#include "rsa.h"
#include "rand.h"
#include <stdbool.h>
#include <stdint.h>

int gcd(int a, int b) {
    while (b != 0) {
        int temp = b;
        b = a % b;
        a = temp;
    }

    return a;
}

int totient(int n) {
    int result = n;

    // Check for prime factors
    for (int p = 2; p * p <= n; p++) {
        if (n % p == 0) {
            // If p is a prime factor of n, remove all occurrences of p
            while (n % p == 0) {
                n /= p;
            }
            result -= result / p;
        }
    }

    // If n is still greater than 1, then it's a prime factor itself
    if (n > 1) {
        result -= result / n;
    }

    return result;
}

uint64_t modexp(uint64_t a, uint64_t b, uint64_t m) {
    uint64_t result = 1;
    a = a % m; // In case a is greater than m

    while (b > 0) {
        // If b is odd, multiply a with result
        if (b % 2 == 1)
            result = (result * a) % m;

        // b must be even now
        b = b >> 1;      // b = b // 2
        a = (a * a) % m; // Change a to a^2
    }

    return result;
}

uint64_t gen_prime(uint64_t min, uint64_t max) {
    uint64_t cand = 0;
    while (!miller_rabin(cand, 10)) cand = prand_range(min, max);

    return cand;
}

bool is_prime(int n) {
    if (n < 2)
        return false;

    for (int i = 2; i < n / 2 + 1; i++) {
        if (n % i == 0)
            return false;
    }

    return true;
}

bool miller_rabin(int n, int k) {
    if (n < 2)
        return false;

    int d = n - 1;
    int s = 0;

    while (d % 2 == 0) {
        d /= 2;
        s++;
    }

    for (int i = 0; i < k; i++) {
        int a = prand_range(2, n - 2);
        int x = modexp(a, d, n);

        if (x == 1 || x == n - 1)
            continue;

        for (int r = 1; r < s; r++) {
            x = modexp(x, 2, n);
            if (x == n - 1)
                break;
        }

        if (x != n - 1)
            return false; // Not prime
    }

    return true; // Likely prime
}

int mod_inverse(int e, int phi) {
    for (int d = 0; d < phi; d++) {
        if ((d * e) % phi == 1)
            return d;
    }

    return 0;
}