// https://wokwi.com/projects/380383323394002945
// https://forum.arduino.cc/t/how-to-identify-moment-of-analog-sinusoidal-signal-peaking/1184837

int localMax;
int globalMax;

bool seenZero;

void setup() {
  Serial.begin(115200);
  Serial.println("hello there.");

  seenZero = false;
}

void loop() {
  delay(100); // whoa!
  int reading = analogRead(A0) - 512; // -512 to 512 then
  //  Serial.println(reading);

// first get the green marks point
  if (reading < 0) {
    if (!seenZero) {
      Serial.println("crossed zero going down");
      seenZero = true;

// bump globalMax if
      if (localMax > globalMax) {
        globalMax = localMax;
        Serial.print("new global max "); Serial.println(globalMax);         
      }
      else { // test for 
        Serial.print("SO IT WAS "); Serial.println(globalMax);
        globalMax = 0;  // reset for next cycle
      }
      localMax = 0;  // reset search for local maximum
    }
  }
  else /* reading >= 0 */ seenZero = false;

  if (reading > localMax) {
    Serial.print("new local max ");Serial.println(reading); 
    localMax = reading;
  }
}

/* hacking fragments you have been warned

return;

  needGlobal = true;

  if (reading < 0) {

    needLocal = true;

    if (testMax > globalMax) {
      globalMax = testMax;
      Serial.print("new global max "); Serial.println(globalMax);
    }


    localMax = 0;
    testMax = 0;


  }

  if (needLocal && reading > 0) {
    if (reading > testMax) {
      testMax = reading;
    }

    Serial.print("          max "); Serial.println(testMax);

    // found local max, assumes monotonic increasing input

    //    if (testMax > localMax) {
    //      testMax = localMax;
    //    }

  }

  if (reading < 0) {
    if (testMax > globalMax) {
      globalMax = testMax;
    }
    else {
      // new local maximum is less than candidate globalMax, so

      if (globalMax > 0) {
        Serial.print(" HERE "); Serial.println(globalMax);
      }

      globalMax = 0;
//      Serial.flush();
 //     for (; ;);   // figure out how to get out of here and reset the mechanism
    }
  }
}

////


    else {
// here now is new candidate for global max

Serial.println("now going down");
    }
*/

/*
else {
  if (needGlobal) {
    Serial.println("                        here");
    needGlobal = false;

    if (globalMax > trueMax) {
      trueMax = globalMax;
    }
    else {
      Serial.print("true maximum is "); Serial.println(globalMax);
      needGlobal = false;
    }
  }
}
*/