#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysym.h>
#include <errno.h>
#include <fcntl.h>
#include <pty.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <termios.h>
#include <unistd.h>

#include "config.h"

// There isn't a need for MAX_ROWS or MAX_COLS, but ¯\_(ツ)_/¯
#define MAX_ROWS 1000
#define MAX_COLS 1000
#define CHAR_WIDTH 8
#define CHAR_HEIGHT 16

// General window/terminal stuff
static pid_t child_pid;
static char **terminal_buffer = NULL;
static unsigned long **color_buffer = NULL;
static int **attr_buffer = NULL;
static int term_rows;
static int term_cols;
static unsigned long current_color;
static int current_attr = 0;
static GC gc = NULL;
static GC gc_bold = NULL;
static Display *display = NULL;
static struct timeval last_refresh;
static Pixmap buffer_pixmap = None;
static int master_fd = -1;
static int needs_refresh = 0;
static int window_focused = 0;
static int scroll_top = 0;    // 0 means entire terminal
static int scroll_bottom = 0; // 0 means entire terminal

// Cursor stuff
static int cursor_visible = 1;
static struct timeval last_blink;
static int cursor_x = 0;
static int cursor_y = 0;

// Font stuff
static XFontStruct *regular_font = NULL;
static XFontStruct *bold_font = NULL;
static XFontStruct *italic_font = NULL;
static unsigned long current_bg_color;
static unsigned long **bg_color_buffer = NULL;

// Alternatives to handle the ANSI escape codes
static char **saved_terminal = NULL;
static unsigned long **saved_colors = NULL;
static int **saved_attrs = NULL;
static int saved_cursor_x = 0;
static int saved_cursor_y = 0;
static int using_alternate = 0;

#define ATTR_BOLD (1 << 0)
#define ATTR_ITALIC (1 << 1)
#define ATTR_REVERSE (1 << 2)
#define ATTR_DIM (1 << 4)
#define ATTR_BLINK (1 << 5)

// Pesky static smth smth error, so we "declare" it early
static void draw_terminal(Display *display, Window window);
static void draw_char(Display *display, Drawable d, int x, int y);

// Cursor gameplay <== ==>
static void draw_cursor(Display *display, Window window) {
  if (!gc || !terminal_buffer || !color_buffer || cursor_y >= term_rows ||
      cursor_x >= term_cols)
    return;

  // First restore the character that was under the cursor
  if (cursor_x < term_cols && cursor_y < term_rows) {
    draw_char(display, buffer_pixmap, cursor_x, cursor_y);
  }

  if (cursor_visible) {
    // Save original color
    unsigned long original_color = color_buffer[cursor_y][cursor_x];

    if (!window_focused) {
      XSetForeground(display, gc, original_color);
      XDrawRectangle(display, buffer_pixmap, gc, cursor_x * CHAR_WIDTH,
                     cursor_y * CHAR_HEIGHT, CHAR_WIDTH - 1, CHAR_HEIGHT - 1);
    } else {
      XSetForeground(display, gc, original_color);
      XFillRectangle(display, buffer_pixmap, gc, cursor_x * CHAR_WIDTH,
                     cursor_y * CHAR_HEIGHT, CHAR_WIDTH, CHAR_HEIGHT);

      if (cursor_x < term_cols && cursor_y < term_rows) {
        char str[2] = {terminal_buffer[cursor_y][cursor_x], '\0'};
        XSetForeground(display, gc,
                       XBlackPixel(display, DefaultScreen(display)));

        XFontStruct *font = regular_font;
        if (attr_buffer[cursor_y][cursor_x] & ATTR_BOLD) {
          font = bold_font;
        } else if (attr_buffer[cursor_y][cursor_x] & ATTR_ITALIC) {
          font = italic_font;
        }
        XSetFont(display, gc, font->fid);

        XDrawString(display, buffer_pixmap, gc, cursor_x * CHAR_WIDTH,
                    (cursor_y + 1) * CHAR_HEIGHT - 2, str, 1);
      }
    }
  }

  // Copy the relevant area to the window
  XCopyArea(display, buffer_pixmap, window, gc, cursor_x * CHAR_WIDTH,
            cursor_y * CHAR_HEIGHT, CHAR_WIDTH, CHAR_HEIGHT,
            cursor_x * CHAR_WIDTH, cursor_y * CHAR_HEIGHT);
}

static void update_cursor_state(Display *display, Window window) {
  if (window_focused) {
    cursor_visible = 1;
    return;
  }
}

// resize_buffers visual:
//
// Old buffer (3x3):     New buffer (4x4):
// [a][b][c]            [a][b][c][ ]
// [d][e][f]     ->     [d][e][f][ ]
// [g][h][i]            [g][h][i][ ]
//                      [ ][ ][ ][ ]
//
// 1. Allocates new larger buffer
// 2. Copies existing content
// 3. Fills new space with blanks
// 4. Updates cursor position
// 5. Frees old buffer
static void resize_buffers(int new_rows, int new_cols) {
  if (new_rows > MAX_ROWS)
    new_rows = MAX_ROWS;
  if (new_cols > MAX_COLS)
    new_cols = MAX_COLS;
  if (new_rows < 1)
    new_rows = 1;
  if (new_cols < 1)
    new_cols = 1;

