// Simple one-line text editor with
// Emacs keybindings.  I was planning
// to do more, but this already took
// me an hour and a half, and I am
// getting sleepy.
// Supported keys are left arrow, right
// arrow, ^F, ^B, delete (and ^H), ^A,
// ^E, ^W (which deletes a word), alt-F,
// and alt-B.
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include "scbreak.h"

char buf[80];
int pos = 0, end = 0;
enum { 
    state_normal, state_esc, state_csi 
} input_state = state_normal;

#define CTRL(ch) ((ch) & 31)

void redraw()
{
    printf("\r∆");
    fflush(stdout);
    write(1, buf, end);
    // clear to end of line
    printf("\033[K");
    // then move cursor left
    if (end > pos) {
        printf("\033[%dD", end - pos); 
    }
    fflush(stdout);
}

void backward_delete_char() 
{
    if (pos == 0) return;
    memmove(buf+pos-1, buf+pos, end-pos);
    end--;
    pos--;
}

static int seeing_wsp()
{
    return pos < end && buf[pos] == ' ';
}

static int seeing_nonwsp()
{
    return pos < end && !seeing_wsp();
}

static int following_wsp()
{
    return pos && buf[pos-1] == ' ';
}

static int following_nonwsp()
{
    return pos && !following_wsp();
}

void dispatch_esc(char c)
{
    input_state = state_normal;
    if (c == 'b') {
        while (following_wsp()) pos--;
        while (following_nonwsp()) pos--;
    } else if (c == 'f') {
        while (seeing_wsp()) pos++;
        while (seeing_nonwsp()) pos++;
    } else if (c == '[') {
        input_state = state_csi;
    }
}

void dispatch_csi(char c)
{
    input_state = state_normal;
    if (c == 'C') {
        if (pos < end) pos++;
    } else if (c == 'D') {
        if (pos) pos--;
    }
}

int main(int argc, char **argv)
{
    const char *err = enable_cbreak(0);
    if (err) {
        fprintf(stderr, 
                "%s: cbreak: %s\n",
                argv[0], err);
        return 1;
    }

    // switch to alternate screen
    printf("\033[?1049h");
    for (;;) {
        redraw();

        char c;
        read(0, &c, 1);
        if (input_state == state_esc) {
            dispatch_esc(c);
        } else if (input_state ==
                state_csi) {
            dispatch_csi(c);
        } else if (c == 127 || 
                c == CTRL('H')) {
            backward_delete_char();
        } else if (c == CTRL('J')) {
            printf("\n");
            break;
        } else if (c == CTRL('F')) {
            if (pos == end) continue;
            pos++;
        } else if (c == CTRL('B')) {
            if (pos) pos--;
        } else if (c == CTRL('E')) {
            pos = end;
        } else if (c == CTRL('A')) {
            pos = 0;
        } else if (c == CTRL('W')) {
            while (following_wsp()) {
                backward_delete_char();
            }

            while (following_nonwsp()) {
                backward_delete_char();
            }
        } else if (c == '\033') {
            input_state = state_esc;
        } else if (c >= ' ') {
            memmove(buf+pos+1, buf+pos,
                    end-pos);
            buf[pos++] = c;
            end++;
        }
    }

    // restore from alternate screen
    printf("\033[?1049l");
    return 0;
}