src/cx/list.h

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
/**
 * @file list.h
 * @brief Interface for list implementations.
 * @author Mike Becker
 * @author Olaf Wintermann
 * @copyright 2-Clause BSD License
 */

#ifndef UCX_LIST_H
#define UCX_LIST_H

#include "common.h"
#include "collection.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * List class type.
 */
typedef struct cx_list_class_s cx_list_class;

/**
 * Structure for holding the base data of a list.
 */
struct cx_list_s {
    /**
     * Common members for collections.
     */
    CX_COLLECTION_BASE;
    /**
     * The list class definition.
     */
    const cx_list_class *cl;
    /**
     * The actual implementation in case the list class is delegating.
     */
    const cx_list_class *climpl;
};

/**
 * The class definition for arbitrary lists.
 */
struct cx_list_class_s {
    /**
     * Destructor function.
     *
     * Implementations SHALL invoke the content destructor functions if provided
     * and SHALL deallocate the entire list memory.
     */
    void (*deallocate)(struct cx_list_s *list);

    /**
     * Member function for inserting a single element.
     * The data pointer may be @c NULL, in which case the function shall only allocate memory.
     * Returns a pointer to the allocated memory or @c NULL if allocation fails.
     */
    void *(*insert_element)(struct cx_list_s *list, size_t index, const void *data);

    /**
     * Member function for inserting multiple elements.
     *
     * The data pointer may be @c NULL, in which case the function shall only allocate memory.
     * Returns the number of successfully inserted or allocated elements.
     *
     * @see cx_list_default_insert_array()
     */
    size_t (*insert_array)(struct cx_list_s *list, size_t index, const void *data, size_t n);

    /**
     * Member function for inserting sorted elements into a sorted list.
     * Returns the number of successfully inserted elements.
     *
     * @see cx_list_default_insert_sorted()
     */
    size_t (*insert_sorted)(struct cx_list_s *list, const void *sorted_data, size_t n);

    /**
     * Member function for inserting multiple elements if they do not exist.
     * Implementations shall return the number of successfully processed elements
     * (including those which were not added because they are already contained).
     * @see cx_list_default_insert_unique()
     */
    size_t (*insert_unique)(struct cx_list_s *list, const void *sorted_data, size_t n);

    /**
     * Member function for inserting an element relative to an iterator position.
     */
    int (*insert_iter)(struct cx_iterator_s *iter, const void *elem, int prepend);

    /**
     * Member function for removing elements.
     *
     * Implementations SHALL check if @p targetbuf is set and copy the elements
     * to the buffer without invoking any destructor.
     * When @p targetbuf is not set, the destructors SHALL be invoked.
     *
     * The function SHALL return the actual number of elements removed, which
     * might be lower than @p num when going out of bounds.
     */
    size_t (*remove)(struct cx_list_s *list, size_t index, size_t num, void *targetbuf);

    /**
     * Member function for removing all elements.
     */
    void (*clear)(struct cx_list_s *list);

    /**
     * Member function for swapping two elements.
     *
     * @see cx_list_default_swap()
     */
    int (*swap)(struct cx_list_s *list, size_t i, size_t j);

    /**
     * Member function for element lookup.
     */
    void *(*at)(const struct cx_list_s *list, size_t index);

    /**
     * Member function for finding and optionally removing an element.
     */
    size_t (*find_remove)(struct cx_list_s *list, const void *elem, bool remove);

    /**
     * Member function for sorting the list.
     *
     * @see cx_list_default_sort()
     */
    void (*sort)(struct cx_list_s *list);

    /**
     * Optional member function for comparing this list
     * to another list of the same type.
     * If set to @c NULL, the comparison won't be optimized.
     */
    int (*compare)(const struct cx_list_s *list, const struct cx_list_s *other);

    /**
     * Member function for reversing the order of the items.
     */
    void (*reverse)(struct cx_list_s *list);

    /**
     * Optional member function for changing the capacity.
     * If the list does not support overallocation, this can be set to @c NULL.
     */
    int (*change_capacity)(struct cx_list_s *list, size_t new_capacity);

    /**
     * Member function for returning an iterator pointing to the specified index.
     */
    struct cx_iterator_s (*iterator)(const struct cx_list_s *list, size_t index, bool backward);
};

/**
 * Common type for all list implementations.
 */
typedef struct cx_list_s CxList;

/**
 * A shared instance of an empty list.
 *
 * Writing to that list is not allowed.
 *
 * You can use this as a placeholder for initializing CxList pointers
 * for which you do not want to reserve memory right from the beginning.
 */
CX_EXPORT extern CxList *const cxEmptyList;

