#define _GNU_SOURCE
#include "snapverify.h"

#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

/* Mirrors persist.c's SNAPSHOT_FORMAT_VERSION / header layout exactly — see
 * persist.c write_snapshot() (~line 1758) and load_snapshot() (~line 2325).
 * config-upgrade-snapshot task 1 bumped persist.c's SNAPSHOT_FORMAT_VERSION
 * 1->2 (host/queue admin-state frames migrated to capnp, Req 1.9/5.7) --
 * this MUST track that bump, or this tool hard-rejects every real
 * checkpoint the current codebase writes (task 8.4 finding). */
#define SNAP_FORMAT_VERSION 2u
#define SNAP_HEADER_MAX     (16 + 1 + 8 + 32) /* magic+lsn + optional cfgref tail */

static void fail(snapverify_report_t* rep, int rc, off_t off, const char* why)
{
    rep->ok          = 0;
    rep->fail_offset = off;
    snprintf(rep->fail_reason, sizeof(rep->fail_reason), "%s", why);
    (void)rc;
}

int snapverify_path(const char* path, FILE* out, snapverify_report_t* rep)
{
    if (!path)
        return -EINVAL;

    snapverify_report_t local;
    memset(&local, 0, sizeof(local));
    local.ok          = 1;
    local.fail_offset = -1;

    int fd = open(path, O_RDONLY);
    if (fd < 0) {
        int saved = errno;
        fail(&local, -saved, -1, strerror(saved));
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s\n", path, strerror(saved));
        return -saved;
    }

    struct stat st;
    if (fstat(fd, &st) != 0) {
        int saved = errno;
        close(fd);
        fail(&local, -saved, -1, strerror(saved));
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: fstat: %s\n", path, strerror(saved));
        return -saved;
    }
    local.file_size = st.st_size;

    char    header[SNAP_HEADER_MAX];
    ssize_t n = read(fd, header, sizeof(header));
    if (n < 16) {
        close(fd);
        fail(&local, -EIO, 0, "short read on header (need >= 16 bytes)");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s\n", path, local.fail_reason);
        return -EIO;
    }

    if (memcmp(header, "XCESNAP\0", 8) != 0) {
        close(fd);
        fail(&local, -EINVAL, 0, "bad magic (not XCESNAP)");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s\n", path, local.fail_reason);
        return -EINVAL;
    }

    memcpy(&local.checkpoint_lsn, header + 8, 8);
    if (n >= SNAP_HEADER_MAX) {
        /* Decode the tag/hash UNCONDITIONALLY whenever the header extends
         * this far, regardless of the presence byte -- so a caller can
         * inspect the raw bytes even in edge cases. has_cfgref keeps its
         * existing meaning (whether those bytes are semantically
         * meaningful) untouched. */
        memcpy(&local.cfgref_tag, header + 17, 8);
        memcpy(local.cfgref_sha, header + 25, 32);
        if (header[16] != 0)
            local.has_cfgref = 1;
    }

    off_t consumed = (off_t)n;

    if (st.st_size <= consumed) {
        /* Legacy, position-only checkpoint — not a defect (design.md). */
        close(fd);
        local.consumed = consumed;
        if (rep)
            *rep = local;
        if (out)
            fprintf(out,
                    "snapverify: %s: OK (legacy position-only, lsn=%" PRIu64
                    ", size=%jd)\n",
                    path, local.checkpoint_lsn, (intmax_t)local.file_size);
        return 0;
    }

    uint32_t fmt = 0;
    if (read(fd, &fmt, sizeof(fmt)) != (ssize_t)sizeof(fmt)) {
        close(fd);
        fail(&local, -EIO, consumed, "short read on format_version");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s (offset %jd)\n", path,
                    local.fail_reason, (intmax_t)consumed);
        return -EIO;
    }
    consumed += (off_t)sizeof(fmt);
    local.has_entity_section = 1;
    local.format_version     = fmt;

    if (fmt != SNAP_FORMAT_VERSION) {
        close(fd);
        fail(&local, -EINVAL, consumed - (off_t)sizeof(fmt),
             "unrecognized format_version");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s (got %u, expected %u, offset %jd)\n",
                    path, local.fail_reason, fmt, SNAP_FORMAT_VERSION,
                    (intmax_t)local.fail_offset);
        return -EINVAL;
    }

