#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <termios.h>
#include <unistd.h>
#include <wchar.h>

#include "termbox.h"

#define ENTER_MOUSE_SEQ "\x1b[?1000h\x1b[?1002h\x1b[?1015h\x1b[?1006h"
#define EXIT_MOUSE_SEQ "\x1b[?1006l\x1b[?1015l\x1b[?1002l\x1b[?1000l"
#define EUNSUPPORTED_TERM -1
#define TI_MAGIC 0432
#define TI_ALT_MAGIC 542
#define TI_HEADER_LENGTH 12
#define TB_KEYS_NUM 22
#define CELL(buf, x, y) (buf)->cells[(y) * (buf)->width + (x)]
#define IS_CURSOR_HIDDEN(cx, cy) (cx == -1 || cy == -1)
#define LAST_COORD_INIT -1
#define WRITE_LITERAL(X) bytebuffer_append(&output_buffer, (X), sizeof(X) - 1)
#define WRITE_INT(X) bytebuffer_append(&output_buffer, buf, convertnum((X), buf))

struct cellbuf {
    int width;
    int height;
    struct tb_cell *cells;
};

struct bytebuffer {
    char *buf;
    int len;
    int cap;
};

enum {
    T_ENTER_CA,
    T_EXIT_CA,
    T_SHOW_CURSOR,
    T_HIDE_CURSOR,
    T_CLEAR_SCREEN,
    T_SGR0,
    T_UNDERLINE,
    T_BOLD,
    T_BLINK,
    T_REVERSE,
    T_ENTER_KEYPAD,
    T_EXIT_KEYPAD,
    T_ENTER_MOUSE,
    T_EXIT_MOUSE,
    T_FUNCS_NUM,
};

static int init_term_builtin(void);
static char *read_file(const char *file);
static char *terminfo_try_path(const char *path, const char *term);
static char *load_terminfo(void);
static const char *terminfo_copy_string(char *data, int str, int table);
static int init_term(void);
static void shutdown_term(void);
static bool starts_with(const char *s1, int len, const char *s2);
static int parse_mouse_event(struct tb_event *event, const char *buf, int len);
static int parse_escape_seq(struct tb_event *event, const char *buf, int len);
static int convertnum(uint32_t num, char *buf);
static void write_cursor(int x, int y);
static void write_sgr(uint16_t fg, uint16_t bg);
static void cellbuf_init(struct cellbuf *buf, int width, int height);
static void cellbuf_resize(struct cellbuf *buf, int width, int height);
static void cellbuf_clear(struct cellbuf *buf);
static void cellbuf_free(struct cellbuf *buf);
static void get_term_size(int *w, int *h);
static void update_term_size(void);
static void send_attr(uint16_t fg, uint16_t bg);
static void send_char(int x, int y, uint32_t c);
static void send_clear(void);
static void sigwinch_handler(int xxx);
static void update_size(void);
static int read_up_to(int n);
static int wait_fill_event(struct tb_event *event, struct timeval *timeout);
static void bytebuffer_reserve(struct bytebuffer *b, int cap);
static void bytebuffer_init(struct bytebuffer *b, int cap);
static void bytebuffer_free(struct bytebuffer *b);
static void bytebuffer_clear(struct bytebuffer *b);
static void bytebuffer_append(struct bytebuffer *b, const char *data, int len);
static void bytebuffer_puts(struct bytebuffer *b, const char *str);
static void bytebuffer_resize(struct bytebuffer *b, int len);
static void bytebuffer_flush(struct bytebuffer *b, int fd);
static void bytebuffer_truncate(struct bytebuffer *b, int n);

static struct termios orig_tios;

static struct cellbuf back_buffer;
static struct cellbuf front_buffer;
static struct bytebuffer output_buffer;
static struct bytebuffer input_buffer;

static int termw = -1;
static int termh = -1;

static int inputmode = TB_INPUT_ESC;
static int outputmode = TB_OUTPUT_NORMAL;

static int inout;
static int winch_fds[2];

static int lastx = LAST_COORD_INIT;
static int lasty = LAST_COORD_INIT;
static int cursor_x = -1;
static int cursor_y = -1;

static uint16_t background = TB_DEFAULT;
static uint16_t foreground = TB_DEFAULT;

/* may happen in a different thread */
static volatile int buffer_size_change_request;

// rxvt-256color
static const char *rxvt_256color_keys[] = {
    "\033[11~", "\033[12~", "\033[13~", "\033[14~", "\033[15~", "\033[17~",
    "\033[18~", "\033[19~", "\033[20~", "\033[21~", "\033[23~", "\033[24~",
    "\033[2~",  "\033[3~",  "\033[7~",  "\033[8~",  "\033[5~",  "\033[6~",
    "\033[A",   "\033[B",   "\033[D",   "\033[C",   0};
static const char *rxvt_256color_funcs[] = {
    "\0337\033[?47h", "\033[2J\033[?47l\0338",
    "\033[?25h",      "\033[?25l",
    "\033[H\033[2J",  "\033[m",
    "\033[4m",        "\033[1m",
    "\033[5m",        "\033[7m",
    "\033=",          "\033>",
    ENTER_MOUSE_SEQ,  EXIT_MOUSE_SEQ,
};

