/* Copyright (C) 2025 Open Information Security Foundation

 *

 * You can copy, redistribute or modify this Program under the terms of

 * the GNU General Public License version 2 as published by the Free

 * Software Foundation.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * version 2 along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

 * 02110-1301, USA.

 */

#include "suricata-common.h"

#include "detect.h"

#include "detect-parse.h"

#include "detect-engine.h"

#include "detect-engine-buffer.h"

#include "detect-entropy.h"

#include "util-var-name.h"

#include "flow-var.h"

#include "rust.h"

static int DetectEntropySetup(DetectEngineCtx *de_ctx, Signature *s, const char *arg)

{

    DetectEntropyData *ded = SCDetectEntropyParse(arg);

    if (ded == NULL) {

        goto error;

    }

    int sm_list = DETECT_SM_LIST_PMATCH;

    if (s->init_data->list != DETECT_SM_LIST_NOTSET) {

        /* sticky buffer */

        if (DetectBufferGetActiveList(de_ctx, s) == -1)

            goto error;

        sm_list = s->init_data->list;

        const char *name;

        if (sm_list == DETECT_SM_LIST_BASE64_DATA) {

            name = "base64_data";

        } else {

            name = DetectEngineBufferTypeGetNameById(de_ctx, sm_list);

            if (name == NULL) {

                DEBUG_VALIDATE_BUG_ON(1);

                name = "unknown";

            }

        }

        ded->fv_idx = VarNameStoreRegister(name, VAR_TYPE_FLOW_FLOAT);

    } else {

        ded->fv_idx = VarNameStoreRegister("content", VAR_TYPE_FLOW_FLOAT);

    }

    if (ded->fv_idx == 0) {

        goto error;

    }

    if (SCSigMatchAppendSMToList(de_ctx, s, DETECT_ENTROPY, (SigMatchCtx *)ded, sm_list) != NULL) {

        SCReturnInt(0);

    }

    /* fall through */

error:

    SCLogDebug("error during entropy setup");

    if (ded != NULL) {

        SCDetectEntropyFree(ded);

    }

    SCReturnInt(-1);

}

static void DetectEntropyFree(DetectEngineCtx *de_ctx, void *ptr)

{

    if (ptr) {

        DetectEntropyData *ded = (DetectEntropyData *)ptr;

        VarNameStoreUnregister(ded->fv_idx, VAR_TYPE_FLOW_FLOAT);

        SCDetectEntropyFree(ptr);

    }

}

bool DetectEntropyDoMatch(DetectEngineThreadCtx *det_ctx, const Signature *s,

        const SigMatchCtx *ctx, Flow *flow, const uint8_t *buffer, const uint32_t buffer_len)

{

    double entropy = -1.0;

    bool rc = SCDetectEntropyMatch(buffer, buffer_len, (const DetectEntropyData *)ctx, &entropy);

    if (flow && entropy != -1.0) {

        DetectEntropyData *ded = (DetectEntropyData *)ctx;

        FlowVarAddFloat(flow, ded->fv_idx, entropy);

    }

    return rc;

}

void DetectEntropyRegister(void)

{

    sigmatch_table[DETECT_ENTROPY].name = "entropy";

    sigmatch_table[DETECT_ENTROPY].desc = "calculate entropy";

    sigmatch_table[DETECT_ENTROPY].url = "/rules/payload-keywords.html#entropy";

    sigmatch_table[DETECT_ENTROPY].Free = DetectEntropyFree;

    sigmatch_table[DETECT_ENTROPY].Setup = DetectEntropySetup;

}