#include "list_ops.h"
#include <string.h>

// constructs a new list
list_t *new_list(size_t length, list_element_t elements[]) {
    list_t *newList = malloc(sizeof(list_t) + length * sizeof(list_element_t));
    if (newList != NULL) {
        newList->length = length;
        if (length > 0 && elements != NULL) {
            memcpy(newList->elements, elements, length * sizeof(list_element_t));
        }
    }
    return newList;
}


// append entries to a list and return the new list
list_t *append_list(list_t *list1, list_t *list2) {
    if (list1 == NULL && list2 == NULL) {
        return NULL; // Both lists are empty
    } else if (list1 == NULL) {
        return list2; // Only list1 is empty, return list2
    } else if (list2 == NULL) {
        return list1; // Only list2 is empty, return list1
    }

    size_t new_length = list1->length + list2->length;
    list_t *new_list = malloc(sizeof(list_t) + new_length * sizeof(list_element_t));
    if (new_list == NULL) {
        return NULL; // Memory allocation failed
    }

    memcpy(new_list->elements, list1->elements, list1->length * sizeof(list_element_t));
    memcpy(new_list->elements + list1->length, list2->elements, list2->length * sizeof(list_element_t));

    new_list->length = new_length;

    return new_list;
}

// filter list returning only values that satisfy the filter function
list_t *filter_list(list_t *list, bool (*filter)(list_element_t)) {
    if (list == NULL) return NULL;
    
    size_t filteredLength = 0;
    for (size_t i = 0; i < list->length; ++i) {
        if (filter(list->elements[i])) {
            ++filteredLength;
        }
    }

    list_t *filtered = malloc(sizeof(list_t) + filteredLength * sizeof(list_element_t));
    if (filtered != NULL) {
        filtered->length = filteredLength;
        for (size_t i = 0; i < list->length; ++i) {
            if (filter(list->elements[i])) {
                filtered->elements[i] = list->elements[i];
            }
        }   
    }
    return filtered;
}


// returns the length of the list
size_t length_list(list_t *list) {
    return (list != NULL) ? list->length : 0;
}

// return a list of elements whose values equal the list value transformed by
// the mapping function
list_t *map_list(list_t *list, list_element_t (*map)(list_element_t)) {
    if (list == NULL) return NULL;
    
    list_t *mappedList = new_list(list->length, list->elements);
    if (mappedList != NULL) {
        for (size_t i = 0; i < list->length; ++i) {
            mappedList->elements[i] = map(list->elements[i]);
        }
    }
    return mappedList;
}

// folds (reduces) the given list from the left with a function
list_element_t foldl_list(list_t *list, list_element_t initial,
                          list_element_t (*foldl)(list_element_t, list_element_t)) {
    list_element_t accumulator = initial;
    if (list != NULL) {
        for (size_t i = 0; i < list->length; ++i) {
            accumulator = foldl(list->elements[i], accumulator);
        }
    }
    return accumulator;
}

// folds (reduces) the given list from the right with a function
list_element_t foldr_list(list_t *list, list_element_t initial,
                          list_element_t (*foldr)(list_element_t, list_element_t)) {
    list_element_t accumulator = initial;
    if (list != NULL) {
        for (size_t i = list->length; i > 0; --i) {
            accumulator = foldr(list->elements[i - 1], accumulator);
        }
    }
    return accumulator;
}

// reverse the elements of the list
list_t *reverse_list(list_t *list) {
    if (list == NULL) return NULL;
    
    list_t *reversedList = new_list(list->length, list->elements);
    if (reversedList != NULL) {
        for (size_t i = 0; i < list->length / 2; ++i) {
            list_element_t temp = reversedList->elements[i];
            reversedList->elements[i] = reversedList->elements[list->length - i - 1];
            reversedList->elements[list->length - i - 1] = temp;
        }
    }
    return reversedList;
}


// destroy the entire list
// list will be a dangling pointer after calling this method on it
void delete_list(list_t *list) {
    free(list);
}