  size_t row_size = ((new_cols * sizeof(char) + 15) & ~15);
  size_t color_row_size = ((new_cols * sizeof(unsigned long) + 15) & ~15);
  size_t attr_row_size = ((new_cols * sizeof(int) + 15) & ~15);
  size_t bg_color_row_size = ((new_cols * sizeof(unsigned long) + 15) & ~15);

  char **new_term_buffer = malloc(new_rows * sizeof(char *));
  unsigned long **new_color_buffer = malloc(new_rows * sizeof(unsigned long *));
  int **new_attr_buffer = malloc(new_rows * sizeof(int *));
  unsigned long **new_bg_color_buffer =
      malloc(new_rows * sizeof(unsigned long *));

  if (!new_term_buffer || !new_color_buffer || !new_attr_buffer ||
      !new_bg_color_buffer) {
    fprintf(stderr, "Failed to allocate memory for buffers\n");
    return;
  }

  for (int i = 0; i < new_rows; i++) {
    new_term_buffer[i] = malloc(row_size);
    new_color_buffer[i] = malloc(color_row_size);
    new_attr_buffer[i] = malloc(attr_row_size);
    new_bg_color_buffer[i] = malloc(bg_color_row_size);

    if (!new_term_buffer[i] || !new_color_buffer[i] || !new_attr_buffer[i] ||
        !new_bg_color_buffer[i]) {
      fprintf(stderr, "Failed to allocate memory for buffer row\n");
      // Clean up allocated memory
      for (int j = 0; j < i; j++) {
        free(new_term_buffer[j]);
        free(new_color_buffer[j]);
        free(new_attr_buffer[j]);
        free(new_bg_color_buffer[j]);
      }
      free(new_term_buffer);
      free(new_color_buffer);
      free(new_attr_buffer);
      free(new_bg_color_buffer);
      return;
    }

    if (i < term_rows && i < new_rows && terminal_buffer && color_buffer &&
        attr_buffer && bg_color_buffer) {
      int copy_cols = (new_cols < term_cols) ? new_cols : term_cols;
      memcpy(new_term_buffer[i], terminal_buffer[i], copy_cols * sizeof(char));
      memcpy(new_color_buffer[i], color_buffer[i],
             copy_cols * sizeof(unsigned long));
      memcpy(new_attr_buffer[i], attr_buffer[i], copy_cols * sizeof(int));
      memcpy(new_bg_color_buffer[i], bg_color_buffer[i],
             copy_cols * sizeof(unsigned long));
      if (new_cols > term_cols) {
        memset(new_term_buffer[i] + term_cols, ' ', new_cols - term_cols);
        for (int x = term_cols; x < new_cols; x++) {
          new_color_buffer[i][x] = current_color;
          new_attr_buffer[i][x] = current_attr;
          new_bg_color_buffer[i][x] = current_bg_color;
        }
      }
    } else {
      memset(new_term_buffer[i], ' ', new_cols);
      for (int x = 0; x < new_cols; x++) {
        new_color_buffer[i][x] = current_color;
        new_attr_buffer[i][x] = current_attr;
        new_bg_color_buffer[i][x] = current_bg_color;
      }
    }
  }

  // Free old buffers after successful allocation
  if (terminal_buffer && color_buffer && attr_buffer && bg_color_buffer) {
    for (int i = 0; i < term_rows; i++) {
      free(terminal_buffer[i]);
      free(color_buffer[i]);
      free(attr_buffer[i]);
      free(bg_color_buffer[i]);
    }
    free(terminal_buffer);
    free(color_buffer);
    free(attr_buffer);
    free(bg_color_buffer);
  }

  terminal_buffer = new_term_buffer;
  color_buffer = new_color_buffer;
  attr_buffer = new_attr_buffer;
  bg_color_buffer = new_bg_color_buffer;
  term_rows = new_rows;
  term_cols = new_cols;

  cursor_x = (cursor_x >= term_cols) ? term_cols - 1 : cursor_x;
  cursor_y = (cursor_y >= term_rows) ? term_rows - 1 : cursor_y;

  // Resize buffer pixmap
  if (buffer_pixmap != None) {
    XFreePixmap(display, buffer_pixmap);
  }
  buffer_pixmap = XCreatePixmap(display, DefaultRootWindow(display),
                                term_cols * CHAR_WIDTH, term_rows * CHAR_HEIGHT,
                                DefaultDepth(display, DefaultScreen(display)));
  needs_refresh = 1;
}

static void destroy_cb(Display *display, Window window) {
  if (child_pid > 0) {
    kill(child_pid, SIGTERM);
    waitpid(child_pid, NULL, 0);
  }
  if (gc)
    XFreeGC(display, gc);
  if (gc_bold)
    XFreeGC(display, gc_bold);
  if (buffer_pixmap != None)
    XFreePixmap(display, buffer_pixmap);
  if (display)
    XCloseDisplay(display);
  if (terminal_buffer) {
    for (int i = 0; i < term_rows; i++) {
      free(terminal_buffer[i]);
    }
    free(terminal_buffer);
  }
  if (color_buffer) {
    for (int i = 0; i < term_rows; i++) {
      free(color_buffer[i]);
    }
    free(color_buffer);
  }
  if (attr_buffer) {
    for (int i = 0; i < term_rows; i++) {
      free(attr_buffer[i]);
    }
    free(attr_buffer);
  }
  if (bg_color_buffer) {
    for (int i = 0; i < term_rows; i++) {
      free(bg_color_buffer[i]);
    }
    free(bg_color_buffer);
  }
  if (master_fd >= 0)
    close(master_fd);
  exit(0);
}

