/* The compositor: a cell buffer for the whole screen, and a diff that turns
 * two of them into the minimal byte stream for the real terminal. */
#define _GNU_SOURCE
#include "slosh.h"

#include <ghostty/vt.h>

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "json.h"

/* ---- hit list ----------------------------------------------------------- */

void hit_reset(hitlist_t *hl) { hl->len = 0; }

void hit_add(hitlist_t *hl, uint16_t x, uint16_t y, uint16_t w, uint16_t h,
             const char *action) {
  if (hl->len == hl->cap) {
    hl->cap = hl->cap ? hl->cap * 2 : 16;
    hl->items = realloc(hl->items, hl->cap * sizeof *hl->items);
  }
  hit_t *e = &hl->items[hl->len++];
  e->x = x;
  e->y = y;
  e->w = w;
  e->h = h;
  snprintf(e->action, sizeof e->action, "%s", action);
}

const char *hit_test(const hitlist_t *hl, uint16_t x, uint16_t y) {
  for (size_t i = hl->len; i-- > 0;) {
    const hit_t *e = &hl->items[i];
    if (x >= e->x && x < e->x + e->w && y >= e->y && y < e->y + e->h)
      return e->action;
  }
  return NULL;
}

/* The rect an action was registered with, for a caller that has to grow or
 * paint over something it did not place itself. Searched backwards, like
 * hit_test, so the answer is the entry a click at those cells would find. */
const hit_t *hit_find(const hitlist_t *hl, const char *action) {
  for (size_t i = hl->len; i-- > 0;)
    if (strcmp(hl->items[i].action, action) == 0) return &hl->items[i];
  return NULL;
}

static void out_reserve(screen_t *s, size_t n) {
  if (s->out_len + n <= s->out_cap) return;
  size_t cap = s->out_cap ? s->out_cap : 8192;
  while (cap < s->out_len + n) cap *= 2;
  s->out = realloc(s->out, cap);
  s->out_cap = cap;
}

static void out_bytes(screen_t *s, const char *b, size_t n) {
  out_reserve(s, n);
  memcpy(s->out + s->out_len, b, n);
  s->out_len += n;
}

static void out_str(screen_t *s, const char *b) { out_bytes(s, b, strlen(b)); }

static void out_fmt(screen_t *s, const char *fmt, ...) {
  char buf[128];
  va_list ap;
  va_start(ap, fmt);
  int n = vsnprintf(buf, sizeof buf, fmt, ap);
  va_end(ap);
  if (n > 0) out_bytes(s, buf, (size_t)n);
}

static cell_t blank_cell(void) {
  cell_t c = {0};
  c.text[0] = ' ';
  c.len = 1;
  c.width = 1;
  return c;
}

#define LINKS_MAX 4096 /* unique URIs a screen will carry; then they drop */

void screen_init(screen_t *s, uint16_t cols, uint16_t rows) {
  memset(s, 0, sizeof *s);
  s->cols = cols;
  s->rows = rows;
  size_t n = (size_t)cols * rows;
  s->cur = calloc(n, sizeof(cell_t));
  s->prev = calloc(n, sizeof(cell_t));
  s->cur_link = calloc(n, sizeof(uint16_t));
  s->prev_link = calloc(n, sizeof(uint16_t));
  s->force_full = true;
  screen_clear(s);
}

void screen_free(screen_t *s) {
  free(s->cur);
  free(s->prev);
  free(s->cur_link);
  free(s->prev_link);
  for (size_t i = 0; i < s->nlinks; i++) free(s->links[i]);
  free(s->links);
  free(s->out);
  free(s->hits.items);
  memset(s, 0, sizeof *s);
}

void screen_resize(screen_t *s, uint16_t cols, uint16_t rows) {
  if (cols == s->cols && rows == s->rows) return;
  free(s->cur);
  free(s->prev);
  free(s->cur_link);
  free(s->prev_link);
  s->cols = cols;
  s->rows = rows;
  size_t n = (size_t)cols * rows;
  s->cur = calloc(n, sizeof(cell_t));
  s->prev = calloc(n, sizeof(cell_t));
  s->cur_link = calloc(n, sizeof(uint16_t));
  s->prev_link = calloc(n, sizeof(uint16_t));
  /* The URI table survives a resize on purpose: ids in flight stay
   * meaningful, and a resize is not a reason to forget what a link was. */
  s->force_full = true;
  screen_clear(s);
}

