db_user_password, host = "/var/run/postgresql", port = "6432")

            cur = conn.cursor()

            cur.execute(insert_sql, (server, federated_with, now, now, 'f'))

            print(f'writing {server} to world database')

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def save_time(self, program, start, finish):

        insert_sql = "INSERT INTO execution_time(program, start, finish) VALUES(%s,%s,%s) ON CONFLICT DO NOTHING"

        conn = None

        try:

            conn = psycopg2.connect(database = self.fediverse_db, user = self.fediverse_db_user, password = self.fediverse_db_user_password, host = "/var/run/postgresql", port = "6432")

            cur = conn.cursor()

            cur.execute(insert_sql, (program, start, finish,))

            cur.execute("UPDATE execution_time SET start=(%s), finish=(%s) where program=(%s)", (start, finish, program))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def write_api(self, server, software, users, mau, alive, api, soft_version):

        now = datetime.now()

        insert_sql = "INSERT INTO fediverse(server, updated_at, software, users, mau, alive, users_api, version) VALUES(%s,%s,%s,%s,%s,%s,%s,%s) ON CONFLICT DO NOTHING"

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            print(f'Writing {server} nodeinfo data...')

            cur.execute(insert_sql, (server, now, software, users, mau, alive, api, soft_version))

            cur.execute(
                "UPDATE fediverse SET updated_at=(%s), software=(%s), users=(%s), mau=(%s), alive=(%s), users_api=(%s), version=(%s) where server=(%s)",
                (now, software, users, mau, alive, api, soft_version, server)
                )

            cur.execute("UPDATE world SET checked='t' where server=(%s)", (server,))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def get_world_servers(self):

        world_servers = []

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            # get world servers list

            cur.execute("select server from world where checked='f'")

            rows = cur.fetchall()

            for row in rows:

                world_servers.append(row[0])

            cur.close()

            print("Remaining servers: " + str(len(world_servers)))

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return world_servers

    def get_last_checked_servers(self):

        # get last checked servers from fediverse DB

        alive_servers = []

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            # get world servers list

            cur.execute("select server from world where server in (select server from fediverse where users_api != '')")

            rows = cur.fetchall()

            for row in rows:

                alive_servers.append(row[0])

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return alive_servers

    def set_world_servers_check_to_false(self):

        # set all world servers's checked column to False

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("UPDATE world SET checked='f'")

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def delete_dead_servers(self):

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select server from fediverse where downs > '14' and not alive and now() - first_checked_at > interval '7 days'")

            rows = cur.fetchall()

            for row in rows:

                print(f'Deleting server {row[0]}...')

                cur.execute("delete from fediverse where server=(%s)", (row[0],))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def write_alive_server(self, server, software, soft_version, alive, api, users, downs, first_checked_at, mau):

        now = datetime.now()

        insert_sql = "INSERT INTO fediverse(server, users, updated_at, software, alive, users_api, version, first_checked_at, last_checked_at, downs, mau) VALUES(%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s) ON CONFLICT DO NOTHING"

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute(insert_sql, (server, users, now, software, alive, api, soft_version, now, now, downs, mau))

            if first_checked_at != None:

                cur.execute("UPDATE fediverse SET users=(%s), updated_at=(%s), software=(%s), alive=(%s), users_api=(%s), version=(%s), last_checked_at=(%s), downs=(%s), mau=(%s) where server=(%s)", (users, now, software, alive, api, soft_version, now, downs, mau, server))

            else:

                cur.execute("UPDATE fediverse SET users=(%s), updated_at=(%s), software=(%s), alive=(%s), users_api=(%s), version=(%s), first_checked_at=(%s), last_checked_at=(%s), downs=(%s), mau=(%s) where server=(%s)", (users, now, software, alive, api, soft_version, now, now, downs, mau, server))

                cur.execute("UPDATE world SET checked='t' where server=(%s)", (server,))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def write_not_alive_server(self, server, software, soft_version, alive, api, users, downs, first_checked_at, mau):

        now = datetime.now()

