binaryexpressionparser.cpp

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/*
Copyright (C) 2002-2020 UFO: Alien Invasion.

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

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
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

*/

#include "binaryexpressionparser.h"
#include "common.h"

typedef enum
{
    BEPERR_NONE, BEPERR_BRACE, BEPERR_NOEND, BEPERR_NOTFOUND
} binaryExpressionParserError_t;

class BinaryExpressionParser {
private:
    binaryExpressionParserError_t binaryExpressionParserError;
    BEPEvaluteCallback_t varFunc;
    char varName[MAX_VAR];
    bool result;
    const void* userdata;

    inline void SkipWhiteSpaces (const char** s) const
    {
        while (**s == ' ' || **s == '\t')
            (*s)++;
    }

    inline void NextChar (const char** s) const
    {
        (*s)++;
        /* skip white-spaces too */
        SkipWhiteSpaces(s);
    }

    const char* GetSwitchName (const char** s)
    {
        int pos = 0;

        /* skip non printable chars and special chars that are used to define the binary expression */
        while (**s > ' ' && **s != '^' && **s != '|' && **s != '&' && **s != '!' && **s != '(' && **s != ')') {
            varName[pos++] = **s;
            (*s)++;
        }
        varName[pos] = '\0';

        return varName;
    }

    bool CheckOR (const char** s)
    {
        bool result = false;
        enum {
            BEP_NONE, BEP_OR, BEP_EXCLUSIVE_OR
        };
        int goOn = BEP_NONE;

        SkipWhiteSpaces(s);
        do {
            if (goOn == BEP_EXCLUSIVE_OR)
                result ^= CheckAND(s);
            else
                result |= CheckAND(s);

            if (**s == '|') {
                goOn = BEP_OR;
                NextChar(s);
            } else if (**s == '^') {
                goOn = BEP_EXCLUSIVE_OR;
                NextChar(s);
            } else {
                goOn = BEP_NONE;
            }
        } while (goOn != BEP_NONE && !binaryExpressionParserError);

        return result;
    }

    bool CheckAND (const char** s)
    {
        bool result = true;
        bool negate = false;
        bool goOn = false;

        do {
            /* parse all negate chars and swap the flag accordingly */
            while (**s == '!') {
                negate ^= true;
                NextChar(s);
            }
            /* handling braces */
            if (**s == '(') {
                NextChar(s);
                /* and the result of the inner clause by calling the entry
                 * point again (and apply the negate flag) */
                result &= CheckOR(s) ^ negate;
                if (**s != ')')
                    binaryExpressionParserError = BEPERR_BRACE;
                NextChar(s);
            } else {
                /* get the variable state by calling the evaluate callback */
                const int value = varFunc(GetSwitchName(s), userdata);
                if (value == -1)
                    binaryExpressionParserError = BEPERR_NOTFOUND;
                else
                    result &= value ^ negate;
                SkipWhiteSpaces(s);
            }

            /* check whether there is another and clause */
            if (**s == '&') {
                goOn = true;
                NextChar(s);
            } else {
                goOn = false;
            }
            negate = false;
        } while (goOn && !binaryExpressionParserError);

        return result;
    }

public:
    BinaryExpressionParser (const char* expr, BEPEvaluteCallback_t varFuncParam, const void* userdataPtr) :
        binaryExpressionParserError(BEPERR_NONE), varFunc(varFuncParam), userdata(userdataPtr)
    {
        varName[0] = 0;
        const char* str = expr;
        result = CheckOR(&str);
        /* check for no end error */
        if (Q_strvalid(str) && !binaryExpressionParserError)
            binaryExpressionParserError = BEPERR_NOEND;
    }

    inline bool getResult() const
    {
        return result;
    }

    inline binaryExpressionParserError_t getError() const
    {
        return binaryExpressionParserError;
    }
};

bool BEP_Evaluate (const char* expr, BEPEvaluteCallback_t varFuncParam, const void* userdata)
{
    if (!Q_strvalid(expr))
        return true;

    BinaryExpressionParser bep(expr, varFuncParam, userdata);
    const bool result = bep.getResult();
    const binaryExpressionParserError_t error = bep.getError();

    switch (error) {
    case BEPERR_NONE:
        /* do nothing */
        return result;
    case BEPERR_BRACE:
        Com_Printf("')' expected in binary expression (%s).\n", expr);
        return true;
    case BEPERR_NOEND:
        Com_Printf("Unexpected end of condition in binary expression (%s).\n", expr);
        return result;
    case BEPERR_NOTFOUND:
        Com_Printf("Variable not found in binary expression (%s).\n", expr);
        return false;
    }
    Com_Error(ERR_FATAL, "Unknown CheckBEP error in binary expression (%s)", expr);
}