import "dart:math" show pow;

import 'package:test/test.dart';

// octal number to decimal number conversion

//

// function to take oct string value and return decmal string value

String ocatal_to_decimal(String oct_val) {

// checking for unexpected values

oct_val = oct_val.trim();

if (oct_val.isEmpty) {

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

}

// negative number check

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

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

int oct;

try {

oct = int.parse(oct_val);

} catch (e) {

throw new FormatException("An invalid value was passed to the function");

}

// checking number not valid for octal is passed(0-7)

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

if (!(int.parse(oct_val.substring(i, i + 1)) < 8)) {

throw new FormatException("An invalid value was passed to the function");

}

;

}

// converting octal to decimal

int dec_val = 0, i = 0;

while (oct != 0) {

dec_val = dec_val + ((oct % 10) * pow(8, i).toInt());

i++;

oct = oct ~/ 10;

}

// returning the value

if (is_negative) {

return "-" + dec_val.toString();

}

return dec_val.toString();

}

// driver function

void main() {

// test cases for different input

test("ocatal_to_decimal 75", () {

expect(ocatal_to_decimal("75"), equals("61"));

});

test("ocatal_to_decimal -62", () {

expect(ocatal_to_decimal("-62"), equals("-50"));

});

test("ocatal_to_decimal rasies error when number is invalid", () {

expect(() => ocatal_to_decimal("84"), throwsFormatException);

});

test("ocatal_to_decimal rasies error when number is invalid", () {

expect(() => ocatal_to_decimal("as23"), throwsFormatException);

});

test("ocatal_to_decimal of empty string raises error", () {

expect(() => ocatal_to_decimal(""), throwsFormatException);

});

}