/* vi: set sw=4 ts=4: */
/*
 * A text-mode VNC like program for Linux virtual terminals.
 *
 * pascal.bellard@ads-lu.com
 *
 * Based on Russell Stuart's conspy.c
 *   http://ace-host.stuart.id.au/russell/files/conspy.c
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

//applet:IF_CONSPY(APPLET(conspy, BB_DIR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_CONSPY) += conspy.o

//config:config CONSPY
//config:       bool "conspy"
//config:       default y
//config:       select PLATFORM_LINUX
//config:       help
//config:         A text-mode VNC like program for Linux virtual terminals.
//config:         example:  conspy NUM      shared access to console num
//config:         or        conspy -nd NUM  screenshot of console num
//config:         or        conspy -cs NUM  poor man's GNU screen like

//usage:#define conspy_trivial_usage
//usage:        "[-vcsndfFQ] [-x COL] [-y LINE] [CONSOLE_NO]"
//usage:#define conspy_full_usage "\n\n"
//usage:     "A text-mode VNC like program for Linux virtual consoles."
//usage:     "\nTo exit, quickly press ESC 3 times."
//usage:     "\n"
//usage:     "\n        -v      Don't send keystrokes to the console"
//usage:     "\n        -c      Create missing /dev/{tty,vcsa}N"
//usage:     "\n        -s      Open a SHELL session"
//usage:     "\n        -n      Black & white"
//usage:     "\n        -d      Dump console to stdout"
//usage:     "\n        -f      Follow cursor"
//usage:     "\n        -F      Assume console is on a framebuffer device"
//usage:     "\n        -Q      Disable exit on ESC-ESC-ESC"
//usage:     "\n        -x COL  Starting column"
//usage:     "\n        -y LINE Starting line"

#include "libbb.h"
#include <sys/kd.h>

#define ESC "\033"
#define CURSOR_ON       -1
#define CURSOR_OFF      1

#define DEV_TTY         "/dev/tty"
#define DEV_VCSA        "/dev/vcsa"

struct screen_info {
        unsigned char lines, cols, cursor_x, cursor_y;
};

#define CHAR(x) (*(uint8_t*)(x))
#define ATTR(x) (((uint8_t*)(x))[1])
#define NEXT(x) ((x) += 2)
#define DATA(x) (*(uint16_t*)(x))

struct globals {
        char* data;
        int size;
        int x, y;
        int kbd_fd;
        int ioerror_count;
        int key_count;
        int escape_count;
        int nokeys;
        int current;
        int first_line_offset;
        int last_attr;
        // cached local tty parameters
        unsigned width;
        unsigned height;
        unsigned col;
        unsigned line;
        smallint curoff; // unknown:0 cursor on:-1 cursor off:1
        char attrbuf[sizeof("0;1;5;30;40m")];
        // remote console
        struct screen_info remote;
        // saved local tty terminfo
        struct termios term_orig;
        char vcsa_name[sizeof(DEV_VCSA "NN")];
};

#define G (*ptr_to_globals)
#define INIT_G() do { \
        SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
        G.width = G.height = UINT_MAX; \
        G.last_attr--; \
} while (0)

enum {
        FLAG_v,  // view only
        FLAG_c,  // create device if need
        FLAG_Q,  // never exit
        FLAG_s,  // session
        FLAG_n,  // no colors
        FLAG_d,  // dump screen
        FLAG_f,  // follow cursor
        FLAG_F,  // framebuffer
};
#define FLAG(x) (1 << FLAG_##x)
#define BW (option_mask32 & FLAG(n))

static void putcsi(const char *s)
{
        fputs(ESC"[", stdout);
        fputs(s, stdout);
}

static void clrscr(void)
{
        // Home, clear till end of screen
        putcsi("1;1H" ESC"[J");
        G.col = G.line = 0;
}

static void set_cursor(int state)
{
        if (G.curoff != state) {
                G.curoff = state;
                putcsi("?25");
                bb_putchar("h?l"[1 + state]);
        }
}

static void gotoxy(int col, int line)
{
        if (G.col != col || G.line != line) {
                G.col = col;
                G.line = line;
                printf(ESC"[%u;%uH", line + 1, col + 1);
        }
}

static void cleanup(int code) NORETURN;
static void cleanup(int code)
{
        set_cursor(CURSOR_ON);
        tcsetattr(G.kbd_fd, TCSANOW, &G.term_orig);
        if (ENABLE_FEATURE_CLEAN_UP) {
                close(G.kbd_fd);
        }
        // Reset attributes
        if (!BW)
                putcsi("0m");
        bb_putchar('\n');
        if (code > EXIT_FAILURE)
                kill_myself_with_sig(code);
        exit(code);
}

static void screen_read_close(void)
{
        unsigned i, j;
        int vcsa_fd;
        char *data;