static void draw_char(Display *display, Drawable d, int x, int y) {
  if (!gc || !terminal_buffer || !color_buffer || !attr_buffer ||
      !bg_color_buffer)
    return;
  if (x < 0 || x >= term_cols || y < 0 || y >= term_rows)
    return;

  char c = terminal_buffer[y][x];
  if (c < 32 || c > 126) // Only allow printable ASCII characters
    return;

  unsigned long fg = color_buffer[y][x];
  unsigned long bg = bg_color_buffer[y][x];
  int attr = attr_buffer[y][x];
  static unsigned long last_bg = 0;
  static int last_x = -1;
  static int last_y = -1;

  if (attr & ATTR_REVERSE) {
    unsigned long tmp = fg;
    fg = bg;
    bg = tmp;
  }

  if (last_x != x || last_y != y || last_bg != bg) {
    XSetForeground(display, gc, bg);
    XFillRectangle(display, d, gc, x * CHAR_WIDTH, y * CHAR_HEIGHT,
                   CHAR_WIDTH + 1, CHAR_HEIGHT);
    last_x = x;
    last_y = y;
    last_bg = bg;
  }

  XSetForeground(display, gc, fg);

  char str[2] = {c, '\0'};
  XFontStruct *font = regular_font;

  if (attr & ATTR_BOLD)
    font = bold_font;
  else if (attr & ATTR_ITALIC)
    font = italic_font;

  XSetFont(display, gc, font->fid);
  XDrawString(display, d, gc, x * CHAR_WIDTH, (y + 1) * CHAR_HEIGHT - 4, str,
              1);
}

static void draw_terminal(Display *display, Window window) {
  if (!gc) {
    gc = XCreateGC(display, window, 0, NULL);
    regular_font = XLoadQueryFont(display, REGULAR_FONT);
    bold_font = XLoadQueryFont(display, BOLD_FONT);
    italic_font = XLoadQueryFont(display, ITALICS_FONT);

    if (!regular_font)
      regular_font = XLoadQueryFont(display, "fixed");
    if (!bold_font)
      bold_font = regular_font;
    if (!italic_font)
      italic_font = regular_font;

    XSetFont(display, gc, regular_font->fid);
  }

  if (!terminal_buffer || !color_buffer || !attr_buffer)
    return;

  if (buffer_pixmap == None)
    buffer_pixmap = XCreatePixmap(
        display, DefaultRootWindow(display), term_cols * CHAR_WIDTH,
        term_rows * CHAR_HEIGHT, DefaultDepth(display, DefaultScreen(display)));

  if (needs_refresh) {
    int start_y = scroll_top ? scroll_top - 1 : 0;
    int end_y = scroll_bottom ? scroll_bottom : term_rows;

    if (end_y > term_rows) {
      end_y = term_rows;
    }

    if (scroll_top == 0 && scroll_bottom == 0) {
      // Full screen refresh
      for (int y = 0; y < term_rows; y++) {
        for (int x = 0; x < term_cols; x++) {
          draw_char(display, buffer_pixmap, x, y);
        }
      }
    } else {
      // Only refresh scroll region
      for (int y = start_y; y < end_y; y++) {
        for (int x = 0; x < term_cols; x++) {
          draw_char(display, buffer_pixmap, x, y);
        }
      }
    }
  }

  XCopyArea(display, buffer_pixmap, window, gc, 0, 0, term_cols * CHAR_WIDTH,
            term_rows * CHAR_HEIGHT, 0, 0);

  draw_cursor(display, window);
  XFlush(display);
  needs_refresh = 0;
}

static void check_refresh(Display *display, Window window) {
  if (!needs_refresh)
    return;

  struct timeval now;
  gettimeofday(&now, NULL);

  long elapsed = (now.tv_sec - last_refresh.tv_sec) * 1000000 +
                 (now.tv_usec - last_refresh.tv_usec);

  if (elapsed >= REFRESH_INTERVAL) {
    draw_terminal(display, window);
    last_refresh = now;
  }
}

static void scroll_region_up(int amount) {
  int start = scroll_top ? scroll_top - 1 : 0;
  int end = scroll_bottom ? scroll_bottom - 1 : term_rows - 1;
  if (end >= term_rows)
    end = term_rows - 1;
  if (start > end)
    return;

  for (int i = start; i <= end - amount; i++) {
    memcpy(terminal_buffer[i], terminal_buffer[i + amount], term_cols);
    memcpy(color_buffer[i], color_buffer[i + amount],
           term_cols * sizeof(unsigned long));
    memcpy(attr_buffer[i], attr_buffer[i + amount], term_cols * sizeof(int));
    memcpy(bg_color_buffer[i], bg_color_buffer[i + amount],
           term_cols * sizeof(unsigned long));
  }

  for (int i = end - amount + 1; i <= end; i++) {
    memset(terminal_buffer[i], ' ', term_cols);
    for (int x = 0; x < term_cols; x++) {
      color_buffer[i][x] = current_color;
      attr_buffer[i][x] = current_attr;
      bg_color_buffer[i][x] = current_bg_color;
    }
  }

