#include <iostream>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sys/time.h>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <sstream>

using namespace std;

#define MAX 100000
#define MAX_DEPTH 3

struct SharedData {
    int arr[MAX];
};

string now() {
    timeval tv;
    gettimeofday(&tv, NULL);

    ostringstream oss;
    oss << tv.tv_sec << "."
        << setfill('0') << setw(6) << tv.tv_usec;

    return oss.str();
}

void merge(int *arr, int l, int m, int r) {
    int *temp = new int[r - l + 1];

    int i = l, j = m + 1, k = 0;

    while (i <= m && j <= r) {
        if (arr[i] < arr[j]) temp[k++] = arr[i++];
        else temp[k++] = arr[j++];
    }

    while (i <= m) temp[k++] = arr[i++];
    while (j <= r) temp[k++] = arr[j++];

    for (int x = 0; x < k; x++) arr[l + x] = temp[x];

    delete[] temp;
}

void local_sort(int *arr, int l, int r) {
    if (l >= r) return;
    int m = (l + r) / 2;
    local_sort(arr, l, m);
    local_sort(arr, m + 1, r);
    merge(arr, l, m, r);
}

void parallel_sort(int l, int r, int depth, int shmid) {
    SharedData *data = (SharedData*) shmat(shmid, NULL, 0);
    int *arr = data->arr;

    string start_time = now();

    cout << "START PID=" << getpid()
         << " PPID=" << getppid()
         << " depth=" << depth
         << " range=[" << l << "," << r << "]"
         << " time=" << start_time << "\n";

    if (l >= r) {
        string end_time = now();
        cout << "END   PID=" << getpid()
             << " range=[" << l << "," << r << "]"
             << " time=" << end_time << "\n";
        shmdt(data);
        return;
    }

    int m = (l + r) / 2;

    if (depth >= MAX_DEPTH) {
        local_sort(arr, l, r);

        string end_time = now();
        cout << "END   PID=" << getpid()
             << " depth=" << depth
             << " range=[" << l << "," << r << "]"
             << " time=" << end_time << "\n";

        shmdt(data);
        return;
    }

    pid_t left = fork();

    if (left == 0) {
        parallel_sort(l, m, depth + 1, shmid);
        _exit(0);
    }

    pid_t right = fork();

    if (right == 0) {
        parallel_sort(m + 1, r, depth + 1, shmid);
        _exit(0);
    }

    waitpid(left, NULL, 0);
    waitpid(right, NULL, 0);

    merge(arr, l, m, r);

    string end_time = now();

    cout << "END   PID=" << getpid()
         << " depth=" << depth
         << " range=[" << l << "," << r << "]"
         << " time=" << end_time << "\n";

    shmdt(data);
}

int main() {
    key_t key = ftok("shmfile", 65);
    int shmid = shmget(key, sizeof(SharedData), 0666 | IPC_CREAT);

    SharedData *data = (SharedData*) shmat(shmid, NULL, 0);

    int n = 20000;

    srand(time(NULL));

    for (int i = 0; i < n; i++)
        data->arr[i] = rand() % 100000;

    cout << "Before:\n";
    for (int i = 0; i < 20; i++)
        cout << data->arr[i] << " ";
    cout << "\n\n";

    parallel_sort(0, n - 1, 0, shmid);

    cout << "\nAfter:\n";
    for (int i = 0; i < 20; i++)
        cout << data->arr[i] << " ";
    cout << "\n";

    shmdt(data);
    shmctl(shmid, IPC_RMID, NULL);

    return 0;
}