        // Close & re-open vcsa in case they have swapped virtual consoles
        vcsa_fd = xopen(G.vcsa_name, O_RDONLY);
        xread(vcsa_fd, &G.remote, 4);
        i = G.remote.cols * 2;
        G.first_line_offset = G.y * i;
        i *= G.remote.lines;
        if (G.data == NULL) {
                G.size = i;
                G.data = xzalloc(2 * i);
        }
        if (G.size != i) {
                cleanup(EXIT_FAILURE);
        }
        data = G.data + G.current;
        xread(vcsa_fd, data, G.size);
        close(vcsa_fd);
        for (i = 0; i < G.remote.lines; i++) {
                for (j = 0; j < G.remote.cols; j++, NEXT(data)) {
                        unsigned x = j - G.x; // if will catch j < G.x too
                        unsigned y = i - G.y; // if will catch i < G.y too

                        if (y >= G.height || x >= G.width)
                                DATA(data) = 0;
                        else {
                                uint8_t ch = CHAR(data);
                                if (ch < ' ')
                                        CHAR(data) = ch | 0x40;
                                else if (ch > 0x7e)
                                        CHAR(data) = '?';
                        }
                }
        }
}

static void screen_char(char *data)
{
        if (!BW) {
                uint8_t attr_diff;
                uint8_t attr = ATTR(data);

                if (option_mask32 & FLAG(F)) {
                        attr >>= 1;
                }
                attr_diff = G.last_attr ^ attr;
                if (attr_diff) {
// Attribute layout for VGA compatible text videobuffer:
// blinking text
// |red bkgd
// ||green bkgd
// |||blue bkgd
// vvvv
// 00000000 <- lsb bit on the right
//     bold text / text 8th bit
//      red text
//       green text
//        blue text
// TODO: apparently framebuffer-based console uses different layout
// (bug? attempt to get 8th text bit in better position?)
// red bkgd
// |green bkgd
// ||blue bkgd
// vvv
// 00000000 <- lsb bit on the right
//    bold text
//     red text
//      green text
//       blue text
//        text 8th bit
                        // converting RGB color bit triad to BGR:
                        static const char color[8] = "04261537";
                        const uint8_t fg_mask = 0x07, bold_mask  = 0x08;
                        const uint8_t bg_mask = 0x70, blink_mask = 0x80;
                        char *ptr;

                        ptr = G.attrbuf;

                        // (G.last_attr & ~attr) has 1 only where
                        // G.last_attr has 1 but attr has 0.
                        // Here we check whether we have transition
                        // bold->non-bold or blink->non-blink:
                        if (G.last_attr < 0  // initial value
                         || ((G.last_attr & ~attr) & (bold_mask | blink_mask)) != 0
                        ) {
                                *ptr++ = '0'; // "reset all attrs"
                                *ptr++ = ';';
                                // must set fg & bg, maybe need to set bold or blink:
                                attr_diff = attr | ~(bold_mask | blink_mask);
                        }
                        G.last_attr = attr;
                        if (attr_diff & bold_mask) {
                                *ptr++ = '1';
                                *ptr++ = ';';
                        }
                        if (attr_diff & blink_mask) {
                                *ptr++ = '5';
                                *ptr++ = ';';
                        }
                        if (attr_diff & fg_mask) {
                                *ptr++ = '3';
                                *ptr++ = color[attr & fg_mask];
                                *ptr++ = ';';
                        }
                        if (attr_diff & bg_mask) {
                                *ptr++ = '4';
                                *ptr++ = color[(attr & bg_mask) >> 4];
                                ptr++; // last attribute
                        }
                        if (ptr != G.attrbuf) {
                                ptr[-1] = 'm';
                                *ptr = '\0';
                                putcsi(G.attrbuf);
                        }
                }
        }
        putchar(CHAR(data));
        G.col++;
}

static void screen_dump(void)
{
        int linefeed_cnt;
        int line, col;
        int linecnt = G.remote.lines - G.y;
        char *data = G.data + G.current + G.first_line_offset;

        linefeed_cnt = 0;
        for (line = 0; line < linecnt && line < G.height; line++) {
                int space_cnt = 0;
                for (col = 0; col < G.remote.cols; col++, NEXT(data)) {
                        unsigned tty_col = col - G.x; // if will catch col < G.x too

