/* ============================================
  code is placed under the MIT license
  Copyright (c) 2024 J-M-L
  For the Arduino Forum : https://forum.arduino.cc/u/j-m-l

  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  THE SOFTWARE.
  ===============================================
*/


// test with "¥XYZab1¥XYZac0¥XYt12w" which will match the frame format for 3 frames

const byte startMarker = 0xA5;   // Start marker
const byte payloadLength = 5;    // Length of the payload
byte payload[payloadLength];     // Buffer to hold the payload
byte payloadIndex = 0;           // Current index in the payload buffer
enum State { WAIT_FOR_START, RECEIVE_PAYLOAD, RECEIVE_CHECKSUM, PROCESS_FRAME } currentState = WAIT_FOR_START;

void processSerialData() {
  while (Serial.available()) {
    byte incomingByte = Serial.read(); // Read the incoming byte

    switch (currentState) {
      case WAIT_FOR_START:
        if (incomingByte == startMarker) {
          payloadIndex = 0;              // Start a new frame
          currentState = RECEIVE_PAYLOAD;
        }
        break;

      case RECEIVE_PAYLOAD:
        payload[payloadIndex++] = incomingByte; // Store payload byte
        if (payloadIndex >= payloadLength) {
          currentState = RECEIVE_CHECKSUM;
        }
        break;

      case RECEIVE_CHECKSUM:
        { // compound statement needed because we define a local variable to this case
          byte cksum = 0;
          // Calculate checksum
          for (int i = 0; i < payloadLength; i++) cksum += payload[i];
          cksum ^= 0xFF;

          // Verify checksum
          if (cksum == incomingByte) {
            currentState = PROCESS_FRAME; // Move to processing state
          } else {
            Serial.println("Checksum error");
            Serial.print("Calculated Checksum = "); Serial.println(cksum);
            Serial.print("Expected Checksum = "); Serial.println(incomingByte);
            currentState = WAIT_FOR_START; // Reset state machine
          }
        }
        break;

      case PROCESS_FRAME:
        Serial.print("Frame received correctly: ");
        for (byte b : payload) {
          if (b < 0x10) Serial.write('0'); // Print leading zero for single-digit hex
          Serial.print(b, HEX);
          Serial.write(' ');
        }
        Serial.println();
        currentState = WAIT_FOR_START; // Reset to waiting for the next start marker
        break;
    }
  }
}

void setup() {
  Serial.begin(115200);  // Initialize Serial with baud rate 115200
  Serial.println(F("ready"));
}

void loop() {
  processSerialData();   // Call the function to process serial data
  // here you can do other stuff
}