Fluent Calculator

Your task is to create a class that implements a simple calculator with fluent syntax.

FluentCalculator::init();

that has sets of properties and method of values and operations that can be accessed/called.

Rules:

• Values are zero, one, two, three, four, five, six, seven, eight and nine.
• Operations are plus, minus, times, dividedBy.
• Accessing a property of value and/or operation should be stackable to infinity,
• Accessing a value more than once will make the input value stacked (see example for more information),
• Accessing an operation more than once will overwrite the previous operation (see example for more information),
• Call to a value or operation should resolve to a primitive integer (round down to the nearest integer, if necessary) and returns the most recent calculation value.
• Accessing a property or call to a method other than values and operations should throw InvalidInputException (you don't have to re-declare the exception class, it's been done for you).
• class FluentCalculator cannot have more than 3 (three) methods including init().
• Maximum input and calculation value is 9 digit, if user try to input more than 9 digit or some calculation returns a value longer than 9 digit, throw a DigitCountOverflowException (you don't have to re-declare the exception class, it's been done for you).
• If a number is divided by zero, throw a DivisionByZeroException (you don't have to re-declare the exception class, it's been done for you).

Examples:

FluentCalculator::init()->one();                   // should return 1
FluentCalculator::init()->one->zero();             // should return 10
FluentCalculator::init()->one->plus->two();        // should return 3 (1 + 2)

FluentCalculator::init()->one->two->three->four->five->six->seven->eight->nine->zero();
// should throw DigitCountOverflowException since the input is more than 9 digit (1,234,567,890)

FluentCalculator::init()->nine->nine->nine->nine->nine->nine->nine->nine->nine->plus->one();
// should throw DigitCountOverflowException since the calculation will result more than 9 digit (999,999,999 + 1 = 1,000,000,000)

FluentCalculator::init()->one->plus->minus->two();
// returns -1 (operation "plus" is overwriten by "minus")

FluentCalculator::init()->one->add->two();
// should throw InvalidInputException since there is no value/operation named "add"

FluentCalculator::init()->one->plus->two->dividedBy->three->times->one->zero->minus->three->plus->eight();
/* should return 15
 * input: 1 + 2 / 3 * 10 - 3 + 8
 * calculation steps:
 * 1 + 2 = 3
 * 3 / 3 = 1
 * 1 * 10 = 10
 * 10 - 3 = 7
 * 7 + 8 = 15
 */