// readStringUntilLimitedTimeout.ino
// Reads chars into a String until newline '\n'
// https://www.forward.com.au/pfod/ArduinoProgramming/SerialReadingParsing/index.html
// Pros: Simple. Non-Blocking, Robust against unexpectedly long input lines and missing termination, until_c char
// Cons: Nothing really.

String input;

void setup() {
  Serial.begin(9600);
  for (int i = 10; i > 0; i--) {
    Serial.print(' '); Serial.print(i);
    delay(500);
  }
  Serial.println();
  Serial.println(F("readStringUntilLimitedTimeout.ino"));
  input.reserve(20); // expected line size, see Taming Arduino Strings
  // https://www.forward.com.au/pfod/ArduinoProgramming/ArduinoStrings/index.html
}

// read Serial until until_c char found or limit char read or timeout, returns true when found/limited else false
// non-blocking, until_c, if found, is returned as last char in String, updates input String with chars read
bool readStringUntil(String& input, char until_c, size_t char_limit) { // call with char_limit == 0 for no limit
  static bool timerRunning; static unsigned long timerStart;     // timeout static variables
  static const unsigned long timeout_mS = 1000; // 1sec  set to 0 for no timeout

  while (Serial.available()) {
    timerRunning = false; // set true below if don't return first
    char c = Serial.read();
    input += c;
    if (c == until_c) {
      return true;
    }
    if (char_limit && (input.length() >= char_limit)) {
      return true;
    }
    // restart timer running
    if (timeout_mS > 0) {  // only start if we have a non-zero timeout
      timerRunning = true;
      timerStart = millis();
    }
  }
  if (timerRunning && ((millis() - timerStart) > timeout_mS)) {
    timerRunning = false;
    return true;
  }
  return false;
}

char terminatingChar = '\n';
void loop() {
  if (readStringUntil(input, terminatingChar, 20)) { // read until find newline or have read 20 chars, use 0 for unlimited no chars
    if (input.lastIndexOf(terminatingChar) >= 0) {   // could also use check  if (input[input.length()-1] == terminatingChar) {
      Serial.print(F(" got a line of input '")); Serial.print(input); Serial.println("'");
    } else {
      Serial.print(F(" reached limit or timeout without newline '")); Serial.print(input); Serial.println("'");
    }
    input = ""; // clear after processing for next line
  }
}