/*
 * Tardygrada VM — Crypto Implementation
 * Minimal SHA-256. No dependencies.
 * SHA-256 (hand-written) + ed25519 (Monocypher). Zero dependencies.
 */

#include "crypto.h"
#include <string.h>
#include <fcntl.h>
#include <unistd.h>

/* ============================================
 * SHA-256 — Minimal implementation
 * Based on FIPS 180-4
 * ============================================ */

static const uint32_t K[64] = {
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
    0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
    0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
    0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
    0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
    0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
    0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
    0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
    0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
};

#define ROTR(x, n) (((x) >> (n)) | ((x) << (32 - (n))))
#define CH(x, y, z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x, y, z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) (ROTR(x, 2) ^ ROTR(x, 13) ^ ROTR(x, 22))
#define EP1(x) (ROTR(x, 6) ^ ROTR(x, 11) ^ ROTR(x, 25))
#define SIG0(x) (ROTR(x, 7) ^ ROTR(x, 18) ^ ((x) >> 3))
#define SIG1(x) (ROTR(x, 17) ^ ROTR(x, 19) ^ ((x) >> 10))

static void sha256_transform(uint32_t state[8], const uint8_t block[64])
{
    uint32_t w[64];
    uint32_t a, b, c, d, e, f, g, h, t1, t2;

    for (int i = 0; i < 16; i++) {
        w[i] = ((uint32_t)block[i * 4] << 24) |
               ((uint32_t)block[i * 4 + 1] << 16) |
               ((uint32_t)block[i * 4 + 2] << 8) |
               ((uint32_t)block[i * 4 + 3]);
    }
    for (int i = 16; i < 64; i++)
        w[i] = SIG1(w[i - 2]) + w[i - 7] + SIG0(w[i - 15]) + w[i - 16];

    a = state[0]; b = state[1]; c = state[2]; d = state[3];
    e = state[4]; f = state[5]; g = state[6]; h = state[7];

    for (int i = 0; i < 64; i++) {
        t1 = h + EP1(e) + CH(e, f, g) + K[i] + w[i];
        t2 = EP0(a) + MAJ(a, b, c);
        h = g; g = f; f = e; e = d + t1;
        d = c; c = b; b = a; a = t1 + t2;
    }

    state[0] += a; state[1] += b; state[2] += c; state[3] += d;
    state[4] += e; state[5] += f; state[6] += g; state[7] += h;
}

void tardy_sha256(const void *data, size_t len, tardy_hash_t *out)
{
    uint32_t state[8] = {
        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
        0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
    };

    const uint8_t *msg = (const uint8_t *)data;
    uint8_t block[64];
    size_t i;

    /* Process full blocks */
    for (i = 0; i + 64 <= len; i += 64)
        sha256_transform(state, msg + i);

    /* Padding */
    size_t remaining = len - i;
    memset(block, 0, 64);
    if (remaining > 0)
        memcpy(block, msg + i, remaining);
    block[remaining] = 0x80;

    if (remaining >= 56) {
        sha256_transform(state, block);
        memset(block, 0, 64);
    }

    /* Length in bits, big-endian */
    uint64_t bits = (uint64_t)len * 8;
    for (int j = 0; j < 8; j++)
        block[56 + j] = (uint8_t)(bits >> (56 - j * 8));

    sha256_transform(state, block);

    /* Output */
    for (int j = 0; j < 8; j++) {
        out->bytes[j * 4]     = (uint8_t)(state[j] >> 24);
        out->bytes[j * 4 + 1] = (uint8_t)(state[j] >> 16);
        out->bytes[j * 4 + 2] = (uint8_t)(state[j] >> 8);
        out->bytes[j * 4 + 3] = (uint8_t)(state[j]);
    }
}

bool tardy_hash_eq(const tardy_hash_t *a, const tardy_hash_t *b)
{
    /* Constant-time comparison */
    uint8_t diff = 0;
    for (int i = 0; i < 32; i++)
        diff |= a->bytes[i] ^ b->bytes[i];
    return diff == 0;
}

/* ============================================
 * ed25519 — Real implementation via Monocypher
 * Public domain, single .c file, battle-tested.
 * ============================================ */

#include "monocypher.h"

void tardy_keygen(tardy_keypair_t *kp)
{
    /* Read 32 bytes of entropy for the secret seed */
    uint8_t seed[32];
    int fd = open("/dev/urandom", O_RDONLY);
    if (fd >= 0) {
        ssize_t n = read(fd, seed, 32);
        (void)n;
        close(fd);
    } else {
        memset(seed, 0x42, 32); /* fallback — should not happen */
    }

    /* Monocypher: derive keypair from seed
     * secret = seed (32 bytes) + public key (32 bytes) = 64 bytes
     * public = 32 bytes */
    crypto_eddsa_key_pair(kp->secret, kp->public, seed);

    /* Wipe seed from stack */
    crypto_wipe(seed, 32);
}

void tardy_sign(const tardy_keypair_t *kp, const void *data, size_t len,
                tardy_signature_t *out)
{
    crypto_eddsa_sign(out->bytes, kp->secret, data, len);
}

bool tardy_verify(const uint8_t pub[32], const void *data, size_t len,
                  const tardy_signature_t *sig)
{
    return crypto_eddsa_check(sig->bytes, pub, data, len) == 0;
}