// Eterm
static const char *eterm_keys[] = {
    "\033[11~", "\033[12~", "\033[13~", "\033[14~", "\033[15~", "\033[17~",
    "\033[18~", "\033[19~", "\033[20~", "\033[21~", "\033[23~", "\033[24~",
    "\033[2~",  "\033[3~",  "\033[7~",  "\033[8~",  "\033[5~",  "\033[6~",
    "\033[A",   "\033[B",   "\033[D",   "\033[C",   0};
static const char *eterm_funcs[] = {
    "\0337\033[?47h",
    "\033[2J\033[?47l\0338",
    "\033[?25h",
    "\033[?25l",
    "\033[H\033[2J",
    "\033[m",
    "\033[4m",
    "\033[1m",
    "\033[5m",
    "\033[7m",
    "",
    "",
    "",
    "",
};

// screen
static const char *screen_keys[] = {
    "\033OP",   "\033OQ",   "\033OR",   "\033OS",   "\033[15~", "\033[17~",
    "\033[18~", "\033[19~", "\033[20~", "\033[21~", "\033[23~", "\033[24~",
    "\033[2~",  "\033[3~",  "\033[1~",  "\033[4~",  "\033[5~",  "\033[6~",
    "\033OA",   "\033OB",   "\033OD",   "\033OC",   0};
static const char *screen_funcs[] = {
    "\033[?1049h",   "\033[?1049l",  "\033[34h\033[?25h", "\033[?25l",
    "\033[H\033[J",  "\033[m",       "\033[4m",           "\033[1m",
    "\033[5m",       "\033[7m",      "\033[?1h\033=",     "\033[?1l\033>",
    ENTER_MOUSE_SEQ, EXIT_MOUSE_SEQ,
};

// rxvt-unicode
static const char *rxvt_unicode_keys[] = {
    "\033[11~", "\033[12~", "\033[13~", "\033[14~", "\033[15~", "\033[17~",
    "\033[18~", "\033[19~", "\033[20~", "\033[21~", "\033[23~", "\033[24~",
    "\033[2~",  "\033[3~",  "\033[7~",  "\033[8~",  "\033[5~",  "\033[6~",
    "\033[A",   "\033[B",   "\033[D",   "\033[C",   0};
static const char *rxvt_unicode_funcs[] = {
    "\033[?1049h",   "\033[r\033[?1049l", "\033[?25h", "\033[?25l",
    "\033[H\033[2J", "\033[m\033(B",      "\033[4m",   "\033[1m",
    "\033[5m",       "\033[7m",           "\033=",     "\033>",
    ENTER_MOUSE_SEQ, EXIT_MOUSE_SEQ,
};

// linux
static const char *linux_keys[] = {
    "\033[[A",  "\033[[B",  "\033[[C",  "\033[[D",  "\033[[E",  "\033[17~",
    "\033[18~", "\033[19~", "\033[20~", "\033[21~", "\033[23~", "\033[24~",
    "\033[2~",  "\033[3~",  "\033[1~",  "\033[4~",  "\033[5~",  "\033[6~",
    "\033[A",   "\033[B",   "\033[D",   "\033[C",   0};
static const char *linux_funcs[] = {
    "",
    "",
    "\033[?25h\033[?0c",
    "\033[?25l\033[?1c",
    "\033[H\033[J",
    "\033[0;10m",
    "\033[4m",
    "\033[1m",
    "\033[5m",
    "\033[7m",
    "",
    "",
    "",
    "",
};

// xterm
static const char *xterm_keys[] = {
    "\033OP",   "\033OQ",   "\033OR",   "\033OS",   "\033[15~", "\033[17~",
    "\033[18~", "\033[19~", "\033[20~", "\033[21~", "\033[23~", "\033[24~",
    "\033[2~",  "\033[3~",  "\033OH",   "\033OF",   "\033[5~",  "\033[6~",
    "\033OA",   "\033OB",   "\033OD",   "\033OC",   0};
static const char *xterm_funcs[] = {
    "\033[?1049h",   "\033[?1049l",   "\033[?12l\033[?25h",
    "\033[?25l",     "\033[H\033[2J", "\033(B\033[m",
    "\033[4m",       "\033[1m",       "\033[5m",
    "\033[7m",       "\033[?1h\033=", "\033[?1l\033>",
    ENTER_MOUSE_SEQ, EXIT_MOUSE_SEQ,
};

static struct term {
    const char *name;
    const char **keys;
    const char **funcs;
} terms[] = {
    {"rxvt-256color", rxvt_256color_keys, rxvt_256color_funcs},
    {"Eterm",         eterm_keys,         eterm_funcs},
    {"screen",        screen_keys,        screen_funcs},
    {"rxvt-unicode",  rxvt_unicode_keys,  rxvt_unicode_funcs},
    {"linux",         linux_keys,         linux_funcs},
    {"xterm",         xterm_keys,         xterm_funcs},
    {0, 0, 0},
};

static bool init_from_terminfo = false;
static const char **keys;
static const char **funcs;

static int try_compatible(const char *term, const char *name,
                          const char **tkeys, const char **tfuncs) {
    if (strstr(term, name)) {
        keys = tkeys;
        funcs = tfuncs;
        return 0;
    }

    return EUNSUPPORTED_TERM;
}

static int init_term_builtin(void) {
    int i;
    const char *term = getenv("TERM");

    if (term) {
        for (i = 0; terms[i].name; i++) {
            if (!strcmp(terms[i].name, term)) {
                keys = terms[i].keys;
                funcs = terms[i].funcs;
                return 0;
            }
        }