  needs_refresh = 1;
}

static void scroll_region_down(int amount) {
  int start = ((scroll_top - 1) < 0) ? 0 : scroll_top - 1;
  int end = ((scroll_bottom - 1) < 0) ? 0 : scroll_bottom - 1;
  if (end >= term_rows)
    end = term_rows - 1;

  char **tbuf = malloc(term_rows * sizeof(char *));
  unsigned long **cbuf = malloc(term_rows * sizeof(unsigned long *));
  int **abuf = malloc(term_rows * sizeof(int *));
  unsigned long **bbuf = malloc(term_rows * sizeof(unsigned long *));

  if (!tbuf || !cbuf || !abuf || !bbuf) {
    fprintf(stderr, "scroll down: malloc failed\n");
    goto cleanup;
  }

  for (int i = 0; i < term_rows; i++) {
    tbuf[i] = malloc(term_cols);
    cbuf[i] = malloc(term_cols * sizeof(unsigned long));
    abuf[i] = malloc(term_cols * sizeof(int));
    bbuf[i] = malloc(term_cols * sizeof(unsigned long));

    if (!tbuf[i] || !cbuf[i] || !abuf[i] || !bbuf[i]) {
      fprintf(stderr, "scroll down: malloc failed\n");
      goto cleanup;
    }
  }

  if (scroll_top == 0 && scroll_bottom == 0) {
    for (int i = 0; i < term_rows; i++) {
      memcpy(tbuf[i], terminal_buffer[i], term_cols);
      memcpy(cbuf[i], color_buffer[i], term_cols * sizeof(unsigned long));
      memcpy(abuf[i], attr_buffer[i], term_cols * sizeof(int));
      memcpy(bbuf[i], bg_color_buffer[i], term_cols * sizeof(unsigned long));
    }
    for (int j = 0; j < amount; j++) {
      for (int y = term_rows - 1; y > 0; y--) {
        memcpy(terminal_buffer[y], tbuf[y - 1], term_cols);
        memcpy(color_buffer[y], cbuf[y - 1], term_cols * sizeof(unsigned long));
        memcpy(attr_buffer[y], abuf[y - 1], term_cols * sizeof(int));
        memcpy(bg_color_buffer[y], bbuf[y - 1],
               term_cols * sizeof(unsigned long));
      }
      memset(terminal_buffer[0], ' ', term_cols);
      for (int x = 0; x < term_cols; x++) {
        color_buffer[0][x] = current_color;
        attr_buffer[0][x] = current_attr;
        bg_color_buffer[0][x] = current_bg_color;
      }
    }
  } else {
    for (int i = 0; i < term_rows; i++) {
      memcpy(tbuf[i], terminal_buffer[i], term_cols);
      memcpy(cbuf[i], color_buffer[i], term_cols * sizeof(unsigned long));
      memcpy(abuf[i], attr_buffer[i], term_cols * sizeof(int));
      memcpy(bbuf[i], bg_color_buffer[i], term_cols * sizeof(unsigned long));
    }
    for (int j = 0; j < amount; j++) {
      for (int y = end; y > start; y--) {
        memcpy(terminal_buffer[y], tbuf[y - 1], term_cols);
        memcpy(color_buffer[y], cbuf[y - 1], term_cols * sizeof(unsigned long));
        memcpy(attr_buffer[y], abuf[y - 1], term_cols * sizeof(int));
        memcpy(bg_color_buffer[y], bbuf[y - 1],
               term_cols * sizeof(unsigned long));
      }
      memset(terminal_buffer[start], ' ', term_cols);
      for (int x = 0; x < term_cols; x++) {
        color_buffer[start][x] = current_color;
        attr_buffer[start][x] = current_attr;
        bg_color_buffer[start][x] = current_bg_color;
      }
    }
  }

cleanup:
  if (tbuf) {
    for (int i = 0; i < term_rows; i++)
      free(tbuf[i]);
    free(tbuf);
  }
  if (cbuf) {
    for (int i = 0; i < term_rows; i++)
      free(cbuf[i]);
    free(cbuf);
  }
  if (abuf) {
    for (int i = 0; i < term_rows; i++)
      free(abuf[i]);
    free(abuf);
  }
  if (bbuf) {
    for (int i = 0; i < term_rows; i++)
      free(bbuf[i]);
    free(bbuf);
  }
  needs_refresh = 1;
}

// Alternative buffer visual:
//
// Normal buffer:             Alternate buffer:
// [C][o][w]                  [ ][ ][ ]
// [T][e][r]                  [ ][ ][ ]
// [m][!][ ]       <->        [ ][ ][ ]
//
// When applications like vim switch to alternate buffer it SHOULD:
// 1. Save the current buffer state (saved_terminal etc.)
// 2. creates a new empty alternate buffer
// 3. The application draws to the alternate buffer
// 4. When done, alternate buffer is freed
// 5. And the original buffer state is restored
//
// References:
// saved_terminal = backup of normal buffer
// saved_colors/attrs = backup of attributes
// using_alternate = tracks which buffer is active
static void handle_alternate_buffer(const char *buf, int *idx, int max_len,
                                    Window window) {
  char num_buf[32] = {0};
  size_t num_idx = 0;

