/*
reset
Faster smaller replacement for ncurses "reset" command.
Taylor Gurney, 2022.
Public domain.
*/

#define _POSIX_C_SOURCE 200809L

#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>

char* argv0;

void emsg(const char* s, ...) {
    va_list ap;
    int e = errno;
    fprintf(stderr, "%s: ", argv0);
    va_start(ap, s);
    vfprintf(stderr, s, ap);
    va_end(ap);
    if (e) {
        fprintf(stderr, ": %s", strerror(e));
    }
    fputc('\n', stderr);
    fflush(stderr);
}

// ANSI codes:
// c: reset
// (B: set default charset
// [0m: reset display attributes
// [2J: clear screen
const char* RESET_CODE = "\033c\033(B\033[0m\033[2J";

void usage(void) {
    fprintf(stderr, "usage: %s\n", argv0);
    exit(1);
}

ssize_t writeall(int fd, const void* buf, size_t n) {
    const char* bufptr = (const char*)buf;
    ssize_t bytes_out = 0;
    while (n) {
        bytes_out = write(fd, bufptr, n);
        if (bytes_out < 0) {
            return bytes_out;
        }
        n -= bytes_out;
        bufptr += bytes_out;
    }
    return bytes_out;
}

int main(int argc, char* argv[]) {
    int rval = 0;
    int fd = 1;
    int i;
    struct termios term;

    argv0 = argv[0];

    for (i = 1; i < argc; i++) {
        if (strcmp(argv[i], "--") != 0) {
            usage();
        }
    }

    if (!isatty(fd)) {
        fd = open("/dev/tty", O_RDWR);
        if (fd < 0) {
            emsg("%s", "error opening /dev/tty");
            exit(1);
        }
    }

    // set sane attributes 
    if (tcgetattr(fd, &term) < 0) {
        // Move on and still try the ANSI part if this fails.
        emsg("%s", "tcgetattr failed");
        rval = 1;
    } else {
        term.c_iflag |= (BRKINT | IGNPAR | ICRNL | IXON);
        term.c_cflag |= (CREAD | CS8);
        term.c_lflag |= (ECHO | ECHOE | ECHOK | ICANON | ISIG | IEXTEN);
        term.c_oflag |= (ONLCR | OPOST);
        term.c_iflag &= ~(IGNBRK | PARMRK | INPCK | ISTRIP);
        term.c_iflag &= ~(IGNCR | INLCR | IXANY | IXOFF);
        term.c_cflag &= ~(CS5 | CS6 | CS7 | CSTOPB | PARENB | PARODD);
        term.c_lflag &= ~(ECHONL | NOFLSH | TOSTOP);
        term.c_oflag &= ~(OCRNL | OFILL | ONLRET | ONOCR);
        if (tcsetattr(fd, TCSADRAIN, &term) < 0) {
            // NOTE: tcsetattr only returns nonzero if none of the flags
            // could be applied. So it could partially work and return zero.
            // Don't care for practical purposes.
            emsg("%s", "tcsetattr failed");
            rval = 1;
        }
    }

    if (writeall(fd, RESET_CODE, strlen(RESET_CODE)) < 0) {
        if (fd == 1) {
            emsg("%s", "<stdout>");
        } else {
            emsg("%s", "/dev/tty");
        }
        rval = 1;
    }
    close(fd);
    return rval;
}