/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.util.Comparator;

import std.traits;
debug import hunt.logging;

/**
 * A comparison function, which imposes a <i>total ordering</i> on some
 * collection of objects.  Comparators can be passed to a sort method (such
 * as {@link Collections#sort(List,Comparator) Collections.sort} or {@link
 * Arrays#sort(Object[],Comparator) Arrays.sort}) to allow precise control
 * over the sort order.  Comparators can also be used to control the order of
 * certain data structures (such as {@link SortedSet sorted sets} or {@link
 * SortedMap sorted maps}), or to provide an ordering for collections of
 * objects that don't have a {@link Comparable natural ordering}.<p>
 *
 * The ordering imposed by a comparator <tt>c</tt> on a set of elements
 * <tt>S</tt> is said to be <i>consistent with equals</i> if and only if
 * <tt>c.compare(e1, e2)==0</tt> has the same bool value as
 * <tt>e1.equals(e2)</tt> for every <tt>e1</tt> and <tt>e2</tt> in
 * <tt>S</tt>.<p>
 *
 * Caution should be exercised when using a comparator capable of imposing an
 * ordering inconsistent with equals to order a sorted set (or sorted map).
 * Suppose a sorted set (or sorted map) with an explicit comparator <tt>c</tt>
 * is used with elements (or keys) drawn from a set <tt>S</tt>.  If the
 * ordering imposed by <tt>c</tt> on <tt>S</tt> is inconsistent with equals,
 * the sorted set (or sorted map) will behave "strangely."  In particular the
 * sorted set (or sorted map) will violate the general contract for set (or
 * map), which is defined in terms of <tt>equals</tt>.<p>
 *
 * For example, suppose one adds two elements {@code a} and {@code b} such that
 * {@code (a.equals(b) && c.compare(a, b) != 0)}
 * to an empty {@code TreeSet} with comparator {@code c}.
 * The second {@code add} operation will return
 * true (and the size of the tree set will increase) because {@code a} and
 * {@code b} are not equivalent from the tree set's perspective, even though
 * this is contrary to the specification of the
 * {@link Set#add Set.add} method.<p>
 *
 * Note: It is generally a good idea for comparators to also implement
 * <tt>java.io.Serializable</tt>, as they may be used as ordering methods in
 * serializable data structures (like {@link TreeSet}, {@link TreeMap}).  In
 * order for the data structure to serialize successfully, the comparator (if
 * provided) must implement <tt>Serializable</tt>.<p>
 *
 * For the mathematically inclined, the <i>relation</i> that defines the
 * <i>imposed ordering</i> that a given comparator <tt>c</tt> imposes on a
 * given set of objects <tt>S</tt> is:<pre>
 *       {(x, y) such that c.compare(x, y) &lt;= 0}.
 * </pre> The <i>quotient</i> for this total order is:<pre>
 *       {(x, y) such that c.compare(x, y) == 0}.
 * </pre>
 *
 * It follows immediately from the contract for <tt>compare</tt> that the
 * quotient is an <i>equivalence relation</i> on <tt>S</tt>, and that the
 * imposed ordering is a <i>total order</i> on <tt>S</tt>.  When we say that
 * the ordering imposed by <tt>c</tt> on <tt>S</tt> is <i>consistent with
 * equals</i>, we mean that the quotient for the ordering is the equivalence
 * relation defined by the objects' {@link Object#equals(Object)
 * equals(Object)} method(s):<pre>
 *     {(x, y) such that x.equals(y)}. </pre>
 *
 * <p>Unlike {@code Comparable}, a comparator may optionally permit
 * comparison of null arguments, while maintaining the requirements for
 * an equivalence relation.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param (T) the type of objects that may be compared by this comparator
 *
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @see Comparable
 * @see java.io.Serializable
 */
interface Comparator(T) {
    /**
     * Compares its two arguments for order.  Returns a negative integer,
     * zero, or a positive integer as the first argument is less than, equal
     * to, or greater than the second.<p>
     *
     * In the foregoing description, the notation
     * <tt>sgn(</tt><i>expression</i><tt>)</tt> designates the mathematical
     * <i>signum</i> function, which is defined to return one of <tt>-1</tt>,
     * <tt>0</tt>, or <tt>1</tt> according to whether the value of
     * <i>expression</i> is negative, zero or positive.<p>
     *
     * The implementor must ensure that <tt>sgn(compare(x, y)) ==
     * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>.  (This
     * implies that <tt>compare(x, y)</tt> must throw an exception if and only
     * if <tt>compare(y, x)</tt> throws an exception.)<p>
     *
     * The implementor must also ensure that the relation is transitive:
     * <tt>((compare(x, y)&gt;0) &amp;&amp; (compare(y, z)&gt;0))</tt> implies
     * <tt>compare(x, z)&gt;0</tt>.<p>
     *
     * Finally, the implementor must ensure that <tt>compare(x, y)==0</tt>
     * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
     * <tt>z</tt>.<p>
     *
     * It is generally the case, but <i>not</i> strictly required that
     * <tt>(compare(x, y)==0) == (x.equals(y))</tt>.  Generally speaking,
     * any comparator that violates this condition should clearly indicate
     * this fact.  The recommended language is "Note: this comparator
     * imposes orderings that are inconsistent with equals."
     *
     * @param o1 the first object to be compared.
     * @param o2 the second object to be compared.
     * @return a negative integer, zero, or a positive integer as the
     *         first argument is less than, equal to, or greater than the
     *         second.
     * @throws NullPointerException if an argument is null and this
     *         comparator does not permit null arguments
     * @throws ClassCastException if the arguments' types prevent them from
     *         being compared by this comparator.
     */
    int compare(T o1, T o2) nothrow;

