Fix prefix path of the header link

Author: takezoe

src/main/scala/Plugin.scala

@@ -1,22 +1,25 @@
+import gitbucket.core.service.SystemSettingsService
 import gitbucket.gist.controller.GistController
 import gitbucket.core.plugin.PluginRegistry
 import gitbucket.core.util.Version
 import java.io.File
 import javax.servlet.ServletContext
 import gitbucket.gist.util.Configurations._
 
-class Plugin extends gitbucket.core.plugin.Plugin {
+class Plugin extends gitbucket.core.plugin.Plugin with SystemSettingsService {
   override val pluginId: String = "gist"
   override val pluginName: String = "Gist Plugin"
   override val description: String = "Provides Gist feature on GitBucket."
   override val versions: List[Version] = List(Version(1, 0))
 
   override def initialize(registry: PluginRegistry, context: ServletContext): Unit = {
     // Add Snippet link to the header
+    val settings = loadSystemSettings()
+    val path = settings.baseUrl.getOrElse(context.getContextPath)
     registry.addJavaScript(".*",
       s"""
         |$$('a.brand').after(
-        |  $$('<span style="float: left; margin-top: 10px;">|&nbsp;&nbsp;&nbsp;&nbsp;<a href="${context.getContextPath}/gist" style="color: black;">Snippet</a></span>')
+        |  $$('<span style="float: left; margin-top: 10px;">|&nbsp;&nbsp;&nbsp;&nbsp;<a href="${path}/gist" style="color: black;">Snippet</a></span>')
         |);
       """.stripMargin)