Adds update warnings (URL needs to be updated once Spigot resource is created)

src/main/java/net/knarcraft/permissionsigns/PermissionSigns.java

@@ -13,6 +13,7 @@ import net.knarcraft.permissionsigns.manager.PermissionManager;
 import net.knarcraft.permissionsigns.manager.SignManager;
 import net.knarcraft.permissionsigns.thread.PermissionTimeoutThread;
 import net.knarcraft.permissionsigns.thread.SignCreationRequestTimeoutThread;
+import net.knarcraft.permissionsigns.utility.UpdateChecker;
 import net.milkbowl.vault.economy.Economy;
 import net.milkbowl.vault.permission.Permission;
 import org.bukkit.Bukkit;
@@ -145,8 +146,6 @@ public final class PermissionSigns extends JavaPlugin {
         PluginDescriptionFile pluginDescriptionFile = this.getDescription();
         pluginVersion = pluginDescriptionFile.getVersion();
 
-        //TODO: Display a notice in the console if a new version is available (requires Spigot resource first)
-
         //Load config and write the default config if necessary
         FileConfiguration config = this.getConfig();
         config.options().copyDefaults(true);
@@ -159,6 +158,8 @@ public final class PermissionSigns extends JavaPlugin {
 
         SignManager.loadSigns();
         PermissionManager.loadTemporaryPermissions();
+
+        UpdateChecker.checkForUpdate(this, "", () -> pluginVersion, null);
     }
 
     /**

src/main/java/net/knarcraft/permissionsigns/utility/FileHelper.java

@@ -25,4 +25,15 @@ public class FileHelper {
         return new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
     }
 
+    /**
+     * Gets a buffered reader given an input stream
+     *
+     * @param inputStream <p>The input stream to read</p>
+     * @return <p>A buffered reader reading the input stream</p>
+     */
+    public static BufferedReader getBufferedReaderFromInputStream(InputStream inputStream) {
+        InputStreamReader inputStreamReader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
+        return new BufferedReader(inputStreamReader);
+    }
+
 }

src/main/java/net/knarcraft/permissionsigns/utility/UpdateChecker.java

@@ -0,0 +1,92 @@
+package net.knarcraft.permissionsigns.utility;
+
+import org.bukkit.plugin.Plugin;
+import org.bukkit.scheduler.BukkitScheduler;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import java.util.logging.Level;
+
+/**
+ * The update checker is responsible for looking for new updates
+ */
+public final class UpdateChecker {
+
+    private final static String updateNotice = "A new update is available: %s (You are still on %s)";
+
+    private UpdateChecker() {
+
+    }
+
+    /**
+     * Checks if there's a new update available, and alerts the user if necessary
+     */
+    public static void checkForUpdate(Plugin plugin, String apiResourceURL, Supplier<String> getVersionMethod,
+                                      Consumer<String> setVersionMethod) {
+        BukkitScheduler scheduler = plugin.getServer().getScheduler();
+        scheduler.runTaskAsynchronously(plugin, () -> UpdateChecker.queryAPI(plugin, apiResourceURL, getVersionMethod,
+                setVersionMethod));
+    }
+
+    /**
+     * Queries the spigot API to check for a newer version, and informs the user
+     */
+    private static void queryAPI(Plugin plugin, String APIResourceURL, Supplier<String> getVersionMethod,
+                                 Consumer<String> setVersionMethod) {
+        try {
+            InputStream inputStream = new URL(APIResourceURL).openStream();
+            BufferedReader reader = FileHelper.getBufferedReaderFromInputStream(inputStream);
+            //There should only be one line of output
+            String newVersion = reader.readLine();
+            reader.close();
+
+            String oldVersion = getVersionMethod.get();
+            //If there is a newer version, notify the user
+            if (isVersionHigher(oldVersion, newVersion)) {
+                plugin.getLogger().log(Level.INFO, getUpdateAvailableString(newVersion, oldVersion));
+                if (setVersionMethod != null) {
+                    setVersionMethod.accept(newVersion);
+                }
+            }
+        } catch (IOException e) {
+            plugin.getLogger().log(Level.WARNING, "Unable to get newest version.");
+        }
+    }
+
+    /**
+     * Gets the string to display to a user to alert about a new update
+     *
+     * @param newVersion <p>The new available plugin version</p>
+     * @param oldVersion <p>The old (current) plugin version</p>
+     * @return <p>The string to display</p>
+     */
+    public static String getUpdateAvailableString(String newVersion, String oldVersion) {
+        return String.format(updateNotice, newVersion, oldVersion);
+    }
+
+    /**
+     * Decides whether one version number is higher than another
+     *
+     * @param oldVersion <p>The old version to check</p>
+     * @param newVersion <p>The new version to check</p>
+     * @return <p>True if the new version is higher than the old one</p>
+     */
+    public static boolean isVersionHigher(String oldVersion, String newVersion) {
+        String[] oldVersionParts = oldVersion.split("\\.");
+        String[] newVersionParts = newVersion.split("\\.");
+        int versionLength = Math.max(oldVersionParts.length, newVersionParts.length);
+        for (int i = 0; i < versionLength; i++) {
+            int oldVersionNumber = oldVersionParts.length > i ? Integer.parseInt(oldVersionParts[i]) : 0;
+            int newVersionNumber = newVersionParts.length > i ? Integer.parseInt(newVersionParts[i]) : 0;
+            if (newVersionNumber != oldVersionNumber) {
+                return newVersionNumber > oldVersionNumber;
+            }
+        }
+        return false;
+    }
+
+}