supporter: Support donors upgrading to supporters.

With a valid URL, a past donor can upgrade to a supporter by donating
the rest of the amount.  Django validates the data and, if it passes,
puts it in the form.  The JavaScript does most of the work from there.

www/conservancy/__init__.py

@@ -1,6 +1,27 @@
+import hashlib
+
+from django.conf import settings
 from django.shortcuts import render_to_response
 from django.template import RequestContext
 
+HASH_ENCODING = 'utf-8'
+
 def render_template_with_context(request, template_path, context_dict):
     return render_to_response(template_path, context_dict,
                               context_instance=RequestContext(request))
+
+def param_if_valid(params, param_name, hash_param_name, default=None):
+    try:
+        seed = settings.CONSERVANCY_SECRET_KEY
+        param_value = params[param_name]
+        param_bytes = param_value.encode(HASH_ENCODING)
+        given_hash = params[hash_param_name]
+    except (AttributeError, KeyError, UnicodeEncodeError):
+        return default
+    good_hash = hashlib.sha256()
+    good_hash.update(seed)
+    good_hash.update(param_bytes)
+    if given_hash == unicode(good_hash.hexdigest()):
+        return param_value
+    else:
+        return default

www/conservancy/apps/supporter/urls.py

@@ -0,0 +1,11 @@
+from django.conf.urls import patterns
+
+INDEX_VIEW = 'conservancy.apps.supporter.views.index'
+pattern_pairs = [(r'^/?$', INDEX_VIEW)]
+pattern_pairs.extend(
+    (r'^{}(?:\.html|/|)$'.format(basename), INDEX_VIEW)
+    for basename in ['index', '2015-supporter-appeal', '2016-supporter-appeal']
+)
+pattern_pairs.append((r'', 'conservancy.static.views.index'))
+
+urlpatterns = patterns('', *pattern_pairs)

www/conservancy/apps/supporter/views.py

@@ -0,0 +1,9 @@
+import conservancy
+
+def index(request):
+    partial_amount = conservancy.param_if_valid(request.GET, 'upgrade', 'upgrade_id', 0)
+    context = {
+        'partial_amount': partial_amount,
+        'minimum_amount': 120 - partial_amount,
+    }
+    return conservancy.render_template_with_context(request, "supporter/index.html", context)

www/conservancy/static/js/supporter-page.js

@@ -173,7 +173,11 @@ $(document).ready(function() {
     };
     $window.bind("hashchange", selectSupportTypeFromHash);
     var $selectorLink = selectSupportTypeFromHash();
-    if ($selectorLink.length === 0) {
+    if (parseInt($("form#annual").upgradeFromAmount) > 0) {
+        supportTypeSelector("#annual").click();
+        $(".supporter-type-selector").hide();
+    }
+    else if ($selectorLink.length === 0) {
         supportTypeSelector("#annual").click();
     }
 

www/conservancy/static/supporter/2015-supporter-appeal.html

@@ -1 +0,0 @@
-2016-supporter-appeal.html

www/conservancy/static/supporter/index.html

@@ -1 +0,0 @@
-2016-supporter-appeal.html

www/conservancy/templates/supporter/index.html

@@ -61,7 +61,8 @@
 <p><strong>Note:</strong> annual supporter is not an automatic renewal
   relationship.  If you join today, you'll receive an email in about one year to remind you to
   optionally renew.</p>
-<form id="annual" class="supporter-form" action="https://www.paypal.com/cgi-bin/webscr" method="post" name="supporter">
+<form id="annual" class="supporter-form" action="https://www.paypal.com/cgi-bin/webscr" method="post" name="supporter"
+      data-upgrade-from-amount="{{ partial_amount }}">
 <div class="supporter-form-inputs">
             <input type="hidden" name="return" value="https://sfconservancy.org/supporter/thank-you.html" />
             <input type="hidden" name="cmd" value="_xclick" />
@@ -69,7 +70,7 @@
             <input type="hidden" name="item_name" value="Conservancy Supporter, Annual" />
             <input id="no_shipping" type="hidden" name="no_shipping" value="0" />
   <label for="amount"><strong>Amount:</strong> $</label>
-  <input id="amount" type="number" name="amount" size="7" min="120" value="120" />
+  <input id="amount" type="number" name="amount" size="7" min="{{ minimum_amount }}" value="{{ minimum_amount }}" />
   <span id="error" class="form-error-show">$120 is a minimum for Conservancy
   Supporters.  <a href="/donate">Donate smaller amounts here</a>.</span><br/>