        /* let's do some heuristic, maybe it's a compatible terminal */
        if (try_compatible(term, "xterm", xterm_keys, xterm_funcs) == 0)
            return 0;
        if (try_compatible(term, "rxvt", rxvt_unicode_keys,
                           rxvt_unicode_funcs) == 0)
            return 0;
        if (try_compatible(term, "linux", linux_keys, linux_funcs) == 0)
            return 0;
        if (try_compatible(term, "Eterm", eterm_keys, eterm_funcs) == 0)
            return 0;
        if (try_compatible(term, "screen", screen_keys, screen_funcs) == 0)
            return 0;
        if (try_compatible(term, "tmux", screen_keys, screen_funcs) == 0)
            return 0;
        /* let's assume that 'cygwin' is xterm compatible */
        if (try_compatible(term, "cygwin", xterm_keys, xterm_funcs) == 0)
            return 0;
    }

    return EUNSUPPORTED_TERM;
}

//----------------------------------------------------------------------
// terminfo
//----------------------------------------------------------------------

static char *read_file(const char *file) {
    FILE *f = fopen(file, "rb");
    if (!f)
        return 0;

    struct stat st;
    if (fstat(fileno(f), &st) != 0) {
        fclose(f);
        return 0;
    }

    char *data = malloc(st.st_size);
    if (!data) {
        fclose(f);
        return 0;
    }

    if (fread(data, 1, st.st_size, f) != (size_t)st.st_size) {
        fclose(f);
        free(data);
        return 0;
    }

    fclose(f);
    return data;
}

static char *terminfo_try_path(const char *path, const char *term) {
    char tmp[4096];
    snprintf(tmp, sizeof(tmp), "%s/%c/%s", path, term[0], term);
    tmp[sizeof(tmp) - 1] = '\0';
    char *data = read_file(tmp);
    if (data) {
        return data;
    }

    // fallback to darwin specific dirs structure
    snprintf(tmp, sizeof(tmp), "%s/%x/%s", path, term[0], term);
    tmp[sizeof(tmp) - 1] = '\0';
    return read_file(tmp);
}

static char *load_terminfo(void) {
    char tmp[4096];
    const char *term = getenv("TERM");
    if (!term) {
        return 0;
    }

    // if TERMINFO is set, no other directory should be searched
    const char *terminfo = getenv("TERMINFO");
    if (terminfo) {
        return terminfo_try_path(terminfo, term);
    }

    // next, consider ~/.terminfo
    const char *home = getenv("HOME");
    if (home) {
        snprintf(tmp, sizeof(tmp), "%s/.terminfo", home);
        tmp[sizeof(tmp) - 1] = '\0';
        char *data = terminfo_try_path(tmp, term);
        if (data)
            return data;
    }

    // next, TERMINFO_DIRS
    const char *dirs = getenv("TERMINFO_DIRS");
    if (dirs) {
        snprintf(tmp, sizeof(tmp), "%s", dirs);
        tmp[sizeof(tmp) - 1] = '\0';
        char *dir = strtok(tmp, ":");
        while (dir) {
            const char *cdir = dir;
            if (strcmp(cdir, "") == 0) {
                cdir = "/usr/share/terminfo";
            }
            char *data = terminfo_try_path(cdir, term);
            if (data)
                return data;
            dir = strtok(0, ":");
        }
    }

    // fallback to /usr/share/terminfo
    return terminfo_try_path("/usr/share/terminfo", term);
}

static const char *terminfo_copy_string(char *data, int str, int table) {
    const int16_t off = *(int16_t *)(data + str);
    const char *src = data + table + off;
    int len = strlen(src);
    char *dst = malloc(len + 1);
    strcpy(dst, src);
    return dst;
}

static const int16_t ti_funcs[] = {
    28, 40, 16, 13, 5, 39, 36, 27, 26, 34, 89, 88,
};

static const int16_t ti_keys[] = {
    66,  68 /* apparently not a typo; 67 is F10 for whatever reason */,
    69,  70,
    71,  72,
    73,  74,
    75,  67,
    216, 217,
    77,  59,
    76,  164,
    82,  81,
    87,  61,
    79,  83,
};

static int init_term(void) {
    int i;
    char *data = load_terminfo();
    if (!data) {
        init_from_terminfo = false;
        return init_term_builtin();
    }

    int16_t *header = (int16_t *)data;

    const int number_sec_len = header[0] == TI_ALT_MAGIC ? 4 : 2;

    if ((header[1] + header[2]) % 2) {
        // old quirk to align everything on word boundaries
        header[2] += 1;
    }

    const int str_offset =
        TI_HEADER_LENGTH + header[1] + header[2] + number_sec_len * header[3];
    const int table_offset = str_offset + 2 * header[4];

    keys = malloc(sizeof(const char *) * (TB_KEYS_NUM + 1));
    for (i = 0; i < TB_KEYS_NUM; i++) {
        keys[i] = terminfo_copy_string(data, str_offset + 2 * ti_keys[i],
                                       table_offset);
    }
    keys[TB_KEYS_NUM] = 0;

    funcs = malloc(sizeof(const char *) * T_FUNCS_NUM);
    // the last two entries are reserved for mouse. because the table offset is
    // not there, the two entries have to fill in manually
    for (i = 0; i < T_FUNCS_NUM - 2; i++) {
        funcs[i] = terminfo_copy_string(data, str_offset + 2 * ti_funcs[i],
                                        table_offset);
    }

    funcs[T_FUNCS_NUM - 2] = ENTER_MOUSE_SEQ;
    funcs[T_FUNCS_NUM - 1] = EXIT_MOUSE_SEQ;

    init_from_terminfo = true;
    free(data);
    return 0;
}

static void shutdown_term(void) {
    if (init_from_terminfo) {
        int i;
        for (i = 0; i < TB_KEYS_NUM; i++) {
            free((void *)keys[i]);
        }
        // the last two entries are reserved for mouse. because the table offset
        // is not there, the two entries have to fill in manually and do not
        // need to be freed.
        for (i = 0; i < T_FUNCS_NUM - 2; i++) {
            free((void *)funcs[i]);
        }
        free(keys);
        free(funcs);
    }
}

