#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <string.h>
#include <stdbool.h>
#include "numbers.h"

//TODO: getDuplicate und createNumbers implementieren
/*  *   * Erzeugen eines Arrays mit der vom Nutzer eingegebenen Anzahl an Zufallszahlen.
  * Sicherstellen, dass beim Befüllen keine Duplikate entstehen.
  * Duplizieren eines zufälligen Eintrags im Array.
  * in `getDuplicate()`: Sortieren des Arrays und Erkennen der doppelten Zahl durch Vergleich benachbarter Elemente. */

// Returns len random numbers between 1 and 2x len in random order which are all different, except for two entries.
// Returns NULL on errors. Use your implementation of the binary search tree to check for possible duplicates while
// creating random numbers.
unsigned int *createNumbers(unsigned int len)
{
    if (len < 2) {
        // Mindestens zwei Elemente nötig, damit ein Duplikat existiert
        return NULL;
    }

    unsigned int *numbers = malloc(len * sizeof(unsigned int));
    if (!numbers) return NULL;

    bool *used = calloc(2 * len + 1, sizeof(bool));
    if (!used) {
        free(numbers);
        return NULL;
    }

    static int initialized = 0;
    if (!initialized) {
        srand((unsigned int)time(NULL));
        initialized = 1;
    }

    // Einzigartige Zufallszahlen generieren
    for (unsigned int i = 0; i < len - 1; ) {
        unsigned int num = (rand() % (2 * len)) + 1;
        if (!used[num]) {
            used[num] = true;
            numbers[i++] = num;
        }
    }

    // Eine der Zahlen duplizieren
    unsigned int duplicateIndex = rand() % (len - 1);
    numbers[len - 1] = numbers[duplicateIndex];

    // Fisher–Yates shuffle
    for (unsigned int i = len - 1; i > 0; i--) {
        unsigned int j = rand() % (i + 1);
        unsigned int tmp = numbers[i];
        numbers[i] = numbers[j];
        numbers[j] = tmp;
    }

    free(used);
    return numbers;
}

// Returns only the only number in numbers which is present twice. Returns zero on errors.
unsigned int getDuplicate(const unsigned int numbers[], unsigned int len)
{
    if (numbers == NULL || len < 2) {
        return 0;
    }

    unsigned int *sortedNumbers = malloc(len * sizeof(unsigned int));
    if (sortedNumbers == NULL) {
        return 0;
    }
    memcpy(sortedNumbers, numbers, len * sizeof(unsigned int));

    // Einfacher bubble sort
    for (unsigned int i = 0; i < len - 1; i++) {
        for (unsigned int j = 0; j < len - i - 1; j++) {
            if (sortedNumbers[j] > sortedNumbers[j + 1]) {
                unsigned int temp = sortedNumbers[j];
                sortedNumbers[j] = sortedNumbers[j + 1];
                sortedNumbers[j + 1] = temp;
            }
        }
    }

    unsigned int duplicate = 0;
    for (unsigned int i = 0; i < len - 1; i++) {
        if (sortedNumbers[i] == sortedNumbers[i + 1]) {
            duplicate = sortedNumbers[i];
            break;
        }
    }

    free(sortedNumbers);
    return duplicate;
}