void screen_clear(screen_t *s) {
  size_t n = (size_t)s->cols * s->rows;
  cell_t b = blank_cell();
  for (size_t i = 0; i < n; i++) s->cur[i] = b;
  memset(s->cur_link, 0, n * sizeof(uint16_t));
}

void screen_project(screen_t *dst, const screen_t *src, uint16_t x0,
                    uint16_t y0) {
  screen_clear(dst);
  hit_reset(&dst->hits);
  dst->cursor_visible = false;

  for (uint16_t y = 0; y < dst->rows && (uint32_t)y0 + y < src->rows; y++) {
    uint16_t sy = (uint16_t)(y0 + y);
    for (uint16_t x = 0; x < dst->cols && (uint32_t)x0 + x < src->cols; x++) {
      uint16_t sx = (uint16_t)(x0 + x);
      size_t si = (size_t)sy * src->cols + sx;
      size_t di = (size_t)y * dst->cols + x;
      const cell_t *c = &src->cur[si];

      /* A viewport cannot display half a wide grapheme. A tail at its left
       * edge and a head at its right edge both remain filler rather than
       * relying on terminal-dependent wrapping or replacement glyphs. */
      if (c->width == 0) continue;
      if (c->width == 2 &&
          ((uint32_t)sx + 1 >= src->cols || (uint32_t)x + 1 >= dst->cols))
        continue;

      dst->cur[di] = *c;
      uint16_t link = src->cur_link[si];
      if (link && link <= src->nlinks) {
        const char *uri = src->links[link - 1];
        dst->cur_link[di] = screen_link_id(dst, uri, strlen(uri));
      }
      if (c->width == 2) {
        dst->cur[di + 1] = src->cur[si + 1];
        uint16_t tail_link = src->cur_link[si + 1];
        if (tail_link && tail_link <= src->nlinks) {
          const char *uri = src->links[tail_link - 1];
          dst->cur_link[di + 1] = screen_link_id(dst, uri, strlen(uri));
        }
        x++;
      }
    }
  }

  if (src->cursor_visible && src->cursor_x >= x0 && src->cursor_y >= y0 &&
      (uint32_t)src->cursor_x < (uint32_t)x0 + dst->cols &&
      (uint32_t)src->cursor_y < (uint32_t)y0 + dst->rows) {
    dst->cursor_visible = true;
    dst->cursor_x = (uint16_t)(src->cursor_x - x0);
    dst->cursor_y = (uint16_t)(src->cursor_y - y0);
  }
}

void screen_follow_cursor(const screen_t *src, uint16_t cols, uint16_t rows,
                          uint16_t *x, uint16_t *y) {
  uint16_t vx = x ? *x : 0, vy = y ? *y : 0;
  uint16_t max_x = src->cols > cols ? (uint16_t)(src->cols - cols) : 0;
  uint16_t max_y = src->rows > rows ? (uint16_t)(src->rows - rows) : 0;
  if (!max_x)
    vx = 0;
  else if (src->cursor_visible) {
    if (src->cursor_x < vx)
      vx = src->cursor_x;
    else if ((uint32_t)src->cursor_x >= (uint32_t)vx + cols)
      vx = (uint16_t)(src->cursor_x - cols + 1);
  }
  if (!max_y)
    vy = 0;
  else if (src->cursor_visible) {
    if (src->cursor_y < vy)
      vy = src->cursor_y;
    else if ((uint32_t)src->cursor_y >= (uint32_t)vy + rows)
      vy = (uint16_t)(src->cursor_y - rows + 1);
  }
  if (vx > max_x) vx = max_x;
  if (vy > max_y) vy = max_y;
  if (x) *x = vx;
  if (y) *y = vy;
}

uint16_t screen_link_id(screen_t *s, const char *uri, size_t len) {
  if (!uri || !len || len > 1024) return 0;
  /* A URI is emitted verbatim inside an OSC, so a control byte in one is a
   * way to write escape sequences into the client's terminal. lib-vt cannot
   * hand us its own terminators, but the rest of C0 is cheap to refuse and
   * free to never think about again. */
  for (size_t i = 0; i < len; i++)
    if ((unsigned char)uri[i] < 0x20 || uri[i] == 0x7f) return 0;
  for (size_t i = 0; i < s->nlinks; i++)
    if (strlen(s->links[i]) == len && memcmp(s->links[i], uri, len) == 0)
      return (uint16_t)(i + 1);
  if (s->nlinks >= LINKS_MAX) return 0;
  char *copy = malloc(len + 1);
  if (!copy) return 0;
  memcpy(copy, uri, len);
  copy[len] = 0;
  s->links = realloc(s->links, (s->nlinks + 1) * sizeof *s->links);
  s->links[s->nlinks++] = copy;
  return (uint16_t)s->nlinks;
}

