/*! \file
 *  \brief Communication via the \ref Serial interface (RS-232)
 */

#pragma once
#include "../types.h"

/*! \brief Serial interface.
 *  \ingroup io
 *
 *  This class provides a serial interface (COM1 - COM4) for communication with
 * the outside world.
 *
 *  The first IBM PC used the external chip [8250
 * UART](https://de.wikipedia.org/wiki/NSC_8250), whereas, in today's systems,
 * this functionality is commonly integrated into the motherboard chipset, but
 * remained compatible.
 *
 * \see [PC8250A Data Sheet](uart-8250a.pdf#page=11) (Registers on page 11)
 * \see [PC16550D Data Sheet](uart-16550d.pdf#page=16) (Successor, for optional
 * FIFO buffer, page 16)
 */

class Serial {
   public:
	/*! \brief COM-Port
	 *
	 *  The serial interface and its hardware addresses. Modern desktop PCs
	 * have, at most, a single, physical COM-port (`COM1`)
	 */
	enum class ComPort : uint16_t {
		COM1 = 0x3f8,
		COM2 = 0x2f8,
		COM3 = 0x3e8,
		COM4 = 0x2e8,
	};

	/*! \brief Transmission speed
	 *
	 *  The unit Baud describes the transmission speed in number of symbols per
	 * seconds. 1 Baud therefore equals the transmission of 1 symbol per second.
	 *  The possible Baud rates are whole-number dividers of the clock frequency
	 * of 115200 Hz..
	 */
	enum class BaudRate : uint16_t {
		B300 = 384,
		B600 = 192,
		B1200 = 96,
		B2400 = 48,
		B4800 = 24,
		B9600 = 12,
		B19200 = 6,
		B38400 = 3,
		B57600 = 2,
		B115200 = 1,
	};

	/*! \brief Number of data bits per character */
	enum class DataBits : uint8_t {
		D5 = 0,
		D6 = 1,
		D7 = 2,
		D8 = 3,
	};

	/*! \brief Number of stop bits per character */
	enum class StopBits : uint8_t {
		S1 = 0,
		S1_5 = 4,
		S2 = 4,
	};

	/*! \brief parity bit */
	enum class Parity : uint8_t {
		NONE = 0,
		ODD = 8,
		EVEN = 24,
		MARK = 40,
		SPACE = 56,
	};

   private:
	/*! \brief register index */
	enum class RegisterIndex : uint8_t {
		RECEIVE_BUFFER = 0,
		TRANSMIT_BUFFER = 0,
		INTERRUPT_ENABLE = 1,
		DIVISOR_LOW = 0,
		DIVISOR_HIGH = 1,
		INTERRUPT_IDENT = 2,
		FIFO_CONTROL = 2,
		LINE_CONTROL = 3,
		MODEM_CONTROL = 4,
		LINE_STATUS = 5,
		MODEM_STATUS = 6
	};

	/*! \brief Mask for the respective register */
	enum class RegisterMask : uint8_t {
		RECEIVED_DATA_AVAILABLE = 1 << 0,
		TRANSMITTER_HOLDING_REGISTER_EMPTY = 1 << 1,
		RECEIVER_LINE_STATUS = 1 << 2,
		MODEM_STATUS = 1 << 3,

		// Interrupt Ident Register
		INTERRUPT_PENDING = 1 << 0,	 ///< 0 means interrupt pending
		INTERRUPT_ID_0 = 1 << 1,
		INTERRUPT_ID_1 = 1 << 2,

		// FIFO Control Register
		ENABLE_FIFO = 1 << 0,  ///< 0 means disabled ^= conforming to 8250a
		CLEAR_RECEIVE_FIFO = 1 << 1,
		CLEAR_TRANSMIT_FIFO = 1 << 2,
		DMA_MODE_SELECT = 1 << 3,
		TRIGGER_RECEIVE = 1 << 6,

		// Line Control Register
		//  bits per character:  5   6   7   8
		WORD_LENGTH_SELECT_0 = 1 << 0,	//  Setting Select0:     0   1   0   1
		WORD_LENGTH_SELECT_1 = 1 << 1,	//  Setting Select1:     0   0   1   1
		NUMBER_OF_STOP_BITS = 1 << 2,  //  0 ≙ one stop bit, 1 ≙ 1.5/2 stop bits
		PARITY_ENABLE = 1 << 3,
		EVEN_PARITY_SELECT = 1 << 4,
		STICK_PARITY = 1 << 5,
		SET_BREAK = 1 << 6,
		DIVISOR_LATCH_ACCESS_BIT = 1 << 7,	// DLAB

		// Modem Control Register
		DATA_TERMINAL_READY = 1 << 0,
		REQUEST_TO_SEND = 1 << 1,
		OUT_1 = 1 << 2,
		OUT_2 = 1 << 3,	 // must be set for interrupts!
		LOOP = 1 << 4,

		// Line Status Register
		DATA_READY = 1 << 0,  // Set when there is a value in the receive buffer
		OVERRUN_ERROR = 1 << 1,
		PARITY_ERROR = 1 << 2,
		FRAMING_ERROR = 1 << 3,
		BREAK_INTERRUPT = 1 << 4,
		TRANSMITTER_HOLDING_REGISTER = 1 << 5,
		TRANSMITTER_EMPTY = 1 << 6,	 // Send buffer empty (ready to send)

		// Modem Status Register
		DELTA_CLEAR_TO_SEND = 1 << 0,
		DELTA_DATA_SET_READY = 1 << 1,
		TRAILING_EDGE_RING_INDICATOR = 1 << 2,
		DELTA_DATA_CARRIER_DETECT = 1 << 3,
		CLEAR_TO_SEND = 1 << 4,
		DATA_SET_READY = 1 << 5,
		RING_INDICATOR = 1 << 6,
		DATA_CARRIER_DETECT = 1 << 7
	};

	/*! \brief Read value from register
	 *
	 *
	 *  \param reg Register index
	 *  \return The value read from register
	 */
	uint8_t readReg(RegisterIndex reg);

	/*! \brief Write value to register
	 *
	 *
	 *  \param reg Register index
	 *  \param out value to be written
	 */
	void writeReg(RegisterIndex reg, uint8_t out);

   protected:
	/*! \brief Selected COM port */
	const ComPort port;

   public:
	/*! \brief Constructor
	 *
	 * Creates a Serial object that encapsulates the used COM port, as well as
	 * the parameters used for the serial connection. Default values are `8N1`
	 * (8 bit, no parity bit, one stop bit) with 115200 Baud using COM1.
	 *
	 */
	explicit Serial(ComPort port = ComPort::COM1,
					BaudRate baud_rate = BaudRate::B115200,
					DataBits data_bits = DataBits::D8,
					StopBits stop_bits = StopBits::S1,
					Parity parity = Parity::NONE);

	/*! \brief Write one byte to the serial interface
	 *
	 *
	 *  \param out Byte to be written
	 *  \return Byte written (or `-1` if writing byte failed)
	 */
	int write(uint8_t out);
};