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package org.javimmutable.collections.indexed;

import org.javimmutable.collections.Indexed;

import javax.annotation.Nonnull;
import java.util.ArrayList;
import java.util.List;

/**
 * Provides a number of static utility methods for producing Indexed objects
 * from raw values.  Useful when you need an Indexed but don't have or want
 * to create an array just to get an Indexed of them.
 */
public class IndexedHelper
{
    private IndexedHelper()
    {
    }

    @Nonnull
    public static  Indexed empty()
    {
        return new Indexed()
        {
            @Override
            public T get(int index)
            {
                throw new ArrayIndexOutOfBoundsException();
            }

            @Override
            public int size()
            {
                return 0;
            }
        };
    }

    /**
     * Returns an Indexed containing a single value.
     * Note that the type of the Indexed may be a subclass of the type of the value.
     */
    @Nonnull
    public static  Indexed indexed(V a)
    {
        return new Indexed()
        {
            @Override
            public T get(int index)
            {
                switch (index) {
                case 0:
                    return a;
                default:
                    throw new ArrayIndexOutOfBoundsException();
                }
            }

            @Override
            public int size()
            {
                return 1;
            }
        };
    }

    /**
     * Returns an Indexed containing two values.
     * Note that the type of the Indexed may be a subclass of the type of the value.
     */
    @Nonnull
    public static  Indexed indexed(V a,
                                                      V b)
    {
        return new Indexed()
        {
            @Override
            public T get(int index)
            {
                switch (index) {
                case 0:
                    return a;
                case 1:
                    return b;
                default:
                    throw new ArrayIndexOutOfBoundsException();
                }
            }

            @Override
            public int size()
            {
                return 2;
            }
        };
    }

    /**
     * Returns an Indexed containing three values.
     * Note that the type of the Indexed may be a subclass of the type of the value.
     */
    @Nonnull
    public static  Indexed indexed(V a,
                                                      V b,
                                                      V c)
    {
        return new Indexed()
        {
            @Override
            public T get(int index)
            {
                switch (index) {
                case 0:
                    return a;
                case 1:
                    return b;
                case 2:
                    return c;
                default:
                    throw new ArrayIndexOutOfBoundsException();
                }
            }

            @Override
            public int size()
            {
                return 3;
            }
        };
    }

    @Nonnull
    public static  Indexed repeating(T value,
                                           int count)
    {
        return new Indexed()
        {
            @Override
            public T get(int index)
            {
                if (index < 0 || index >= count) {
                    throw new ArrayIndexOutOfBoundsException();
                } else {
                    return value;
                }
            }

            @Override
            public int size()
            {
                return count;
            }
        };
    }

    @Nonnull
    public static Indexed range(int low,
                                         int high)
    {
        final int size = high - low + 1;
        return new Indexed()
        {
            @Override
            public Integer get(int index)
            {
                if (index < 0 || index >= size) {
                    throw new ArrayIndexOutOfBoundsException();
                }
                return low + index;
            }

            @Override
            public int size()
            {
                return size;
            }
        };
    }

    /**
     * Creates a mutable List containing all values from the Indexed.
     */
    @Nonnull
    public static  List asList(@Nonnull Indexed indexed)
    {
        final List answer = new ArrayList<>(indexed.size());
        for (int i = 0; i < indexed.size(); ++i) {
            answer.add(indexed.get(i));
        }
        return answer;
    }
}