    uint32_t job_count = 0;
    if (read(fd, &job_count, sizeof(job_count)) != (ssize_t)sizeof(job_count)) {
        close(fd);
        fail(&local, -EIO, consumed, "short read on job_count");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s (offset %jd)\n", path,
                    local.fail_reason, (intmax_t)consumed);
        return -EIO;
    }
    consumed += (off_t)sizeof(job_count);
    local.job_count = job_count;

    for (uint32_t i = 0; i < job_count; i++) {
        off_t    len_off = consumed;
        uint32_t plen     = 0;
        if (read(fd, &plen, sizeof(plen)) != (ssize_t)sizeof(plen)) {
            close(fd);
            fail(&local, -EIO, len_off, "short read on job payload_len");
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: job %u: %s (offset %jd)\n", path,
                        i, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }
        consumed += (off_t)sizeof(plen);

        if (plen == 0 || (off_t)plen > st.st_size - consumed) {
            close(fd);
            char why[160];
            snprintf(why, sizeof(why),
                     "bad payload_len=%u (remaining=%jd)", plen,
                     (intmax_t)(st.st_size - consumed));
            fail(&local, -EIO, len_off, why);
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: job %u: %s (length field at "
                             "offset %jd)\n",
                        path, i, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }

        if (lseek(fd, plen, SEEK_CUR) < 0) {
            close(fd);
            fail(&local, -EIO, consumed, "seek past job payload failed");
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: job %u: %s\n", path, i,
                        local.fail_reason);
            return -EIO;
        }
        consumed += (off_t)plen;
        local.jobs_ok++;
    }

    uint32_t queue_count = 0;
    if (read(fd, &queue_count, sizeof(queue_count)) !=
            (ssize_t)sizeof(queue_count)) {
        close(fd);
        fail(&local, -EIO, consumed, "short read on queue_count");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s (offset %jd)\n", path,
                    local.fail_reason, (intmax_t)consumed);
        return -EIO;
    }
    consumed += (off_t)sizeof(queue_count);
    local.queue_count = queue_count;

    for (uint32_t i = 0; i < queue_count; i++) {
        off_t    len_off = consumed;
        uint32_t plen     = 0;
        if (read(fd, &plen, sizeof(plen)) != (ssize_t)sizeof(plen)) {
            close(fd);
            fail(&local, -EIO, len_off, "short read on queue payload_len");
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: queue %u: %s (offset %jd)\n",
                        path, i, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }
        consumed += (off_t)sizeof(plen);

        if (plen == 0 || (off_t)plen > st.st_size - consumed) {
            close(fd);
            char why[160];
            snprintf(why, sizeof(why),
                     "bad payload_len=%u (remaining=%jd)", plen,
                     (intmax_t)(st.st_size - consumed));
            fail(&local, -EIO, len_off, why);
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: queue %u: %s (length field at "
                             "offset %jd)\n",
                        path, i, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }

        if (lseek(fd, plen, SEEK_CUR) < 0) {
            close(fd);
            fail(&local, -EIO, consumed, "seek past queue payload failed");
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: queue %u: %s\n", path, i,
                        local.fail_reason);
            return -EIO;
        }
        consumed += (off_t)plen;
        local.queues_ok++;
    }

    /* Host section (config-upgrade-snapshot task 4/8.4, SNAPSHOT_FORMAT_
     * VERSION=2): new after the queue section (design.md "Checkpoint File
     * Layout", persist.c load_snapshot_entities()/write_snapshot()). Same
     * [payload_len][bytes] per-frame structural shape as the job/queue
     * loops above -- this tool validates structure only, never decodes the
     * capnp payload. */
    uint32_t host_count = 0;
    if (read(fd, &host_count, sizeof(host_count)) !=
            (ssize_t)sizeof(host_count)) {
        close(fd);
        fail(&local, -EIO, consumed, "short read on host_count");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s (offset %jd)\n", path,
                    local.fail_reason, (intmax_t)consumed);
        return -EIO;
    }
    consumed += (off_t)sizeof(host_count);
    local.host_count = host_count;

    for (uint32_t i = 0; i < host_count; i++) {
        off_t    len_off = consumed;
        uint32_t plen     = 0;
        if (read(fd, &plen, sizeof(plen)) != (ssize_t)sizeof(plen)) {
            close(fd);
            fail(&local, -EIO, len_off, "short read on host payload_len");
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: host %u: %s (offset %jd)\n",
                        path, i, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }
        consumed += (off_t)sizeof(plen);

