/*
 * Text detection based on ascmagic.c from the file(1) utility.
 *
 * Portions Copyright (C) 2013-2019 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
 * Portions Copyright (C) 2008-2013 Sourcefire, Inc.
 *
 * Copyright (c) Ian F. Darwin 1986-1995.
 * Software written by Ian F. Darwin and others;
 * maintained 1995-present by Christos Zoulas and others.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice immediately at the beginning of the file, without modification,
 *    this list of conditions, and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *  
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if HAVE_CONFIG_H
#include "clamav-config.h"
#endif

#include <stdio.h>
#include <string.h>
#include <memory.h>
#include <ctype.h>
#include <stdlib.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "clamav.h"
#include "filetypes.h"
#include "textdet.h"
#include "others.h"

#define F 0 /* character never appears in text */
#define T 1 /* character appears in plain ASCII text */
#define I 2 /* character appears in ISO-8859 text */
#define X 3 /* character appears in non-ISO extended ASCII (Mac, IBM PC) */

// clang-format off
static char text_chars[256] = {
    /*                  BEL BS HT LF    FF CR    */
    F, F, F, F, F, F, F, T, T, T, T, F, T, T, F, F,  /* 0x0X */
    /*                              ESC          */
    F, F, F, F, F, F, F, F, F, F, F, T, F, F, F, F,  /* 0x1X */
    T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T,  /* 0x2X */
    T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T,  /* 0x3X */
    T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T,  /* 0x4X */
    T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T,  /* 0x5X */
    T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T,  /* 0x6X */
    T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, F,  /* 0x7X */
    /*            NEL                            */
    X, X, X, X, X, T, X, X, X, X, X, X, X, X, X, X,  /* 0x8X */
    X, X, X, X, X, X, X, X, X, X, X, X, X, X, X, X,  /* 0x9X */
    I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I,  /* 0xaX */
    I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I,  /* 0xbX */
    I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I,  /* 0xcX */
    I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I,  /* 0xdX */
    I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I,  /* 0xeX */
    I, I, I, I, I, I, I, I, I, I, I, I, I, I, I, I   /* 0xfX */
};
// clang-format on

static int td_isascii(const unsigned char *buf, unsigned int len)
{
    unsigned int i;

    // @TODO:  UTF8 BOM Detection.
    //    The following BOM detection results in False Negatives in regression testing
    //    which can be eliminated by adding a condition to call cli_scanhtml for CL_TYPE_TEXT_UTF8
    //    in scanners.c:cli_scanraw().  However, cli_scanhtml was written for ASCII and has
    //    not been validated to correctly handle multibyte UTF8.
    // /* Check for the Byte-Order-Mark for UTF-8 */
    // if ((len >= 3) &&
    //    (buf[0] == 0xEF) &&
    //    (buf[1] == 0xBB) &&
    //    (buf[2] == 0xBF))
    // {
    //    return 0;
    // }

    /* Validate that the data all falls within the bounds of 
	 * plain ASCII, ISO-8859 text, and non-ISO extended ASCII (Mac, IBM PC)
	 */
    for (i = 0; i < len; i++)
        if (text_chars[buf[i]] == F)
            return 0;

    return 1;
}

static int td_isutf8(const unsigned char *buf, unsigned int len)
{
    unsigned int i, j, gotone = 0;

    for (i = 0; i < len; i++) {
        if ((buf[i] & 0x80) == 0) { /* 0xxxxxxx is plain ASCII */
            /*
	     * Even if the whole file is valid UTF-8 sequences,
	     * still reject it if it uses weird control characters.
	     */
            if (text_chars[buf[i]] != T)
                return 0;

        } else if ((buf[i] & 0x40) == 0) { /* 10xxxxxx never 1st byte */
            return 0;
        } else { /* 11xxxxxx begins UTF-8 */
            unsigned int following;

            if ((buf[i] & 0x20) == 0) { /* 110xxxxx */
                /* c = buf[i] & 0x1f; */
                following = 1;
            } else if ((buf[i] & 0x10) == 0) { /* 1110xxxx */
                /* c = buf[i] & 0x0f; */
                following = 2;
            } else if ((buf[i] & 0x08) == 0) { /* 11110xxx */
                /* c = buf[i] & 0x07; */
                following = 3;
            } else if ((buf[i] & 0x04) == 0) { /* 111110xx */
                /* c = buf[i] & 0x03; */
                following = 4;
            } else if ((buf[i] & 0x02) == 0) { /* 1111110x */
                /* c = buf[i] & 0x01; */
                following = 5;
            } else {
                return 0;
            }

            for (j = 0; j < following; j++) {
                if (++i >= len)
                    return gotone;

                if ((buf[i] & 0x80) == 0 || (buf[i] & 0x40))
                    return 0;

                /* c = (c << 6) + (buf[i] & 0x3f); */
            }

            gotone = 1;
        }
    }

    return gotone;
}

static int td_isutf16(const unsigned char *buf, unsigned int len)
{
    unsigned int be = 1, nobom = 0, i, c, bad = 0, high = 0;

    if (len < 2)
        return 0;

    if (buf[0] == 0xff && buf[1] == 0xfe)
        be = 0;
    else if (buf[0] == 0xfe && buf[1] == 0xff)
        be = 1;
    else
        nobom = 1;

    for (i = 2; i + 1 < len; i += 2) {
        if (be)
            c = buf[i + 1] + 256 * buf[i];
        else
            c = buf[i] + 256 * buf[i + 1];

        if (c == 0xfffe)
            return 0;

        if (c < 128 && text_chars[c] != T) {
            if (nobom)
                return 0;
            else
                bad++;
        } else if (c >= 128) {
            high++;
        }
    }

    //   if (nobom && high >= len / 4)
    //        return 0;

    if (!nobom && bad >= len / 2)
        return 0;

    return 1 + be;
}

cli_file_t cli_texttype(const unsigned char *buf, unsigned int len)
{
    int ret;

    if (td_isascii(buf, len)) {
        cli_dbgmsg("Recognized ASCII text\n");
        return CL_TYPE_TEXT_ASCII;
    } else if (td_isutf8(buf, len)) {
        cli_dbgmsg("Recognized UTF-8 character data\n");
        return CL_TYPE_TEXT_UTF8;
    } else if ((ret = td_isutf16(buf, len))) {
        cli_dbgmsg("Recognized %s character data\n", (ret == 1) ? "UTF-16LE" : "UTF-16BE");
        return (ret == 1) ? CL_TYPE_TEXT_UTF16LE : CL_TYPE_TEXT_UTF16BE;
    } else {
        cli_dbgmsg("Recognized binary data\n");
        return CL_TYPE_BINARY_DATA;
    }
}