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//                   __                _      _   ________               //
//                  / /   ____  ____ _(_)____/ | / / ____/               //
//                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
//                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
//               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
//                           /____/                                      //
//                                                                       //
//               The Next Generation Logic Library                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////
//                                                                       //
//  Copyright 2015-20xx Christoph Zengler                                //
//                                                                       //
//  Licensed under the Apache License, Version 2.0 (the "License");      //
//  you may not use this file except in compliance with the License.     //
//  You may obtain a copy of the License at                              //
//                                                                       //
//  http://www.apache.org/licenses/LICENSE-2.0                           //
//                                                                       //
//  Unless required by applicable law or agreed to in writing, software  //
//  distributed under the License is distributed on an "AS IS" BASIS,    //
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
//  implied.  See the License for the specific language governing        //
//  permissions and limitations under the License.                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

package org.logicng.collections;

import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * A simple vector implementation (inspired by MiniSat, CleaneLing, Sat4J).
 * @param <T> the type of the elements
 * @version 1.0
 * @since 1.0
 */
public final class LNGVector<T> implements Iterable<T> {

    private T[] elements;
    private int size;

    /**
     * Creates a vector with an initial capacity of 5 elements.
     */
    public LNGVector() {
        this(5);
    }

    /**
     * Creates a vector with a given capacity.
     * @param size the capacity of the vector.
     */
    @SuppressWarnings("unchecked")
    public LNGVector(final int size) {
        this.elements = (T[]) new Object[size];
    }

    /**
     * Creates a vector with a given capacity and a given initial element.
     * @param size the capacity of the vector
     * @param pad  the initial element
     */
    @SuppressWarnings("unchecked")
    public LNGVector(final int size, final T pad) {
        this.elements = (T[]) new Object[size];
        Arrays.fill(this.elements, pad);
        this.size = size;
    }

    /**
     * Creates a vector with the given elements.
     * @param elems the elements
     */
    @SafeVarargs
    public LNGVector(final T... elems) {
        this.elements = Arrays.copyOf(elems, elems.length);
        this.size = elems.length;
    }

    /**
     * Creates a vector with the given elements
     * @param elems the elements
     */
    @SuppressWarnings("unchecked")
    public LNGVector(final Collection<T> elems) {
        this.elements = (T[]) new Object[elems.size()];
        int count = 0;
        for (final T e : elems) {
            this.elements[count++] = e;
        }
        this.size = elems.size();
    }

    /**
     * Returns whether the vector is empty or not.
     * @return {@code true} if the vector is empty, {@code false} otherwise
     */
    public boolean empty() {
        return this.size == 0;
    }

    /**
     * Returns the size of the vector.
     * @return the size of the vector
     */
    public int size() {
        return this.size;
    }

    /**
     * Returns the last element of the vector and leaves it on the vector.
     * @return the last element of the vector
     */
    public T back() {
        return this.elements[this.size - 1];
    }

    /**
     * Pushes an element at the end of the vector.
     * @param element the element
     */
    public void push(final T element) {
        final int newSize = this.size + 1;
        this.ensure(newSize);
        this.elements[this.size++] = element;
    }

    /**
     * Pushes an element and assumes that there is enough space on the vector.
     * @param element the element to push
     * @throws ArrayIndexOutOfBoundsException if there was not enough space on the vector
     */
    public void unsafePush(final T element) {
        this.elements[this.size++] = element;
    }

    /**
     * Returns the element at a given position in the vector.
     * @param position the position
     * @return the element at the position
     * @throws ArrayIndexOutOfBoundsException if the position is not found in the vector
     */
    public T get(final int position) {
        return this.elements[position];
    }

    /**
     * Sets an element at a given position in the vector.
     * @param position the position
     * @param element  the element
     * @throws ArrayIndexOutOfBoundsException if the position is not found in the vector
     */
    public void set(final int position, final T element) {
        this.elements[position] = element;
    }

    /**
     * Removes the last element of the vector.
     */
    public void pop() {
        this.elements[--this.size] = null;
    }

    /**
     * Shrinks the vector to a given size if the new size is less than the current size.  Otherwise, the size remains
     * the same.
     * @param newSize the new size
     */
    public void shrinkTo(final int newSize) {
        if (newSize < this.size) {
            for (int i = this.size; i > newSize; i--) {
                this.elements[i - 1] = null;
            }
            this.size = newSize;
        }
    }

    /**
     * Grows the vector to a new size and initializes the new elements with a given value.
     * @param size the new size
     * @param pad  the value for new elements
     */
    public void growTo(final int size, final T pad) {
        if (this.size >= size) {
            return;
        }
        this.ensure(size);
        for (int i = this.size; i < size; i++) {
            this.elements[i] = pad;
        }
        this.size = size;
    }

    /**
     * Grows the vector to a new size and initializes the new elements with {@code null}.
     * @param size the new size
     */
    public void growTo(final int size) {
        if (this.size >= size) {
            return;
        }
        this.ensure(size);
        this.size = size;
    }