/**
 * Default implementation of an array insert.
 *
 * This function uses the element insert function for each element of the array.
 *
 * Use this in your own list class if you do not want to implement an optimized
 * version for your list.
 *
 * @param list the list
 * @param index the index where to insert the data
 * @param data a pointer to the array of data to insert
 * @param n the number of elements to insert
 * @return the number of elements actually inserted
 */
cx_attr_nonnull
CX_EXPORT size_t cx_list_default_insert_array(struct cx_list_s *list,
        size_t index, const void *data, size_t n);

/**
 * Default implementation of a sorted insert.
 *
 * This function uses the array insert function to insert consecutive groups
 * of sorted data.
 *
 * The source data @em must already be sorted wrt. the list's compare function.
 *
 * Use this in your own list class if you do not want to implement an optimized
 * version for your list.
 *
 * @param list the list
 * @param sorted_data a pointer to the array of pre-sorted data to insert
 * @param n the number of elements to insert
 * @return the number of elements actually inserted
 */
cx_attr_nonnull
CX_EXPORT size_t cx_list_default_insert_sorted(struct cx_list_s *list,
        const void *sorted_data, size_t n);

/**
 * Default implementation of an array insert where only elements are inserted when they don't exist in the list.
 *
 * This function is similar to cx_list_default_insert_sorted(), except it skips elements that are already in the list.
 *
 * @note The return value of this function denotes the number of elements from the @p sorted_data that are definitely
 * contained in the list after completing the call. It is @em not the number of elements that were newly inserted.
 * That means, when no error occurred, the return value should be @p n.
 *
 * Use this in your own list class if you do not want to implement an optimized version for your list.
 *
 * @param list the list
 * @param sorted_data a pointer to the array of pre-sorted data to insert
 * @param n the number of elements to insert
 * @return the number of elements from the @p sorted_data that are definitely present in the list after this call
 */
cx_attr_nonnull
CX_EXPORT size_t cx_list_default_insert_unique(struct cx_list_s *list,
        const void *sorted_data, size_t n);

/**
 * Default unoptimized sort implementation.
 *
 * This function will copy all data to an array, sort the array with standard
 * qsort, and then copy the data back to the list memory.
 *
 * Use this in your own list class if you do not want to implement an optimized
 * version for your list.
 *
 * @param list the list that shall be sorted
 */
cx_attr_nonnull
CX_EXPORT void cx_list_default_sort(struct cx_list_s *list);

/**
 * Default unoptimized swap implementation.
 *
 * Use this in your own list class if you do not want to implement an optimized
 * version for your list.
 *
 * @param list the list in which to swap
 * @param i index of one element
 * @param j index of the other element
 * @retval zero success
 * @retval non-zero when indices are out of bounds or memory
 * allocation for the temporary buffer fails
 */
cx_attr_nonnull
CX_EXPORT int cx_list_default_swap(struct cx_list_s *list, size_t i, size_t j);

/**
 * Initializes a list struct.
 *
 * Only use this function if you are creating your own list implementation.
 * The purpose of this function is to be called in the initialization code
 * of your list to set certain members correctly.
 *
 * This is particularly important when you want your list to support
 * #CX_STORE_POINTERS as @p elem_size. This function will wrap the list
 * class accordingly and make sure that you can implement your list as if
 * it was only storing objects, and the wrapper will automatically enable
 * the feature of storing pointers.
 *
 * @par Example
 *
 * @code
 * CxList *myCustomListCreate(
 *         const CxAllocator *allocator,
 *         cx_compare_func comparator,
 *         size_t elem_size
 * ) {
 *     if (allocator == NULL) {
 *         allocator = cxDefaultAllocator;
 *     }
 *
 *     MyCustomList *list = cxCalloc(allocator, 1, sizeof(MyCustomList));
 *     if (list == NULL) return NULL;
 *
 *     // initialize
 *     cx_list_init((CxList*)list, &my_custom_list_class,
 *             allocator, comparator, elem_size);
 *
 *     // ... some more custom stuff ...
 *
 *     return (CxList *) list;
 * }
 * @endcode
 *
 * @param list the list to initialize
 * @param cl the list class
 * @param allocator the allocator for the elements
 * @param comparator a compare function for the elements
 * @param elem_size the size of one element
 */
cx_attr_nonnull_arg(1, 2, 3)
CX_EXPORT void cx_list_init(struct cx_list_s *list,
    struct cx_list_class_s *cl, const struct cx_allocator_s *allocator,
    cx_compare_func comparator, size_t elem_size);

