implement simplified PluginManager API

scm-webapp/src/main/java/sonia/scm/plugin/PluginCenter.java

@@ -0,0 +1,55 @@
+package sonia.scm.plugin;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import sonia.scm.SCMContextProvider;
+import sonia.scm.cache.Cache;
+import sonia.scm.cache.CacheManager;
+import sonia.scm.config.ScmConfiguration;
+import sonia.scm.util.HttpUtil;
+import sonia.scm.util.SystemUtil;
+
+import javax.inject.Inject;
+import java.util.Set;
+
+public class PluginCenter {
+
+  private static final String CACHE_NAME = "sonia.cache.plugins";
+
+  private static final Logger LOG = LoggerFactory.getLogger(PluginCenter.class);
+
+  private final SCMContextProvider context;
+  private final ScmConfiguration configuration;
+  private final PluginCenterLoader loader;
+  private final Cache<String, Set<AvailablePlugin>> cache;
+
+  @Inject
+  public PluginCenter(SCMContextProvider context, CacheManager cacheManager, ScmConfiguration configuration, PluginCenterLoader loader) {
+    this.context = context;
+    this.configuration = configuration;
+    this.loader = loader;
+    this.cache = cacheManager.getCache(CACHE_NAME);
+  }
+
+  synchronized Set<AvailablePlugin> getAvailable() {
+    String url = buildPluginUrl(configuration.getPluginUrl());
+    Set<AvailablePlugin> plugins = cache.get(url);
+    if (plugins == null) {
+      LOG.debug("no cached available plugins found, start fetching");
+      plugins = loader.load(url);
+      cache.put(url, plugins);
+    } else {
+      LOG.debug("return available plugins from cache");
+    }
+    return plugins;
+  }
+
+  private String buildPluginUrl(String url) {
+    String os = HttpUtil.encode(SystemUtil.getOS());
+    String arch = SystemUtil.getArch();
+    return url.replace("{version}", context.getVersion())
+      .replace("{os}", os)
+      .replace("{arch}", arch);
+  }
+
+}