Use fallback maven if maven.ic2.player.to is unavailable (#218)

* Use fallback maven if maven.ic2.player.to is unavailable

* Add sugested change

Co-authored-by: Raven Szewczyk <git@eigenraven.me>

* Use `content` instead of `filter`

Co-authored-by: Raven Szewczyk <git@eigenraven.me>

---------

Co-authored-by: Raven Szewczyk <git@eigenraven.me>

build.gradle

@@ -600,15 +600,10 @@ repositories {
         }
         maven {
             name = "ic2"
-            url = "https://maven.ic2.player.to/"
-            metadataSources {
-                mavenPom()
-                artifact()
+            url = getURL("https://maven.ic2.player.to/", "https://maven2.ic2.player.to/")
+            content {
+                includeGroup "net.industrial-craft"
             }
-        }
-        maven {
-            name = "ic2-mirror"
-            url = "https://maven2.ic2.player.to/"
             metadataSources {
                 mavenPom()
                 artifact()
@@ -1576,6 +1571,25 @@ def getSecondaryArtifacts() {
     return secondaryArtifacts
 }
 
+def getURL(String main, String fallback) {
+    return pingURL(main, 10000) ? main : fallback
+}
+
+// credit: https://stackoverflow.com/a/3584332
+def pingURL(String url, int timeout) {
+    url = url.replaceFirst("^https", "http") // Otherwise an exception may be thrown on invalid SSL certificates.
+    try {
+        HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection()
+        connection.setConnectTimeout(timeout)
+        connection.setReadTimeout(timeout)
+        connection.setRequestMethod("HEAD")
+        int responseCode = connection.getResponseCode()
+        return 200 <= responseCode && responseCode <= 399
+    } catch (IOException ignored) {
+        return false
+    }
+}
+
 // For easier scripting of things that require variables defined earlier in the buildscript
 if (file('addon.late.gradle.kts').exists()) {
     apply from: 'addon.late.gradle.kts'