spotify-lib-vis/spotifyvis/views.py

from django.shortcuts import render, redirect
from django.http import HttpResponse, HttpResponseBadRequest
import math
import random
import requests
import os
import urllib
from datetime import datetime

TIME_FORMAT = '%Y-%m-%d-%H-%M-%S'

def generate_random_string(length):
    """Generates a random string of a certain length

    Args:
        length: the desired length of the randomized string
    
    Returns:
        A random string
    """
    rand_str = ""
    possible_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

    for _ in range(length):
        rand_str += possible_chars[random.randint(0, len(possible_chars) - 1)]
    
    return rand_str


def token_expired(token_obtained_at, valid_for):
    """Returns True if token expired, False if otherwise

    Args:
        token_obtained_at: datetime object representing the date and time when the token was obtained
        valid_for: the time duration for which the token is valid, in seconds
    """
    time_elapsed = (datetime.today() - token_obtained_at).total_seconds()
    return time_elapsed >= valid_for


# Create your views here.
def index(request):
    return render(request, 'spotifyvis/index.html')


def login(request):

    # use a randomly generated state string to prevent cross-site request forgery attacks
    state_str = generate_random_string(16)
    request.session['state_string'] = state_str 

    payload = {
        'client_id': os.environ['SPOTIFY_CLIENT_ID'],
        'response_type': 'code',
        'redirect_uri': 'http://localhost:8000/callback',
        'state': state_str,
        'scope': 'user-library-read',
        'show_dialog': False
    }

    params = urllib.parse.urlencode(payload) # turn the payload dict into a query string
    authorize_url = "https://accounts.spotify.com/authorize/?{}".format(params)
    return redirect(authorize_url)

def callback(request):
    # Attempt to retrieve the authorization code from the query string
    try:
        code = request.GET['code']
    except KeyError:
        return HttpResponseBadRequest("<h1>Problem with login</h1>")

    payload = {
        'grant_type': 'authorization_code',
        'code': code,
        'redirect_uri': 'http://localhost:8000/callback',
        'client_id': os.environ['SPOTIFY_CLIENT_ID'],
        'client_secret': os.environ['SPOTIFY_CLIENT_SECRET'],
    }

    response = requests.post('https://accounts.spotify.com/api/token', data = payload).json()
    # despite its name, datetime.today() returns a datetime object, not a date object
    # use datetime.strptime() to get a datetime object from a string
    request.session['token_obtained_at'] = datetime.strftime(datetime.today(), TIME_FORMAT) 
    request.session['access_token'] = response['access_token']
    request.session['refresh_token'] = response['refresh_token']
    request.session['valid_for'] = response['expires_in']
    print(response)

    return redirect('user_data')


def user_data(request):

    token_obtained_at = datetime.strptime(request.session['token_obtained_at'], TIME_FORMAT)
    valid_for = int(request.session['valid_for'])

    if token_expired(token_obtained_at, valid_for):
        req_body = {
            'grant_type': 'refresh_token',
            'refresh_token': request.session['refresh_token'],
            'client_id': os.environ['SPOTIFY_CLIENT_ID'],
            'client_secret': os.environ['SPOTIFY_CLIENT_SECRET']
        }
        
        refresh_token_response = requests.post('https://accounts.spotify.com/api/token', data = req_body).json()
        request.session['access_token'] = refresh_token_response['access_token']
        request.session['valid_for'] = refresh_token_response['expires_in']

    auth_token_str = "Bearer " + request.session['access_token']
    headers = {
        'Authorization': auth_token_str
    }

    user_data_response = requests.get('https://api.spotify.com/v1/me', headers = headers).json()
    context = {
        'user_name': user_data_response['display_name'],
        'id': user_data_response['id'],
    }
    return render(request, 'spotifyvis/user_data.html', context)



def get_features(track_id, token):
    """Returns the features of a soundtrack

    Args:
        track_id: the id of the soundtrack, needed to query the Spotify API
        token: an access token for the Spotify API
 
    Returns:
        A dictionary with the features as its keys
    """

    headers = {
        'Authorization': token,
    }
    response = requests.get("https://api.spotify.com/v1/audio-features/{}".format(track_id), headers = headers).json()
    features_dict = {}

    # Data that we don't need
    useless_keys = [ 
        "key", "mode", "type", "liveness", "id", "uri", "track_href", "analysis_url", "time_signature",
    ]
    for key, val in response.items():
        if key not in useless_keys:
            features_dict[key] = val

    return features_dict


def update_std_dev(cur_mean, new_data_point, sample_size):
    """Calculates the standard deviation for a sample without storing all data points

    Args:
        cur_mean: the current mean for N = (sample_size - 1)
        new_data_point: a new data point
        sample_size: sample size including the new data point
    
    Returns:
        (updated_mean, std_dev)
    """
    # This is an implementationof Welford's method
    # http://jonisalonen.com/2013/deriving-welfords-method-for-computing-variance/
    new_mean = ((sample_size - 1) * cur_mean + new_data_point) / sample_size
    std_dev = (new_data_point - new_mean) * (new_data_point - cur_mean)
    return new_mean, std_dev