//
//  String.swift
//  EmployeeDirectory
//
//  Created by Matt Bruce on 1/20/25.
//

import Foundation

extension String {
    /// Formats a string into a US phone number format (XXX-XXX-XXXX).
    /// Non-numeric characters are removed, and formatting is applied based on the length of the string.
    /// - Returns: A formatted phone number as a string.
    internal func formatUSNumber() -> String {
        // mask for the phone numver
        let mask = "XXX-XXX-XXXX"
        
        let numbers = filter { $0.isNumber }
        var result = ""
        var index = numbers.startIndex // numbers iterator

        // iterate over the mask characters until the iterator of numbers ends
        for ch in mask where index < numbers.endIndex {
            if ch == "X" {
                // mask requires a number in this place, so take the next one
                result.append(numbers[index])

                // move numbers iterator to the next index
                index = numbers.index(after: index)

            } else {
                result.append(ch) // just append a mask character
            }
        }
        return result
    }    
}