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            if first_checked_at != None:

                cur.execute("UPDATE fediverse SET updated_at=(%s), alive=(%s), downs=(%s), mau=(%s) where server=(%s)", (now, alive, downs, mau, server))

            else:

                cur.execute("UPDATE fediverse SET updated_at=(%s), alive=(%s), first_checked_at=(%s), downs=(%s), mau=(%s) where server=(%s)", (now, alive, now, downs, mau, server))

            cur.execute("UPDATE world SET checked='f' where server=(%s)", (server,))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def write_blocked_software(self, server, software, soft_version, alive, api, users, downs, first_checked_at):

        now = datetime.now()

        insert_sql = "INSERT INTO blocked(server, users, updated_at, software, alive, users_api, version, first_checked_at, last_checked_at, downs) VALUES(%s,%s,%s,%s,%s,%s,%s,%s,%s,%s) ON CONFLICT DO NOTHING"

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute(insert_sql, (server, users, now, software, alive, api, soft_version, now, now, downs))

            if first_checked_at != None:

                cur.execute("UPDATE blocked SET users=(%s), updated_at=(%s), software=(%s), alive=(%s), users_api=(%s), version=(%s), last_checked_at=(%s), downs=(%s) where server=(%s)", (users, now, software, alive, api, soft_version, now, downs, server))

            else:

                cur.execute("UPDATE blocked SET users=(%s), updated_at=(%s), software=(%s), alive=(%s), users_api=(%s), version=(%s), first_checked_at=(%s), last_checked_at=(%s), downs=(%s) where server=(%s)", (users, now, software, alive, api, soft_version, now, now, downs, server))

                cur.execute("UPDATE world SET checked='t' where server=(%s)", (server,))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def soft_totals(self):

        # get current total servers and users, get users from every software

        now = datetime.now()

        gettotals_sql = "select count(server), sum(users), sum(mau) from fediverse where alive"
        get_soft_totals_sql = "select software, sum(users) as users, sum(mau) as mau, count(server) as servers from fediverse where users != 0 and mau is not null and alive group by software order by mau desc"

        soft_total_project = []
        soft_total_users = []
        soft_total_mau = []
        soft_total_servers = []

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute(gettotals_sql)

            row = cur.fetchone()

            total_servers = row[0]

            total_users = row[1]

            total_mau = row[2]

            cur.execute(get_soft_totals_sql)

            rows = cur.fetchall()

            for row in rows:

                soft_total_project.append(row[0])
                soft_total_users.append(row[1])
                soft_total_mau.append(row[2])
                soft_total_servers.append(row[3])

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return (soft_total_project, soft_total_users, soft_total_mau, soft_total_servers, total_servers, total_users, total_mau)

    def last_values(self, total_servers, total_users, total_mau):

        #  get last check values and write current total ones

        now = datetime.now()

        evo_servers = 0

        evo_users = 0

        evo_mau = 0

        select_sql = "select total_servers, total_users, total_mau from totals order by datetime desc limit 1"

        insert_sql = "INSERT INTO totals(datetime, total_servers, total_users, total_mau) VALUES(%s,%s,%s,%s)"

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute(select_sql)

            row = cur.fetchone()

            if row is not None:

                servers_before = row[0]

                users_before = row[1]

                mau_before = row[2]

            else:

                servers_before = 0

                users_before = 0

                mau_before = 0

            cur.execute(insert_sql, (now, total_servers, total_users, total_mau))

            conn.commit()

            cur.close()

            evo_servers = total_servers - servers_before

            evo_users = total_users - users_before

            evo_mau = total_mau - mau_before

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return (evo_servers, evo_users, evo_mau)

    def write_evo(self, evo_servers, evo_users, evo_mau):

        #  write evo values

        now = datetime.now()

        insert_sql = "INSERT INTO evo(datetime, servers, users, mau) VALUES(%s,%s,%s,%s)"

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute(insert_sql, (now, evo_servers, evo_users, evo_mau))

            conn.commit()

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def last_world_datetime(self):

        # get world's last update datetime

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select updated_at from world order by updated_at desc limit 1")

            row = cur.fetchone()

            last_update = row[0]

            last_update = last_update.strftime('%m/%d/%Y, %H:%M:%S')

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return last_update

    def max(self):

        # get max servers and mau

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select MAX(total_servers) from totals")

            row = cur.fetchone()

            if row is not None:

                max_servers = row[0]

            else:

                max_servers = 0

            cur.execute("select MAX(total_mau) from totals")

            row = cur.fetchone()

            if row is not None:

                max_mau = row[0]

            else:

                max_mau = 0

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return (max_servers, max_mau)

    def get_plots(self):