/**
 * Returns the number of elements currently stored in the list.
 *
 * @param list the list
 * @return the number of currently stored elements
 */
cx_attr_nonnull
CX_EXPORT size_t cxListSize(const CxList *list);

/**
 * Adds an item to the end of the list.
 *
 * @param list the list
 * @param elem a pointer to the element to add
 * @retval zero success
 * @retval non-zero memory allocation failure
 * @see cxListAddArray()
 * @see cxListEmplace()
 */
cx_attr_nonnull
CX_EXPORT int cxListAdd(CxList *list, const void *elem);

/**
 * Adds multiple items to the end of the list.
 *
 * This method is more efficient than invoking cxListAdd() multiple times.
 *
 * If there is not enough memory to add all elements, the returned value is
 * less than @p n.
 *
 * If this list is storing pointers instead of objects, @p array is expected to
 * be an array of pointers.
 *
 * @param list the list
 * @param array a pointer to the elements to add
 * @param n the number of elements to add
 * @return the number of added elements
 * @see cxListEmplaceArray()
 */
cx_attr_nonnull
CX_EXPORT size_t cxListAddArray(CxList *list, const void *array, size_t n);

/**
 * Inserts an item at the specified index.
 *
 * If the @p index equals the list @c size, this is effectively cxListAdd().
 *
 * @param list the list
 * @param index the index the element shall have
 * @param elem a pointer to the element to add
 * @retval zero success
 * @retval non-zero memory allocation failure or the index is out of bounds
 * @see cxListInsertAfter()
 * @see cxListInsertBefore()
 * @see cxListEmplaceAt()
 */
cx_attr_nonnull
CX_EXPORT int cxListInsert(CxList *list, size_t index, const void *elem);

/**
 * Allocates memory for an element at the specified index and returns a pointer to that memory.
 *
 * @remark When the list is storing pointers, this will return a @c void**.
 *
 * @param list the list
 * @param index the index where to emplace the element
 * @return a pointer to the allocated memory; @c NULL when the operation fails, or the index is out-of-bounds
 * @see cxListEmplace()
 * @see cxListEmplaceArrayAt()
 * @see cxListInsert()
 */
cx_attr_nonnull
CX_EXPORT void *cxListEmplaceAt(CxList *list, size_t index);

/**
 * Allocates memory for an element at the end of the list and returns a pointer to that memory.
 *
 * @remark When the list is storing pointers, this will return a @c void**.
 *
 * @param list the list
 * @return a pointer to the allocated memory; @c NULL when the operation fails, or the index is out-of-bounds
 * @see cxListEmplaceAt()
 * @see cxListAdd()
 */
cx_attr_nonnull
CX_EXPORT void *cxListEmplace(CxList *list);

/**
 * Allocates memory for multiple elements and returns an iterator.
 *
 * The iterator will only iterate over the successfully allocated elements.
 * The @c elem_count attribute is set to that number, and the @c index attribute
 * will range from zero to @c elem_count minus one.
 *
 * @remark When the list is storing pointers, the iterator will iterate over
 * the @c void** elements.
 *
 * @param list the list
 * @param index the index where to insert the new data
 * @param n the number of elements for which to allocate the memory
 * @return an iterator, iterating over the new memory
 * @see cxListEmplaceAt()
 * @see cxListInsertArray()
 */
cx_attr_nonnull
CX_EXPORT CxIterator cxListEmplaceArrayAt(CxList *list, size_t index, size_t n);

/**
 * Allocates memory for multiple elements and returns an iterator.
 *
 * The iterator will only iterate over the successfully allocated elements.
 * The @c elem_count attribute is set to that number, and the @c index attribute
 * will range from zero to @c elem_count minus one.
 *
 * @remark When the list is storing pointers, the iterator will iterate over
 * the @c void** elements.
 *
 * @param list the list
 * @param n the number of elements for which to allocate the memory
 * @return an iterator, iterating over the new memory
 * @see cxListEmplace()
 * @see cxListAddArray()
 */
cx_attr_nonnull
CX_EXPORT CxIterator cxListEmplaceArray(CxList *list, size_t n);

/**
 * Inserts an item into a sorted list.
 *
 * If the list is not sorted already, the behavior is undefined.
 *
 * @param list the list
 * @param elem a pointer to the element to add
 * @retval zero success
 * @retval non-zero memory allocation failure
 */
cx_attr_nonnull
CX_EXPORT int cxListInsertSorted(CxList *list, const void *elem);

