TimeLogger for Combine Debugging

TimeLogger+Combine.swift

// Note: This snipped comes from Ray Wenderlich's "Combine" book.
// https://store.raywenderlich.com/products/combine-asynchronous-programming-with-swift

class TimeLogger: TextOutputStream {
    private var previous = Date()
    private let formatter = NumberFormatter()
    
    init() {
        formatter.maximumFractionDigits = 5
        formatter.minimumFractionDigits = 5
    }
    
    func write(_ string: String) {
        let trimmed = string.trimmingCharacters(in: .whitespacesAndNewLines)
        guard !trimmed.isEmpty else { return }
        
        let now = Date()
        
        print("+\(formatter.string(for: now.timeIntervalSince(previous))!)s: \(string)")
        previous = now
    }
}