void screen_set_link(screen_t *s, uint16_t x, uint16_t y, uint16_t id) {
  if (x >= s->cols || y >= s->rows) return;
  s->cur_link[(size_t)y * s->cols + x] = id;
}

cell_t *screen_at(screen_t *s, uint16_t x, uint16_t y) {
  if (x >= s->cols || y >= s->rows) return NULL;
  return &s->cur[(size_t)y * s->cols + x];
}

static size_t u8_len(unsigned char b) {
  if (b < 0x80) return 1;
  if ((b & 0xe0) == 0xc0) return 2;
  if ((b & 0xf0) == 0xe0) return 3;
  if ((b & 0xf8) == 0xf0) return 4;
  return 1;
}

/* Decode UTF-8 into codepoints, bounded. Returns how many were written and,
 * via `used`, how many bytes they came from -- the caller needs both to walk a
 * string cluster by cluster. */
static size_t decode_utf8(const char *txt, size_t len, uint32_t *cps,
                          size_t max, size_t *used) {
  size_t n = 0, i = 0;
  while (i < len && n < max) {
    size_t l = u8_len((unsigned char)txt[i]);
    if (l == 0 || i + l > len) break;
    uint32_t cp;
    switch (l) {
    case 1: cp = (unsigned char)txt[i]; break;
    case 2:
      cp = ((uint32_t)((unsigned char)txt[i] & 0x1f) << 6) |
           ((unsigned char)txt[i + 1] & 0x3f);
      break;
    case 3:
      cp = ((uint32_t)((unsigned char)txt[i] & 0x0f) << 12) |
           ((uint32_t)((unsigned char)txt[i + 1] & 0x3f) << 6) |
           ((unsigned char)txt[i + 2] & 0x3f);
      break;
    default:
      cp = ((uint32_t)((unsigned char)txt[i] & 0x07) << 18) |
           ((uint32_t)((unsigned char)txt[i + 1] & 0x3f) << 12) |
           ((uint32_t)((unsigned char)txt[i + 2] & 0x3f) << 6) |
           ((unsigned char)txt[i + 3] & 0x3f);
      break;
    }
    cps[n++] = cp;
    i += l;
  }
  if (used) *used = i;
  return n;
}

/* How many columns the first grapheme cluster takes, asked of the same table
 * the terminal uses (lib-vt's). Guessing 1 for everything is what made a
 * two-column bell mark shift the rest of a pane's title row: the cell was
 * booked as one column and drawn as two, and every glyph after it landed a
 * column early. */
uint8_t screen_width_of(const char *txt, size_t len) {
  uint32_t cps[16];
  size_t n = decode_utf8(txt, len, cps, sizeof cps / sizeof *cps, NULL);
  if (!n) return 1;
  uint8_t w = 1;
  ghostty_unicode_grapheme_width(cps, n, &w);
  /* A zero-width cluster still owns the cell it was written into: chrome is
   * laid out in cells, and a mark that claims no space would be overwritten
   * by whatever comes next. */
  return w ? w : 1;
}

/* Columns a whole string occupies.
 *
 * Cluster by cluster, using the codepoint count lib-vt reports as consumed --
 * summing per-codepoint widths is a different and wrong answer, because an
 * emoji with a variation selector is two codepoints and one cluster. */
uint16_t screen_cells(const char *txt) {
  if (!txt) return 0;
  uint32_t cps[256];
  uint16_t total = 0;
  size_t len = strlen(txt), at = 0;
  while (at < len) {
    size_t used = 0;
    size_t n =
        decode_utf8(txt + at, len - at, cps, sizeof cps / sizeof *cps, &used);
    if (!n) break;
    for (size_t i = 0; i < n;) {
      uint8_t w = 1;
      size_t eaten = ghostty_unicode_grapheme_width(cps + i, n - i, &w);
      if (!eaten) break;
      i += eaten;
      total = (uint16_t)(total + w);
    }
    at += used;
  }
  return total;
}