// if s1 starts with s2 returns true, else false
// len is the length of s1
// s2 should be null-terminated
static bool starts_with(const char *s1, int len, const char *s2) {
    int n = 0;
    while (*s2 && n < len) {
        if (*s1++ != *s2++)
            return false;
        n++;
    }
    return *s2 == 0;
}

static int parse_mouse_event(struct tb_event *event, const char *buf, int len) {
    if (len >= 6 && starts_with(buf, len, "\033[M")) {
        // X10 mouse encoding, the simplest one
        // \033 [ M Cb Cx Cy
        int b = buf[3] - 32;
        switch (b & 3) {
        case 0:
            if ((b & 64) != 0)
                event->key = TB_KEY_MOUSE_WHEEL_UP;
            else
                event->key = TB_KEY_MOUSE_LEFT;
            break;
        case 1:
            if ((b & 64) != 0)
                event->key = TB_KEY_MOUSE_WHEEL_DOWN;
            else
                event->key = TB_KEY_MOUSE_MIDDLE;
            break;
        case 2:
            event->key = TB_KEY_MOUSE_RIGHT;
            break;
        case 3:
            event->key = TB_KEY_MOUSE_RELEASE;
            break;
        default:
            return -6;
        }
        event->type = TB_EVENT_MOUSE; // TB_EVENT_KEY by default
        if ((b & 32) != 0)
            event->mod |= TB_MOD_MOTION;

        // the coord is 1,1 for upper left
        event->x = (uint8_t)buf[4] - 1 - 32;
        event->y = (uint8_t)buf[5] - 1 - 32;

        return 6;
    } else if (starts_with(buf, len, "\033[<") ||
               starts_with(buf, len, "\033[")) {
        // xterm 1006 extended mode or urxvt 1015 extended mode
        // xterm: \033 [ < Cb ; Cx ; Cy (M or m)
        // urxvt: \033 [ Cb ; Cx ; Cy M
        int i, mi = -1, starti = -1;
        int isM, isU, s1 = -1, s2 = -1;
        int n1 = 0, n2 = 0, n3 = 0;

        for (i = 0; i < len; i++) {
            // We search the first (s1) and the last (s2) ';'
            if (buf[i] == ';') {
                if (s1 == -1)
                    s1 = i;
                s2 = i;
            }

            // We search for the first 'm' or 'M'
            if ((buf[i] == 'm' || buf[i] == 'M') && mi == -1) {
                mi = i;
                break;
            }
        }
        if (mi == -1)
            return 0;

        // whether it's a capital M or not
        isM = (buf[mi] == 'M');

        if (buf[2] == '<') {
            isU = 0;
            starti = 3;
        } else {
            isU = 1;
            starti = 2;
        }

        if (s1 == -1 || s2 == -1 || s1 == s2)
            return 0;

        n1 = strtoul(&buf[starti], NULL, 10);
        n2 = strtoul(&buf[s1 + 1], NULL, 10);
        n3 = strtoul(&buf[s2 + 1], NULL, 10);

        if (isU)
            n1 -= 32;

        switch (n1 & 3) {
        case 0:
            if ((n1 & 64) != 0) {
                event->key = TB_KEY_MOUSE_WHEEL_UP;
            } else {
                event->key = TB_KEY_MOUSE_LEFT;
            }
            break;
        case 1:
            if ((n1 & 64) != 0) {
                event->key = TB_KEY_MOUSE_WHEEL_DOWN;
            } else {
                event->key = TB_KEY_MOUSE_MIDDLE;
            }
            break;
        case 2:
            event->key = TB_KEY_MOUSE_RIGHT;
            break;
        case 3:
            event->key = TB_KEY_MOUSE_RELEASE;
            break;
        default:
            return mi + 1;
        }

        if (!isM) {
            // on xterm mouse release is signaled by lowercase m
            event->key = TB_KEY_MOUSE_RELEASE;
        }

        event->type = TB_EVENT_MOUSE; // TB_EVENT_KEY by default
        if ((n1 & 32) != 0)
            event->mod |= TB_MOD_MOTION;

        event->x = (uint8_t)n2 - 1;
        event->y = (uint8_t)n3 - 1;

        return mi + 1;
    }

    return 0;
}

// convert escape sequence to event, and return consumed bytes on success
// (failure == 0)
static int parse_escape_seq(struct tb_event *event, const char *buf, int len) {
    int mouse_parsed = parse_mouse_event(event, buf, len);

    if (mouse_parsed != 0)
        return mouse_parsed;

    // it's pretty simple here, find 'starts_with' match and return
    // success, else return failure
    int i;
    for (i = 0; keys[i]; i++) {
        if (starts_with(buf, len, keys[i])) {
            event->ch = 0;
            event->key = 0xFFFF - i;
            return strlen(keys[i]);
        }
    }
    return 0;
}

static bool extract_event(struct tb_event *event, struct bytebuffer *inbuf,
                          int inputmode) {
    const char *buf = inbuf->buf;
    const int len = inbuf->len;
    if (len == 0)
        return false;

    if (buf[0] == '\033') {
        int n = parse_escape_seq(event, buf, len);
        if (n != 0) {
            bool success = true;
            if (n < 0) {
                success = false;
                n = -n;
            }
            bytebuffer_truncate(inbuf, n);
            return success;
        } else {
            // it's not escape sequence, then it's ALT or ESC,
            // check inputmode
            if (inputmode & TB_INPUT_ESC) {
                // if we're in escape mode, fill ESC event, pop
                // buffer, return success
                event->ch = 0;
                event->key = TB_KEY_ESC;
                event->mod = 0;
                bytebuffer_truncate(inbuf, 1);
                return true;
            } else if (inputmode & TB_INPUT_ALT) {
                // if we're in alt mode, set ALT modifier to
                // event and redo parsing
                event->mod = TB_MOD_ALT;
                bytebuffer_truncate(inbuf, 1);
                return extract_event(event, inbuf, inputmode);
            }
            assert(!"never got here");
        }
    }