/**
 * Inserts an item into a list if it does not exist.
 *
 * If the list is not sorted already, this function will check all elements
 * and append the new element when it was not found.
 * It is strongly recommended to use this function only on sorted lists, where
 * the element, if it is not contained, is inserted at the correct position.
 *
 * @param list the list
 * @param elem a pointer to the element to add
 * @retval zero success (also when the element was already in the list)
 * @retval non-zero memory allocation failure
 */
cx_attr_nonnull
CX_EXPORT int cxListInsertUnique(CxList *list, const void *elem);

/**
 * Inserts multiple items to the list at the specified index.
 * If the @p index equals the list size, this is effectively cxListAddArray().
 *
 * This method is usually more efficient than invoking cxListInsert()
 * multiple times.
 *
 * If there is not enough memory to add all elements, the returned value is
 * less than @p n.
 *
 * If this list is storing pointers instead of objects, @p array is expected to
 * be an array of pointers.
 *
 * @param list the list
 * @param index the index where to add the elements
 * @param array a pointer to the elements to add
 * @param n the number of elements to add
 * @return the number of added elements
 * @see cxListEmplaceArrayAt()
 */
cx_attr_nonnull
CX_EXPORT size_t cxListInsertArray(CxList *list, size_t index, const void *array, size_t n);

/**
 * Inserts a sorted array into a sorted list.
 *
 * This method is usually more efficient than inserting each element separately
 * because consecutive chunks of sorted data are inserted in one pass.
 *
 * If there is not enough memory to add all elements, the returned value is
 * less than @p n.
 *
 * If this list is storing pointers instead of objects, @p array is expected to
 * be an array of pointers.
 *
 * If the list is not sorted already, the behavior is undefined.
 *
 * @param list the list
 * @param array a pointer to the elements to add
 * @param n the number of elements to add
 * @return the number of added elements
 */
cx_attr_nonnull
CX_EXPORT size_t cxListInsertSortedArray(CxList *list, const void *array, size_t n);

/**
 * Inserts an array into a list, skipping duplicates.
 *
 * The @p list does not need to be sorted (in contrast to cxListInsertSortedArray()).
 * But it is strongly recommended to use this function only on sorted lists,
 * because otherwise it will fall back to an inefficient algorithm which inserts
 * all elements one by one.
 * If the @p list is not sorted, the @p array also does not need to be sorted.
 * But when the @p list is sorted, the @p array must also be sorted.
 *
 * This method is usually more efficient than inserting each element separately
 * because consecutive chunks of sorted data are inserted in one pass.
 *
 * If there is not enough memory to add all elements, the returned value is
 * less than @p n.
 *
 * @note The return value of this function denotes the number of elements
 * from the @p sorted_data that are definitely contained in the list after
 * completing the call. It is @em not the number of elements that were newly
 * inserted. That means, when no error occurred, the return value should
 * be @p n.
 *
 * If this list is storing pointers instead of objects @p array is expected to
 * be an array of pointers.
 *
 * @param list the list
 * @param array a pointer to the elements to add
 * @param n the number of elements to add
 * @return the number of added elements
 *
 * @return the number of elements from the @p sorted_data that are definitely present in the list after this call
 */
cx_attr_nonnull
CX_EXPORT size_t cxListInsertUniqueArray(CxList *list, const void *array, size_t n);

/**
 * Inserts an element after the current location of the specified iterator.
 *
 * The used iterator remains operational, but all other active iterators should
 * be considered invalidated.
 *
 * If @p iter is not a list iterator, the behavior is undefined.
 * If @p iter is a past-the-end iterator, the new element gets appended to the list.
 *
 * @param iter an iterator
 * @param elem the element to insert
 * @retval zero success
 * @retval non-zero memory allocation failure
 * @see cxListInsert()
 * @see cxListInsertBefore()
 */
cx_attr_nonnull
CX_EXPORT int cxListInsertAfter(CxIterator *iter, const void *elem);

/**
 * Inserts an element before the current location of the specified iterator.
 *
 * The used iterator remains operational, but all other active iterators should
 * be considered invalidated.
 *
 * If @p iter is not a list iterator, the behavior is undefined.
 * If @p iter is a past-the-end iterator, the new element gets appended to the list.
 *
 * @param iter an iterator
 * @param elem the element to insert
 * @retval zero success
 * @retval non-zero memory allocation failure
 * @see cxListInsert()
 * @see cxListInsertAfter()
 */
cx_attr_nonnull
CX_EXPORT int cxListInsertBefore(CxIterator *iter, const void *elem);

