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package jsonvalues;


import java.util.Optional;

import static java.util.Objects.requireNonNull;

/**
 represents the index of a value in an json array.
 */
public final class Index implements Position {

    /**
     prism between the sum type Position and Index
     */
    public static final Prism prism = new Prism<>(
            pos -> pos.isIndex() ?
                   Optional.of(pos.asIndex().n) :
                   Optional.empty(),
            Index::of
    );

    /**
     The index number.
     */
    public final int n;

    private Index(final int n) {
        this.n = n;
    }

    /**
     Returns a new instance witch represents the given index in an array. The special index -1
     points to the last element of an array.

     @param index the given position
     @return an Index object
     @throws IndexOutOfBoundsException if the index is less than -1
     */
    public static Index of(final int index) {
        if (index < -1) throw new IndexOutOfBoundsException(String.format("%s is not between [-1,U+221E)",
                                                                          index
                                                                         ));
        return new Index(index);
    }

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

     @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)
                .isIndex()) return Integer.compare(n,
                                                   o.asIndex().n
                                                  );
        return toString().compareTo(o.asKey().name);
    }

    /**
     throws an UserError exception.

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

    /**
     Returns this index.

     @return this object
     */
    @Override
    public Index asIndex() {
        return this;
    }

    /**
     Returns true.

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

    /**
     Returns false.

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

    /**
     Returns the hashcode of this index.

     @return the index value
     */
    @Override
    public int hashCode() {
        return n;
    }

    /**
     Returns true if that is an index and both have the same value.

     @param that other object
     @return true if both objects are indexes representing the same position
     */
    @Override
    public boolean equals(final Object that) {
        if (that == null || getClass() != that.getClass()) return false;
        if (this == that) return true;
        final Index thatObj = (Index) that;
        return n == thatObj.n;
    }

    /**
     Returns the value of the index as a string.

     @return the value of the index as a string
     */
    @Override
    public String toString() {
        return String.valueOf(n);
    }
}