        # get plots

        servers_plots = []

        mau_plots = []

        global_week = []

        global_servers = []

        global_users = []

        global_mau = []

        conn = None

        try:

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select total_servers, total_mau from totals order by datetime desc limit 14")

            rows = cur.fetchall()

            for row in rows:

                servers_plots.append(row[0])

                mau_plots.append(row[1])

            cur.execute("select distinct on (date_trunc('week', datetime)) datetime::TIMESTAMP::DATE, total_servers, total_users, total_mau from totals group by date_trunc('month', datetime), datetime")

            rows = cur.fetchall()

            for row in rows:

                global_week.append(row[0])

                global_servers.append(row[1])

                global_users.append(row[2])

                global_mau.append(row[3])

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return (servers_plots, mau_plots, global_week, global_servers, global_users, global_mau)

    def get_server_data(self, server):

        was_alive = None
        software = None
        api = None
        soft_version = None
        first_checked_at = None
        downs_qty = None
        mau = 0

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password = self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select alive, software, users_api, version, first_checked_at, downs, mau from fediverse where server=(%s)", (server,))

            row = cur.fetchone()

            if row is not None:

                was_alive = row[0]
                software = row[1]
                api = row[2]
                soft_version = row[3]
                first_checked_at = row[4]
                downs_qty = row[5]
                mau = row[6]

            cur.close()

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

        return (was_alive, software, api, soft_version, first_checked_at, downs_qty, mau)

    def get_soft_data(self, search_soft):

        try:

            conn = None

            conn = psycopg2.connect(database = self.fediverse_db, user = self.fediverse_db_user, password = self.fediverse_db_user_password, host = "/var/run/postgresql", port = "6432")

            cur = conn.cursor()

            cur.execute("select count(server), sum(users), sum(mau) from fediverse where software=(%s) and alive", (search_soft,))

            row = cur.fetchone()

            if row != None:

                servers = row[0]

                users = row[1]

                mau = row[2]

            else:

                servers = 0

                users = 0

                mau = 0

            cur.close()

            return (servers, users, mau)

        except (Exception, psycopg2.DatabaseError) as error:

            sys.exit(error)

        finally:

            if conn is not None:

                conn.close()

    def fediquery_server_data(self, search_server):

        try:

            conn = None

            conn = psycopg2.connect(database = self.fediverse_db, user = self.fediverse_db_user, password = self.fediverse_db_user_password, host = "/var/run/postgresql", port = "6432")

            cur = conn.cursor()

            cur.execute("select server, software, version, users, mau, alive from fediverse where server=(%s)", (search_server,))

            row = cur.fetchone()

            if row != None:

                server = row[0]

                software = row[1]

                version = row[2]

                users = row[3]

                if row[4] != None:

                    mau = row[4]

                else:

                    mau = 0

                alive = row[5]

            else:

                server = ''

                software = ''

                version = ''

                users = 0

                mau = 0

                alive = False

            cur.close()

            return (server, software, version, users, mau, alive)

        except (Exception, psycopg2.DatabaseError) as error:

            sys.exit(error)

        finally:

            if conn is not None:

                conn.close()

    def get_uptime(self):
    
        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password=self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select count(server) from fediverse where alive")

            row = cur.fetchone()

            alive_servers = row[0]

            cur.execute("select MAX(date_trunc('day', last_checked_at) - date_trunc('days', first_checked_at)) from fediverse;")

            row = cur.fetchone()

            max_uptime = row[0]

            cur.execute("select count(server) from fediverse where date_trunc('days', last_checked_at)-date_trunc('days',first_checked_at)=(%s)", (max_uptime,))

            row = cur.fetchone()

            if row is not None:

                best_servers = row[0]

            cur.execute("select software, count(*) as servers from fediverse where date_trunc('days',last_checked_at)-date_trunc('days', first_checked_at)=(%s) group by software order by servers desc", (max_uptime,))

            rows = cur.fetchall()

            software_lst = []

            servers_lst = []

            for row in rows:

                software_lst.append(row[0])

                servers_lst.append(row[1])

            cur.close()

            return (alive_servers, max_uptime, best_servers, software_lst, servers_lst)