    // /**
    //  * Indicates whether some other object is &quot;equal to&quot; this
    //  * comparator.  This method must obey the general contract of
    //  * {@link Object#equals(Object)}.  Additionally, this method can return
    //  * <tt>true</tt> <i>only</i> if the specified object is also a comparator
    //  * and it imposes the same ordering as this comparator.  Thus,
    //  * <code>comp1.equals(comp2)</code> implies that <tt>sgn(comp1.compare(o1,
    //  * o2))==sgn(comp2.compare(o1, o2))</tt> for every object reference
    //  * <tt>o1</tt> and <tt>o2</tt>.<p>
    //  *
    //  * Note that it is <i>always</i> safe <i>not</i> to override
    //  * <tt>Object.equals(Object)</tt>.  However, overriding this method may,
    //  * in some cases, improve performance by allowing programs to determine
    //  * that two distinct comparators impose the same order.
    //  *
    //  * @param   obj   the reference object with which to compare.
    //  * @return  <code>true</code> only if the specified object is also
    //  *          a comparator and it imposes the same ordering as this
    //  *          comparator.
    //  * @see Object#equals(Object)
    //  * @see Object#hashCode()
    //  */
    // bool equals(Object obj);

    // /**
    //  * Returns a comparator that imposes the reverse ordering of this
    //  * comparator.
    //  *
    //  * @return a comparator that imposes the reverse ordering of this
    //  *         comparator.
    //  */
    // Comparator!(T) reversed() {
    //     return Collections.reverseOrder(this);
    // }

    // /**
    //  * Returns a lexicographic-order comparator with another comparator.
    //  * If this {@code Comparator} considers two elements equal, i.e.
    //  * {@code compare(a, b) == 0}, {@code other} is used to determine the order.
    //  *
    //  * <p>The returned comparator is serializable if the specified comparator
    //  * is also serializable.
    //  *
    //  * @apiNote
    //  * For example, to sort a collection of {@code string} based on the length
    //  * and then case-insensitive natural ordering, the comparator can be
    //  * composed using following code,
    //  *
    //  * <pre>{@code
    //  *     Comparator<string> cmp = Comparator.comparingInt(string::length)
    //  *             .thenComparing(string.CASE_INSENSITIVE_ORDER);
    //  * }</pre>
    //  *
    //  * @param  other the other comparator to be used when this comparator
    //  *         compares two objects that are equal.
    //  * @return a lexicographic-order comparator composed of this and then the
    //  *         other comparator
    //  * @throws NullPointerException if the argument is null.
    //  */
    // Comparator!(T) thenComparing(Comparator<T> other) {
    //     Objects.requireNonNull(other);
    //     return (Comparator!(T) & Serializable) (c1, c2) -> {
    //         int res = compare(c1, c2);
    //         return (res != 0) ? res : other.compare(c1, c2);
    //     };
    // }