  (*idx)++;
  while (*idx < max_len && buf[*idx] != 'h' && buf[*idx] != 'l') {
    if (num_idx >= sizeof(num_buf) - 1)
      break;
    if (buf[*idx] >= '0' && buf[*idx] <= '9')
      num_buf[num_idx++] = buf[*idx];
    (*idx)++;
  }

  if (!num_buf[0])
    return;

  int code = atoi(num_buf);
  if (buf[*idx] != 'h' && buf[*idx] != 'l')
    return;

  switch (code) {
  case 1047: // Alt buffer
    if (buf[*idx] == 'h') {
      if (saved_terminal)
        return;

      saved_terminal = terminal_buffer;
      saved_colors = color_buffer;
      saved_attrs = attr_buffer;
      saved_colors = bg_color_buffer;

      terminal_buffer = malloc(term_rows * sizeof(char *));
      color_buffer = malloc(term_rows * sizeof(unsigned long *));
      attr_buffer = malloc(term_rows * sizeof(int *));
      bg_color_buffer = malloc(term_rows * sizeof(unsigned long *));

      if (!terminal_buffer || !color_buffer || !attr_buffer || !bg_color_buffer)
        return;

      for (int i = 0; i < term_rows; i++) {
        terminal_buffer[i] = calloc(term_cols, 1);
        color_buffer[i] = calloc(term_cols, sizeof(unsigned long));
        attr_buffer[i] = calloc(term_cols, sizeof(int));
        bg_color_buffer[i] = calloc(term_cols, sizeof(unsigned long));

        if (!terminal_buffer[i] || !color_buffer[i] || !attr_buffer[i] ||
            !bg_color_buffer[i])
          return;

        memset(terminal_buffer[i], ' ', term_cols);
        memset(attr_buffer[i], 0, term_cols * sizeof(int));
        memset(color_buffer[i], current_color,
               term_cols * sizeof(unsigned long));
        memset(bg_color_buffer[i], current_bg_color,
               term_cols * sizeof(unsigned long));
      }
      using_alternate = 1;
      needs_refresh = 1;
      draw_terminal(display, window);
    } else if (using_alternate) {
      for (int i = 0; i < term_rows; i++) {
        free(terminal_buffer[i]);
        free(color_buffer[i]);
        free(attr_buffer[i]);
        free(bg_color_buffer[i]);
      }
      free(terminal_buffer);
      free(color_buffer);
      free(attr_buffer);
      free(bg_color_buffer);

      terminal_buffer = saved_terminal;
      color_buffer = saved_colors;
      attr_buffer = saved_attrs;
      bg_color_buffer = saved_colors;
      saved_terminal = NULL;
      using_alternate = 0;
      needs_refresh = 1;
      draw_terminal(display, window);
    }
    break;

  case 1048: // Save/restore cursor
    if (buf[*idx] == 'h') {
      saved_cursor_x = cursor_x;
      saved_cursor_y = cursor_y;
    } else {
      cursor_x = saved_cursor_x;
      cursor_y = saved_cursor_y;
    }
    break;

  case 1049: // Alt buffer + cursor
    if (buf[*idx] == 'h') {
      saved_cursor_x = cursor_x;
      saved_cursor_y = cursor_y;
      if (saved_terminal)
        return;

      saved_terminal = terminal_buffer;
      saved_colors = color_buffer;
      saved_attrs = attr_buffer;
      saved_colors = bg_color_buffer;

      terminal_buffer = malloc(term_rows * sizeof(char *));
      color_buffer = malloc(term_rows * sizeof(unsigned long *));
      attr_buffer = malloc(term_rows * sizeof(int *));
      bg_color_buffer = malloc(term_rows * sizeof(unsigned long *));

      if (!terminal_buffer || !color_buffer || !attr_buffer || !bg_color_buffer)
        return;

      for (int i = 0; i < term_rows; i++) {
        terminal_buffer[i] = calloc(term_cols, 1);
        color_buffer[i] = calloc(term_cols, sizeof(unsigned long));
        attr_buffer[i] = calloc(term_cols, sizeof(int));
        bg_color_buffer[i] = calloc(term_cols, sizeof(unsigned long));

        if (!terminal_buffer[i] || !color_buffer[i] || !attr_buffer[i] ||
            !bg_color_buffer[i])
          return;

        memset(terminal_buffer[i], ' ', term_cols);
        memset(attr_buffer[i], 0, term_cols * sizeof(int));
        memset(color_buffer[i], current_color,
               term_cols * sizeof(unsigned long));
        memset(bg_color_buffer[i], current_bg_color,
               term_cols * sizeof(unsigned long));
      }
      using_alternate = 1;
      needs_refresh = 1;
      draw_terminal(display, window);
    } else if (using_alternate) {
      for (int i = 0; i < term_rows; i++) {
        free(terminal_buffer[i]);
        free(color_buffer[i]);
        free(attr_buffer[i]);
        free(bg_color_buffer[i]);
      }
      free(terminal_buffer);
      free(color_buffer);
      free(attr_buffer);
      free(bg_color_buffer);

      terminal_buffer = saved_terminal;
      color_buffer = saved_colors;
      attr_buffer = saved_attrs;
      bg_color_buffer = saved_colors;
      saved_terminal = NULL;
      cursor_x = saved_cursor_x;
      cursor_y = saved_cursor_y;
      using_alternate = 0;
      needs_refresh = 1;
      draw_terminal(display, window);
    }
    break;
  }
}

static unsigned long get_ansi_color(int index) {
  static const unsigned long colors[] = {0x000000, RED,     GREEN, YELLOW,
                                         BLUE,     MAGENTA, CYAN,  0xFFFFFF};
  return colors[index & 7];
}

static unsigned long get_bright_ansi_color(int index) {
  static const unsigned long colors[] = {
      DARK_GRAY,  LIGHT_RED,     LIGHT_GREEN, LIGHT_YELLOW,
      LIGHT_BLUE, LIGHT_MAGENTA, LIGHT_CYAN,  0xFFFFFF};
  return colors[index & 7];
}

