#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;


ofstream log_file; // файл лога

class Cell
{
public:
    double val;
    Cell* next;
    Cell* prev;
    Cell(double v)
    {
        val = v;
        next = NULL;
        prev = NULL;
    }
};

class List
{
private:
    Cell* head = NULL;
    Cell* tail = NULL;
public:

    Cell* begin() {
        return head;
    }

    Cell* end() {
        return tail;
    }

    int size() {
        int c = 0;
        Cell* h = head;
        while (h != NULL) {
            h = h->next;
            c++;
        }
        return c;
    }

    void push_front(double v)
    {
        if (head == NULL)
        {
            head = new Cell(v);
            tail = head;
        }
        else
        {
            Cell* n = new Cell(v);
            n->next = head;
            head->prev = n;
            head = n;
        }
    }

    void push_back(double v)
    {
        if (head == NULL) {
            head = new Cell(v);
            tail = head;
        }
        else
        {
            Cell* n = new Cell(v);
            n->prev = tail;
            tail->next = n;
            tail = n;
        }
    }


    void remove(int index) {
        Cell* elem = head;
        for (int i = 0; i < index; i++) {
            elem = elem->next;
        }
        elem->prev->next = elem->next;
        elem->next->prev = elem->prev;
    }

    int find(double elem) {
        Cell* curr = head;
        int i = 0;
        while (curr != NULL)
        {
            if (curr->val == elem) {
                return i;
            }
            curr = curr->next;
            i++;
        }
        return -1;
    }

    void clear() {
        int s = size();
        for (int i = 0; i < s; i++) {
            remove(0);
        }
    }

    void print()
    {
        Cell* curr = head;
        while (curr != NULL)
        {
            cout << curr->val << " ";
            curr = curr->next;
        }
        cout << endl;
    }
};


// считывает число
int get_int_input() {

    bool only_nums = false;
    string in;
    while (!only_nums) {
        cin >> in;
        only_nums = true;
        for (int i = 0; i < in.length(); i++) {
            if (!(in[i] >= '0' && in[i] <= '9')) {
                only_nums = false;
            }
        }
        if (!only_nums) {
            cout << "Incorect input: ";
            log_file << "WARNING: getting incorect input " << in << endl;
        }
    }
    return stoi(in);
}


void task1(List& data) {
    log_file << "call task1 function" << endl;
    int n;
    cout << "Enert n: ";
    n = get_int_input();

    if (n >= 2) {

        //List data;

        for (int i = 0; i < n; i++) {

            double elem;
            cout << "Enter " << i + 1 << " element: ";
            cin >> elem;
            data.push_back(elem);

        }

        double ans = 1;
        Cell* start = data.begin();
        Cell* end = data.end();
        for (int i = 0; i < n; i++) {
            double elem;
            elem = start->val * end->val;
            start = start->next;
            end = end->prev;
            ans = ans * elem;
        }

        cout << "Answer is " << ans << endl;
    }
    else {
        cout << "ERROR: n is too small" << endl;
        log_file << "ERROR: n is too small" << endl;
    }
}



void task1_file(List& data) {
    log_file << "call task1_file function" << endl;
    string in_file;
    string out_file;
    cout << "Enter input filename: ";
    cin >> in_file;
    cout << "Enter output filename: ";
    cin >> out_file;

    ifstream in(in_file);
    ofstream out(out_file);
    int n;
    in >> n;


    if (n >= 2) {

        //List data;

        for (int i = 0; i < n; i++) {

            double elem;
            //cout << "Enter " << i + 1 << " element: ";
            in >> elem;
            data.push_back(elem);

        }

        double ans = 1;
        Cell* start = data.begin();
        Cell* end = data.end();
        for (int i = 0; i < n; i++) {
            double elem;
            elem = start->val * end->val;
            start = start->next;
            end = end->prev;
            ans = ans * elem;
        }

        out << "Answer is " << ans << endl;
    }
    else {
        out << "ERROR: n is too small" << endl;
    }

    in.close();
    out.close();
}




void add_elem(List& data) {
    log_file << "call add_elem function" << endl;
    cout << "Enter element: ";
    int elem = get_int_input();
    data.push_back(elem);
}

void find_elem(List& data) {
    log_file << "call find_elem function" << endl;
    cout << "Enter element: ";
    int elem = get_int_input();
    cout << "elem on index " << data.find(elem) << endl;
}

void remove_elem(List& data) {
    log_file << "call remove_elem function" << endl;
    cout << "Enter element Index: ";
    int index = get_int_input();
    if (index < 0 || index >= data.size()) {
        cout << "ERROR: Incorect index";
        log_file << "ERROR: Incorect index";
    }
    else {
        data.remove(index);
    }
}

void clear_list(List& data) {
    log_file << "call clear function" << endl;
    data.clear();
}

void print_list(List& data) {
    log_file << "call print_list function" << endl;
    data.print();
}


int main()
{
    log_file.open("log_file.txt");

    vector<void(*)(List&)> menu; // массив указателей на функции
    // функции
    menu.push_back(task1);
    menu.push_back(task1_file);
    menu.push_back(add_elem);
    menu.push_back(find_elem);
    menu.push_back(remove_elem);
    menu.push_back(clear_list);
    menu.push_back(print_list);

    List data;

    bool exit = false;

    while (!exit) {

        cout << "1) Variant task" << endl;
        cout << "2) Variant task with files" << endl;
        cout << "3) Add element" << endl;
        cout << "4) Find element" << endl;
        cout << "5) Remove element" << endl;
        cout << "6) Clear list" << endl;
        cout << "7) Print list" << endl;
        cout << "0) Exit" << endl;
        cout << "Select item: ";

        int input = get_int_input();

        if (input < 0 || input > menu.size()) {
            cout << endl << "Invalid item" << endl << endl;
        }
        else {

            if (input != 0) {
                menu[input - 1](data);
            }
            else {
                exit = true;
            }
        }
    }

    log_file << "Program successfully ended" << endl;
    log_file.close();
    return 0;
}