Add self-updater for github builds

mastodon/src/main/java/org/joinmastodon/android/updater/GithubSelfUpdater.java

@@ -0,0 +1,54 @@
+package org.joinmastodon.android.updater;
+
+import android.app.Activity;
+import android.content.Intent;
+
+import org.joinmastodon.android.BuildConfig;
+
+public abstract class GithubSelfUpdater{
+	private static GithubSelfUpdater instance;
+
+	public static GithubSelfUpdater getInstance(){
+		if(instance==null){
+			try{
+				Class<?> c=Class.forName("org.joinmastodon.android.updater.GithubSelfUpdaterImpl");
+				instance=(GithubSelfUpdater) c.newInstance();
+			}catch(IllegalAccessException|InstantiationException|ClassNotFoundException ignored){
+			}
+		}
+		return instance;
+	}
+
+	public static boolean needSelfUpdating(){
+		return BuildConfig.BUILD_TYPE.equals("githubRelease");
+	}
+
+	public abstract void maybeCheckForUpdates();
+
+	public abstract GithubSelfUpdater.UpdateState getState();
+
+	public abstract GithubSelfUpdater.UpdateInfo getUpdateInfo();
+
+	public abstract void downloadUpdate();
+
+	public abstract void installUpdate(Activity activity);
+
+	public abstract float getDownloadProgress();
+
+	public abstract void cancelDownload();
+
+	public abstract void handleIntentFromInstaller(Intent intent, Activity activity);
+
+	public enum UpdateState{
+		NO_UPDATE,
+		CHECKING,
+		UPDATE_AVAILABLE,
+		DOWNLOADING,
+		DOWNLOADED
+	}
+
+	public static class UpdateInfo{
+		public String version;
+		public long size;
+	}
+}