                        if (tty_col >= G.width)
                                continue;
                        space_cnt++;
                        if (BW && CHAR(data) == ' ')
                                continue;
                        while (linefeed_cnt != 0) {
                                //bb_putchar('\r'); - tty driver does it for us
                                bb_putchar('\n');
                                linefeed_cnt--;
                        }
                        while (--space_cnt)
                                bb_putchar(' ');
                        screen_char(data);
                }
                linefeed_cnt++;
        }
}

static void curmove(void)
{
        unsigned cx = G.remote.cursor_x - G.x;
        unsigned cy = G.remote.cursor_y - G.y;
        int cursor = CURSOR_OFF;

        if (cx < G.width && cy < G.height) {
                gotoxy(cx, cy);
                cursor = CURSOR_ON;
        }
        set_cursor(cursor);
}

static void create_cdev_if_doesnt_exist(const char* name, dev_t dev)
{
        int fd = open(name, O_RDONLY);
        if (fd != -1)
                close(fd);
        else if (errno == ENOENT)
                mknod(name, S_IFCHR | 0660, dev);
}

static NOINLINE void start_shell_in_child(const char* tty_name)
{
        int pid = xvfork();
        if (pid == 0) {
                struct termios termchild;
                const char *shell = get_shell_name();

                signal(SIGHUP, SIG_IGN);
                // set tty as a controlling tty
                setsid();
                // make tty to be input, output, error
                close(0);
                xopen(tty_name, O_RDWR); // uses fd 0
                xdup2(0, 1);
                xdup2(0, 2);
                ioctl(0, TIOCSCTTY, 1);
                tcsetpgrp(0, getpid());
                tcgetattr(0, &termchild);
                termchild.c_lflag |= ECHO;
                termchild.c_oflag |= ONLCR | XTABS;
                termchild.c_iflag |= ICRNL;
                termchild.c_iflag &= ~IXOFF;
                tcsetattr_stdin_TCSANOW(&termchild);
                execl(shell, shell, "-i", (char *) NULL);
                bb_simple_perror_msg_and_die(shell);
        }
}

int conspy_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int conspy_main(int argc UNUSED_PARAM, char **argv)
{
        char tty_name[sizeof(DEV_TTY "NN")];
#define keybuf bb_common_bufsiz1
        struct termios termbuf;
        unsigned opts;
        unsigned ttynum;
        int poll_timeout_ms;
#if ENABLE_LONG_OPTS
        static const char getopt_longopts[] ALIGN1 =
                "viewonly\0"     No_argument "v"
                "createdevice\0" No_argument "c"
                "neverquit\0"    No_argument "Q"
                "session\0"      No_argument "s"
                "nocolors\0"     No_argument "n"
                "dump\0"         No_argument "d"
                "follow\0"       No_argument "f"
                "framebuffer\0"  No_argument "F"
                ;

        applet_long_options = getopt_longopts;
#endif
        INIT_G();
        strcpy(G.vcsa_name, DEV_VCSA);

        opt_complementary = "x+:y+"; // numeric params
        opts = getopt32(argv, "vcQsndfFx:y:", &G.x, &G.y);
        argv += optind;
        ttynum = 0;
        if (argv[0]) {
                ttynum = xatou_range(argv[0], 0, 63);
                sprintf(G.vcsa_name + sizeof(DEV_VCSA)-1, "%u", ttynum);
        }
        sprintf(tty_name, "%s%u", DEV_TTY, ttynum);
        if (opts & FLAG(c)) {
                if ((opts & (FLAG(s)|FLAG(v))) != FLAG(v))
                        create_cdev_if_doesnt_exist(tty_name, makedev(4, ttynum));
                create_cdev_if_doesnt_exist(G.vcsa_name, makedev(7, 128 + ttynum));
        }
        if ((opts & FLAG(s)) && ttynum) {
                start_shell_in_child(tty_name);
        }

        screen_read_close();
        if (opts & FLAG(d)) {
                screen_dump();
                bb_putchar('\n');
                return 0;
        }

        bb_signals(BB_FATAL_SIGS, cleanup);

        // All characters must be passed through to us unaltered
        G.kbd_fd = xopen(CURRENT_TTY, O_RDONLY);
        tcgetattr(G.kbd_fd, &G.term_orig);
        termbuf = G.term_orig;
        termbuf.c_iflag &= ~(BRKINT|INLCR|ICRNL|IXON|IXOFF|IUCLC|IXANY|IMAXBEL);
        //termbuf.c_oflag &= ~(OPOST); - no, we still want \n -> \r\n
        termbuf.c_lflag &= ~(ISIG|ICANON|ECHO);
        termbuf.c_cc[VMIN] = 1;
        termbuf.c_cc[VTIME] = 0;
        tcsetattr(G.kbd_fd, TCSANOW, &termbuf);

        poll_timeout_ms = 250;
        while (1) {
                struct pollfd pfd;
                int bytes_read;
                int i, j;
                char *data, *old;