/**
 * Removes the element at the specified index.
 *
 * If an element destructor function is specified, it is called before
 * removing the element.
 *
 * @param list the list
 * @param index the index of the element
 * @retval zero success
 * @retval non-zero index out of bounds
 */
cx_attr_nonnull
CX_EXPORT int cxListRemove(CxList *list, size_t index);

/**
 * Removes and returns the element at the specified index.
 *
 * No destructor is called, and instead the element is copied to the
 * @p targetbuf which MUST be large enough to hold the removed element.
 * If the list is storing pointers, only the pointer is copied to @p targetbuf.
 *
 * @param list the list
 * @param index the index of the element
 * @param targetbuf a buffer where to copy the element
 * @retval zero success
 * @retval non-zero index out of bounds
 */
cx_attr_nonnull cx_attr_access_w(3)
CX_EXPORT int cxListRemoveAndGet(CxList *list, size_t index, void *targetbuf);

/**
 * Removes and returns the first element of the list.
 *
 * No destructor is called, and instead the element is copied to the
 * @p targetbuf which MUST be large enough to hold the removed element.
 * If the list is storing pointers, only the pointer is copied to @p targetbuf.
 *
 * @param list the list
 * @param targetbuf a buffer where to copy the element
 * @retval zero success
 * @retval non-zero the list is empty
 * @see cxListPopFront()
 * @see cxListRemoveAndGetLast()
 */
cx_attr_nonnull cx_attr_access_w(2)
CX_EXPORT int cxListRemoveAndGetFirst(CxList *list, void *targetbuf);

/**
 * Removes and returns the first element of the list.
 *
 * Alias for cxListRemoveAndGetFirst().
 *
 * No destructor is called, and instead the element is copied to the
 * @p targetbuf which MUST be large enough to hold the removed element.
 * If the list is storing pointers, only the pointer is copied to @p targetbuf.
 *
 * @param list (@c CxList*) the list
 * @param targetbuf (@c void*) a buffer where to copy the element
 * @retval zero success
 * @retval non-zero the list is empty
 * @see cxListRemoveAndGetFirst()
 * @see cxListPop()
 */
#define cxListPopFront(list, targetbuf) cxListRemoveAndGetFirst((list), (targetbuf))


/**
 * Removes and returns the last element of the list.
 *
 * No destructor is called, and instead the element is copied to the
 * @p targetbuf which MUST be large enough to hold the removed element.
 * If the list is storing pointers, only the pointer is copied to @p targetbuf.
 *
 * @param list the list
 * @param targetbuf a buffer where to copy the element
 * @retval zero success
 * @retval non-zero the list is empty
 */
cx_attr_nonnull cx_attr_access_w(2)
CX_EXPORT int cxListRemoveAndGetLast(CxList *list, void *targetbuf);

/**
 * Removes and returns the last element of the list.
 *
 * Alias for cxListRemoveAndGetLast().
 *
 * No destructor is called, and instead the element is copied to the
 * @p targetbuf which MUST be large enough to hold the removed element.
 * If the list is storing pointers, only the pointer is copied to @p targetbuf.
 *
 * @param list (@c CxList*) the list
 * @param targetbuf (@c void*) a buffer where to copy the element
 * @retval zero success
 * @retval non-zero the list is empty
 * @see cxListRemoveAndGetLast()
 * @see cxListPopFront()
 */
#define cxListPop(list, targetbuf) cxListRemoveAndGetLast((list), (targetbuf))

/**
 * Removes multiple element starting at the specified index.
 *
 * If an element destructor function is specified, it is called for each
 * element. It is guaranteed that the destructor is called before removing
 * the element. However, due to possible optimizations, it is neither guaranteed
 * that the destructors are invoked for all elements before starting to remove
 * them, nor that the element is removed immediately after the destructor call
 * before proceeding to the next element.
 *
 * @param list the list
 * @param index the index of the element
 * @param num the number of elements to remove
 * @return the actual number of removed elements
 */
cx_attr_nonnull
CX_EXPORT size_t cxListRemoveArray(CxList *list, size_t index, size_t num);

/**
 * Removes and returns multiple elements starting at the specified index.
 *
 * No destructor is called, and instead the elements are copied to the
 * @p targetbuf which MUST be large enough to hold all removed elements.
 * If the list is storing pointers, @p targetbuf is expected to be an array of pointers.
 *
 * @param list the list
 * @param index the index of the element
 * @param num the number of elements to remove
 * @param targetbuf a buffer where to copy the elements
 * @return the actual number of removed elements
 */
cx_attr_nonnull cx_attr_access_w(4)
CX_EXPORT size_t cxListRemoveArrayAndGet(CxList *list, size_t index, size_t num, void *targetbuf);