// Handles those pesky ANSI color escape codes that terminals use.
// When \033[<number>m is sent to the terminal, it changes text color:
//   30 = Black    31 = Red      32 = Green   33 = Yellow
//   34 = Blue     35 = Magenta  36 = Cyan    37 = White
// 0 sets everything back to plain white
// P.S. yes I had to google this up
static void parse_ansi_code(const char *buf, int *idx, int max_len,
                            Window window) {
  char num_buf[32] = {0};
  int params[32] = {0};
  size_t num_idx = 0;
  size_t param_idx = 0;
  (*idx)++; // Skip [

  // Handle '?' prefix for private sequences
  if (buf[*idx] == '?') {
    handle_alternate_buffer(buf, idx, max_len, window);
    return;
  }

  // Parse parameters
  while (*idx < max_len) {
    char c = buf[*idx];
    if (c == 'm' || c == 'H' || c == 'A' || c == 'B' || c == 'C' || c == 'D' ||
        c == 'K' || c == 'J' || c == 'f' || c == 'r' || c == 's' || c == 'u' ||
        c == 'h' || c == 'l' || c == 'E' || c == 'F' || c == 'G' || c == 'S' ||
        c == 'T' || c == '@' || c == 'P' || c == 'M' || c == 'L' || c == 'd') {
      break;
    }

    if (num_idx >= sizeof(num_buf) - 1 ||
        param_idx >= sizeof(params) / sizeof(params[0]) - 1) {
      break;
    }

    if (c >= '0' && c <= '9') {
      num_buf[num_idx++] = c;
    } else if (c == ';') {
      if (num_buf[0] != '\0') {
        params[param_idx++] = atoi(num_buf);
        memset(num_buf, 0, sizeof(num_buf));
        num_idx = 0;
      }
    }
    (*idx)++;
  }

  if (num_buf[0] != '\0' && param_idx < sizeof(params) / sizeof(params[0])) {
    params[param_idx++] = atoi(num_buf);
  }