    // if we're here, this is not an escape sequence and not an alt sequence
    // so, it's a FUNCTIONAL KEY or a UNICODE character

    // first of all check if it's a functional key
    if ((unsigned char)buf[0] <= TB_KEY_SPACE ||
        (unsigned char)buf[0] == TB_KEY_BACKSPACE2) {
        // fill event, pop buffer, return success */
        event->ch = 0;
        event->key = (uint16_t)buf[0];
        bytebuffer_truncate(inbuf, 1);
        return true;
    }

    // feh... we got utf8 here

    // check if there is all bytes
    if (len >= tb_utf8_char_length(buf[0])) {
        /* everything ok, fill event, pop buffer, return success */
        tb_utf8_char_to_unicode(&event->ch, buf);
        event->key = 0;
        bytebuffer_truncate(inbuf, tb_utf8_char_length(buf[0]));
        return true;
    }

    // event isn't recognized, perhaps there is not enough bytes in utf8
    // sequence
    return false;
}

/* -------------------------------------------------------- */

int tb_init_fd(int inout_) {
    inout = inout_;
    if (inout == -1) {
        return TB_EFAILED_TO_OPEN_TTY;
    }

    if (init_term() < 0) {
        close(inout);
        return TB_EUNSUPPORTED_TERMINAL;
    }

    if (pipe(winch_fds) < 0) {
        close(inout);
        return TB_EPIPE_TRAP_ERROR;
    }

    struct sigaction sa;
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = sigwinch_handler;
    sa.sa_flags = 0;
    sigaction(SIGWINCH, &sa, 0);

    tcgetattr(inout, &orig_tios);

    struct termios tios;
    memcpy(&tios, &orig_tios, sizeof(tios));

    tios.c_iflag &=
        ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);
    tios.c_oflag &= ~OPOST;
    tios.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
    tios.c_cflag &= ~(CSIZE | PARENB);
    tios.c_cflag |= CS8;
    tios.c_cc[VMIN] = 0;
    tios.c_cc[VTIME] = 0;
    tcsetattr(inout, TCSAFLUSH, &tios);

    bytebuffer_init(&input_buffer, 128);
    bytebuffer_init(&output_buffer, 32 * 1024);

    bytebuffer_puts(&output_buffer, funcs[T_ENTER_CA]);
    bytebuffer_puts(&output_buffer, funcs[T_ENTER_KEYPAD]);
    bytebuffer_puts(&output_buffer, funcs[T_HIDE_CURSOR]);
    send_clear();

    update_term_size();
    cellbuf_init(&back_buffer, termw, termh);
    cellbuf_init(&front_buffer, termw, termh);
    cellbuf_clear(&back_buffer);
    cellbuf_clear(&front_buffer);

    return 0;
}

int tb_init_file(const char *name) { return tb_init_fd(open(name, O_RDWR)); }

int tb_init(void) { return tb_init_file("/dev/tty"); }

void tb_shutdown(void) {
    if (termw == -1) {
        fputs("tb_shutdown() should not be called twice.", stderr);
        abort();
    }

    bytebuffer_puts(&output_buffer, funcs[T_SHOW_CURSOR]);
    bytebuffer_puts(&output_buffer, funcs[T_SGR0]);
    bytebuffer_puts(&output_buffer, funcs[T_CLEAR_SCREEN]);
    bytebuffer_puts(&output_buffer, funcs[T_EXIT_CA]);
    bytebuffer_puts(&output_buffer, funcs[T_EXIT_KEYPAD]);
    bytebuffer_puts(&output_buffer, funcs[T_EXIT_MOUSE]);
    bytebuffer_flush(&output_buffer, inout);
    tcsetattr(inout, TCSAFLUSH, &orig_tios);

    shutdown_term();
    close(inout);
    close(winch_fds[0]);
    close(winch_fds[1]);

    cellbuf_free(&back_buffer);
    cellbuf_free(&front_buffer);
    bytebuffer_free(&output_buffer);
    bytebuffer_free(&input_buffer);
    termw = termh = -1;
}

void tb_present(void) {
    int x, y, w, i;
    struct tb_cell *back, *front;