                // in the first loop G.width = G.height = 0: refresh
                i = G.width;
                j = G.height;
                get_terminal_width_height(G.kbd_fd, &G.width, &G.height);
                if (option_mask32 & FLAG(f)) {
                        int nx = G.remote.cursor_x - G.width + 1;
                        int ny = G.remote.cursor_y - G.height + 1;

                        if (G.remote.cursor_x < G.x) {
                                G.x = G.remote.cursor_x;
                                i = 0; // force refresh
                        }
                        if (nx > G.x) {
                                G.x = nx;
                                i = 0; // force refresh
                        }
                        if (G.remote.cursor_y < G.y) {
                                G.y = G.remote.cursor_y;
                                i = 0; // force refresh
                        }
                        if (ny > G.y) {
                                G.y = ny;
                                i = 0; // force refresh
                        }
                }

                // Scan console data and redraw our tty where needed
                old = G.data + G.current;
                G.current = G.size - G.current;
                data = G.data + G.current;
                screen_read_close();
                if (i != G.width || j != G.height) {
                        clrscr();
                        screen_dump();
                } else {
                        // For each remote line
                        old += G.first_line_offset;
                        data += G.first_line_offset;
                        for (i = G.y; i < G.remote.lines; i++) {
                                char *first = NULL; // first char which needs updating
                                char *last = last;  // last char which needs updating
                                unsigned iy = i - G.y;

                                if (iy >= G.height)
                                        break;
                                for (j = 0; j < G.remote.cols; j++, NEXT(old), NEXT(data)) {
                                        unsigned jx = j - G.x; // if will catch j >= G.x too

                                        if (jx < G.width && DATA(data) != DATA(old)) {
                                                last = data;
                                                if (!first) {
                                                        first = data;
                                                        gotoxy(jx, iy);
                                                }
                                        }
                                }
                                if (first) {
                                        // Rewrite updated data on the local screen
                                        for (; first <= last; NEXT(first))
                                                screen_char(first);
                                }
                        }
                }
                curmove();

                // Wait for local user keypresses
                fflush_all();
                pfd.fd = G.kbd_fd;
                pfd.events = POLLIN;
                bytes_read = 0;
                switch (poll(&pfd, 1, poll_timeout_ms)) {
                        char *k;
                case -1:
                        if (errno != EINTR)
                                goto abort;
                        break;
                case 0:
                        if (++G.nokeys >= 4)
                                G.nokeys = G.escape_count = 0;
                        break;
                default:
                        // Read the keys pressed
                        k = keybuf + G.key_count;
                        bytes_read = read(G.kbd_fd, k, sizeof(keybuf) - G.key_count);
                        if (bytes_read < 0)
                                goto abort;

                        // Do exit processing
                        if (!(option_mask32 & FLAG(Q))) {
                                for (i = 0; i < bytes_read; i++) {
                                        if (k[i] != '\033')
                                                G.escape_count = -1;
                                        if (++G.escape_count >= 3)
                                                cleanup(EXIT_SUCCESS);
                                }
                        }
                }
                poll_timeout_ms = 250;
                if (option_mask32 & FLAG(v)) continue;

                // Insert all keys pressed into the virtual console's input
                // buffer.  Don't do this if the virtual console is in scan
                // code mode - giving ASCII characters to a program expecting
                // scan codes will confuse it.
                G.key_count += bytes_read;
                if (G.escape_count == 0) {
                        int handle, result;
                        long kbd_mode;

                        handle = xopen(tty_name, O_WRONLY);
                        result = ioctl(handle, KDGKBMODE, &kbd_mode);
                        if (result >= 0) {
                                char *p = keybuf;

                                G.ioerror_count = 0;
                                if (kbd_mode != K_XLATE && kbd_mode != K_UNICODE) {
                                        G.key_count = 0; // scan code mode
                                }
                                for (; G.key_count != 0; p++, G.key_count--) {
                                        result = ioctl(handle, TIOCSTI, p);
                                        if (result < 0) {
                                                memmove(keybuf, p, G.key_count);
                                                break;
                                        }
                                        // If there is an application on console which reacts
                                        // to keypresses, we need to make our first sleep
                                        // shorter to quickly redraw whatever it printed there.
                                        poll_timeout_ms = 20;
                                }
                        }
                        // We sometimes get spurious IO errors on the TTY
                        // as programs close and re-open it
                        else if (errno != EIO || ++G.ioerror_count > 4) {
                                if (ENABLE_FEATURE_CLEAN_UP)
                                        close(handle);
                                goto abort;
                        }
                        // Close & re-open tty in case they have
                        // swapped virtual consoles
                        close(handle);
                }
        } /* while (1) */
  abort:
        cleanup(EXIT_FAILURE);
}