/**
 * Removes all elements from this list.
 *
 * If element destructor functions are specified, they are called for each
 * element before removing them.
 *
 * @param list the list
 */
cx_attr_nonnull
CX_EXPORT void cxListClear(CxList *list);

/**
 * Swaps two items in the list.
 *
 * Implementations should only allocate temporary memory for the swap if
 * it is necessary.
 *
 * @param list the list
 * @param i the index of the first element
 * @param j the index of the second element
 * @retval zero success
 * @retval non-zero one of the indices is out of bounds,
 * or the swap needed extra memory, but allocation failed
 */
cx_attr_nonnull
CX_EXPORT int cxListSwap(CxList *list, size_t i, size_t j);

/**
 * Returns a pointer to the element at the specified index.
 *
 * If the list is storing pointers, returns the pointer stored at the specified index.
 *
 * @param list the list
 * @param index the index of the element
 * @return a pointer to the element or @c NULL if the index is out of bounds
 */
cx_attr_nonnull
CX_EXPORT void *cxListAt(const CxList *list, size_t index);

/**
 * Returns a pointer to the first element.
 *
 * If the list is storing pointers, returns the first pointer stored in the list.
 *
 * @param list the list
 * @return a pointer to the first element or @c NULL if the list is empty
 */
cx_attr_nonnull
CX_EXPORT void *cxListFirst(const CxList *list);

/**
 * Returns a pointer to the last element.
 *
 * If the list is storing pointers, returns the last pointer stored in the list.
 *
 * @param list the list
 * @return a pointer to the last element or @c NULL if the list is empty
 */
cx_attr_nonnull
CX_EXPORT void *cxListLast(const CxList *list);

/**
 * Sets the element at the specified index in the list.
 *
 * This overwrites the element in-place without calling any destructor
 * on the overwritten element.
 *
 * @param list the list to set the element in
 * @param index the index to set the element at
 * @param elem element to set
 * @retval zero on success
 * @retval non-zero when index is out of bounds
 */
cx_attr_nonnull
CX_EXPORT int cxListSet(CxList *list, size_t index, const void *elem);

/**
 * Returns an iterator pointing to the item at the specified index.
 *
 * The returned iterator is position-aware.
 *
 * If the index is out of range or @p list is @c NULL, a past-the-end iterator will be returned.
 *
 * @param list the list
 * @param index the index where the iterator shall point at
 * @return a new iterator
 */
cx_attr_nodiscard
CX_EXPORT CxIterator cxListIteratorAt(const CxList *list, size_t index);

/**
 * Returns a backwards iterator pointing to the item at the specified index.
 *
 * The returned iterator is position-aware.
 *
 * If the index is out of range or @p list is @c NULL, a past-the-end iterator will be returned.
 *
 * @param list the list
 * @param index the index where the iterator shall point at
 * @return a new iterator
 */
cx_attr_nodiscard
CX_EXPORT CxIterator cxListBackwardsIteratorAt(const CxList *list, size_t index);

/**
 * Returns an iterator pointing to the first item of the list.
 *
 * The returned iterator is position-aware.
 *
 * If the list is empty or @c NULL, a past-the-end iterator will be returned.
 *
 * @param list the list
 * @return a new iterator
 */
cx_attr_nodiscard
CX_EXPORT CxIterator cxListIterator(const CxList *list);

/**
 * Returns a backwards iterator pointing to the last item of the list.
 *
 * The returned iterator is position-aware.
 *
 * If the list is empty or @c NULL, a past-the-end iterator will be returned.
 *
 * @param list the list
 * @return a new iterator
 */
cx_attr_nodiscard
CX_EXPORT CxIterator cxListBackwardsIterator(const CxList *list);

/**
 * Returns the index of the first element that equals @p elem.
 *
 * Determining equality is performed by the list's comparator function.
 *
 * @param list the list
 * @param elem the element to find
 * @return the index of the element or the size of the list when the element is not found
 * @see cxListIndexValid()
 * @see cxListContains()
 */
cx_attr_nonnull cx_attr_nodiscard
CX_EXPORT size_t cxListFind(const CxList *list, const void *elem);

/**
 * Checks if the list contains the specified element.
 *
 * The elements are compared with the list's comparator function.
 *
 * @param list the list
 * @param elem the element to find
 * @retval true if the element is contained
 * @retval false if the element is not contained
 * @see cxListFind()
 */
cx_attr_nonnull cx_attr_nodiscard
CX_EXPORT bool cxListContains(const CxList* list, const void* elem);

