#include <Arduino.h>

#include "helper/SimpleRingBuffer.h"
#include "helper/DleEncoder.h"
#include "helper/crc_ccitt.h"

#include <avr/io.h>

//SPI is formally a library, so it is not part of the objects compiled
//from the core and we need to include it explicitly
#include "arduino_core/ArduinoCore-avr/libraries/SPI/src/SPI.h"

//Define which port to use for the SPI Chip Select
#define CS_PORT PORTC
#define CS_DDR DDRC

#define RING_BUFFER_SIZE 100
#define MAX_PACKET_LENGTH 20

static const uint8_t COMMAND_TRANSFER_SPI = 1;

SimpleRingBuffer ringBuffer(RING_BUFFER_SIZE, true);

uint8_t rawData[2 * RING_BUFFER_SIZE];
size_t rawDataSize = 0;

/**
 * Encode and send the data, last two bytes of data are assumed to be for the checksum
 * and will be overwritten with it
 */
void sendData(uint8_t *data, size_t len) {
	uint16_t crc = Calculate_CRC(data, len - 2);
	data[len - 2] = crc >> 8;
	data[len - 1] = crc;
	//we're being conservative here
	//TODO move this to global so other protocols can use it too
	uint8_t buffer[2 * len + 2];
	buffer[0] = DleEncoder::STX;
	size_t writtenLen;
	ReturnValue_t result = DleEncoder::encode(data, len, buffer, sizeof(buffer),
			&writtenLen, true);
	if (result != HasReturnvaluesIF::RETURN_OK) {
		return;
	}
	Serial.write(buffer, writtenLen);
}

void transferSPI(uint8_t address, uint8_t *data, size_t datalen) {
	SPI.beginTransaction(SPISettings(14000000, MSBFIRST, SPI_MODE0));
	CS_PORT = ~address;
	SPI.transfer(data, datalen);
	delay(100);
	CS_PORT = 0xff;
	SPI.endTransaction();

}

void handlePacket(uint8_t *packet, size_t packetLen) {
	//Paket layout is:
	// 8 bit command | 8 bit address | 16bit length | <length> byte data | 16 bit crc

	uint16_t crc = Calculate_CRC(packet, packetLen);

	if (crc != 0) {
		//Serial.println("invalid Checksum");
		return;
	}

	uint16_t payloadLen = (packet[2] << 8) | packet[3];

	if (payloadLen != packetLen - 6) {
		//Serial.println("invalid len");
		return;
	}

	uint8_t command = packet[0];
	uint8_t address = packet[1];

	switch (command) {
	case COMMAND_TRANSFER_SPI:
		transferSPI(address, packet + 4, payloadLen);
		//echo the data back, no need to change the header fields, they are the same
		//checksum will be written by sendData()
		sendData(packet, packetLen);
		break;
	default:
		//Serial.println("invalid command");
		break;
	}

}

void handleNewData() {
	ringBuffer.readData(rawData, sizeof(rawData), true, &rawDataSize);

	if (rawDataSize == 0) {
		return;
	}

	//look for STX
	size_t firstSTXinRawData = 0;
	while ((firstSTXinRawData < rawDataSize)
			&& (rawData[firstSTXinRawData] != DleEncoder::STX)) {
		firstSTXinRawData++;
	}

	if (rawData[firstSTXinRawData] != DleEncoder::STX) {
		//there is no STX in our data, throw it away...
		ringBuffer.deleteData(rawDataSize);
		return;
	}

	uint8_t packet[MAX_PACKET_LENGTH];
	size_t packetLen;

	size_t readSize;

	ReturnValue_t result = DleEncoder::decode(rawData + firstSTXinRawData,
			rawDataSize - firstSTXinRawData, &readSize, packet, sizeof(packet),
			&packetLen);

	size_t toDelete = firstSTXinRawData;
	if (result == HasReturnvaluesIF::RETURN_OK) {
		handlePacket(packet, packetLen);

		//after handling the packet, we can delete it from the raw stream, it has been copied to packet
		toDelete += readSize;
	}

	//remove Data which was processed
	ringBuffer.deleteData(toDelete);

}

//TODO check if this is thread safe by arduino
void serialEvent() {
	while (Serial.available()) {
		uint8_t byte = Serial.read();
		ringBuffer.writeData(&byte, 1);
	}
}

void setup() {
	CS_DDR = 0xff;
	CS_PORT = 0xff;
	Serial.begin(9600);
	SPI.begin();
}

void loop() {
	handleNewData();
	delay(100);
}