/// @file protocol.h
#pragma once
#include <stdint.h>
#include "mmu2_crc.h"

namespace modules {

/// @brief The MMU communication protocol implementation and related stuff.
///
/// See description of the new protocol in the MMU 2021 doc
namespace protocol {

/// Definition of request message codes
enum class RequestMsgCodes : uint8_t {
    unknown = 0,
    Query = 'Q',
    Tool = 'T',
    Load = 'L',
    Mode = 'M',
    Unload = 'U',
    Reset = 'X',
    Finda = 'P',
    Version = 'S',
    Button = 'B',
    Eject = 'E',
    Write = 'W',
    Cut = 'K',
    FilamentType = 'F',
    FilamentSensor = 'f',
    Home = 'H',
    Read = 'R'
};

/// Definition of response message parameter codes
enum class ResponseMsgParamCodes : uint8_t {
    unknown = 0,
    Processing = 'P',
    Error = 'E',
    Finished = 'F',
    Accepted = 'A',
    Rejected = 'R',
    Button = 'B' // the MMU registered a button press and is sending it to the printer for processing
};

/// A request message - requests are being sent by the printer into the MMU.
struct RequestMsg {
    RequestMsgCodes code; ///< code of the request message
    uint8_t value; ///< value of the request message or address of variable to read/write
    uint16_t value2; ///< in case or write messages - value to be written into the register

    /// CRC8 check - please note we abuse this byte for CRC of ResponseMsgs as well.
    /// The crc8 byte itself is not added into the CRC computation (obviously ;) )
    /// Beware - adding any members of this data structure may need changing the way CRC is being computed!
    uint8_t crc8;

    constexpr uint8_t ComputeCRC8() const {
        uint8_t crc = 0;
        crc = modules::crc::CRC8::CCITT_updateCX(0, (uint8_t)code);
        crc = modules::crc::CRC8::CCITT_updateCX(crc, value);
        crc = modules::crc::CRC8::CCITT_updateW(crc, value2);
        return crc;
    }

    /// @param code of the request message
    /// @param value of the request message
    inline constexpr RequestMsg(RequestMsgCodes code, uint8_t value)
        : code(code)
        , value(value)
        , value2(0)
        , crc8(ComputeCRC8()) {
    }

    /// Intended for write requests
    /// @param code of the request message ('W')
    /// @param address of the register
    /// @param value to write into the register
    inline constexpr RequestMsg(RequestMsgCodes code, uint8_t address, uint16_t value)
        : code(code)
        , value(address)
        , value2(value)
        , crc8(ComputeCRC8()) {
    }

    constexpr uint8_t CRC() const { return crc8; }
};

/// A response message - responses are being sent from the MMU into the printer as a response to a request message.
struct ResponseMsg {
    RequestMsg request; ///< response is always preceeded by the request message
    ResponseMsgParamCodes paramCode; ///< code of the parameter
    uint16_t paramValue; ///< value of the parameter

    constexpr uint8_t ComputeCRC8() const {
        uint8_t crc = request.ComputeCRC8();
        crc = modules::crc::CRC8::CCITT_updateCX(crc, (uint8_t)paramCode);
        crc = modules::crc::CRC8::CCITT_updateW(crc, paramValue);
        return crc;
    }

    /// @param request the source request message this response is a reply to
    /// @param paramCode code of the parameter
    /// @param paramValue value of the parameter
    inline constexpr ResponseMsg(RequestMsg request, ResponseMsgParamCodes paramCode, uint16_t paramValue)
        : request(request)
        , paramCode(paramCode)
        , paramValue(paramValue) {
        this->request.crc8 = ComputeCRC8();
    }

    constexpr uint8_t CRC() const { return request.crc8; }
};

/// Combined commandStatus and its value into one data structure (optimization purposes)
struct ResponseCommandStatus {
    ResponseMsgParamCodes code;
    uint16_t value;
    inline constexpr ResponseCommandStatus(ResponseMsgParamCodes code, uint16_t value)
        : code(code)
        , value(value) {}
};

/// Message decoding return values
enum class DecodeStatus : uint_fast8_t {
    MessageCompleted, ///< message completed and successfully lexed
    NeedMoreData, ///< message incomplete yet, waiting for another byte to come
    Error, ///< input character broke message decoding
};

/// Protocol class is responsible for creating/decoding messages in Rx/Tx buffer
///
/// Beware - in the decoding more, it is meant to be a statefull instance which works through public methods
/// processing one input byte per call.
class Protocol {
public:
    inline Protocol()
        : rqState(RequestStates::Code)
        , requestMsg(RequestMsgCodes::unknown, 0)
        , rspState(ResponseStates::RequestCode)
        , responseMsg(RequestMsg(RequestMsgCodes::unknown, 0), ResponseMsgParamCodes::unknown, 0) {
    }

    /// Takes the input byte c and steps one step through the state machine
    /// @returns state of the message being decoded
    DecodeStatus DecodeRequest(uint8_t c);

    /// Decodes response message in rxbuff
    /// @returns decoded response message structure
    DecodeStatus DecodeResponse(uint8_t c);