/**
 * Checks if the specified index is within bounds.
 *
 * @param list the list
 * @param index the index
 * @retval true if the index is within bounds
 * @retval false if the index is out of bounds
 */
cx_attr_nonnull cx_attr_nodiscard
CX_EXPORT bool cxListIndexValid(const CxList *list, size_t index);

/**
 * Removes and returns the index of the first element that equals @p elem.
 *
 * Determining equality is performed by the list's comparator function.
 *
 * @param list the list
 * @param elem the element to find and remove
 * @return the index of the now removed element or the list size
 * when the element is not found or could not be removed
 * @see cxListIndexValid()
 */
cx_attr_nonnull
CX_EXPORT size_t cxListFindRemove(CxList *list, const void *elem);

/**
 * Sorts the list.
 *
 * @remark The underlying sort algorithm is implementation defined.
 *
 * @param list the list
 */
cx_attr_nonnull
CX_EXPORT void cxListSort(CxList *list);

/**
 * Reverses the order of the items.
 *
 * @param list the list
 */
cx_attr_nonnull
CX_EXPORT void cxListReverse(CxList *list);

/**
 * Compares a list to another list of the same type.
 *
 * First, the list sizes are compared.
 * If they match, the lists are compared element-wise.
 *
 * @param list the list
 * @param other the list to compare to
 * @retval zero both lists are equal element wise
 * @retval negative the first list is smaller,
 * or the first non-equal element in the first list is smaller
 * @retval positive the first list is larger
 * or the first non-equal element in the first list is larger
 */
cx_attr_nonnull cx_attr_nodiscard
CX_EXPORT int cxListCompare(const CxList *list, const CxList *other);

/**
 * Deallocates the memory of the specified list structure.
 *
 * Also calls the content destructor functions for each element, if specified.
 *
 * @param list the list that shall be freed
 */
CX_EXPORT void cxListFree(CxList *list);


/**
 * Performs a deep clone of one list into another.
 *
 * If the destination list already contains elements, the cloned elements
 * are appended to that list.
 *
 * @attention If the cloned elements need to be destroyed by a destructor
 * function, you must make sure that the destination list also uses this
 * destructor function.
 *
 * @param dst the destination list
 * @param src the source list
 * @param clone_func the clone function for the elements
 * @param clone_allocator the allocator that is passed to the clone function
 * @param data optional additional data that is passed to the clone function
 * @retval zero when all elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListCloneSimple()
 */
cx_attr_nonnull_arg(1, 2, 3)
CX_EXPORT int cxListClone(CxList *dst, const CxList *src,
        cx_clone_func clone_func, const CxAllocator *clone_allocator, void *data);

/**
 * Clones elements from a list only if they are not present in another list.
 *
 * If the @p minuend does not contain duplicates, this is equivalent to adding
 * the set difference to the destination list.
 *
 * This function is optimized for the case when both the @p minuend and the
 * @p subtrahend are sorted.
 *
 * @param dst the destination list
 * @param minuend the list to subtract elements from
 * @param subtrahend the elements that shall be subtracted
 * @param clone_func the clone function for the elements
 * @param clone_allocator the allocator that is passed to the clone function
 * @param data optional additional data that is passed to the clone function
 * @retval zero when the elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListDifferenceSimple()
 */
cx_attr_nonnull_arg(1, 2, 3, 4)
CX_EXPORT int cxListDifference(CxList *dst,
        const CxList *minuend, const CxList *subtrahend,
        cx_clone_func clone_func, const CxAllocator *clone_allocator, void *data);

/**
 * Clones elements from a list only if they are also present in another list.
 *
 * This function is optimized for the case when both the @p src and the
 * @p other list are sorted.
 *
 * If the destination list already contains elements, the intersection is appended
 * to that list.
 *
 * @param dst the destination list
 * @param src the list to clone the elements from
 * @param other the list to check the elements for existence
 * @param clone_func the clone function for the elements
 * @param clone_allocator the allocator that is passed to the clone function
 * @param data optional additional data that is passed to the clone function
 * @retval zero when the elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListIntersectionSimple()
 */
cx_attr_nonnull_arg(1, 2, 3, 4)
CX_EXPORT int cxListIntersection(CxList *dst, const CxList *src, const CxList *other,
        cx_clone_func clone_func, const CxAllocator *clone_allocator, void *data);

