1 files changed, 88 insertions, 0 deletions
diff --git a/libnetdata/eval/eval.h b/libnetdata/eval/eval.h
new file mode 100644
index 00000000..57dae9d0
--- /dev/null
+++ b/libnetdata/eval/eval.h
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_EVAL_H
+#define NETDATA_EVAL_H 1
+
+#include "../libnetdata.h"
+
+#define EVAL_MAX_VARIABLE_NAME_LENGTH 300
+
+typedef enum rrdcalc_status {
+    RRDCALC_STATUS_REMOVED       = -2,
+    RRDCALC_STATUS_UNDEFINED     = -1,
+    RRDCALC_STATUS_UNINITIALIZED =  0,
+    RRDCALC_STATUS_CLEAR         =  1,
+    RRDCALC_STATUS_RAISED        =  2,
+    RRDCALC_STATUS_WARNING       =  3,
+    RRDCALC_STATUS_CRITICAL      =  4
+} RRDCALC_STATUS;
+
+typedef struct eval_variable {
+    char *name;
+    uint32_t hash;
+    struct eval_variable *next;
+} EVAL_VARIABLE;
+
+typedef struct eval_expression {
+    const char *source;
+    const char *parsed_as;
+
+    RRDCALC_STATUS *status;
+    calculated_number *this;
+    time_t *after;
+    time_t *before;
+
+    calculated_number result;
+
+    int error;
+    BUFFER *error_msg;
+
+    // hidden EVAL_NODE *
+    void *nodes;
+
+    // custom data to be used for looking up variables
+    struct rrdcalc *rrdcalc;
+} EVAL_EXPRESSION;
+
+#define EVAL_VALUE_INVALID    0
+#define EVAL_VALUE_NUMBER     1
+#define EVAL_VALUE_VARIABLE   2
+#define EVAL_VALUE_EXPRESSION 3
+
+// parsing and evaluation
+#define EVAL_ERROR_OK                             0
+
+// parsing errors
+#define EVAL_ERROR_MISSING_CLOSE_SUBEXPRESSION    1
+#define EVAL_ERROR_UNKNOWN_OPERAND                2
+#define EVAL_ERROR_MISSING_OPERAND                3
+#define EVAL_ERROR_MISSING_OPERATOR               4
+#define EVAL_ERROR_REMAINING_GARBAGE              5
+#define EVAL_ERROR_IF_THEN_ELSE_MISSING_ELSE      6
+
+// evaluation errors
+#define EVAL_ERROR_INVALID_VALUE                101
+#define EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS   102
+#define EVAL_ERROR_VALUE_IS_NAN                 103
+#define EVAL_ERROR_VALUE_IS_INFINITE            104
+#define EVAL_ERROR_UNKNOWN_VARIABLE             105
+
+// parse the given string as an expression and return:
+//   a pointer to an expression if it parsed OK
+//   NULL in which case the pointer to error has the error code
+extern EVAL_EXPRESSION *expression_parse(const char *string, const char **failed_at, int *error);
+
+// free all resources allocated for an expression
+extern void expression_free(EVAL_EXPRESSION *expression);
+
+// convert an error code to a message
+extern const char *expression_strerror(int error);
+
+// evaluate an expression and return
+// 1 = OK, the result is in: expression->result
+// 2 = FAILED, the error message is in: buffer_tostring(expression->error_msg)
+extern int expression_evaluate(EVAL_EXPRESSION *expression);
+
+extern int health_variable_lookup(const char *variable, uint32_t hash, struct rrdcalc *rc, calculated_number *result);
+
+#endif //NETDATA_EVAL_H