src/main/java/org/zwobble/hobgoblin/compiler/util/ManyToMany.java


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package org.zwobble.hobgoblin.compiler.util;

import java.util.*;

public class ManyToMany<TLeft, TRight> {
    private final Map<TLeft, List<TRight>> leftToRight = new HashMap<>();
    private final Map<TRight, List<TLeft>> rightToLeft = new HashMap<>();

    public ManyToMany() {}

    public List<TRight> leftToRight(TLeft left) {
        var rights = this.leftToRight.get(left);
        if (rights == null) {
            return List.of();
        } else {
            return Collections.unmodifiableList(rights);
        }
    }

    public List<TLeft> rightToLeft(TRight right) {
        var lefts = this.rightToLeft.get(right);
        if (lefts == null) {
            return List.of();
        } else {
            return Collections.unmodifiableList(lefts);
        }
    }

    public void add(TLeft left, TRight right) {
        this.leftToRight.putIfAbsent(left, new ArrayList<>());
        this.leftToRight.get(left).add(right);
        this.rightToLeft.putIfAbsent(right, new ArrayList<>());
        this.rightToLeft.get(right).add(left);
    }
}