    /* invalidate cursor position */
    lastx = LAST_COORD_INIT;
    lasty = LAST_COORD_INIT;

    if (buffer_size_change_request) {
        update_size();
        buffer_size_change_request = 0;
    }

    for (y = 0; y < front_buffer.height; ++y) {
        for (x = 0; x < front_buffer.width;) {
            back = &CELL(&back_buffer, x, y);
            front = &CELL(&front_buffer, x, y);
            w = wcwidth(back->ch);
            if (w < 1)
                w = 1;
            if (memcmp(back, front, sizeof(struct tb_cell)) == 0) {
                x += w;
                continue;
            }
            memcpy(front, back, sizeof(struct tb_cell));
            send_attr(back->fg, back->bg);
            if (w > 1 && x >= front_buffer.width - (w - 1)) {
                // Not enough room for wide ch, so send spaces
                for (i = x; i < front_buffer.width; ++i) {
                    send_char(i, y, ' ');
                }
            } else {
                send_char(x, y, back->ch);
                for (i = 1; i < w; ++i) {
                    front = &CELL(&front_buffer, x + i, y);
                    front->ch = 0;
                    front->fg = back->fg;
                    front->bg = back->bg;
                }
            }
            x += w;
        }
    }
    if (!IS_CURSOR_HIDDEN(cursor_x, cursor_y))
        write_cursor(cursor_x, cursor_y);
    bytebuffer_flush(&output_buffer, inout);
}

void tb_set_cursor(int cx, int cy) {
    if (IS_CURSOR_HIDDEN(cursor_x, cursor_y) && !IS_CURSOR_HIDDEN(cx, cy))
        bytebuffer_puts(&output_buffer, funcs[T_SHOW_CURSOR]);

    if (!IS_CURSOR_HIDDEN(cursor_x, cursor_y) && IS_CURSOR_HIDDEN(cx, cy))
        bytebuffer_puts(&output_buffer, funcs[T_HIDE_CURSOR]);

    cursor_x = cx;
    cursor_y = cy;
    if (!IS_CURSOR_HIDDEN(cursor_x, cursor_y))
        write_cursor(cursor_x, cursor_y);
}

void tb_put_cell(int x, int y, const struct tb_cell *cell) {
    if ((unsigned)x >= (unsigned)back_buffer.width)
        return;
    if ((unsigned)y >= (unsigned)back_buffer.height)
        return;
    CELL(&back_buffer, x, y) = *cell;
}

void tb_change_cell(int x, int y, uint32_t ch, uint16_t fg, uint16_t bg) {
    struct tb_cell c = {ch, fg, bg};
    tb_put_cell(x, y, &c);
}

void tb_blit(int x, int y, int w, int h, const struct tb_cell *cells) {
    if (x + w < 0 || x >= back_buffer.width)
        return;
    if (y + h < 0 || y >= back_buffer.height)
        return;
    int xo = 0, yo = 0, ww = w, hh = h;
    if (x < 0) {
        xo = -x;
        ww -= xo;
        x = 0;
    }
    if (y < 0) {
        yo = -y;
        hh -= yo;
        y = 0;
    }
    if (ww > back_buffer.width - x)
        ww = back_buffer.width - x;
    if (hh > back_buffer.height - y)
        hh = back_buffer.height - y;

    int sy;
    struct tb_cell *dst = &CELL(&back_buffer, x, y);
    const struct tb_cell *src = cells + yo * w + xo;
    size_t size = sizeof(struct tb_cell) * ww;

    for (sy = 0; sy < hh; ++sy) {
        memcpy(dst, src, size);
        dst += back_buffer.width;
        src += w;
    }
}

struct tb_cell *tb_cell_buffer(void) {
    return back_buffer.cells;
}

int tb_poll_event(struct tb_event *event) { return wait_fill_event(event, 0); }

int tb_peek_event(struct tb_event *event, int timeout) {
    struct timeval tv;
    tv.tv_sec = timeout / 1000;
    tv.tv_usec = (timeout - (tv.tv_sec * 1000)) * 1000;
    return wait_fill_event(event, &tv);
}

int tb_width(void) { return termw; }

int tb_height(void) { return termh; }

void tb_clear(void) {
    if (buffer_size_change_request) {
        update_size();
        buffer_size_change_request = 0;
    }
    cellbuf_clear(&back_buffer);
}

int tb_select_input_mode(int mode) {
    if (mode) {
        if ((mode & (TB_INPUT_ESC | TB_INPUT_ALT)) == 0)
            mode |= TB_INPUT_ESC;

        /* technically termbox can handle that, but let's be nice and show here
           what mode is actually used */
        if ((mode & (TB_INPUT_ESC | TB_INPUT_ALT)) ==
            (TB_INPUT_ESC | TB_INPUT_ALT))
            mode &= ~TB_INPUT_ALT;

        inputmode = mode;
        if (mode & TB_INPUT_MOUSE) {
            bytebuffer_puts(&output_buffer, funcs[T_ENTER_MOUSE]);
            bytebuffer_flush(&output_buffer, inout);
        } else {
            bytebuffer_puts(&output_buffer, funcs[T_EXIT_MOUSE]);
            bytebuffer_flush(&output_buffer, inout);
        }
    }
    return inputmode;
}

int tb_select_output_mode(int mode) {
    if (mode)
        outputmode = mode;
    return outputmode;
}

void tb_set_clear_attributes(uint16_t fg, uint16_t bg) {
    foreground = fg;
    background = bg;
}

/* -------------------------------------------------------- */

static int convertnum(uint32_t num, char *buf) {
    int i, l = 0;
    int ch;
    do {
        buf[l++] = '0' + (num % 10);
        num /= 10;
    } while (num);
    for (i = 0; i < l / 2; i++) {
        ch = buf[i];
        buf[i] = buf[l - 1 - i];
        buf[l - 1 - i] = ch;
    }
    return l;
}

static void write_cursor(int x, int y) {
    char buf[32];
    WRITE_LITERAL("\033[");
    WRITE_INT(y + 1);
    WRITE_LITERAL(";");
    WRITE_INT(x + 1);
    WRITE_LITERAL("H");
}

static void write_sgr(uint16_t fg, uint16_t bg) {
    char buf[32];

    if (fg == TB_DEFAULT && bg == TB_DEFAULT)
        return;