/**
 * Performs a deep clone of one list into another, skipping duplicates.
 *
 * This function is optimized for the case when both the @p src and the
 * @p other list are sorted.
 * In that case, the union will also be sorted.
 *
 * If the destination list already contains elements, the union is appended
 * to that list. In that case the destination is not necessarily sorted.
 *
 * @param dst the destination list
 * @param src the primary source list
 * @param other the other list, where elements are only cloned from
 * when they are not in @p src
 * @param clone_func the clone function for the elements
 * @param clone_allocator the allocator that is passed to the clone function
 * @param data optional additional data that is passed to the clone function
 * @retval zero when the elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListUnionSimple()
 */
cx_attr_nonnull_arg(1, 2, 3, 4)
CX_EXPORT int cxListUnion(CxList *dst, const CxList *src, const CxList *other,
        cx_clone_func clone_func, const CxAllocator *clone_allocator, void *data);

/**
 * Performs a shallow clone of one list into another.
 *
 * This function uses the default allocator, if needed, and performs
 * shallow clones with @c memcpy().
 *
 * If the destination list already contains elements, the cloned elements
 * are appended to that list.
 *
 * @attention If the cloned elements need to be destroyed by a destructor
 * function, you must make sure that the destination list also uses this
 * destructor function.
 *
 * @param dst the destination list
 * @param src the source list
 * @retval zero when all elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListClone()
 */
cx_attr_nonnull
CX_EXPORT int cxListCloneSimple(CxList *dst, const CxList *src);

/**
 * Clones elements from a list only if they are not present in another list.
 *
 * This function uses the default allocator, if needed, and performs
 * shallow clones with @c memcpy().
 *
 * If the @p minuend does not contain duplicates, this is equivalent to adding
 * the set difference to the destination list.
 *
 * This function is optimized for the case when both the @p minuend and the
 * @p subtrahend are sorted.
 *
 * @param dst the destination list
 * @param minuend the list to subtract elements from
 * @param subtrahend the elements that shall be subtracted
 * @retval zero when the elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListDifference()
 */
cx_attr_nonnull
CX_EXPORT int cxListDifferenceSimple(CxList *dst,
        const CxList *minuend, const CxList *subtrahend);

/**
 * Clones elements from a list only if they are also present in another list.
 *
 * This function uses the default allocator, if needed, and performs
 * shallow clones with @c memcpy().
 *
 * This function is optimized for the case when both the @p src and the
 * @p other list are sorted.
 *
 * If the destination list already contains elements, the intersection is appended
 * to that list.
 *
 * @param dst the destination list
 * @param src the list to clone the elements from
 * @param other the list to check the elements for existence
 * @retval zero when the elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListIntersection()
 */
cx_attr_nonnull
CX_EXPORT int cxListIntersectionSimple(CxList *dst, const CxList *src, const CxList *other);

/**
 * Performs a deep clone of one list into another, skipping duplicates.
 *
 * This function uses the default allocator, if needed, and performs
 * shallow clones with @c memcpy().
 *
 * This function is optimized for the case when both the @p src and the
 * @p other list are sorted.
 * In that case, the union will also be sorted.
 *
 * If the destination list already contains elements, the union is appended
 * to that list. In that case the destination is not necessarily sorted.
 *
 * @param dst the destination list
 * @param src the primary source list
 * @param other the other list, where elements are only cloned from
 * when they are not in @p src
 * @retval zero when the elements were successfully cloned
 * @retval non-zero when an allocation error occurred
 * @see cxListUnion()
 */
cx_attr_nonnull
CX_EXPORT int cxListUnionSimple(CxList *dst, const CxList *src, const CxList *other);

/**
 * Asks the list to reserve enough memory for a given total number of elements.
 *
 * List implementations are free to choose if reserving memory upfront makes
 * sense.
 * For example, array-based implementations usually do support reserving memory
 * for additional elements while linked lists usually don't.
 *
 * @note When the requested capacity is smaller than the current size,
 * this function returns zero without performing any action.
 *
 * @param list the list
 * @param capacity the expected total number of elements
 * @retval zero on success or when overallocation is not supported
 * @retval non-zero when an allocation error occurred
 * @see cxListShrink()
 */
cx_attr_nonnull
CX_EXPORT int cxListReserve(CxList *list, size_t capacity);

/**
 * Advises the list to free any overallocated memory.
 *
 * Lists that do not support overallocation simply return zero.
 *
 * This function usually returns zero, except for very special and custom
 * list and/or allocator implementations where freeing memory can fail.
 *
 * @param list the list
 * @return usually zero
 */
cx_attr_nonnull
CX_EXPORT int cxListShrink(CxList *list);

#ifdef __cplusplus
} // extern "C"
#endif

#endif // UCX_LIST_H