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eval.go
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eval.go
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package kahoot
import (
"regexp"
"strconv"
"strings"
)
var simpleExprRegexp = regexp.MustCompile(`\(([0-9\+\*\s]*)\)`)
// eval evaluates a mathematical expression, such as:
//
// ((76 * 21) * (((81 + 4) * 55) + 10))
//
// This is necessary to obtain session tokens.
func eval(expr string) (int64, error) {
for {
// Evaluate a simple sub-expression.
match := simpleExprRegexp.FindStringSubmatch(expr)
if match == nil {
break
}
simple := match[1]
val, err := evalSimple(simple)
if err != nil {
return 0, err
}
valStr := strconv.FormatInt(val, 10)
expr = strings.Replace(expr, match[0], valStr, 1)
}
return evalSimple(expr)
}
// evalSimple evaluates an expression with no nested
// parentheses, like
//
// 23 + 64 + 35 * 35
//
func evalSimple(expr string) (int64, error) {
var sum int64
for _, sumTerm := range strings.Split(expr, "+") {
product := int64(1)
for _, numStr := range strings.Split(sumTerm, "*") {
num, err := strconv.ParseInt(strings.TrimSpace(numStr), 10, 64)
if err != nil {
return 0, err
}
product *= num
}
sum += product
}
return sum, nil
}