scratch

main.cpp

#include "scratch.h"

int delta(const char *const msg)
{
    char lhs[32] = {};
    float rhs = 0.0;

    printf("\n[ECHO] %s\n", msg);
    sscanf(msg, "%[a-zA-Z0-9] = %f", lhs, &rhs);
    printf("lhs: %s, rhs: %f", lhs, rhs);

    return 0;
}

int main(void)
{
    IO comm;

    comm.set_delta(delta);
    comm.run_delta();

    return 0;
}

scratch.cpp

#include "scratch.h"

IO::IO()
{
    delta = NULL;
    clear();
}

IO::IO(const IO &other)
{
    for (int i = 0; i < len(buffer); i++) {
        buffer[i] = other.buffer[i];
    }
    cursor = other.cursor;
    result = other.result;
    theend = other.theend;
    delta  = other.delta;
}

IO::~IO()
{
}

void IO::clear()
{
    for (int i = 0; i < len(buffer); i++) {
        buffer[i] = '\0';
    }
    cursor = 0;
    theend = 0;
}

bool IO::put_char(const int ch)
{
    switch (ch) {
    default:
        if (cursor < 0) {
            result = NULL;
            return false;
        }
        if (cursor > theend) {
            result = NULL;
            return false;
        }
        if (theend + 1 >= len(buffer)) {
            result = NULL;
            return false;
        }
        for (int i = theend; i >= cursor; i--) {
            buffer[i + 1] = buffer[i];
        }
        buffer[cursor++] = ch;
        buffer[++theend] = '\0';
        print();
        result = NULL;
        return false;
    case '\b':
        if (cursor > theend) {
            result = NULL;
            return false;
        }
        if (theend + 1 >= len(buffer)) {
            result = NULL;
            return false;
        }
        if (cursor <= 0) {
            result = NULL;
            return false;
        }
        for (int i = --cursor; i < theend; i++) {
            buffer[i] = buffer[i + 1];
        }
        if (theend > 0) {
            buffer[theend--] = '\0';
        }
        print();
        result = NULL;
        return false;
    case '\n':
    case '\r':
        result = buffer;
        return true;
    case '\0':
        return false;
    case ESC:
        clear();
        printf("\n");
        result = NULL;
        return true;
    case 224:
        if (theend + 1 >= len(buffer)) {
            result = NULL;
            return false;
        }
        switch (getch()) {
        case LEFT_DIRECTION:
            if (cursor > 0) {
                cursor--;
            }
            print();
            result = NULL;
            return false;
        case RIGHT_DIRECTION:
            if (cursor < theend) {
                cursor++;
            }
            print();
            result = NULL;
            return false;
        }
    }
    return false;
}

void IO::sync(char *&msg)
{
    msg = result;
}

void IO::set_delta(int (*const delta)(const char *msg))
{
    this->delta = delta;
}

int IO::run_delta()
{
    char *msg    = NULL;
    int  ch      = '\0';
    bool entered = false;
    int  result  = 0;

    while ((ch = getch()) != ESC) {
        entered = put_char(ch);
        if (entered) {
            sync(msg);
            result = delta(msg);
            clear();
            break;
        }
    }
    return result;
}

void IO::print()
{
    int i = 0;
    printf("\r");
    for (i = 0; i < len(buffer); i++) {
        printf(" ");    
    }
    printf("\r");
    for (i = 0; i < cursor; i++) {
        printf(" ");
    }
    for (i = cursor; i < theend; i++) {
        printf("%c", buffer[i]);
    }
    buffer[i] = '\0';
    printf("\r");
    for (int i = 0; i < cursor; i++) {
        printf("%c", buffer[i]);
    }
    fflush(stdout);
}

scratch.h

#ifndef SCRATCH_H
#define SCRATCH_H

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <conio.h>

#define len(xs)         (sizeof(xs)/sizeof(*(xs)))
#define ESC 	        27
#define LEFT_DIRECTION  75
#define RIGHT_DIRECTION 77

class IO {
    char        buffer[64];
    int         cursor;
    int         theend;
    char        *result;
    int         (*delta)(const char *msg);
public:
    IO();
    IO(const IO &other);
    ~IO();
    void clear(void);
    bool put_char(int ch);
    void sync(char *&msg);
    void set_delta(int (*delta)(const char *msg));
    int  run_delta(void);
private:
    void print(void);
};

#endif