void screen_put_utf8(screen_t *s, uint16_t x, uint16_t y, const char *txt,
                     size_t len, color_t fg, color_t bg, uint16_t attrs) {
  cell_t *c = screen_at(s, x, y);
  if (!c) return;
  /* Clamped on a codepoint boundary. A grapheme cluster can be longer than
   * this cell holds -- a family emoji is eighteen bytes -- and cutting one in
   * the middle of a codepoint puts invalid UTF-8 on the wire, which is worse
   * than losing the tail of a cluster nobody can see anyway. */
  if (len > sizeof c->text) {
    len = sizeof c->text;
    while (len && ((unsigned char)txt[len] & 0xC0) == 0x80) len--;
  }
  memset(c->text, 0, sizeof c->text);
  memcpy(c->text, txt, len);
  c->len = (uint8_t)len;
  c->width = screen_width_of(txt, len);
  /* Chrome over a link is chrome: writing a cell through here takes any
   * hyperlink a pane left on it, or a frame drawn across a URL would be
   * clickable. */
  screen_set_link(s, x, y, 0);
  /* The second half of a wide cell is a tail: never painted, and skipped by
   * the diff. Without claiming it, the cell to the right keeps whatever was
   * there and the terminal draws both. */
  if (c->width == 2) {
    cell_t *tail = screen_at(s, (uint16_t)(x + 1), y);
    if (tail) {
      memset(tail, 0, sizeof *tail);
      tail->fg = fg;
      tail->bg = bg;
      screen_set_link(s, (uint16_t)(x + 1), y, 0);
    } else {
      c->width = 1; /* no room for the tail: do not claim what is not there */
    }
  }
  c->fg = fg;
  c->bg = bg;
  c->attrs = attrs;
}

uint16_t screen_text(screen_t *s, uint16_t x, uint16_t y, const char *txt,
                     color_t fg, color_t bg, uint16_t attrs) {
  uint16_t n = 0;
  for (const char *p = txt; *p;) {
    size_t len = u8_len((unsigned char)*p);
    if (x + n >= s->cols) break;
    screen_put_utf8(s, (uint16_t)(x + n), y, p, len, fg, bg, attrs);
    cell_t *c = screen_at(s, (uint16_t)(x + n), y);
    n = (uint16_t)(n + (c && c->width ? c->width : 1));
    p += len;
  }
  return n; /* columns written, so a caller can lay out what follows */
}

static bool color_eq(color_t a, color_t b) {
  if (a.set != b.set) return false;
  if (!a.set) return true;
  return a.r == b.r && a.g == b.g && a.b == b.b;
}

static bool cell_eq(const cell_t *a, const cell_t *b) {
  return a->len == b->len && a->width == b->width && a->attrs == b->attrs &&
         memcmp(a->text, b->text, a->len) == 0 && color_eq(a->fg, b->fg) &&
         color_eq(a->bg, b->bg);
}

/* Reset-first SGR: a few bytes more than the minimal encoding, and it cannot
 * inherit a stale attribute. Emitted only when the style actually changes. */
static void emit_sgr(screen_t *s, const cell_t *c) {
  out_str(s, "\x1b[0");
  if (c->attrs & ATTR_BOLD) out_str(s, ";1");
  if (c->attrs & ATTR_DIM) out_str(s, ";2");
  if (c->attrs & ATTR_ITALIC) out_str(s, ";3");
  if (c->attrs & ATTR_UNDERLINE) out_str(s, ";4");
  if (c->attrs & ATTR_BLINK) out_str(s, ";5");
  if (c->attrs & ATTR_INVERSE) out_str(s, ";7");
  if (c->attrs & ATTR_INVISIBLE) out_str(s, ";8");
  if (c->attrs & ATTR_STRIKE) out_str(s, ";9");
  if (c->fg.set) out_fmt(s, ";38;2;%u;%u;%u", c->fg.r, c->fg.g, c->fg.b);
  if (c->bg.set) out_fmt(s, ";48;2;%u;%u;%u", c->bg.r, c->bg.g, c->bg.b);
  out_str(s, "m");
}

static bool style_eq(const cell_t *a, const cell_t *b) {
  return a->attrs == b->attrs && color_eq(a->fg, b->fg) &&
         color_eq(a->bg, b->bg);
}

void screen_render(screen_t *s) {
  s->out_len = 0;