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def get_percentage(self, uptime_servers, software):

        try:

            conn = None

            conn = psycopg2.connect(database=self.fediverse_db, user=self.fediverse_db_user, password=self.fediverse_db_user_password, host="/var/run/postgresql", port="6432")

            cur = conn.cursor()

            cur.execute("select count(server) from fediverse where alive and software=(%s)", (software,))

            row = cur.fetchone()

            if row is not None:

                soft_total_servers = row[0]

            cur.close()

            soft_uptime_percent = round((uptime_servers * 100) / soft_total_servers, 1)

            return (soft_uptime_percent)

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    @staticmethod
    def __check_dbsetup(self):

        db_setup = False

        try:

            conn = None

            conn = psycopg2.connect(database = self.fediverse_db, user = self.fediverse_db_user, password = self.fediverse_db_user_password, host = "/var/run/postgresql", port = "6432")

            db_setup = True

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        return db_setup

    @staticmethod
    def __createdb(self):

        conn = None

        try:

            conn = psycopg2.connect(dbname='postgres',
                user=self.fediverse_db_user, host='',
                password=self.fediverse_db_user_password)

            conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)

            cur = conn.cursor()

            print(f"Creating database {self.fediverse_db}. Please wait...")

            cur.execute(sql.SQL("CREATE DATABASE {}").format(
                sql.Identifier(self.fediverse_db))
            )
            print(f"Database {self.fediverse_db} created!\n")

            self.__dbtables_schemes(self)

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    @staticmethod
    def __dbtables_schemes(self):

        db = self.fediverse_db
        table = "world"
        sql = "create table "+table+" (server varchar(200) PRIMARY KEY, federated_with varchar(200), updated_at timestamptz, saved_at timestamptz, checked boolean)"
        self.__create_table(self, table, sql)

        table = "fediverse"
        sql = "create table "+table+" (server varchar(200) PRIMARY KEY, users INT, updated_at timestamptz, software varchar(50), alive boolean, users_api varchar(50), version varchar(100), first_checked_at timestamptz, last_checked_at timestamptz, downs int, mau int)"
        self.__create_table(self, table, sql)

        table = "blocked"
        sql = "create table "+table+" (server varchar(200) PRIMARY KEY, users INT, updated_at timestamptz, software varchar(50), alive boolean, users_api varchar(50), version varchar(100), first_checked_at timestamptz, last_checked_at timestamptz, downs int)"
        self.__create_table(self, table, sql)

        table = "totals"
        sql = "create table "+table+" (datetime timestamptz PRIMARY KEY, total_servers INT, total_users INT)"
        self.__create_table(self, table, sql)

        table = "evo"
        sql = "create table "+table+" (datetime timestamptz PRIMARY KEY, servers INT, users INT)"
        self.__create_table(self, table, sql)

        table = "execution_time"
        sql = "create table "+table+" (program varchar(20) PRIMARY KEY, start timestamptz, finish timestamptz)"
        self.__create_table(self, table, sql)

    @staticmethod
    def __create_table(self, table, sql):

        conn = None

        try:

            conn = psycopg2.connect(database = self.fediverse_db, user = self.fediverse_db_user, password = self.fediverse_db_user_password, host = "/var/run/postgresql", port = "6432")

            cur = conn.cursor()

            print(f"Creating table {table}")

            cur.execute(sql)

            conn.commit()

            print(f"Table {table} created!\n")

        except (Exception, psycopg2.DatabaseError) as error:

            print(error)

        finally:

            if conn is not None:

                conn.close()

    def __get_parameter(self, parameter, config_file):

        if not os.path.isfile(config_file):
            print(f"File {config_file} not found..")
            return

        with open( config_file ) as f:
            for line in f:
                if line.startswith( parameter ):
                    return line.replace(parameter + ":", "").strip()

        print(f"{config_file} Missing parameter {parameter}")

        sys.exit(0)

    @staticmethod
    def __create_config(self):

        if not os.path.exists('config'):

            os.makedirs('config')

        if not os.path.exists(self.config_file):

            print(self.config_file + " created!")
            with open(self.config_file, 'w'): pass

    @staticmethod
    def __write_config(self):

        with open(self.config_file, 'a') as the_file:

            the_file.write(f'fediverse_db: {self.fediverse_db}\nfediverse_db_user: {self.fediverse_db_user}\nfediverse_db_user_password: {self.fediverse_db_user_password}')
            print(f"adding parameters to {self.config_file}\n")