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package org.scijava.util;

import java.lang.reflect.Array;
import java.util.AbstractList;

/**
 * Abstract base class for primitive-type extensible arrays.
 * 
 * This class makes it easy to implement extensible arrays backed by fixed-size
 * primitive type arrays, re-allocating and copying data as needed. To avoid
 * frequent re-allocation, by default, the fixed-size array will be expanded by
 * 50% when running out of space.
 * 
 * 
 * @author Johannes Schindelin
 * @author Curtis Rueden
 * @param  Type of the primitive array; e.g., {@code double[]}.
 * @param  Boxed type of the array element; e.g., {@code Double}.
 */
public abstract class AbstractPrimitiveArray extends
	AbstractList implements PrimitiveArray
{

	/** The class boxing the element type. */
	private final Class type;

	/**
	 * The current size of the list.
	 * 
	 * Note that internally, the actual array length may be greater than this
	 * value. The size represents the number of actual elements in the collection.
	 * 
	 */
	private int size;

	/** The maximal growth step. */
	private int maximumGrowth = Integer.MAX_VALUE;

	/**
	 * Constructs an extensible array of primitive type elements, backed by a
	 * fixed-size array.
	 * 
	 * @param type the class of the primitive type
	 */
	public AbstractPrimitiveArray(final Class type) {
		this(type, 0);
	}

	/**
	 * Constructs an extensible array of primitive type elements, backed by a
	 * fixed-size array.
	 * 
	 * @param type the class of the primitive type
	 * @param size the initial size
	 */
	public AbstractPrimitiveArray(final Class type, final int size) {
		this.type = type;
		this.size = size;
		ensureCapacity(size);
	}

	/**
	 * Constructs an extensible array of primitive type elements, backed by the
	 * given fixed-size array.
	 * 
	 * @param array the array to wrap
	 * @param type the class of the primitive type
	 */
	public AbstractPrimitiveArray(final Class type,
		final ArrayType array)
	{
		this.type = type;
		setArray(array);
		size = capacity();
	}

	// -- PrimitiveArray methods --

	@Override
	public int getMaximumGrowth() {
		return maximumGrowth;
	}

	@Override
	public void setMaximumGrowth(final int growth) {
		if (maximumGrowth < 1) {
			throw new IllegalArgumentException("Invalid growth value: " + growth);
		}
		maximumGrowth = growth;
	}

	@Override
	public ArrayType copyArray() {
		return copyArray(size());
	}

	/** Gets the current capacity of the backing array. */
	@Override
	public int capacity() {
		final ArrayType array = getArray();
		return array == null ? 0 : Array.getLength(array);
	}

	@Override
	public void ensureCapacity(final int minCapacity) {
		final int oldCapacity = capacity();
		if (minCapacity <= oldCapacity) return; // no need to grow

		// grow the array by up to 50% (plus a small constant)
		final int growth = Math.min(oldCapacity / 2 + 16, maximumGrowth);
		final int newCapacity;
		if (growth > Integer.MAX_VALUE - oldCapacity) {
			// growth would push array over the maximum array size
			newCapacity = Integer.MAX_VALUE;
		}
		else newCapacity = oldCapacity + growth;
		// ensure the array grows by at least the requested minimum capacity
		final int newLength = Math.max(minCapacity, newCapacity);

		// copy the data into a new array
		setArray(copyArray(newLength));
	}

	/**
	 * Shifts the array to insert space at a specified index.
	 * 
	 * @param index the index where the space should be inserted
	 * @param count the number of values to insert
	 */
	@Override
	public void insert(final int index, final int count) {
		int oldSize = size();
		if (index < 0 || index > oldSize) {
			throw new ArrayIndexOutOfBoundsException("Invalid index value");
		}
		if (count > Integer.MAX_VALUE - oldSize) {
			// insertion would push array over the maximum size
			throw new IllegalArgumentException("Too many elements");
		}
		if (count <= 0) {
			throw new IllegalArgumentException("Count must be positive");
		}
		setSize(oldSize + count);
		if (index < oldSize) {
			final ArrayType array = getArray();
			System.arraycopy(array, index, array, index + count, oldSize - index);
		}
	}

	/**
	 * Shifts the array to delete space starting at a specified index.
	 * 
	 * @param index the index where the space should be deleted
	 * @param count the number of values to delete
	 */
	@Override
	public void delete(final int index, final int count) {
		int oldSize = size();
		if (index < 0 || index > oldSize) {
			throw new ArrayIndexOutOfBoundsException("Invalid index value");
		}
		if (index < 0 || index + count > oldSize) {
			throw new IllegalArgumentException("Invalid range: index=" + index +
				", count=" + count + ", size=" + oldSize);
		}
		setSize(oldSize - count);
		if (index + count < oldSize) {
			final ArrayType array = getArray();
			System.arraycopy(array, index + count, array, index, oldSize - index -
				count);
		}
	}

	// -- List methods --

	// NB: We override and declare abstract to force reimplementation.
	@Override
	public abstract BaseType set(final int index, final BaseType element);

	// NB: We override and declare abstract to force reimplementation.
	@Override
	public abstract void add(final int index, final BaseType element);

	@Override
	public BaseType remove(final int index) {
		final BaseType removed = get(index);
		delete(index, 1);
		return removed;
	}

	// -- Collection methods --

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

	// NB: Overridden for performance.
	@Override
	public void clear() {
		setSize(0);
	}

	// -- Sizable methods --

	@Override
	public void setSize(final int size) {
		ensureCapacity(size);
		this.size = size;
	}

	// -- Internal methods --

	/** Checks that the index is less than the size of the array. */
	protected void checkBounds(final int index) {
		if (index >= size()) {
			throw new ArrayIndexOutOfBoundsException("Invalid index value");
		}
	}

	// -- Helper methods --

	private ArrayType copyArray(final int newLength) {
		@SuppressWarnings("unchecked")
		final ArrayType copy = (ArrayType) Array.newInstance(type, newLength);
		final ArrayType oldArray = getArray();
		if (oldArray != null) System.arraycopy(oldArray, 0, copy, 0, size());
		return copy;
	}

}