raw-terminal/RawReader.h

#ifndef RAWREADER_H
#define RAWREADER_H

#include <cstdio>
#include <cstring>

#include <termios.h>
#include <unistd.h>

template<int N, int H>
class RawReader final {
    struct termios original;
    
    int index;
    char buffer[2][N];
    bool bufferIndex;
    bool noError;
    int move;
    
    char history[H][N];
    int historyOffset;
    int historyIndex;
    int historyLength;
    
    const char* prefix;

public:
    typedef int DeciSeconds;

    RawReader(DeciSeconds timeout, const char* prefix) : index(0), bufferIndex(false), noError(true), move(0),
    historyOffset(0), historyIndex(0), historyLength(0), prefix(prefix) {
        // https://viewsourcecode.org/snaptoken/kilo/02.enteringRawMode.html
        if(tcgetattr(STDIN_FILENO, &original) == -1) {
            markError();
            return;
        }

        struct termios raw;
        if(tcgetattr(STDIN_FILENO, &raw) == -1) {
            markError();
            return;
        };
        raw.c_iflag &= ~(ICRNL | IXON);
        raw.c_lflag &= ~(ECHO | ICANON | IEXTEN | ISIG);
        raw.c_cc[VMIN] = 0;
        raw.c_cc[VTIME] = timeout;

        if(tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw)) {
            markError();
            return;
        }

        buffer[0][0] = '\0';
        buffer[1][0] = '\0';
    }

    ~RawReader() {
        tcsetattr(STDIN_FILENO, TCSAFLUSH, &original);
    }

    RawReader(const RawReader&) = delete;
    RawReader(RawReader&&) = delete;
    RawReader& operator=(const RawReader&) = delete;
    RawReader& operator=(RawReader&&) = delete;

    bool canRead() const {
        return noError;
    }

    const char* readLine() {
        refreshLine();
        while(true) {
            char c = 0;
            int bytes = read(STDIN_FILENO, &c, 1);
            if(bytes < 0) {
                markError();
                break;
            } else if(bytes == 0 || c < 0) {
                break;
            }

            if(c == 27) {
                readEscapeSequence();
            } else if(iscntrl(c)) {
                if(handleControlKey(c)) {
                    clearLine();
                    return swapBuffers();
                }
            } else {
                addChar(c);
            }
            refreshLine();
        }
        clearLine();
        return nullptr;
    }

    void updateLine() {
        refreshLine();
        clearLine();
    }

private:

    void print(const char* s) {
        fputs(s, stdout);
    }

    void clearLine() {
        print("\33[2K\r");
    }

    void markError() {
        noError = false;
    }

    const char* swapBuffers() {
        addToHistory();
        bufferIndex = !bufferIndex;
        clear();
        return buffer[!bufferIndex];
    }

    void refreshLine() {
        clearLine();
        print(prefix);
        print(buffer[bufferIndex]);
        if(move > 0) {
            printf("\33[%dD", move);
        }
        fflush(stdout);
    }

    bool handleControlKey(char c) {
        switch(c) {
            case 3: return clear();
            case 13: return true;
            case 127: return removeChar();
        }
        return false;
    }

    bool clear() {
        index = 0;
        move = 0;
        buffer[bufferIndex][0] = '\0';
        historyOffset = 0;
        return false;
    }

    bool removeChar() {
        int pos = index - move - 1;
        if(pos >= 0) {
            index--;
            while(buffer[bufferIndex][pos] != '\0') {
                buffer[bufferIndex][pos] = buffer[bufferIndex][pos + 1];
                pos++;
            }
        }
        if(index - move < 0) {
            move--;
        }
        return false;
    }

    void addChar(char c) {
        if(index + 1 < N) {
            index++;
            for(int i = 0; i < move + 1; i++) {
                buffer[bufferIndex][index - i] = buffer[bufferIndex][index - i - 1];
            }
            buffer[bufferIndex][index - move - 1] = c;
        }
    }

    char readChar() {
        char c;
        return read(STDIN_FILENO, &c, 1) == 1 ? c : -1;
    }

    void readEscapeSequence() {
        if(readChar() != '[') {
            return;
        }
        switch(readChar()) {
            case 'A':
                handleUpArrow();
                break;
            case 'B':
                handleDownArrow();
                break;
            case 'C':
                handleRightArrow();
                break;
            case 'D':
                handleLeftArrow();
                break;
        }
    }

    void handleUpArrow() {
        if(historyOffset >= historyLength) {
            return;
        }
        historyOffset++;
        copyHistory();
    }

    void handleDownArrow() {
        if(historyOffset <= 1) {
            return;
        }
        historyOffset--;
        copyHistory();
    }

    void handleLeftArrow() {
        if(move < index) {
            move++;
        }
    }

    void handleRightArrow() {
        if(move > 0) {
            move--;
        }
    }

    void addToHistory() {
        if(historyLength < H) {
            historyLength++;
        }
        strncpy(history[historyIndex], buffer[bufferIndex], N);
        historyIndex = (historyIndex + 1) % H;
    }

    void copyHistory() {
        strncpy(buffer[bufferIndex], history[(historyIndex - historyOffset + H) % H], N);
        move = 0;
        index = strnlen(buffer[bufferIndex], N);
    }
};

#endif