/* SPDX-License-Identifier: MIT */
/*
 * Author: Jianhui Zhao <[email protected]>
 *
 * Referenced from https://github.com/B-Con/crypto-algorithms/blob/master/sha256.c
 */

#include <stdbool.h>
#include <stdint.h>

#include "eco.h"

#define ECO_SHA256_MT "eco{sha256}"

#define SHA256_DIGEST_LEN 32

#define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
#define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))

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

struct sha256_ctx {
    uint8_t data[64];
    uint32_t datalen;
    uint64_t bitlen;
    uint32_t state[8];
};

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
};

static void sha256_transform(struct sha256_ctx *ctx, const uint8_t data[])
{
    uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

    for (i = 0, j = 0; i < 16; ++i, j += 4)
        m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
    for ( ; i < 64; ++i)
        m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];

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

    for (i = 0; i < 64; ++i) {
        t1 = h + EP1(e) + CH(e,f,g) + k[i] + m[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;
    }

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

static void sha256_init(struct sha256_ctx *ctx)
{
    ctx->datalen = 0;
    ctx->bitlen = 0;
    ctx->state[0] = 0x6a09e667;
    ctx->state[1] = 0xbb67ae85;
    ctx->state[2] = 0x3c6ef372;
    ctx->state[3] = 0xa54ff53a;
    ctx->state[4] = 0x510e527f;
    ctx->state[5] = 0x9b05688c;
    ctx->state[6] = 0x1f83d9ab;
    ctx->state[7] = 0x5be0cd19;
}

static void sha256_update(struct sha256_ctx *ctx, const uint8_t data[], size_t len)
{
    uint32_t i;

    for (i = 0; i < len; ++i) {
        ctx->data[ctx->datalen] = data[i];
        ctx->datalen++;
        if (ctx->datalen == 64) {
            sha256_transform(ctx, ctx->data);
            ctx->bitlen += 512;
            ctx->datalen = 0;
        }
    }
}

static void sha256_final(struct sha256_ctx *ctx, uint8_t hash[])
{
    uint32_t i;

    i = ctx->datalen;

    /* Pad whatever data is left in the buffer. */
    if (ctx->datalen < 56) {
        ctx->data[i++] = 0x80;
        while (i < 56)
            ctx->data[i++] = 0x00;
    }
    else {
        ctx->data[i++] = 0x80;
        while (i < 64)
            ctx->data[i++] = 0x00;
        sha256_transform(ctx, ctx->data);
        memset(ctx->data, 0, 56);
    }

    /* Append to the padding the total message's length in bits and transform. */
    ctx->bitlen += ctx->datalen * 8;
    ctx->data[63] = ctx->bitlen;
    ctx->data[62] = ctx->bitlen >> 8;
    ctx->data[61] = ctx->bitlen >> 16;
    ctx->data[60] = ctx->bitlen >> 24;
    ctx->data[59] = ctx->bitlen >> 32;
    ctx->data[58] = ctx->bitlen >> 40;
    ctx->data[57] = ctx->bitlen >> 48;
    ctx->data[56] = ctx->bitlen >> 56;
    sha256_transform(ctx, ctx->data);

    /*
     * Since this implementation uses little endian byte ordering and SHA uses big endian,
     * reverse all the bytes when copying the final state to the output hash.
     */
    for (i = 0; i < 4; ++i) {
        hash[i]      = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 4]  = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 8]  = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
        hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
    }
}

static int lua_sha256_sum(lua_State *L)
{
    size_t len;
    const char *data = luaL_checklstring(L, 1, &len);
    struct sha256_ctx ctx;
    uint8_t hash[SHA256_DIGEST_LEN];

    sha256_init(&ctx);
    sha256_update(&ctx, (const uint8_t *)data, len);
    sha256_final(&ctx, hash);

    lua_pushlstring(L, (const char *)hash, SHA256_DIGEST_LEN);

    return 1;
}

static int lua_sha256_update(lua_State *L)
{
    struct sha256_ctx *ctx = luaL_checkudata(L, 1, ECO_SHA256_MT);
    size_t len;
    const char *data = luaL_checklstring(L, 2, &len);

    sha256_update(ctx, (const uint8_t *)data, len);

    return 0;
}

static int lua_sha256_final(lua_State *L)
{
    struct sha256_ctx *ctx = luaL_checkudata(L, 1, ECO_SHA256_MT);
    uint8_t hash[SHA256_DIGEST_LEN];

    sha256_final(ctx, hash);
    lua_pushlstring(L, (const char *)hash, SHA256_DIGEST_LEN);

    return 1;
}

static const struct luaL_Reg sha256_methods[] = {
    {"update", lua_sha256_update},
    {"final", lua_sha256_final},
    {NULL, NULL}
};

static int lua_sha256_new(lua_State *L)
{
    struct sha256_ctx *ctx = lua_newuserdata(L, sizeof(struct sha256_ctx));

    lua_pushvalue(L, lua_upvalueindex(1));
    lua_setmetatable(L, -2);

    sha256_init(ctx);

    return 1;
}

int luaopen_eco_hash_sha256(lua_State *L)
{
    lua_newtable(L);

    lua_pushstring(L, ECO_SHA256_MT);
    lua_setfield(L, -2, "mtname");

    lua_pushcfunction(L, lua_sha256_sum);
    lua_setfield(L, -2, "sum");

    eco_new_metatable(L, ECO_SHA256_MT, sha256_methods);
    lua_pushcclosure(L, lua_sha256_new, 1);
    lua_setfield(L, -2, "new");

    return 1;
}