#include "api.h"

#include "gcrypt.h"

#include <stddef.h>
#include <stdbool.h>

static gcry_mpi_t p;
static gcry_mpi_t q;
static gcry_mpi_t g;

void check(gcry_error_t error) {
	if (error) {
		fprintf (stderr, "Error: %s/%s\n", gcry_strsource (error), gcry_strerror (error));
		exit(1);
	}
}

void print_sexp(gcry_sexp_t exp) {
	size_t required_size = gcry_sexp_sprint(exp, GCRYSEXP_FMT_ADVANCED, NULL, 0); //passing NULL as the buffer will return the size needed.

	char* str = (char *) malloc(sizeof(char)*required_size);

	gcry_sexp_sprint(exp, GCRYSEXP_FMT_ADVANCED, str, 2000); //So we ignore the size here.
	
	printf("size = %zu\n", required_size);
	for(size_t i = 0; i < required_size; i++)
		printf("%c", str[i]);
	printf("\n");

	free(str);
}

void elgamal_initialize(void) {
	if (!gcry_check_version (GCRYPT_VERSION)) {
		fprintf(stderr, "libgcrypt version mismatch\n");
		exit(-1);
	}

	gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);
	gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
	gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
	gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
	
	//leading 0 as specified by libgcrypt
	char p_hex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
	char q_hex[] = "08CF83642A709A097B447997640129DA299B1A47D1EB3750BA308B0FE64F5FBD3";
	char g_hex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
	
	size_t nr_bytes_scanned;
	gcry_error_t error;
	
	error = gcry_mpi_scan(&p, GCRYMPI_FMT_HEX, p_hex, 0, &nr_bytes_scanned);
	check(error);
	
	error = gcry_mpi_scan(&q, GCRYMPI_FMT_HEX, q_hex, 0, &nr_bytes_scanned);
	check(error);
	
	error = gcry_mpi_scan(&g, GCRYMPI_FMT_HEX, g_hex, 0, &nr_bytes_scanned);
	check(error);
}

struct KeyPair elgamal_create_keypair() {
	
	size_t parse_error_offset;
	gcry_error_t error;
	
	void* bytes = gcry_random_bytes_secure(2048/8, GCRY_VERY_STRONG_RANDOM);
	gcry_mpi_t x = gcry_mpi_snew(2048);
	error = gcry_mpi_scan(&x, GCRYMPI_FMT_USG, bytes, 2048/8, &parse_error_offset);
	check(error);
	
	gcry_mpi_t y = gcry_mpi_new(0);
	gcry_mpi_powm(y, g, x, p);
	
	gcry_sexp_t priv_key;
	error = gcry_sexp_build(&priv_key, &parse_error_offset, "(private-key (elg (p %M) (g %M) (y %M) (x %M)))", p, g, y, x);
	check(error);

	error = gcry_pk_testkey(priv_key);
	check(error);

	gcry_sexp_release(priv_key);
	gcry_free(bytes);
	
	return (struct KeyPair){
		x,
		y,
	};
}

void elgamal_keypair_deleter(struct KeyPair* p) {
	gcry_mpi_release((gcry_mpi_t) p->sec);
	gcry_mpi_release((gcry_mpi_t) p->pub);
	p->sec = NULL;
	p->pub = NULL;
}

void elgamal_get_key_array(unsigned char** buffer, size_t* len, void* key) {
	gcry_mpi_t mpi = (gcry_mpi_t) key;
	
	gcry_error_t error;
	
	error = gcry_mpi_aprint(GCRYMPI_FMT_USG, buffer, len, mpi);
	check(error);
}

void* elgamal_get_group_element(bool secure) {
	size_t parse_error_offset;
	gcry_error_t error;
	
	void* bytes = gcry_random_bytes_secure(2048/8, GCRY_VERY_STRONG_RANDOM);
	gcry_mpi_t a = secure ? gcry_mpi_snew(2048) : gcry_mpi_new(2048);
	error = gcry_mpi_scan(&a, GCRYMPI_FMT_USG, bytes, 2048/8, &parse_error_offset);
	check(error);
	
	gcry_free(bytes);
	
	return a;
}

void elgamal_free_group_element(void* el) {
	gcry_mpi_release((gcry_mpi_t) el);
}

void* elgamal_get_key_exchange_value(void* group_el) {
	gcry_mpi_t el = (gcry_mpi_t) group_el;
	
	gcry_mpi_t val = gcry_mpi_new(0);
	gcry_mpi_powm(val, g, el, p);
	
	return val;
}

void elgamal_add_public_share(char** buffer, size_t* out_len, char const* share, size_t in_len, void* pubkey) {
	
	gcry_error_t error;
	size_t parse_error_pos;
	
	gcry_mpi_t y = (gcry_mpi_t) pubkey;
	
	gcry_mpi_t mpi_share;
	error = gcry_mpi_scan(&mpi_share, GCRYMPI_FMT_USG, share, in_len, &parse_error_pos);
	check(error);
	
	gcry_mpi_t result = gcry_mpi_new(0);
	gcry_mpi_mulm(result, mpi_share, y, p);
	
	error = gcry_mpi_aprint(GCRYMPI_FMT_USG, (unsigned char**) buffer, out_len, result);
	check(error);
}

void elgamal_shared_key_deleter(struct SharedKey* s) {
	gcry_mpi_release((gcry_mpi_t) s->shared);
	s->shared = NULL;
}


struct SharedKey elgamal_derive_shared_key(struct KeyPair keypair, unsigned char const* other_pub, size_t pub_len, unsigned char const* value, size_t value_len, void* priv_value, bool swap) {

	gcry_error_t error;
	size_t parse_error_pos;

	gcry_mpi_t ga;
	error = gcry_mpi_scan(&ga, GCRYMPI_FMT_USG, value, value_len, &parse_error_pos);
	check(error);
	
	gcry_mpi_t b = (gcry_mpi_t) priv_value;
	gcry_mpi_t gab = gcry_mpi_snew(0);
	gcry_mpi_powm(gab, ga, b, p);

	gcry_mpi_release(ga);

	return (struct SharedKey){
		gab
	};
}

void elgamal_deinitialize(void) {
	gcry_mpi_release(p);
	gcry_mpi_release(q);
	gcry_mpi_release(g);
}