import sqlite3


def create():
    conn = sqlite3.connect('kv.db')
    c = conn.cursor()

    # create with index
    c.execute('''CREATE TABLE IF NOT EXISTS kv (key text, value text, PRIMARY KEY(key))''')

    conn.commit()
    conn.close()


def set(key, value):
    conn = sqlite3.connect('kv.db')
    c = conn.cursor()

    # check table
    c.execute('''SELECT name FROM sqlite_master WHERE type='table' AND name='kv' ''')
    result = c.fetchone()
    if not result:
        create()

    # create with index
    c.execute('''INSERT OR REPLACE INTO kv (key, value) VALUES (?, ?)''', (key, value))

    conn.commit()
    conn.close()


def get(key):
    conn = sqlite3.connect('kv.db')
    c = conn.cursor()

    # check table
    c.execute('''SELECT name FROM sqlite_master WHERE type='table' AND name='kv' ''')
    result = c.fetchone()
    if not result:
        create()

    # create with index
    c.execute('''SELECT value FROM kv WHERE key=?''', (key,))

    result = c.fetchone()

    conn.commit()
    conn.close()

    if result:
        return result[0]
    else:
        return None


def delete(key):
    conn = sqlite3.connect('kv.db')
    c = conn.cursor()

    # check table
    c.execute('''SELECT name FROM sqlite_master WHERE type='table' AND name='kv' ''')
    result = c.fetchone()
    if not result:
        create()

    # create with index
    c.execute('''DELETE FROM kv WHERE key=?''', (key,))

    conn.commit()
    conn.close()