  /* The cursor is hidden lazily, on the first cell we actually repaint, so a
   * frame with no changes emits nothing at all rather than a hide/show pair.
   * A keystroke that changes nothing should cost zero bytes. */
  bool painted = false;

  if (s->force_full) {
    out_str(s, "\x1b[?25l\x1b[0m\x1b[H\x1b[2J");
    memset(s->prev, 0, (size_t)s->cols * s->rows * sizeof(cell_t));
    memset(s->prev_link, 0, (size_t)s->cols * s->rows * sizeof(uint16_t));
    painted = true;
  }

  bool have_pos = false, have_style = false;
  uint16_t cx = 0, cy = 0;
  cell_t style = {0};
  /* Which hyperlink the output stream currently has open (OSC 8). Only the
   * cells this frame emits pass through it — an unchanged cell keeps the
   * link the terminal already holds for it — and it is closed before the
   * frame ends, so link state never leaks into the cursor restore or the
   * next frame's first cell. */
  uint16_t open_link = 0;

  for (uint16_t y = 0; y < s->rows; y++) {
    for (uint16_t x = 0; x < s->cols; x++) {
      size_t idx = (size_t)y * s->cols + x;
      cell_t *c = &s->cur[idx];
      cell_t *p = &s->prev[idx];
      if (c->width == 0) continue; /* tail of a wide cell: never painted */
      /* A cell whose only change is its link is still a change: the glyph
       * has to be re-sent inside (or outside) the OSC 8 wrapper for the
       * terminal to move it between links. */
      if (cell_eq(c, p) && s->cur_link[idx] == s->prev_link[idx]) continue;

      if (!painted) {
        out_str(s, "\x1b[?25l");
        painted = true;
      }
      if (!have_pos || cx != x || cy != y) {
        out_fmt(s, "\x1b[%u;%uH", y + 1, x + 1);
        cx = x;
        cy = y;
        have_pos = true;
      }
      if (!have_style || !style_eq(c, &style)) {
        emit_sgr(s, c);
        style = *c;
        have_style = true;
      }
      if (s->cur_link[idx] != open_link) {
        if (open_link) out_str(s, "\x1b]8;;\x1b\\");
        open_link = s->cur_link[idx];
        if (open_link) {
          out_str(s, "\x1b]8;;");
          out_str(s, s->links[open_link - 1]);
          out_str(s, "\x1b\\");
        }
      }
      if (c->len)
        out_bytes(s, c->text, c->len);
      else
        out_str(s, " ");

      *p = *c;
      s->prev_link[idx] = s->cur_link[idx];
      cx += c->width ? c->width : 1;
      if (cx >= s->cols) have_pos = false; /* wrap is terminal-dependent */
    }
  }
  if (open_link) out_str(s, "\x1b]8;;\x1b\\");

  bool cursor_moved = s->cursor_visible != s->shown_cursor_visible ||
                      s->cursor_x != s->shown_cursor_x ||
                      s->cursor_y != s->shown_cursor_y;
  if (painted || cursor_moved) {
    if (s->cursor_visible && s->cursor_x < s->cols && s->cursor_y < s->rows) {
      out_fmt(s, "\x1b[%u;%uH", s->cursor_y + 1, s->cursor_x + 1);
      out_str(s, "\x1b[?25h");
    } else if (painted) {
      out_str(s, "\x1b[?25l");
    }
    s->shown_cursor_visible = s->cursor_visible;
    s->shown_cursor_x = s->cursor_x;
    s->shown_cursor_y = s->cursor_y;
  }

  s->force_full = false;
}

void screen_flush(screen_t *s, int fd) {
  screen_render(s);
  size_t off = 0;
  while (off < s->out_len) {
    ssize_t n = write(fd, s->out + off, s->out_len - off);
    if (n <= 0) break;
    off += (size_t)n;
  }
}

