Rankup3/src/main/java/sh/okx/rankup/RankList.java

package sh.okx.rankup;

import lombok.Getter;
import org.bukkit.configuration.ConfigurationSection;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.entity.Player;
import sh.okx.rankup.ranks.Rank;

import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;

public class RankList<T extends Rank> {
  @Getter
  protected final FileConfiguration config;
  protected final Set<T> ranks = new HashSet<>();

  public RankList(FileConfiguration config, Function<ConfigurationSection, T> deserializer) {
    this.config = config;
    for (Map.Entry<String, Object> entry : config.getValues(false).entrySet()) {
      ConfigurationSection rankSection = (ConfigurationSection) entry.getValue();
      ranks.add(deserializer.apply(rankSection));
    }
  }

  public T getFirst() {
    OUTER:
    for (T rank : ranks) {
      // see if anything ranks up to this
      for (T rank0 : ranks) {
        if (!rank0.isLast() && rank0.getNext().equals(rank.getName())) {
          continue OUTER;
        }
      }
      // nothing ranks up to this
      return rank;
    }
    return null;
  }

  public T getLast() {
    T t = getFirst();
    do {
      t = next(t);
    } while(!t.isLast());
    return t;
  }

  public T getByName(String name) {
    for (T rank : ranks) {
      if (rank.getName().equalsIgnoreCase(name)) {
        return rank;
      }
    }
    return null;
  }

  public T getByPlayer(Player player) {
    return ranks.stream()
        .filter(rank -> rank.isIn(player))
        .findFirst()
        .orElse(null);
  }

  public T next(T rank) {
    if (rank.isLast()) {
      return null;
    }

    for (T nextRank : ranks) {
      if (rank.getNext().equalsIgnoreCase(nextRank.getName())) {
        return nextRank;
      }
    }
    // this shouldn't happen but whatever
    return null;
  }
}