    // /**
    //  * Returns a lexicographic-order comparator with a function that
    //  * extracts a key to be compared with the given {@code Comparator}.
    //  *
    //  * @implSpec This implementation behaves as if {@code
    //  *           thenComparing(comparing(keyExtractor, cmp))}.
    //  *
    //  * @param  !(U)  the type of the sort key
    //  * @param  keyExtractor the function used to extract the sort key
    //  * @param  keyComparator the {@code Comparator} used to compare the sort key
    //  * @return a lexicographic-order comparator composed of this comparator
    //  *         and then comparing on the key extracted by the keyExtractor function
    //  * @throws NullPointerException if either argument is null.
    //  * @see #comparing(Function, Comparator)
    //  * @see #thenComparing(Comparator)
    //  */
    // !(U) Comparator!(T) thenComparing(
    //         Function<T, U> keyExtractor,
    //         Comparator<U> keyComparator)
    // {
    //     return thenComparing(comparing(keyExtractor, keyComparator));
    // }

    // /**
    //  * Returns a lexicographic-order comparator with a function that
    //  * extracts a {@code Comparable} sort key.
    //  *
    //  * @implSpec This implementation behaves as if {@code
    //  *           thenComparing(comparing(keyExtractor))}.
    //  *
    //  * @param  !(U)  the type of the {@link Comparable} sort key
    //  * @param  keyExtractor the function used to extract the {@link
    //  *         Comparable} sort key
    //  * @return a lexicographic-order comparator composed of this and then the
    //  *         {@link Comparable} sort key.
    //  * @throws NullPointerException if the argument is null.
    //  * @see #comparing(Function)
    //  * @see #thenComparing(Comparator)
    //  */
    // <U extends Comparable<U>> Comparator!(T) thenComparing(
    //         Function<T, U> keyExtractor)
    // {
    //     return thenComparing(comparing(keyExtractor));
    // }

    // /**
    //  * Returns a lexicographic-order comparator with a function that
    //  * extracts a {@code int} sort key.
    //  *
    //  * @implSpec This implementation behaves as if {@code
    //  *           thenComparing(comparingInt(keyExtractor))}.
    //  *
    //  * @param  keyExtractor the function used to extract the integer sort key
    //  * @return a lexicographic-order comparator composed of this and then the
    //  *         {@code int} sort key
    //  * @throws NullPointerException if the argument is null.
    //  * @see #comparingInt(ToIntFunction)
    //  * @see #thenComparing(Comparator)
    //  */
    // Comparator!(T) thenComparingInt(ToIntFunction<T> keyExtractor) {
    //     return thenComparing(comparingInt(keyExtractor));
    // }

    // /**
    //  * Returns a lexicographic-order comparator with a function that
    //  * extracts a {@code long} sort key.
    //  *
    //  * @implSpec This implementation behaves as if {@code
    //  *           thenComparing(comparingLong(keyExtractor))}.
    //  *
    //  * @param  keyExtractor the function used to extract the long sort key
    //  * @return a lexicographic-order comparator composed of this and then the
    //  *         {@code long} sort key
    //  * @throws NullPointerException if the argument is null.
    //  * @see #comparingLong(ToLongFunction)
    //  * @see #thenComparing(Comparator)
    //  */
    // Comparator!(T) thenComparingLong(ToLongFunction<T> keyExtractor) {
    //     return thenComparing(comparingLong(keyExtractor));
    // }

    // /**
    //  * Returns a lexicographic-order comparator with a function that
    //  * extracts a {@code double} sort key.
    //  *
    //  * @implSpec This implementation behaves as if {@code
    //  *           thenComparing(comparingDouble(keyExtractor))}.
    //  *
    //  * @param  keyExtractor the function used to extract the double sort key
    //  * @return a lexicographic-order comparator composed of this and then the
    //  *         {@code double} sort key
    //  * @throws NullPointerException if the argument is null.
    //  * @see #comparingDouble(ToDoubleFunction)
    //  * @see #thenComparing(Comparator)
    //  */
    // Comparator!(T) thenComparingDouble(ToDoubleFunction<T> keyExtractor) {
    //     return thenComparing(comparingDouble(keyExtractor));
    // }

    // /**
    //  * Returns a comparator that imposes the reverse of the <em>natural
    //  * ordering</em>.
    //  *
    //  * <p>The returned comparator is serializable and throws {@link
    //  * NullPointerException} when comparing {@code null}.
    //  *
    //  * @param  !(T) the {@link Comparable} type of element to be compared
    //  * @return a comparator that imposes the reverse of the <i>natural
    //  *         ordering</i> on {@code Comparable} objects.
    //  * @see Comparable
    //  */
    // static <T extends Comparable<T>> Comparator!(T) reverseOrder() {
    //     return Collections.reverseOrder();
    // }

