#include <ctype.h>
#include <err.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/ttydefaults.h>
#include <termios.h>
#include <unistd.h>

#define ESC "\033"
#define CSI ESC "["

#define prn(...) dprintf(ttyfd, __VA_ARGS__)

int ttyfd;

/* enable/disable "raw" mode */
void raw(bool enable) {
	int r;
	static struct termios orig;
	struct termios raw;

	if (enable) {
		r = tcgetattr(0, &orig);
		if (r == -1) err(1, "tcgetattr");

		raw = orig;
		raw.c_iflag &= ~(BRKINT | ICRNL | INPCK | ISTRIP | IXON);
		raw.c_oflag &= ~OPOST;
		raw.c_cflag |= CS8;
		raw.c_lflag &= ~(ECHO | ICANON | IEXTEN | ISIG);

		r = tcsetattr(0, TCSAFLUSH, &raw);
		if (r == -1) err(1, "tcsetattr");

	} else
		tcsetattr(0, TCSAFLUSH, &orig);
}

/* cursor position report */
int cpr(int *x, int *y) {
	char c, xbuf[4], ybuf[4];
	int i;

	prn(CSI "6n");

	/* get CSI */
	read(1, &c, 1);
	if (c != '\033') return -1;
	read(1, &c, 1);
	if (c != '[') return -1;

	/* get x */
	i = 0;
	while (read(1, &c, 1) && c != ';') {
		if (i > 3 || !isdigit(c)) return -1;
		ybuf[i++] = c;
	}
	if (i == 0) return -1;
	ybuf[i] = '\0';

	/* get y */
	i = 0;
	while (read(1, &c, 1) && c != 'R') {
		if (i > 3 || !isdigit(c)) return -1;
		xbuf[i++] = c;
	}
	if (i == 0) return -1;
	xbuf[i] = '\0';

	*x = atoi(xbuf);
	*y = atoi(ybuf);

	return 0;
}

void up() {}
void down() {}
void right() {}
void left() {}

int main() {
	char c, *p;
	int i, r;
	struct winsize w;
	int height; /* height of output in rows */
	int x, y; /* original cursor position in cols, rows */

	char *ex = "file1 file2 file3\r\nfile4 file5 file6\r\nfile7";

	ttyfd = open("/dev/tty", O_RDWR);
	if (ttyfd == -1) err(1, "open");

	raw(true);

	/* save original cursor position */
	r = cpr(&x, &y);
	if (r == -1) goto quit;

	/* print output */
	prn("%s", ex);

	/* get height of output */
	p = ex - 1;
	height = 0;
	while (*(++p) != '\0')
		if (*p == '\n') height++;

	/* get height of terminal */
	r = ioctl(ttyfd, TIOCGWINSZ, &w);
	if (r == -1) err(1, "ioctl");

	/* correct cursor position if original cursor was near bottom */
	r = y + height - w.ws_row;
	if (r > 0)
		y = y - r;

	/* restore original cursor position (CUP) */
	prn("%s%d;%dH", CSI, y, x);

	while (read(0, &c, 1) != 0) {
		switch (c) {
		case 'q':
			goto quit;
			break;
		case '\033':
			read(0, &c, 1);
			if (c != '[') break;
			read(0, &c, 1);
			if (c == 'A') up();
			if (c == 'B') down();
			if (c == 'C') right();
			if (c == 'D') left();
			break;
		}
	}
	
quit:
	prn(CSI "J"); /* delete from cursor to end of display (ED) */
	raw(false);
}