import sqlite3

import click
from flask import current_app, g
from flask.cli import with_appcontext


def get_db():
    # g is  a special object unique for each request. Connection is stored
    # and reused instead of creating a new connection if get_db is called a second time
    # current_app Flask application handling the request
    # sqlite3.connect() establishes a connection to the file pointed at by DATABASE in config
    # sqlite3.Row tells connection to return rows that behave like dicts. allows accessing by name
    # close_db checks if a connection was created by checking if g.db was set.
    if 'db' not in g:
        g.db = sqlite3.connect(current_app.config['DATABASE'], detect_types=sqlite3.PARSE_DECLTYPES)
        g.db.row_factory = sqlite3.Row

    return g.db


def close_db(e=None):
    db = g.pop('db', None)

    if db is not None:
        db.close()


def init_db():
    db = get_db()

    with current_app.open_resource('schema.sql') as f:
        db.executescript(f.read().decode('utf8'))


@click.command('init-db')
@with_appcontext
def init_db_command():
    # Clear the existing data and create new tables.
    init_db()
    click.echo('Initialized the database.')


def init_app(app):
    app.teardown_appcontext(close_db)
    app.cli.add_command(init_db_command)
