1 /*
2   Copyright 2021 Northern.tech AS
3 
4   This file is part of CFEngine 3 - written and maintained by Northern.tech AS.
5 
6   This program is free software; you can redistribute it and/or modify it
7   under the terms of the GNU General Public License as published by the
8   Free Software Foundation; version 3.
9 
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13   GNU General Public License for more details.
14 
15   You should have received a copy of the GNU General Public License
16   along with this program; if not, write to the Free Software
17   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA
18 
19   To the extent this program is licensed as part of the Enterprise
20   versions of CFEngine, the applicable Commercial Open Source License
21   (COSL) may apply to this file if you as a licensee so wish it. See
22   included file COSL.txt.
23 */
24 
25 #ifndef CFENGINE_LOGIC_EXPRESSIONS_H
26 #define CFENGINE_LOGIC_EXPRESSIONS_H
27 
28 #include <stdbool.h>
29 #include <string_expressions.h>
30 
31 /*
32    Logic expressions grammar:
33 
34    <expr> ::= <or-expr>
35 
36    <or-expr> ::= <and-expr>
37                  <and-expr> | <and-expr>
38                  <and-expr> || <and-expr>
39 
40    <and-expr> ::= <not-expr>
41                   <not-expr> . <not-expr>
42                   <not-expr> & <not-expr>
43 
44    <not-expr> ::= ! <primary>
45                   <primary>
46 
47    <primary> ::= ( <expr> )
48                  <name>
49 
50    Basis of logic evaluation is <name> values which are provided by
51    StringExpression and suitable string->bool evaluator.
52 */
53 
54 typedef enum
55 {
56     LOGICAL_OP_OR,
57     LOGICAL_OP_AND,
58     LOGICAL_OP_NOT,
59     LOGICAL_OP_EVAL
60 } LogicalOp;
61 
62 typedef struct Expression_ Expression;
63 
64 struct Expression_
65 {
66     LogicalOp op;
67     union
68     {
69         struct
70         {
71             Expression *lhs;
72             Expression *rhs;
73         } andor;
74 
75         struct
76         {
77             Expression *arg;
78         } not;
79 
80         struct
81         {
82             StringExpression *name;
83         } eval;
84     } val;
85 };
86 
87 /* Parsing and evaluation */
88 
89 /*
90  * Result of parsing.
91  *
92  * if succeeded, then result is the result of parsing and position is last
93  * character consumed.
94  *
95  * if not succeeded, then result is NULL and position is last character consumed
96  * before the error.
97  */
98 typedef struct
99 {
100     Expression *result;
101     int position;
102 } ParseResult;
103 
104 ParseResult ParseExpression(const char *expr, int start, int end);
105 
106 typedef enum ExpressionValue
107 {
108     EXPRESSION_VALUE_ERROR = -1,
109     EXPRESSION_VALUE_FALSE = false,
110     EXPRESSION_VALUE_TRUE = true,
111 } ExpressionValue;
112 
113 /*
114  * Evaluator should return FALSE, TRUE or ERROR if unable to parse result.  In
115  * later case evaluation will be aborted and ERROR will be returned from
116  * EvalExpression.
117  */
118 typedef ExpressionValue(*NameEvaluator) (const char *name, void *param);
119 
120 /*
121  * Result is heap-allocated. In case evalfn() returns ERROR whole
122  * EvalExpression returns ERROR as well.
123  */
124 ExpressionValue EvalExpression(const Expression *expr,
125                                NameEvaluator nameevalfn, VarRefEvaluator varrefevalfn, void *param);
126 
127 /*
128  * Frees Expression produced by ParseExpression. NULL-safe.
129  */
130 void FreeExpression(Expression *expr);
131 
132 #endif
133