Add placeholder to get the value of a plot flag

Bukkit/src/main/java/com/plotsquared/bukkit/placeholder/Placeholders.java

@@ -29,6 +29,8 @@ import com.plotsquared.core.PlotSquared;
 import com.plotsquared.core.configuration.Settings;
 import com.plotsquared.core.player.PlotPlayer;
 import com.plotsquared.core.plot.Plot;
+import com.plotsquared.core.plot.flag.GlobalFlagContainer;
+import com.plotsquared.core.plot.flag.PlotFlag;
 import me.clip.placeholderapi.PlaceholderAPIPlugin;
 import me.clip.placeholderapi.expansion.PlaceholderExpansion;
 import org.bukkit.Bukkit;
@@ -36,9 +38,13 @@ import org.bukkit.entity.Player;
 
 import java.util.Set;
 import java.util.UUID;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 public class Placeholders extends PlaceholderExpansion {
 
+    private Pattern flagPattern = Pattern.compile("currentplot_flag_(.+)");
+
     public Placeholders() {
     }
 
@@ -59,7 +65,7 @@ public class Placeholders extends PlaceholderExpansion {
     }
 
     @Override public String getVersion() {
-        return "2.4";
+        return "2.5";
     }
 
     @Override public String onPlaceholderRequest(Player p, String identifier) {
@@ -181,6 +187,31 @@ public class Placeholders extends PlaceholderExpansion {
             default:
                 break;
         }
+        final Matcher matcher = this.flagPattern.matcher(identifier);
+        if (matcher.find()) {
+            return getFlag(plot, matcher.group(1));
+        }
+        return "";
+    }
+
+    /**
+     * Return the flag value from its name on the current plot.
+     * If the flag doesn't exist it return an empty string.
+     * If the flag exists but it is not set on current plot it return the default value.
+     *
+     * @param plot     Current plot where the player is
+     * @param flagName Name of flag to get from current plot
+     * @return The value of flag serialized in string
+     */
+    private String getFlag(final Plot plot, final String flagName) {
+        final PlotFlag<?, ?> flag = GlobalFlagContainer.getInstance().getFlagFromString(flagName);
+        if (flag != null) {
+            return plot.getFlags().stream()
+                .filter(pflag -> pflag.getName().equals(flagName)).findFirst()
+                .map(PlotFlag::getValue)
+                .map(Object::toString)
+                .orElseGet(() -> plot.getFlagContainer().getFlagErased(flag.getClass()).toString());
+        }
         return "";
     }
 }