    switch (outputmode) {
    case TB_OUTPUT_256:
    case TB_OUTPUT_216:
    case TB_OUTPUT_GRAYSCALE:
        WRITE_LITERAL("\033[");
        if (fg != TB_DEFAULT) {
            WRITE_LITERAL("38;5;");
            WRITE_INT(fg);
            if (bg != TB_DEFAULT) {
                WRITE_LITERAL(";");
            }
        }
        if (bg != TB_DEFAULT) {
            WRITE_LITERAL("48;5;");
            WRITE_INT(bg);
        }
        WRITE_LITERAL("m");
        break;
    case TB_OUTPUT_NORMAL:
    default:
        WRITE_LITERAL("\033[");
        if (fg != TB_DEFAULT) {
            WRITE_LITERAL("3");
            WRITE_INT(fg - 1);
            if (bg != TB_DEFAULT) {
                WRITE_LITERAL(";");
            }
        }
        if (bg != TB_DEFAULT) {
            WRITE_LITERAL("4");
            WRITE_INT(bg - 1);
        }
        WRITE_LITERAL("m");
        break;
    }
}

static void cellbuf_init(struct cellbuf *buf, int width, int height) {
    buf->cells =
        (struct tb_cell *)malloc(sizeof(struct tb_cell) * width * height);
    assert(buf->cells);
    buf->width = width;
    buf->height = height;
}

static void cellbuf_resize(struct cellbuf *buf, int width, int height) {
    if (buf->width == width && buf->height == height)
        return;

    int oldw = buf->width;
    int oldh = buf->height;
    struct tb_cell *oldcells = buf->cells;

    cellbuf_init(buf, width, height);
    cellbuf_clear(buf);

    int minw = (width < oldw) ? width : oldw;
    int minh = (height < oldh) ? height : oldh;
    int i;

    for (i = 0; i < minh; ++i) {
        struct tb_cell *csrc = oldcells + (i * oldw);
        struct tb_cell *cdst = buf->cells + (i * width);
        memcpy(cdst, csrc, sizeof(struct tb_cell) * minw);
    }

    free(oldcells);
}

static void cellbuf_clear(struct cellbuf *buf) {
    int i;
    int ncells = buf->width * buf->height;

    for (i = 0; i < ncells; ++i) {
        buf->cells[i].ch = ' ';
        buf->cells[i].fg = foreground;
        buf->cells[i].bg = background;
    }
}

static void cellbuf_free(struct cellbuf *buf) {
    free(buf->cells);
}

static void get_term_size(int *w, int *h) {
    struct winsize sz;
    memset(&sz, 0, sizeof(sz));

    ioctl(inout, TIOCGWINSZ, &sz);

    *w = sz.ws_col > 0 ? sz.ws_col : 80;
    *h = sz.ws_row > 0 ? sz.ws_row : 24;
}

static void update_term_size(void) {
    struct winsize sz;
    memset(&sz, 0, sizeof(sz));

    ioctl(inout, TIOCGWINSZ, &sz);

    termw = sz.ws_col > 0 ? sz.ws_col : 80;
    termh = sz.ws_row > 0 ? sz.ws_row : 24;
}

static void send_attr(uint16_t fg, uint16_t bg) {
#define LAST_ATTR_INIT 0xFFFF
    static uint16_t lastfg = LAST_ATTR_INIT, lastbg = LAST_ATTR_INIT;
    if (fg != lastfg || bg != lastbg) {
        bytebuffer_puts(&output_buffer, funcs[T_SGR0]);

        uint16_t fgcol;
        uint16_t bgcol;

        switch (outputmode) {
        case TB_OUTPUT_256:
            fgcol = fg & 0xFF;
            bgcol = bg & 0xFF;
            break;

        case TB_OUTPUT_216:
            fgcol = fg & 0xFF;
            if (fgcol > 215)
                fgcol = 7;
            bgcol = bg & 0xFF;
            if (bgcol > 215)
                bgcol = 0;
            fgcol += 0x10;
            bgcol += 0x10;
            break;

        case TB_OUTPUT_GRAYSCALE:
            fgcol = fg & 0xFF;
            if (fgcol > 23)
                fgcol = 23;
            bgcol = bg & 0xFF;
            if (bgcol > 23)
                bgcol = 0;
            fgcol += 0xe8;
            bgcol += 0xe8;
            break;

        case TB_OUTPUT_NORMAL:
        default:
            fgcol = fg & 0x0F;
            bgcol = bg & 0x0F;
        }

        if (fg & TB_BOLD)
            bytebuffer_puts(&output_buffer, funcs[T_BOLD]);
        if (bg & TB_BOLD)
            bytebuffer_puts(&output_buffer, funcs[T_BLINK]);
        if (fg & TB_UNDERLINE)
            bytebuffer_puts(&output_buffer, funcs[T_UNDERLINE]);
        if ((fg & TB_REVERSE) || (bg & TB_REVERSE))
            bytebuffer_puts(&output_buffer, funcs[T_REVERSE]);

        write_sgr(fgcol, bgcol);

        lastfg = fg;
        lastbg = bg;
    }
}

static void send_char(int x, int y, uint32_t c) {
    char buf[7];
    int bw = tb_utf8_unicode_to_char(buf, c);
    if (x - 1 != lastx || y != lasty)
        write_cursor(x, y);
    lastx = x;
    lasty = y;
    if (!c)
        buf[0] = ' '; // replace 0 with whitespace
    bytebuffer_append(&output_buffer, buf, bw);
}

static void send_clear(void) {
    send_attr(foreground, background);
    bytebuffer_puts(&output_buffer, funcs[T_CLEAR_SCREEN]);
    if (!IS_CURSOR_HIDDEN(cursor_x, cursor_y))
        write_cursor(cursor_x, cursor_y);
    bytebuffer_flush(&output_buffer, inout);