  switch (buf[*idx]) {
  case 'H': // Set cursor position
    if (param_idx >= 2) {
      cursor_y = params[0] - 1 < 0            ? 0
                 : params[0] - 1 >= term_rows ? term_rows - 1
                                              : params[0] - 1;
      cursor_x = params[1] - 1 < 0            ? 0
                 : params[1] - 1 >= term_cols ? term_cols - 1
                                              : params[1] - 1;
    } else {
      cursor_x = cursor_y = 0;
    }
    break;
  case 's': // Save cursor position
    if (param_idx == 0) {
      saved_cursor_x = cursor_x;
      saved_cursor_y = cursor_y;
    }
    break;
  case 'u': // Restore cursor position
    if (param_idx == 0) {
      cursor_x = saved_cursor_x;
      cursor_y = saved_cursor_y;
    }
    break;
  case 'h': // Set mode
  case 'l': // Reset mode
    if (param_idx >= 1) {
      switch (params[0]) {
      case 25: // Show/hide cursor
        cursor_visible = (buf[*idx] == 'h');
        needs_refresh = 1;
        break;
      case 12: // Start/stop blinking cursor
        cursor_visible = 1;
        needs_refresh = 1;
        break;
      default:
        break;
      }
    }
    break;
  case 'f': // Alternative set cursor position
    if (param_idx >= 2) {
      cursor_y = params[0] - 1 < 0            ? 0
                 : params[0] - 1 >= term_rows ? term_rows - 1
                                              : params[0] - 1;
      cursor_x = params[1] - 1 < 0            ? 0
                 : params[1] - 1 >= term_cols ? term_cols - 1
                                              : params[1] - 1;
    } else {
      cursor_x = cursor_y = 0;
    }
    break;
  case 'd': // Line position absolute
    cursor_y = params[0] - 1 < 0            ? 0
               : params[0] - 1 >= term_rows ? term_rows - 1
                                            : params[0] - 1;
    break;
  case 'G': // Column position absolute
    cursor_x = params[0] - 1 < 0            ? 0
               : params[0] - 1 >= term_cols ? term_cols - 1
                                            : params[0] - 1;
    break;
  case 'A': // Cursor up
    cursor_y -= params[0] ? params[0] : 1;
    if (cursor_y < 0)
      cursor_y = 0;
    break;
  case 'B': // Cursor down
    cursor_y += params[0] ? params[0] : 1;
    if (cursor_y >= term_rows)
      cursor_y = term_rows - 1;
    break;
  case 'C': // Cursor forward
    cursor_x += params[0] ? params[0] : 1;
    if (cursor_x >= term_cols)
      cursor_x = term_cols - 1;
    break;
  case 'D': // Cursor back
    cursor_x -= params[0] ? params[0] : 1;
    if (cursor_x < 0)
      cursor_x = 0;
    break;
  case '@': // Insert blank characters
  {
    int n = params[0] ? params[0] : 1;
    if (n > term_cols - cursor_x)
      n = term_cols - cursor_x;
    memmove(&terminal_buffer[cursor_y][cursor_x + n],
            &terminal_buffer[cursor_y][cursor_x], term_cols - cursor_x - n);
    memset(&terminal_buffer[cursor_y][cursor_x], ' ', n);
  } break;
  case 'P': // Delete characters
  {
    int n = params[0] ? params[0] : 1;
    if (n > term_cols - cursor_x)
      n = term_cols - cursor_x;
    memmove(&terminal_buffer[cursor_y][cursor_x],
            &terminal_buffer[cursor_y][cursor_x + n], term_cols - cursor_x - n);
    memset(&terminal_buffer[cursor_y][term_cols - n], ' ', n);
  } break;
  case 'M': // Delete lines
  {
    int n = params[0] ? params[0] : 1;
    if (cursor_y < term_rows - n) {
      memmove(&terminal_buffer[cursor_y], &terminal_buffer[cursor_y + n],
              (term_rows - cursor_y - n) * sizeof(char *));
      for (int i = term_rows - n; i < term_rows; i++)
        memset(terminal_buffer[i], ' ', term_cols);
    }
  } break;
  case 'L': // Insert lines
  {
    int n = params[0] ? params[0] : 1;
    if (cursor_y < term_rows - n) {
      memmove(&terminal_buffer[cursor_y + n], &terminal_buffer[cursor_y],
              (term_rows - cursor_y - n) * sizeof(char *));
      for (int i = cursor_y; i < cursor_y + n; i++)
        memset(terminal_buffer[i], ' ', term_cols);
    }
  } break;
  case 'K': // Clear line
    for (int i = cursor_x; i < term_cols; i++) {
      terminal_buffer[cursor_y][i] = ' ';
      color_buffer[cursor_y][i] = current_color;
      attr_buffer[cursor_y][i] = current_attr;
      bg_color_buffer[cursor_y][i] = current_bg_color;
    }
    break;
  case 'J': // Clear screen
    if (params[0] == 2) {
      for (int y = 0; y < term_rows; y++) {
        memset(terminal_buffer[y], ' ', term_cols);
        for (int x = 0; x < term_cols; x++) {
          color_buffer[y][x] = current_color;
          attr_buffer[y][x] = current_attr;
          bg_color_buffer[y][x] = current_bg_color;
        }
      }
      needs_refresh = 1;
    }
    break;
  case 'r': // Set scrolling region
    if (param_idx == 0) {
      scroll_top = 0; // Entire terminal
      scroll_bottom = 0;
    } else if (param_idx == 1) {
      scroll_top = params[0] <= 0          ? 1
                   : params[0] > term_rows ? term_rows
                                           : params[0];
      scroll_bottom = 0;
    } else if (param_idx >= 2) {
      scroll_top = params[0] <= 0          ? 1
                   : params[0] > term_rows ? term_rows
                                           : params[0];
      scroll_bottom = params[1] <= 0          ? term_rows
                      : params[1] > term_rows ? term_rows
                                              : params[1];
      // if top is bigger than bottom, swap values
      if (scroll_top > scroll_bottom) {
        int tmp = scroll_top;
        scroll_top = scroll_bottom;
        scroll_bottom = tmp;
      }
    }
    break;
  case 'S': // Scroll up
    scroll_region_up(params[0] ? params[0] : 1);
    needs_refresh = 1;
    break;
  case 'T': // Scroll down
    scroll_region_down(params[0] ? params[0] : 1);
    needs_refresh = 1;
    break;
  case 'E': // Cursor next line
    cursor_x = 0;
    cursor_y += params[0] ? params[0] : 1;
    if (cursor_y >= term_rows)
      cursor_y = term_rows - 1;
    break;
  case 'F': // Cursor line before
    cursor_x = 0;
    cursor_y -= params[0] ? params[0] : 1;
    if (cursor_y < 0)
      cursor_y = 0;
    break;
  case 'm': // Handling of text
    for (int i = 0; i < param_idx; i++) {
      if (params[i] == 0) { // Reset Everything
        current_color = XWhitePixel(display, DefaultScreen(display));
        current_bg_color = XBlackPixel(display, DefaultScreen(display));
        current_attr = 0;
      } else if (params[i] == 1) { // Apply ATTRS
        current_attr |= ATTR_BOLD;
      } else if (params[i] == 2) {
        current_attr |= ATTR_DIM;
      } else if (params[i] == 3) {
        current_attr |= ATTR_ITALIC;
      } else if (params[i] == 5) { // Slow blink
        current_attr |= ATTR_BLINK;
      } else if (params[i] == 7) {
        current_attr |= ATTR_REVERSE;
      } else if (params[i] == 22) { // Reset ATTRS
        current_attr &= ~ATTR_BOLD;
      } else if (params[i] == 23) {
        current_attr &= ~ATTR_ITALIC;
      } else if (params[i] == 25) {
        current_attr &= ~ATTR_BLINK;
      } else if (params[i] == 27) {
        current_attr &= ~ATTR_REVERSE;
      } else if (params[i] >= 30 && params[i] <= 37) { // Foreground colors
        current_color = get_ansi_color(params[i] - 30);
      } else if (params[i] >= 40 && params[i] <= 47) { // Background colors
        current_bg_color = get_ansi_color(params[i] - 40);
      } else if (params[i] >= 90 && params[i] <= 97) { // Bright foreground
        current_color = get_bright_ansi_color(params[i] - 90);
      } else if (params[i] >= 100 && params[i] <= 107) { // Bright background
        current_bg_color = get_bright_ansi_color(params[i] - 100);
      }
    }
    break;
  }
}