    // /**
    //  * Returns a comparator that compares {@link Comparable} objects in natural
    //  * order.
    //  *
    //  * <p>The returned comparator is serializable and throws {@link
    //  * NullPointerException} when comparing {@code null}.
    //  *
    //  * @param  !(T) the {@link Comparable} type of element to be compared
    //  * @return a comparator that imposes the <i>natural ordering</i> on {@code
    //  *         Comparable} objects.
    //  * @see Comparable
    //  */
    // @SuppressWarnings("unchecked")
    // static <T extends Comparable<T>> Comparator!(T) naturalOrder() {
    //     return (Comparator!(T)) Comparators.NaturalOrderComparator.INSTANCE;
    // }

    // /**
    //  * Returns a null-friendly comparator that considers {@code null} to be
    //  * less than non-null. When both are {@code null}, they are considered
    //  * equal. If both are non-null, the specified {@code Comparator} is used
    //  * to determine the order. If the specified comparator is {@code null},
    //  * then the returned comparator considers all non-null values to be equal.
    //  *
    //  * <p>The returned comparator is serializable if the specified comparator
    //  * is serializable.
    //  *
    //  * @param  !(T) the type of the elements to be compared
    //  * @param  comparator a {@code Comparator} for comparing non-null values
    //  * @return a comparator that considers {@code null} to be less than
    //  *         non-null, and compares non-null objects with the supplied
    //  *         {@code Comparator}.
    //  */
    // static !(T) Comparator!(T) nullsFirst(Comparator<T> comparator) {
    //     return new Comparators.NullComparator<>(true, comparator);
    // }

    // /**
    //  * Returns a null-friendly comparator that considers {@code null} to be
    //  * greater than non-null. When both are {@code null}, they are considered
    //  * equal. If both are non-null, the specified {@code Comparator} is used
    //  * to determine the order. If the specified comparator is {@code null},
    //  * then the returned comparator considers all non-null values to be equal.
    //  *
    //  * <p>The returned comparator is serializable if the specified comparator
    //  * is serializable.
    //  *
    //  * @param  !(T) the type of the elements to be compared
    //  * @param  comparator a {@code Comparator} for comparing non-null values
    //  * @return a comparator that considers {@code null} to be greater than
    //  *         non-null, and compares non-null objects with the supplied
    //  *         {@code Comparator}.
    //  */
    // static !(T) Comparator!(T) nullsLast(Comparator<T> comparator) {
    //     return new Comparators.NullComparator<>(false, comparator);
    // }

    // /**
    //  * Accepts a function that extracts a sort key from a type {@code T}, and
    //  * returns a {@code Comparator!(T)} that compares by that sort key using
    //  * the specified {@link Comparator}.
    //   *
    //  * <p>The returned comparator is serializable if the specified function
    //  * and comparator are both serializable.
    //  *
    //  * @apiNote
    //  * For example, to obtain a {@code Comparator} that compares {@code
    //  * Person} objects by their last name ignoring case differences,
    //  *
    //  * <pre>{@code
    //  *     Comparator<Person> cmp = Comparator.comparing(
    //  *             Person::getLastName,
    //  *             string.CASE_INSENSITIVE_ORDER);
    //  * }</pre>
    //  *
    //  * @param  !(T) the type of element to be compared
    //  * @param  !(U) the type of the sort key
    //  * @param  keyExtractor the function used to extract the sort key
    //  * @param  keyComparator the {@code Comparator} used to compare the sort key
    //  * @return a comparator that compares by an extracted key using the
    //  *         specified {@code Comparator}
    //  * @throws NullPointerException if either argument is null
    //  */
    // static <T, U> Comparator!(T) comparing(
    //         Function<T, U> keyExtractor,
    //         Comparator<U> keyComparator)
    // {
    //     Objects.requireNonNull(keyExtractor);
    //     Objects.requireNonNull(keyComparator);
    //     return (Comparator!(T) & Serializable)
    //         (c1, c2) -> keyComparator.compare(keyExtractor.apply(c1),
    //                                           keyExtractor.apply(c2));
    // }

