import "dart:math" show pow;

Map<String, int> hex_table = {

"A": 10,

"B": 11,

"C": 12,

"D": 13,

"E": 14,

"F": 15,

};

void main() {

print(hexadecimal_to_decimal("1abc")); // 6844

print(hexadecimal_to_decimal(" -123 ")); // -291

try {

print(hexadecimal_to_decimal("1x")); //error

} catch (ex) {

print(ex);

}

}

int hexadecimal_to_decimal(String hex_string) {

hex_string = hex_string.trim().toUpperCase();

if (hex_string == "") {

throw Exception("An empty value was passed to the function");

}

bool is_negative = hex_string[0] == "-";

if (is_negative) hex_string = hex_string.substring(1);

int decimal_val = 0;

for (int i = 0; i < hex_string.length; i++) {

if (int.tryParse(hex_string[i]) == null &&

hex_table.containsKey(hex_string[i]) == false) {

throw Exception("Non-hex value was passed to the function");

} else {

decimal_val +=

pow(16, hex_string.length - i - 1).toInt() *

(int.tryParse(hex_string[i]) ?? hex_table[hex_string[i]] ?? 0);

}

}

return is_negative ? -1 * decimal_val : decimal_val;

}