// Copyright 2015 Mobilinkd LLC <rob@mobilinkd.com>
// All rights reserved.

#ifndef MOBILINKD__KISS_HPP_
#define MOBILINKD__KISS_HPP_

#include <iterator>
#include <algorithm>
#include <cstdint>

#include "HdlcFrame.hpp"

namespace mobilinkd { namespace tnc { namespace kiss {

const uint8_t FRAME_DATA = 0x00;
const uint8_t FRAME_TX_DELAY = 0x01;
const uint8_t FRAME_P_PERSIST = 0x02;
const uint8_t FRAME_SLOT_TIME = 0x03;
const uint8_t FRAME_TX_TAIL = 0x04;
const uint8_t FRAME_DUPLEX = 0x05;
const uint8_t FRAME_HARDWARE = 0x06;
const uint8_t FRAME_LOG = 0x07;
const uint8_t FRAME_RETURN = 0xFF;

void handle_frame(uint8_t frame_type, hdlc::IoFrame* frame) __attribute__((optimize("-Os")));
// void handle_frame(uint8_t frame_type, hdlc::IoFrame* frame);

struct slip_encoder
{
    typedef std::forward_iterator_tag iterator_category;
    typedef size_t difference_type;
    typedef char value_type;
    typedef char& reference;
    typedef char* pointer;

    static const char FEND = 0xC0;
    static const char FESC = 0xDB;
    static const char TFEND = 0xDC;
    static const char TFESC = 0xDD;

    const char* packet_;
    size_t size_;
    size_t pos_;
    char current_;
    bool shifting_;

    slip_encoder()
    : packet_(0), size_(0), pos_(0), current_(0), shifting_(false)
    {}

    slip_encoder(const char* packet, size_t len)
    : packet_(packet), size_(len), pos_(0), current_(0), shifting_(false)
    {
        set_current();
    }

    void set_current() {
        if ((packet_[pos_] == FEND) or (packet_[pos_] == FESC)) {
            current_ = FESC;
            shifting_ = true;
        } else {
            current_ = packet_[pos_];
        }
    }

    char operator*() const {
        return current_;
    }

    slip_encoder& operator++() {

        if (!size_) return *this;

        if (shifting_) {
            shifting_ = false;
            current_ = (packet_[pos_] == FEND ? TFEND : TFESC);
            return *this;
        }
        pos_ += 1;

        if (pos_ != size_) {
            set_current();
        } else {
            packet_ = 0;
            pos_ = 0;
            size_ = 0;
        }

        return *this;
    }

    slip_encoder operator++(int) {
        slip_encoder tmp(*this);
        ++(*this);
        return tmp;
    }

    bool operator==(const slip_encoder& other) const {
        return (packet_ == other.packet_) and
            (pos_ == other.pos_) and (size_ == other.size_);
    }

    bool operator!=(const slip_encoder& other) const {
        return not ((*this) == other);
    }
};

/**
 * This is a input iterator adapter that SLIP-encodes the data from the
 * underlying frame iterator.  The only requirement is that the underlying
 * iterator meets the requirements of an input iterator and that its value
 * type is convertible to char.
 */
struct slip_encoder2
{
    typedef std::input_iterator_tag iterator_category;
    typedef size_t difference_type;
    typedef char value_type;
    typedef char& reference;
    typedef char* pointer;

    static const char FEND = 0xC0;
    static const char FESC = 0xDB;
    static const char TFEND = 0xDC;
    static const char TFESC = 0xDD;

    hdlc::IoFrame::iterator iter_;
    mutable bool shifting_;

    slip_encoder2() = delete;

    explicit slip_encoder2(hdlc::IoFrame::iterator iter)
    : iter_(iter), shifting_(false)
    {}

    slip_encoder2(const slip_encoder2& other)
    : iter_(other.iter_), shifting_(other.shifting_)
    {}

    void swap(slip_encoder2& other) {
        std::swap(this->iter_, other.iter_);
        std::swap(this->shifting_, other.shifting_);
    }

    slip_encoder2& operator=(const slip_encoder2& other)
    {
        slip_encoder2 tmp{other};
        this->swap(tmp);
        return *this;
    }

    /**
     * Return the current iterator value.  The value will be one of:
     *
     *  - the actual iterator value.
     *  - FESC if the character is FESC/FEND and not shifting.
     *  - TFESC/TFEND, the transposed shift characters when in shift mode.
     *
     * @return the slip-encoded character.
     */
    char operator*() const {
        char c = *iter_;

        if (shifting_) {
            return c == FEND ? TFEND : TFESC;
        }

        if ((c == FEND) or (c == FESC)) {
            return FESC;
        }

        return c;
    }

    /**
     * Iterate through the buffer, doing SLIP encoding.  The iterator is
     * either in normal mode or shift mode.  When moving into shift mode,
     * the frame iterator is not advanced.
     *
     * This either advances the frame iterator or it enters shift mode.
     *
     * The iterator only enters shift mode if the iterator is currently
     * pointing to FEND/FESC.
     *
     * @note It is always legal to dereference the current frame iterator
     *  when we are asked to advance it.  It is undefined behavior to
     *  advance a forward iterator past the end. For forward iterators the
     *  standard states: "++r precondition: r is dereferenceable".
     *
     * @return a reference to *this.
     */
    slip_encoder2& operator++() {
        char c = *iter_;
        if (not shifting_ and ((c == FEND) or (c == FESC))) {
            shifting_ = true;
            return *this;
        }

        shifting_ = false;
        ++iter_;
        return *this;
    }

    slip_encoder2 operator++(int) {
        slip_encoder2 tmp(*this);
        ++(*this);
        return tmp;
    }

    bool operator==(const slip_encoder2& other) const {
        return iter_ == other.iter_;
    }

    bool operator!=(const slip_encoder2& other) const {
        return iter_ != other.iter_;
    }
};

struct slip_decoder
{
    typedef std::forward_iterator_tag iterator_category;
    typedef size_t difference_type;
    typedef char value_type;
    typedef char& reference;
    typedef char* pointer;

    static const char FEND = 0xC0;
    static const char FESC = 0xDB;
    static const char TFEND = 0xDC;
    static const char TFESC = 0xDD;

    const char* packet_;
    size_t size_;
    size_t pos_;
    char current_;

    slip_decoder()
    : packet_(0), size_(0), pos_(0), current_(0)
    {}

    slip_decoder(const char* packet, size_t len)
    : packet_(packet), size_(len), pos_(0), current_(0)
    {
        set_current();
    }

    void set_current() {
        if (packet_[pos_] == FESC) {
            pos_ += 1;
            current_ = (packet_[pos_] == TFEND ? FEND : FESC);
        } else {
            current_ = packet_[pos_];
        }
    }

    char operator*() const {
        return current_;
    }

    slip_decoder& operator++() {

        if (!size_) return *this;

        pos_ += 1;

        if (pos_ != size_) {
            set_current();
        } else {
            packet_ = 0;
            pos_ = 0;
            size_ = 0;
        }

        return *this;
    }

    slip_decoder operator++(int) {
        slip_decoder tmp(*this);
        ++(*this);
        return tmp;
    }

    bool operator==(const slip_decoder& other) const {
        return (packet_ == other.packet_) and
            (pos_ == other.pos_) and (size_ == other.size_);
    }

    bool operator!=(const slip_decoder& other) const {
        return not ((*this) == other);
    }
};

}}} // mobilinkd::tnc::kiss

#endif // MOBILINKD_KISS_HPP_