    /* we need to invalidate cursor position too and these two vars are
     * used only for simple cursor positioning optimization, cursor
     * actually may be in the correct place, but we simply discard
     * optimization once and it gives us simple solution for the case when
     * cursor moved */
    lastx = LAST_COORD_INIT;
    lasty = LAST_COORD_INIT;
}

static void sigwinch_handler(int xxx) {
    (void)xxx;
    const int zzz = 1;
    write(winch_fds[1], &zzz, sizeof(int));
}

static void update_size(void) {
    update_term_size();
    cellbuf_resize(&back_buffer, termw, termh);
    cellbuf_resize(&front_buffer, termw, termh);
    cellbuf_clear(&front_buffer);
    send_clear();
}

static int read_up_to(int n) {
    assert(n > 0);
    const int prevlen = input_buffer.len;
    bytebuffer_resize(&input_buffer, prevlen + n);

    int read_n = 0;
    while (read_n <= n) {
        ssize_t r = 0;
        if (read_n < n) {
            r = read(inout, input_buffer.buf + prevlen + read_n, n - read_n);
        }
#ifdef __CYGWIN__
        // While linux man for tty says when VMIN == 0 && VTIME == 0, read
        // should return 0 when there is nothing to read, cygwin's read returns
        // -1. Not sure why and if it's correct to ignore it, but let's pretend
        // it's zero.
        if (r < 0)
            r = 0;
#endif
        if (r < 0) {
            // EAGAIN / EWOULDBLOCK shouldn't occur here
            assert(errno != EAGAIN && errno != EWOULDBLOCK);
            return -1;
        } else if (r > 0) {
            read_n += r;
        } else {
            bytebuffer_resize(&input_buffer, prevlen + read_n);
            return read_n;
        }
    }
    assert(!"unreachable");
    return 0;
}

static int wait_fill_event(struct tb_event *event, struct timeval *timeout) {
    // ;-)
#define ENOUGH_DATA_FOR_PARSING 64
    fd_set events;
    memset(event, 0, sizeof(struct tb_event));

    // try to extract event from input buffer, return on success
    event->type = TB_EVENT_KEY;
    if (extract_event(event, &input_buffer, inputmode))
        return event->type;

    // it looks like input buffer is incomplete, let's try the short path,
    // but first make sure there is enough space
    int n = read_up_to(ENOUGH_DATA_FOR_PARSING);
    if (n < 0)
        return -1;
    if (n > 0 && extract_event(event, &input_buffer, inputmode))
        return event->type;

    // n == 0, or not enough data, let's go to select
    while (1) {
        FD_ZERO(&events);
        FD_SET(inout, &events);
        FD_SET(winch_fds[0], &events);
        int maxfd = (winch_fds[0] > inout) ? winch_fds[0] : inout;
        int result = select(maxfd + 1, &events, 0, 0, timeout);
        if (!result)
            return 0;
        if (result < 0)
            return -1;

        if (FD_ISSET(inout, &events)) {
            event->type = TB_EVENT_KEY;
            n = read_up_to(ENOUGH_DATA_FOR_PARSING);
            if (n < 0)
                return -1;

            if (n == 0)
                continue;

            if (extract_event(event, &input_buffer, inputmode))
                return event->type;
        }
        if (FD_ISSET(winch_fds[0], &events)) {
            event->type = TB_EVENT_RESIZE;
            int zzz = 0;
            read(winch_fds[0], &zzz, sizeof(int));
            buffer_size_change_request = 1;
            get_term_size(&event->w, &event->h);
            return TB_EVENT_RESIZE;
        }
    }
}

static void bytebuffer_reserve(struct bytebuffer *b, int cap) {
    if (b->cap >= cap) {
        return;
    }

    // prefer doubling capacity
    if (b->cap * 2 >= cap) {
        cap = b->cap * 2;
    }

    char *newbuf = realloc(b->buf, cap);
    b->buf = newbuf;
    b->cap = cap;
}

static void bytebuffer_init(struct bytebuffer *b, int cap) {
    b->cap = 0;
    b->len = 0;
    b->buf = 0;

    if (cap > 0) {
        b->cap = cap;
        b->buf = malloc(cap); // just assume malloc works always
    }
}

static void bytebuffer_free(struct bytebuffer *b) {
    if (b->buf)
        free(b->buf);
}

static void bytebuffer_clear(struct bytebuffer *b) {
    b->len = 0;
}

static void bytebuffer_append(struct bytebuffer *b, const char *data, int len) {
    bytebuffer_reserve(b, b->len + len);
    memcpy(b->buf + b->len, data, len);
    b->len += len;
}

static void bytebuffer_puts(struct bytebuffer *b, const char *str) {
    bytebuffer_append(b, str, strlen(str));
}

static void bytebuffer_resize(struct bytebuffer *b, int len) {
    bytebuffer_reserve(b, len);
    b->len = len;
}

static void bytebuffer_flush(struct bytebuffer *b, int fd) {
    write(fd, b->buf, b->len);
    bytebuffer_clear(b);
}

static void bytebuffer_truncate(struct bytebuffer *b, int n) {
    if (n <= 0)
        return;
    if (n > b->len)
        n = b->len;
    const int nmove = b->len - n;
    memmove(b->buf, b->buf + n, nmove);
    b->len -= n;
}