    /// Encodes request message msg into txbuff memory
    /// It is expected the txbuff is large enough to fit the message
    /// @returns number of bytes written into txbuff
    static uint8_t EncodeRequest(const RequestMsg &msg, uint8_t *txbuff);

    /// Encodes Write request message msg into txbuff memory
    /// It is expected the txbuff is large enough to fit the message
    /// @returns number of bytes written into txbuff
    static uint8_t EncodeWriteRequest(uint8_t address, uint16_t value, uint8_t *txbuff);

    /// @returns the maximum byte length necessary to encode a request message
    /// Beneficial in case of pre-allocating a buffer for enconding a RequestMsg.
    static constexpr uint8_t MaxRequestSize() { return 13; }

    /// @returns the maximum byte length necessary to encode a response message
    /// Beneficial in case of pre-allocating a buffer for enconding a ResponseMsg.
    static constexpr uint8_t MaxResponseSize() { return 14; }

    /// Encode generic response Command Accepted or Rejected
    /// @param msg source request message for this response
    /// @param ar code of response parameter
    /// @param txbuff where to format the message
    /// @returns number of bytes written into txbuff
    static uint8_t EncodeResponseCmdAR(const RequestMsg &msg, ResponseMsgParamCodes ar, uint8_t *txbuff);

    /// Encode response to Read FINDA query
    /// @param msg source request message for this response
    /// @param findaValue 1/0 (on/off) status of FINDA
    /// @param txbuff where to format the message
    /// @returns number of bytes written into txbuff
    static uint8_t EncodeResponseReadFINDA(const RequestMsg &msg, uint8_t findaValue, uint8_t *txbuff);








    /// Encode response to Query operation status
    /// @param msg source request message for this response
    /// @param code status of operation (Processing, Error, Finished)
    /// @param value related to status of operation(e.g. error code or progress)
    /// @param txbuff where to format the message
    /// @returns number of bytes written into txbuff
    static uint8_t EncodeResponseQueryOperation(const RequestMsg &msg, ResponseCommandStatus rcs, uint8_t *txbuff);

    /// Encode response to Read query
    /// @param msg source request message for this response
    /// @param accepted true if the read query was accepted
    /// @param value2 variable value
    /// @param txbuff where to format the message
    /// @returns number of bytes written into txbuff
    static uint8_t EncodeResponseRead(const RequestMsg &msg, bool accepted, uint16_t value2, uint8_t *txbuff);

    /// @returns the most recently lexed request message
    inline const RequestMsg GetRequestMsg() const { return requestMsg; }

    /// @returns the most recently lexed response message
    inline const ResponseMsg GetResponseMsg() const { return responseMsg; }

    /// resets the internal request decoding state (typically after an error)
    void ResetRequestDecoder() {
        rqState = RequestStates::Code;
    }

    /// resets the internal response decoding state (typically after an error)
    void ResetResponseDecoder() {
        rspState = ResponseStates::RequestCode;
    }

#ifndef UNITTEST
private:
#endif
    enum class RequestStates : uint8_t {
        Code, ///< starting state - expects message code
        Value, ///< expecting code value
        Address, ///< expecting address for Write command
        WriteValue, ///< value to be written (Write command)
        CRC, ///< CRC
        Error ///< automaton in error state
    };

    RequestStates rqState;
    RequestMsg requestMsg;

    enum class ResponseStates : uint8_t {
        RequestCode, ///< starting state - expects message code
        RequestValue, ///< expecting code value
        ParamCode, ///< expecting param code
        ParamValue, ///< expecting param value
        CRC, ///< expecting CRC value
        Error ///< automaton in error state
    };

    ResponseStates rspState;
    ResponseMsg responseMsg;

    static constexpr bool IsNewLine(uint8_t c) {
        return c == '\n' || c == '\r';
    }
    static constexpr bool IsDigit(uint8_t c) {
        return c >= '0' && c <= '9';
    }
    static constexpr bool IsCRCSeparator(uint8_t c) {
        return c == '*';
    }
    static constexpr bool IsHexDigit(uint8_t c) {
        return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f');
    }
    static constexpr uint8_t Char2Nibble(uint8_t c) {
        switch (c) {
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
            return c - '0';
        case 'a':
        case 'b':
        case 'c':
        case 'd':
        case 'e':
        case 'f':
            return c - 'a' + 10;
        default:
            return 0;
        }
    }

    static constexpr uint8_t Nibble2Char(uint8_t n) {
        switch (n) {
        case 0:
        case 1:
        case 2:
        case 3:
        case 4:
        case 5:
        case 6:
        case 7:
        case 8:
        case 9:
            return n + '0';
        case 0xa:
        case 0xb:
        case 0xc:
        case 0xd:
        case 0xe:
        case 0xf:
            return n - 10 + 'a';
        default:
            return 0;
        }
    }

    /// @returns number of characters written
    static uint8_t UInt8ToHex(uint8_t value, uint8_t *dst);

    /// @returns number of characters written
    static uint8_t UInt16ToHex(uint16_t value, uint8_t *dst);

    static uint8_t BeginEncodeRequest(const RequestMsg &msg, uint8_t *dst);

    static uint8_t AppendCRC(uint8_t crc, uint8_t *dst);
};

} // namespace protocol
} // namespace modules

namespace mp = modules::protocol;