#include <iostream>
#include <vector>
#include <cstdio>
#include <windows.h>
#include <deque>
#include <ctime>

#define y first
#define x second

#define For(i,z) for(int32_t i=0;i<(z);i++)

using namespace std;

const int N = 20;

/*
    0 - empty
    1 - snake
    2 - fruit
*/
int state[N][N];

int delay;
string conv = "DASW";
vector <pair<int, int> > addpos = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
deque<pair<int, int> > snake;

inline void waitForKey() {
    fflush(stdin);
    while (fgetc(stdin) == 0x0A);
    return;
}

inline bool correct(int y, int x) {
    if (y < 0 || y >= N) return false;
    if (x < 0 || x >= N) return false;
    return (state[y][x] != 1);
}

inline void clearall() {
    delay = 500;
    snake.clear();
    For (i, N)
        For (j, N)
            state[i][j] = 0;
}


string fieldchars = ".XO";
void printfield() {
    system("cls");
    For (i, N) {
        For (j, N)
            cout << fieldchars[state[i][j]];
        cout << '\n';
    }
    cout << endl;
}

int genapple() {
    int nxt;
    while (true) {
        nxt = rand() % (N * N);
        if (state[nxt/N][nxt%N] == 0)
            break;
    }
    state[nxt/N][nxt%N] = 2;
}

void play() {
    clearall();

    snake.emplace_front(0, 0);
    state[0][0] = 1;

    genapple();
    printfield();

    pair<int, int> curAdd = {0, 1};
    while (true) {
        int tt = GetTickCount();
        //int adidx = -1;
        auto wasAdd = curAdd;
        bool space = GetKeyState(VK_SPACE) & 0x8000;

        while (GetTickCount() - tt < delay / (space ? 3 : 1)) {
            For (i, 4)
                if (GetKeyState(conv[i]) & 0x8000)
                    if (wasAdd != make_pair(-addpos[i].y, -addpos[i].x))
                        curAdd = addpos[i];
        }


        int ny = snake.front().y + curAdd.y,
            nx = snake.front().x + curAdd.x;

        if (correct(ny, nx) == false) {
            cout << "DEAD!!! Press any key + Enter to continue" << endl;
            waitForKey();
            return;
        }
        if (state[ny][nx] == 2) {
            state[ny][nx] = 1;
            genapple();
            delay = max(100, delay * 96 / 100);
        } else {
            state[ny][nx] = 1;
            state[snake.back().y][snake.back().x] = 0;
            snake.pop_back();
        }
        snake.emplace_front(ny, nx);
        printfield();
        //Sleep();
    }
}

int32_t main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    srand(time(NULL));

    cout << "Input on WASD" << endl;
    cout << "Space for triple speed" << endl;

    cout << "Press any button + Enter to continue" << endl;
    waitForKey();
    while (true) {
        play();
    }
}