conditionally display OsmAnd download button; template proper apk url, size into same

_scss/pages/home.scss

@@ -223,11 +223,16 @@ h1.homepage-title {
 }
 
 // Apply/Remove this class to conditionally 
-// display the card
+// display the card using main.js
 .hidden-card {
   display: none;
 }
 
+// Generic hidden class
+.hidden {
+  display: none;
+}
+
 .card-icon {
   width: 60px;
   height: 60px;

assets/js/maps.js

@@ -1,6 +1,8 @@
 // Checks to see what map files exist at /usb-butter/osm-map-files/ and displays them
 // using the template hidden in the page
 
+OSM_PACKAGE = "net.osmand";
+
 const getMaps = async (folder_href) => {
     async function populateSpan(response) {
         if (!response.ok) {
@@ -44,4 +46,28 @@ function renderMaps(files) {
     }
 }
 
+// If OSM is in the F-Droid repo, show the download button
+// and point to proper apk with proper size.
+const getOsm = async () => {
+    repoRoot = '/usb-butter/appstore/fdroid/repo/';
+    json_url = repoRoot + 'index-v1.json';
+    const response = fetch(json_url).then(async (response) => {
+        const ix = await response.json();
+        if (ix.packages && ix.packages[OSM_PACKAGE] && ix.packages[OSM_PACKAGE].length > 0) {
+            const button = document.getElementById('osm-dl-button');
+            const links = button.querySelectorAll('a');
+            const apkName = ix.packages[OSM_PACKAGE][0]['apkName'];
+            const size = ix.packages[OSM_PACKAGE][0]['size'];
+            const sizeInMB = Math.floor(size / 1024 / 1024);
+            for (let link of links) {
+                link.href = repoRoot + apkName;
+            }
+            const cta = button.querySelector('.button-sub-text');
+            cta.textContent = `${sizeInMB} MB`;
+            button.classList.remove('hidden');
+        }
+    });
+}
+
+getOsm()
 getMaps('/usb-butter/osm-map-files/');

maps/index.html

@@ -15,7 +15,7 @@ custom_scripts: ["maps.js", "butter-dir-listing.js"]
 
 <div class="step-label">{% t maps.sections.section1.step %}</div>
 <h2>{% t maps.sections.section1.title %}</h2>
-<div class="btn-container">
+<div id="osm-dl-button" class="btn-container hidden">
     {% assign apk_url = site.baseurl | append: "/fdroid/repo/net.osmand.plus_471703.apk" %}
     {% include fancybutton.html main_cta="maps.main_cta" sub_cta="maps.sub_cta" href=apk_url %}
 </div>