    // /**
    //  * Accepts a function that extracts a {@link java.lang.Comparable
    //  * Comparable} sort key from a type {@code T}, and returns a {@code
    //  * Comparator!(T)} that compares by that sort key.
    //  *
    //  * <p>The returned comparator is serializable if the specified function
    //  * is also serializable.
    //  *
    //  * @apiNote
    //  * For example, to obtain a {@code Comparator} that compares {@code
    //  * Person} objects by their last name,
    //  *
    //  * <pre>{@code
    //  *     Comparator<Person> byLastName = Comparator.comparing(Person::getLastName);
    //  * }</pre>
    //  *
    //  * @param  !(T) the type of element to be compared
    //  * @param  !(U) the type of the {@code Comparable} sort key
    //  * @param  keyExtractor the function used to extract the {@link
    //  *         Comparable} sort key
    //  * @return a comparator that compares by an extracted key
    //  * @throws NullPointerException if the argument is null
    //  */
    // static <T, U extends Comparable<U>> Comparator!(T) comparing(
    //         Function<T, U> keyExtractor)
    // {
    //     Objects.requireNonNull(keyExtractor);
    //     return (Comparator!(T) & Serializable)
    //         (c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
    // }

    // /**
    //  * Accepts a function that extracts an {@code int} sort key from a type
    //  * {@code T}, and returns a {@code Comparator!(T)} that compares by that
    //  * sort key.
    //  *
    //  * <p>The returned comparator is serializable if the specified function
    //  * is also serializable.
    //  *
    //  * @param  !(T) the type of element to be compared
    //  * @param  keyExtractor the function used to extract the integer sort key
    //  * @return a comparator that compares by an extracted key
    //  * @see #comparing(Function)
    //  * @throws NullPointerException if the argument is null
    //  */
    // static !(T) Comparator!(T) comparingInt(ToIntFunction<T> keyExtractor) {
    //     Objects.requireNonNull(keyExtractor);
    //     return (Comparator!(T) & Serializable)
    //         (c1, c2) -> Integer.compare(keyExtractor.applyAsInt(c1), keyExtractor.applyAsInt(c2));
    // }

    // /**
    //  * Accepts a function that extracts a {@code long} sort key from a type
    //  * {@code T}, and returns a {@code Comparator!(T)} that compares by that
    //  * sort key.
    //  *
    //  * <p>The returned comparator is serializable if the specified function is
    //  * also serializable.
    //  *
    //  * @param  !(T) the type of element to be compared
    //  * @param  keyExtractor the function used to extract the long sort key
    //  * @return a comparator that compares by an extracted key
    //  * @see #comparing(Function)
    //  * @throws NullPointerException if the argument is null
    //  */
    // static !(T) Comparator!(T) comparingLong(ToLongFunction<T> keyExtractor) {
    //     Objects.requireNonNull(keyExtractor);
    //     return (Comparator!(T) & Serializable)
    //         (c1, c2) -> Long.compare(keyExtractor.applyAsLong(c1), keyExtractor.applyAsLong(c2));
    // }

    // /**
    //  * Accepts a function that extracts a {@code double} sort key from a type
    //  * {@code T}, and returns a {@code Comparator!(T)} that compares by that
    //  * sort key.
    //  *
    //  * <p>The returned comparator is serializable if the specified function
    //  * is also serializable.
    //  *
    //  * @param  !(T) the type of element to be compared
    //  * @param  keyExtractor the function used to extract the double sort key
    //  * @return a comparator that compares by an extracted key
    //  * @see #comparing(Function)
    //  * @throws NullPointerException if the argument is null
    //  */
    // static!(T) Comparator!(T) comparingDouble(ToDoubleFunction<T> keyExtractor) {
    //     Objects.requireNonNull(keyExtractor);
    //     return (Comparator!(T) & Serializable)
    //         (c1, c2) -> Double.compare(keyExtractor.applyAsDouble(c1), keyExtractor.applyAsDouble(c2));
    // }
}


int compare(T)(T x, T y) nothrow if(isOrderingComparable!(T)) {
    try {
        return (x < y) ? -1 : ((x == y) ? 0 : 1);
    } catch(Exception ex) {
        debug warning(ex.msg);
        return 0;
    }
}

// FIXME: Needing refactor or cleanup -@zxp at 12/30/2018, 9:43:22 AM
// opCmp in a class, struct or interface should be nothrow.
bool lessThan(T)(ref T a, ref T b) nothrow if(isOrderingComparable!(T)) {
    try {
        return a < b;
    } catch(Exception ex) {
        debug warning(ex.msg);
        return false;
    }
}

bool greaterthan(T)(ref T a, ref T b) nothrow if(isOrderingComparable!(T)) {
    try {
        return a > b;
    } catch(Exception ex) {
        debug warning(ex.msg);
        return false;
    }
}