/*
 * dm_crypto.c — криптография прямого чата (DM)
 */

#include "dm_crypto.h"
#include "../../lib/debug_config.h"

#define OPENSSL_API_COMPAT 0x10100000L
#include <openssl/evp.h>
#include <openssl/sha.h>

#include <string.h>
#include <stdio.h>

#define DM_ID "dm_crypto"

/* Медиа использует тот же ключ target, но отдельное пространство nonce. */
uint64_t dm_derive_conv_id(uint64_t a, uint64_t b) {
    uint64_t lo = a < b ? a : b;
    uint64_t hi = a < b ? b : a;

    SHA256_CTX ctx;
    uint8_t hash[32];
    SHA256_Init(&ctx);
    SHA256_Update(&ctx, "utun_dm_v1", 9);
    SHA256_Update(&ctx, &lo, 8);
    SHA256_Update(&ctx, &hi, 8);
    SHA256_Final(hash, &ctx);

    uint64_t id;
    memcpy(&id, hash, 8);
    id &= 0x7FFFFFFFFFFFFFFFULL;
    if (id == 0) id = 1;
    return id;
}

int dm_derive_content_key(const uint8_t my_priv[32], const uint8_t peer_pub[32],
                          uint8_t out[DM_CONTENT_KEY_SIZE]) {
    if (!my_priv || !peer_pub || !out) return -1;

    EVP_PKEY* my_pkey = EVP_PKEY_new_raw_private_key(EVP_PKEY_X25519, NULL, my_priv, 32);
    if (!my_pkey) { DEBUG_ERROR(DEBUG_CATEGORY_DM, "%s: EVP_PKEY_new_raw_private_key failed", DM_ID); return -1; }
    EVP_PKEY* peer_pkey = EVP_PKEY_new_raw_public_key(EVP_PKEY_X25519, NULL, peer_pub, 32);
    if (!peer_pkey) { EVP_PKEY_free(my_pkey); DEBUG_ERROR(DEBUG_CATEGORY_DM, "%s: EVP_PKEY_new_raw_public_key failed", DM_ID); return -1; }

    EVP_PKEY_CTX* dctx = EVP_PKEY_CTX_new(my_pkey, NULL);
    uint8_t shared[32];
    size_t shared_len = sizeof(shared);
    int rc = -1;
    if (!dctx) goto out;
    if (EVP_PKEY_derive_init(dctx) <= 0) goto out;
    if (EVP_PKEY_derive_set_peer(dctx, peer_pkey) <= 0) goto out;
    if (EVP_PKEY_derive(dctx, shared, &shared_len) <= 0 || shared_len != sizeof(shared)) goto out;

    SHA256_CTX sctx;
    SHA256_Init(&sctx);
    SHA256_Update(&sctx, shared, sizeof(shared));
    SHA256_Update(&sctx, "utun_dm_content", 15);
    SHA256_Final(out, &sctx);
    rc = 0;

out:
    if (dctx) EVP_PKEY_CTX_free(dctx);
    EVP_PKEY_free(my_pkey);
    EVP_PKEY_free(peer_pkey);
    if (rc != 0) DEBUG_ERROR(DEBUG_CATEGORY_DM, "%s: X25519 derive failed", DM_ID);
    return rc;
}

void dm_build_nonce(uint64_t conv_id, uint64_t author, uint64_t seq, uint8_t nonce[DM_NONCE_SIZE]) {
    SHA256_CTX ctx;
    uint8_t hash[32];
    SHA256_Init(&ctx);
    SHA256_Update(&ctx, &conv_id, 8);
    SHA256_Update(&ctx, &author, 8);
    SHA256_Update(&ctx, &seq, 8);
    SHA256_Final(hash, &ctx);
    memcpy(nonce, hash, DM_NONCE_SIZE);
}