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package jsonvalues;


import java.util.Optional;

import static java.util.Objects.requireNonNull;

/**
 represents the key of a value in a json object
 */
public final class Key implements Position {

    /**
     prism between the sum type Position and Key
     */
    public static final Prism prism = new Prism<>(
            pos -> pos.isKey() ? Optional.of(pos.asKey().name) : Optional.empty(),
            Key::of
    );

    /**
     name of the key.
     */
    public final String name;

    private Key(final String name) {
        this.name = name;
    }

    /**
     Returns a new instance which represents a key with the given name in a json object. Any string,
     but null, can represent a key in a json object, even the empty string.

     @param key the given name of the key
     @return a new Key object
     */
    public static Key of(String key) {
        return new Key(requireNonNull(key));
    }


    /**
     compares this key with another given position. If the given position is a key, both are compared
     lexicographically, if it's an index, both are compared numerically.

     @param o the given position
     @return 0 if they are equal, +1 if this is greater, -1 otherwise
     */
    @Override
    public int compareTo(final Position o) {
        if (requireNonNull(o)
                .isKey()) return name.compareTo(o.asKey().name);
        return name.compareTo(o.asIndex()
                               .toString());

    }

    /**
     Returns this key.

     @return this object
     */
    @Override
    public Key asKey() {
        return this;
    }

    /**
     throws an UserError exception.

     @throws UserError a Key can't be casted into an Index
     */
    @Override
    public Index asIndex() {
        throw UserError.asIndexOfKey();
    }


    /**
     Returns false.

     @return false
     */
    @Override
    public boolean isIndex() {
        return false;
    }

    /**
     Returns true.

     @return true
     */
    @Override
    public boolean isKey() {
        return true;
    }

    /**
     Returns the hashcode of this key.

     @return the hashcode of the name.
     */
    @Override
    public int hashCode() {
        return name.hashCode();
    }

    /**
     Returns true if that is a key and both have the same name.

     @param that other object
     @return true if both object are Keys with the same name
     */
    @Override
    public boolean equals(final Object that) {
        if (that == null || getClass() != that.getClass()) return false;
        if (this == that) return true;
        final Key thatObj = (Key) that;
        return name.equals(thatObj.name);
    }

    /**
     Returns the name of the key.

     @return the name of the key
     */
    @Override
    public String toString() {
        return name;
    }
}