    /**
     * Removes a given number of elements from the vector.
     * @param num the number of elements to remove.
     * @throws ArrayIndexOutOfBoundsException if the number of elements to remove is larger than the size of the vector
     */
    public void removeElements(final int num) {
        int n = num;
        while (n-- > 0) {
            this.elements[--this.size] = null;
        }
    }

    /**
     * Removes the first occurrence of a given element from the vector (the element is compared by {@code equals}).
     * @param element the element to remove
     * @return {@code true} if the element was removed, {@code false} if the element was not in the vector
     */
    public boolean remove(final T element) {
        for (int i = 0; i < this.size; i++) {
            if (this.elements[i].equals(element)) {
                System.arraycopy(this.elements, i + 1, this.elements, i, this.size - (i + 1));
                this.size--;
                return true;
            }
        }
        return false;
    }

    /**
     * Replaces the contents of this vector with the contents of another vector in-place.
     * @param other the other vector
     * @throws IllegalArgumentException if you try to replace a vector with itself
     */
    @SuppressWarnings("unchecked")
    public void replaceInplace(final LNGVector<? extends T> other) {
        if (this == other) {
            throw new IllegalArgumentException("cannot replace a vector in-place with itself");
        }
        this.elements = (T[]) new Object[other.size()];
        for (int i = 0; i < other.size(); i++) {
            this.elements[i] = other.get(i);
        }
        this.size = other.size;
    }

    /**
     * Clears the vector.  This method only sets the size to 0.  The elements are not nulled out.
     * Use {@link #release()} for this purpose.
     */
    public void clear() {
        this.size = 0;
    }

    /**
     * Clears the vector and sets all elements to {@code null}.
     */
    public void release() {
        Arrays.fill(this.elements, null);
        this.size = 0;
    }

    /**
     * Sorts this vector with a given comparator (with JDK sorting).
     * @param comparator the comparator
     */
    public void sort(final Comparator<T> comparator) {
        Arrays.sort(this.elements, 0, this.size, comparator);
    }

    /**
     * Sorts this vector with a given comparator (with manual implemented merge sort).  This method is required for
     * sorting clauses based on activity, since not all requirements of the JDK sorting are met.
     * @param comparator the comparator
     */
    public void manualSort(final Comparator<T> comparator) {
        this.sort(this.elements, 0, this.size, comparator);
    }

    /**
     * Selection sort implementation for a given array.
     * @param array the array
     * @param start the start index for sorting
     * @param end   the end index for sorting
     * @param lt    the comparator for elements of the array
     */
    private void selectionSort(final T[] array, final int start, final int end, final Comparator<T> lt) {
        int i;
        int j;
        int bestI;
        T tmp;
        for (i = start; i < end; i++) {
            bestI = i;
            for (j = i + 1; j < end; j++) {
                if (lt.compare(array[j], array[bestI]) < 0) {
                    bestI = j;
                }
            }
            tmp = array[i];
            array[i] = array[bestI];
            array[bestI] = tmp;
        }
    }

    /**
     * Merge sort implementation for a given array.
     * @param array the array
     * @param start the start index for sorting
     * @param end   the end index for sorting
     * @param lt    the comparator for elements of the array
     */
    private void sort(final T[] array, final int start, final int end, final Comparator<T> lt) {
        if (start == end) {
            return;
        }
        if ((end - start) <= 15) {
            this.selectionSort(array, start, end, lt);
        } else {
            final T pivot = array[start + ((end - start) / 2)];
            T tmp;
            int i = start - 1;
            int j = end;
            while (true) {
                do {
                    i++;
                }
                while (lt.compare(array[i], pivot) < 0);
                do {
                    j--;
                }
                while (lt.compare(pivot, array[j]) < 0);
                if (i >= j) {
                    break;
                }
                tmp = array[i];
                array[i] = array[j];
                array[j] = tmp;
            }
            this.sort(array, start, i, lt);
            this.sort(array, i, end, lt);
        }
    }

    /**
     * Sorts this vector in reverse order.
     * @param comparator the comparator
     */
    public void sortReverse(final Comparator<T> comparator) {
        this.sort(comparator);
        for (int i = 0; i < this.size / 2; i++) {
            final T temp = this.elements[i];
            this.elements[i] = this.elements[this.size - i - 1];
            this.elements[this.size - i - 1] = temp;
        }
    }

    /**
     * Ensures that this vector has the given size.  If not - the size is doubled and the old elements are copied.
     * @param newSize the size to ensure
     */
    @SuppressWarnings("unchecked")
    private void ensure(final int newSize) {
        if (newSize >= this.elements.length) {
            final T[] newArray = (T[]) new Object[Math.max(newSize, this.size * 2)];
            System.arraycopy(this.elements, 0, newArray, 0, this.size);
            this.elements = newArray;
        }
    }

    @Override
    public Iterator<T> iterator() {
        return new Iterator<T>() {
            private int i;

            @Override
            public boolean hasNext() {
                return i < size;
            }

            @Override
            public T next() {
                if (i == size) {
                    throw new NoSuchElementException();
                }
                return elements[i++];
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder("[");
        for (int i = 0; i < this.size; i++) {
            sb.append(this.elements[i]);
            if (i != this.size - 1) {
                sb.append(", ");
            }
        }
        sb.append("]");
        return sb.toString();
    }
}
