chore: compact gem stat config with shared bands

src/main/java/net/tfminecraft/geminfusion/ConfigLoader.java

@@ -65,14 +65,9 @@ public Gemstone getGemFromConfig(FileConfiguration config, String key) {
 		gem.setSocketColour(config.getConfigurationSection("gems."+key).getString("socket_colour"));
 		gem.setSocketNameColour(ChatColor.valueOf(config.getConfigurationSection("gems."+key).getString("socket_name_colour").toUpperCase()));
 		gem.setMMOItem(config.getConfigurationSection("gems."+key).getString("gem"));
-		Set<String> set = config.getConfigurationSection("gems."+key+".rarities").getKeys(false);
-
-		List<String> list = new ArrayList<String>(set);
-		for(String id : list) {
-			GemStat stat = GemStat.parse(key, id, config.getConfigurationSection("gems."+key+".rarities."+id));
-			if (stat != null) {
-				gem.addStat(stat);
-			}
+		for (GemStat stat : GemStat.parseGem(key, config.getConfigurationSection("gems."+key),
+				GemStat.ownSection(config, "stat-bands"))) {
+			gem.addStat(stat);
 		}
 		return gem;
 	}

src/main/java/net/tfminecraft/geminfusion/GemStat.java

@@ -1,11 +1,17 @@
 package net.tfminecraft.geminfusion;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.logging.Logger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import org.bukkit.configuration.ConfigurationSection;
 
 public class GemStat {
+	/** {@code min-max}, or one number for a fixed stat. */
+	private static final Pattern RANGE = Pattern.compile("(\\d+(?:\\.\\d+)?)(?:\\s*-\\s*(\\d+(?:\\.\\d+)?))?");
+
 	private final String id;
 	private final String statId;
 	private final double min;
@@ -35,7 +41,70 @@ public double getMax() {
 	}
 
 	/**
-	 * New shape: {@code stat} / {@code min} / {@code max}.
+	 * Reads a gem's stat for each rarity. Compact shape: one {@code stat} for the gem and {@code bands}, either the
+	 * name of a set under the top-level {@code stat-bands} or a section of {@code <rarity>: min-max}. Older configs
+	 * list {@code rarities.<rarity>} blocks instead (see {@link #parse}), which still load.
+	 * Only keys written in this config count: Bukkit falls back to the bundled config.yml for missing keys, which
+	 * would hand an older server config the bundled bands (or empty sections made from them).
+	 */
+	public static List<GemStat> parseGem(String gemId, ConfigurationSection gem, ConfigurationSection statBands) {
+		List<GemStat> stats = new ArrayList<>();
+		Object bandsValue = gem.get("bands", null);
+		if (bandsValue != null) {
+			if (gem.get("rarities", null) != null) {
+				warn("Gem '" + gemId + "' has both bands and rarities; using bands.");
+			}
+			String statId = gem.getString("stat", null);
+			if (statId == null || statId.isBlank()) {
+				warn("Gem '" + gemId + "' has bands but no stat, skipping its stats.");
+				return stats;
+			}
+			ConfigurationSection bands = bandsValue instanceof ConfigurationSection own ? own
+					: ownSection(statBands, String.valueOf(bandsValue));
+			if (bands == null) {
+				warn("Gem '" + gemId + "' uses unknown stat-bands set '" + bandsValue + "', skipping its stats.");
+				return stats;
+			}
+			for (String rarityId : bands.getKeys(false)) {
+				GemStat stat = parseRange(gemId, rarityId, statId, bands.getString(rarityId, null));
+				if (stat != null) {
+					stats.add(stat);
+				}
+			}
+			return stats;
+		}
+		ConfigurationSection rarities = ownSection(gem, "rarities");
+		if (rarities == null) {
+			warn("Gem '" + gemId + "' has neither bands nor rarities, skipping its stats.");
+			return stats;
+		}
+		for (String rarityId : rarities.getKeys(false)) {
+			GemStat stat = parse(gemId, rarityId, rarities.getConfigurationSection(rarityId));
+			if (stat != null) {
+				stats.add(stat);
+			}
+		}
+		return stats;
+	}
+
+	/** The section written at this key of this config, ignoring the bundled defaults; null when there is none. */
+	static ConfigurationSection ownSection(ConfigurationSection parent, String key) {
+		return parent != null && parent.get(key, null) instanceof ConfigurationSection own ? own : null;
+	}
+
+	private static GemStat parseRange(String gemId, String rarityId, String statId, String text) {
+		Matcher range = RANGE.matcher(String.valueOf(text).trim());
+		if (!range.matches()) {
+			warn("Gem '" + gemId + "' " + rarityId + " band '" + text + "' is not min-max, skipping.");
+			return null;
+		}
+		double min = Double.parseDouble(range.group(1));
+		double max = range.group(2) == null ? min : Double.parseDouble(range.group(2));
+		return new GemStat(rarityId, statId, min, max);
+	}
+
+	/**
+	 * Old per-rarity shape: {@code stat} / {@code min} / {@code max}.
 	 * Legacy: first entry of {@code stats: - type(min-max)}.
 	 * Returns null when the block cannot be used.
 	 */