/* Style runs rather than per-cell objects: a test wants to say "columns 0..5 of
 * row 0 are bold red", and 1920 cell objects per snapshot is unreadable. */
static void dump_style_runs(screen_t *s, json_t *j) {
  json_arr_open(j, "styles");
  for (uint16_t y = 0; y < s->rows; y++) {
    uint16_t x = 0;
    while (x < s->cols) {
      cell_t *c = &s->cur[(size_t)y * s->cols + x];
      bool plain = !c->attrs && !c->fg.set && !c->bg.set;
      if (plain) {
        x++;
        continue;
      }
      uint16_t start = x;
      while (x < s->cols) {
        cell_t *n = &s->cur[(size_t)y * s->cols + x];
        if (n->attrs != c->attrs || !color_eq(n->fg, c->fg) ||
            !color_eq(n->bg, c->bg))
          break;
        x++;
      }
      json_obj_open(j, NULL);
      json_int(j, "x", start);
      json_int(j, "y", y);
      json_int(j, "w", x - start);
      char col[8];
      if (c->fg.set) {
        snprintf(col, sizeof col, "#%02x%02x%02x", c->fg.r, c->fg.g, c->fg.b);
        json_str(j, "fg", col, strlen(col));
      } else {
        json_null(j, "fg");
      }
      if (c->bg.set) {
        snprintf(col, sizeof col, "#%02x%02x%02x", c->bg.r, c->bg.g, c->bg.b);
        json_str(j, "bg", col, strlen(col));
      } else {
        json_null(j, "bg");
      }
      json_arr_open(j, "attrs");
      static const struct {
        uint16_t bit;
        const char *name;
      } names[] = {
          {ATTR_BOLD, "bold"},           {ATTR_DIM, "dim"},
          {ATTR_ITALIC, "italic"},       {ATTR_UNDERLINE, "underline"},
          {ATTR_BLINK, "blink"},         {ATTR_INVERSE, "inverse"},
          {ATTR_INVISIBLE, "invisible"}, {ATTR_STRIKE, "strike"},
      };
      for (size_t i = 0; i < sizeof names / sizeof *names; i++)
        if (c->attrs & names[i].bit)
          json_str(j, NULL, names[i].name, strlen(names[i].name));
      json_arr_close(j);
      json_obj_close(j);
    }
  }
  json_arr_close(j);
}

char *screen_dump_json(screen_t *s) {
  json_t j;
  json_init(&j);
  json_obj_open(&j, NULL);
  json_int(&j, "cols", s->cols);
  json_int(&j, "rows", s->rows);

  json_arr_open(&j, "text");
  char *line = malloc((size_t)s->cols * 4 + 1);
  for (uint16_t y = 0; y < s->rows; y++) {
    size_t o = 0;
    for (uint16_t x = 0; x < s->cols; x++) {
      cell_t *c = &s->cur[(size_t)y * s->cols + x];
      if (c->width == 0) continue;
      if (c->len) {
        memcpy(line + o, c->text, c->len);
        o += c->len;
      } else {
        line[o++] = ' ';
      }
    }
    json_str(&j, NULL, line, o);
  }
  free(line);
  json_arr_close(&j);

  dump_style_runs(s, &j);

  /* Hyperlinks as runs, like the styles: a test wants "these six cells are
   * this URI", not one object per cell. */
  json_arr_open(&j, "links");
  for (uint16_t y = 0; y < s->rows; y++) {
    uint16_t x = 0;
    while (x < s->cols) {
      uint16_t id = s->cur_link[(size_t)y * s->cols + x];
      if (!id) {
        x++;
        continue;
      }
      uint16_t x0 = x;
      while (x < s->cols && s->cur_link[(size_t)y * s->cols + x] == id) x++;
      json_obj_open(&j, NULL);
      json_int(&j, "x", x0);
      json_int(&j, "y", y);
      json_int(&j, "w", (uint16_t)(x - x0));
      json_str(&j, "uri", s->links[id - 1], strlen(s->links[id - 1]));
      json_obj_close(&j);
    }
  }
  json_arr_close(&j);

  json_obj_open(&j, "cursor");
  json_bool(&j, "visible", s->cursor_visible);
  json_int(&j, "x", s->cursor_x);
  json_int(&j, "y", s->cursor_y);
  json_obj_close(&j);

  json_arr_open(&j, "hits");
  for (size_t i = 0; i < s->hits.len; i++) {
    hit_t *e = &s->hits.items[i];
    json_obj_open(&j, NULL);
    json_int(&j, "x", e->x);
    json_int(&j, "y", e->y);
    json_int(&j, "w", e->w);
    json_int(&j, "h", e->h);
    json_str(&j, "action", e->action, strlen(e->action));
    json_obj_close(&j);
  }
  json_arr_close(&j);

  json_obj_close(&j);
  return j.buf; /* caller frees */
}

char *screen_dump(screen_t *s) {
  size_t cap = (size_t)(s->cols + 1) * s->rows * 4 + 1;
  char *buf = malloc(cap);
  size_t o = 0;
  for (uint16_t y = 0; y < s->rows; y++) {
    for (uint16_t x = 0; x < s->cols; x++) {
      cell_t *c = &s->cur[(size_t)y * s->cols + x];
      if (c->width == 0) continue;
      if (c->len) {
        memcpy(buf + o, c->text, c->len);
        o += c->len;
      } else {
        buf[o++] = ' ';
      }
    }
    buf[o++] = '\n';
  }
  buf[o] = 0;
  return buf;
}