        if (plen == 0 || (off_t)plen > st.st_size - consumed) {
            close(fd);
            char why[160];
            snprintf(why, sizeof(why),
                     "bad payload_len=%u (remaining=%jd)", plen,
                     (intmax_t)(st.st_size - consumed));
            fail(&local, -EIO, len_off, why);
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: host %u: %s (length field at "
                             "offset %jd)\n",
                        path, i, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }

        if (lseek(fd, plen, SEEK_CUR) < 0) {
            close(fd);
            fail(&local, -EIO, consumed, "seek past host payload failed");
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: host %u: %s\n", path, i,
                        local.fail_reason);
            return -EIO;
        }
        consumed += (off_t)plen;
        local.hosts_ok++;
    }

    /* Config-bytes section (config-upgrade-snapshot task 2.3/8.4): a
     * single flat length-prefixed blob appended LAST, after the host
     * section -- NOT a [count][frame...] shape like job/queue/host above,
     * since there is exactly one active configuration, never a set
     * (persist.c write_snapshot()). The length field itself may be
     * legitimately ABSENT (a file that ends right after the host section
     * is still a valid, if slightly older, fmt=2-consistent shape) --
     * distinguish that from the length field being present-but-zero
     * (persist.c explicitly writes an empty-but-present section when no
     * local config bytes exist yet) and from a genuinely truncated length
     * field (a short, non-zero partial read -- real corruption). */
    uint32_t cfg_bytes_len = 0;
    ssize_t  cfg_len_n     = read(fd, &cfg_bytes_len, sizeof(cfg_bytes_len));
    if (cfg_len_n == 0) {
        /* Clean EOF right after the host section -- no config-bytes
         * section present at all. Not a defect. */
        local.has_config_bytes_section = 0;
    } else if (cfg_len_n != (ssize_t)sizeof(cfg_bytes_len)) {
        close(fd);
        fail(&local, -EIO, consumed, "short read on config_bytes_len");
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s (offset %jd)\n", path,
                    local.fail_reason, (intmax_t)consumed);
        return -EIO;
    } else {
        off_t len_off = consumed;
        consumed += (off_t)sizeof(cfg_bytes_len);
        local.has_config_bytes_section = 1;
        local.config_bytes_len         = cfg_bytes_len;

        if ((off_t)cfg_bytes_len > st.st_size - consumed) {
            close(fd);
            char why[160];
            snprintf(why, sizeof(why),
                     "bad config_bytes_len=%u (remaining=%jd)", cfg_bytes_len,
                     (intmax_t)(st.st_size - consumed));
            fail(&local, -EIO, len_off, why);
            if (rep)
                *rep = local;
            if (out)
                fprintf(out, "snapverify: %s: %s (length field at offset "
                             "%jd)\n",
                        path, local.fail_reason, (intmax_t)len_off);
            return -EIO;
        }

        if (cfg_bytes_len > 0) {
            if (lseek(fd, cfg_bytes_len, SEEK_CUR) < 0) {
                close(fd);
                fail(&local, -EIO, consumed,
                     "seek past config bytes failed");
                if (rep)
                    *rep = local;
                if (out)
                    fprintf(out, "snapverify: %s: %s\n", path,
                            local.fail_reason);
                return -EIO;
            }
            consumed += (off_t)cfg_bytes_len;
        }
    }

    close(fd);
    local.consumed = consumed;
    if (consumed != st.st_size) {
        char why[160];
        snprintf(why, sizeof(why),
                 "trailing garbage: consumed=%jd but file_size=%jd",
                 (intmax_t)consumed, (intmax_t)st.st_size);
        fail(&local, -EIO, consumed, why);
        if (rep)
            *rep = local;
        if (out)
            fprintf(out, "snapverify: %s: %s\n", path, local.fail_reason);
        return -EIO;
    }

    if (rep)
        *rep = local;
    if (out)
        fprintf(out,
                "snapverify: %s: OK (lsn=%" PRIu64 " fmt=%u jobs=%u queues=%u "
                "hosts=%u cfgref_tag=%016" PRIx64 " cfg_bytes_len=%u "
                "has_cfg_bytes=%d size=%jd)\n",
                path, local.checkpoint_lsn, local.format_version,
                local.job_count, local.queue_count, local.host_count,
                local.cfgref_tag, local.config_bytes_len,
                local.has_config_bytes_section, (intmax_t)local.file_size);
    return 0;
}