Obtain tokens from Spotify

Code now successfully obtains tokens from the Spotify API.

spotifyvis/views.py

@@ -1,10 +1,11 @@
 from django.shortcuts import render, redirect
-from django.http import HttpResponse
+from django.http import HttpResponse, HttpResponseBadRequest
 import math
 import random
 import requests
 import os
 import urllib
+import datetime
 
 def generate_random_string(length):
     """Generates a random string of a certain length
@@ -24,6 +25,17 @@ def generate_random_string(length):
     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.datetime.today() - token_obtained_at).seconds
+    return time_elapsed >= valid_for
+
+
 # Create your views here.
 def index(request):
     return render(request, 'spotifyvis/index.html')
@@ -31,8 +43,8 @@ def index(request):
 
 def login(request):
 
-    state_str = generate_random_string(16)
     # 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 = {
@@ -49,4 +61,25 @@ def login(request):
     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
+    request.session['token_obtained_at'] = datetime.datetime.today()
+    request.session['access_token'] = response['access_token']
+    request.session['refresh_token'] = response['refresh_token']
+    request.session['valid_for'] = response['expires_in']
+    print(response)
     return HttpResponse("At callback")