Add support for list entries in sign templates.

This commit adds support for listing arena players on arena signs by
introducing the following _dynamic variables_:

- `<arena-n>` the _nth_ live arena player
- `<lobby-n>` the _nth_ player in the lobby
- `<ready-n>` the _nth_ ready player in the lobby
- `<notready-n>` the _nth_ player in the lobby who hasn't readied up

Each variable points to a list of players (sorted by name), and the `n`
is the index into that list (1-indexed). This means that putting the
variable `<notready-1>` in a template will result in the name of the
first player in the list of lobby players who haven't readied up, sorted
by player name.

Implements #592

src/main/java/com/garbagemule/MobArena/signs/RendersTemplate.java

@@ -2,11 +2,25 @@ package com.garbagemule.MobArena.signs;
 
 import static java.lang.String.valueOf;
 
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+
 import com.garbagemule.MobArena.framework.Arena;
 import org.bukkit.ChatColor;
+import org.bukkit.entity.Player;
 
 class RendersTemplate {
 
+    // Regex Pattern for player list variables.
+    // Changes to the list types must also be made in getPlayerList.
+    // group(1) is the list type as a String.
+    // group(2) is player index+1 as a String.
+    private final Pattern playerListPattern = Pattern.compile("<(arena|lobby|ready|notready)-([1-9][0-9]?)>");
+
     String[] render(Template template, Arena arena) {
         String[] lines = getTemplateByState(template, arena);
 
@@ -46,7 +60,8 @@ class RendersTemplate {
     }
 
     private String running(String line, Arena arena) {
-        return line
+        String result = replacePlayerListEntry(line, arena);
+        return result
             .replace("<initial-players>", valueOf(arena.getPlayerCount()))
             .replace("<live-players>", valueOf(arena.getPlayersInArena().size()))
             .replace("<dead-players>", valueOf(arena.getPlayerCount() - arena.getPlayersInArena().size()))
@@ -57,7 +72,8 @@ class RendersTemplate {
     }
 
     private String joining(String line, Arena arena) {
-        return line
+        String result = replacePlayerListEntry(line, arena);
+        return result
             .replace("<initial-players>", valueOf(arena.getPlayersInLobby().size()))
             .replace("<live-players>", valueOf(arena.getPlayersInLobby().size()))
             .replace("<dead-players>", "-")
@@ -66,6 +82,50 @@ class RendersTemplate {
             .replace("<ready-players>", valueOf(arena.getReadyPlayersInLobby().size()));
     }
 
+    private String replacePlayerListEntry(String line, Arena arena) {
+        Matcher matcher = playerListPattern.matcher(line);
+        if (!matcher.find()) {
+            return line;
+        }
+        List<String> list = getNameList(matcher.group(1), arena);
+        int index = Integer.parseInt(matcher.group(2)) - 1;
+
+        if (index < list.size()) {
+            String value = list.get(index);
+            return matcher.replaceFirst(value);
+        } else {
+            return matcher.replaceFirst("");
+        }
+    }
+
+    private List<String> getNameList(String name, Arena arena) {
+        return getPlayerList(name, arena)
+            .stream()
+            .map(Player::getName)
+            .sorted()
+            .collect(Collectors.toList());
+    }
+
+    private Collection<Player> getPlayerList(String name, Arena arena) {
+        switch (name) {
+            case "arena": {
+                return arena.getPlayersInArena();
+            }
+            case "lobby": {
+                return arena.getPlayersInLobby();
+            }
+            case "ready": {
+                return arena.getReadyPlayersInLobby();
+            }
+            case "notready": {
+                return arena.getNonreadyPlayers();
+            }
+            default: {
+                return Collections.emptyList();
+            }
+        }
+    }
+
     private String truncate(String rendered) {
         if (rendered.length() <= 15) {
             return rendered;