/*
  StarForth — Steady-State Virtual Machine Runtime

  Copyright (c) 2023–2025 Robert A. James
  All rights reserved.

  This file is part of the StarForth project.

  Licensed under the StarForth License, Version 1.0 (the "License");
  you may not use this file except in compliance with the License.

  You may obtain a copy of the License at:
      https://github.com/star.4th@proton.me/StarForth/LICENSE.txt

  This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
  express or implied, including but not limited to the warranties of
  merchantability, fitness for a particular purpose, and noninfringement.

  See the License for the specific language governing permissions and
  limitations under the License.
*/

/**
 * homeblocks_sig.c - Drive signature check (FABRIC-2.md, Milestone 4).
 * See starkernel/homeblocks_sig.h for the format and interface design.
 */

#include "starkernel/homeblocks_sig.h"

#include <stddef.h>
#include <string.h>

#include "blkio.h"
#include "block_subsystem.h" /* compute_crc64() -- same CRC-64/ISO this file's
                              * check reuses rather than duplicating */

uint64_t homeblocks_sig_compute_crc(const homeblocks_sig_t *sig) {
    /* Covers every field up to but not including hdr_crc itself (and never
     * _pad, which sits after it) -- offsetof is the exact boundary, not a
     * hand-counted byte offset that could drift out of sync with the
     * struct's own field list. */
    size_t crc_span = offsetof(homeblocks_sig_t, hdr_crc);
    return compute_crc64((const uint8_t *)sig, crc_span);
}

homeblocks_sig_result_t homeblocks_sig_check(struct blkio_dev *dev,
                                              uint32_t sig_start_fblock,
                                              homeblocks_sig_t *out_sig) {
    uint8_t          buf[4096];
    uint32_t         i;
    homeblocks_sig_t local;
    uint64_t         expected_crc;

    if (!dev) return HOMEBLOCKS_SIG_READ_ERROR;

    /* homeblocks_sig_t is exactly one 4KiB devblock; blkio's own unit is a
     * 1KiB "forth block" (BLKIO_FORTH_BLOCK_SIZE), so the header spans 4
     * consecutive reads starting at sig_start_fblock. */
    for (i = 0; i < 4; i++) {
        if (blkio_read((blkio_dev_t *)dev, sig_start_fblock + i,
                        buf + (size_t)i * BLKIO_FORTH_BLOCK_SIZE) != BLKIO_OK) {
            return HOMEBLOCKS_SIG_READ_ERROR;
        }
    }

    /* Copy into a properly-aligned local rather than reinterpreting buf's
     * address directly -- buf is only byte-aligned, and homeblocks_sig_t
     * has uint64_t members; a raw cast would be a strict-aliasing and
     * alignment violation for no benefit over one memcpy. */
    memcpy(&local, buf, sizeof(local));

    if (HOMEBLOCKS_SIG_GET_MAGIC(local.magic) != (uint32_t)(HOMEBLOCKS_SIG_MAGIC & 0xFFFFFFFFULL)) {
        return HOMEBLOCKS_SIG_BLANK;
    }

    if (HOMEBLOCKS_SIG_GET_VERSION(local.magic) != HOMEBLOCKS_SIG_VERSION_0) {
        return HOMEBLOCKS_SIG_BAD_VERSION;
    }

    expected_crc = homeblocks_sig_compute_crc(&local);
    if (expected_crc != local.hdr_crc) {
        return HOMEBLOCKS_SIG_BAD_CRC;
    }

    if (out_sig) *out_sig = local;
    return HOMEBLOCKS_SIG_OK;
}