static int master_cb(int fd, void *data, Window window) {
  if (!terminal_buffer || !color_buffer || !attr_buffer || !bg_color_buffer)
    return 0;
  struct {
    Display *display;
    Window window;
  } *ctx = data;

  char buf[4096];
  ssize_t n = read(fd, buf, sizeof(buf));
  if (n <= 0 && errno != EAGAIN && errno != EINTR) {
    destroy_cb(ctx->display, ctx->window);
    return 0;
  }
  if (n <= 0)
    return 1;
  for (int i = 0; i < n; i++) {
    if (buf[i] == '\033' && i + 1 < n && buf[i + 1] == '[') {
      parse_ansi_code(buf, &i, n, window);
      continue;
    }
    switch (buf[i]) {
    case '\n':
      cursor_x = 0;
      if (++cursor_y >= term_rows) {
        scroll_region_up(1);
        cursor_y = term_rows - 1;
      }
      needs_refresh = 1;
      break;
    case '\r':
      cursor_x = 0;
      break;
    case '\b':
      if (cursor_x > 0) {
        cursor_x--;
        needs_refresh = 1;
      } else if (cursor_y > 0) {
        cursor_y--;
        cursor_x = term_cols - 1;
        while (cursor_x > 0 && terminal_buffer[cursor_y][cursor_x - 1] == ' ')
          cursor_x--;
        needs_refresh = 1;
      }
      break;
    default:
      if (cursor_y >= term_rows || cursor_x >= term_cols)
        break;
      terminal_buffer[cursor_y][cursor_x] = buf[i];
      color_buffer[cursor_y][cursor_x] = current_color;
      attr_buffer[cursor_y][cursor_x] = current_attr;
      bg_color_buffer[cursor_y][cursor_x] = current_bg_color;
      needs_refresh = 1;
      if (++cursor_x >= term_cols) {
        cursor_x = 0;
        if (++cursor_y >= term_rows) {
          scroll_region_up(1);
          cursor_y = term_rows - 1;
        }
      }
      break;
    }
  }
  cursor_visible = 1;
  if (needs_refresh)
    check_refresh(ctx->display, ctx->window);
  else {
    draw_cursor(ctx->display, ctx->window);
    XFlush(ctx->display);
  }
  return 1;
}

static void key_press_cb(XKeyEvent *event, void *data) {
  int *master = (int *)data;
  char buf[32];
  KeySym keysym;
  int len;

  len = XLookupString(event, buf, sizeof(buf), &keysym, NULL);

  if (event->state & ControlMask) {
    if ((keysym & 0x1f) == ('L' & 0x1f)) {
      write(*master, "\f", 1);
      return;
    }
    if ((keysym & 0x1f) == ('C' & 0x1f)) {
      write(*master, "\x03", 1);
      return;
    }
    if ((keysym & 0x1f) == ('U' & 0x1f)) {
      write(*master, "\025", 1);
      return;
    }
    if ((keysym & 0x1f) >= '@' && (keysym & 0x1f) <= '_') {
      char ctrl_char = '@' + (keysym & 0x1f);
      write(*master, &ctrl_char, 1);
      return;
    }
    return;
  }

  if (keysym == XK_Return || keysym == XK_KP_Enter) {
    write(*master, "\r", 1); // Shell handles return
  } else if (keysym == XK_BackSpace) {
    write(*master, "\177", 1); // Shell handles backspace
  } else if (keysym == XK_Left) {
    if (cursor_x > 0) {
      write(*master, "\033[D", 3);
    } else if (cursor_y > 0) {
      char seq[8];
      snprintf(seq, sizeof(seq), "\033[A\033[%dC", term_cols);
      write(*master, seq, strlen(seq));
    }
    needs_refresh = 1;
  } else if (keysym == XK_Right) {
    if (cursor_x < term_cols - 1) {
      write(*master, "\033[C", 3);
    } else if (cursor_y < term_rows - 1) {
      write(*master, "\033[B\033[G", 6);
    }
    needs_refresh = 1;
  } else if (keysym == XK_Up) { // Go up through history
    write(*master, "\033[A", 3);
  } else if (keysym == XK_Down) { // Go down through history
    write(*master, "\033[B", 3);
  } else if (keysym == XK_Tab) {
    write(*master, "\t", 1); // Shell handles autocomplete
  } else if (len > 0) {
    if (len > (int)sizeof(buf))
      len = sizeof(buf);
    write(*master, buf, len);
    if (cursor_x >= term_cols - 1) {
      write(*master, "\r\n", 2);
    }
  }
}

int main(void) {
  int master, slave;
  struct winsize ws = {.ws_row = 24,
                       .ws_col = 80,
                       .ws_xpixel = 80 * CHAR_WIDTH,
                       .ws_ypixel = 24 * CHAR_HEIGHT};
  term_rows = ws.ws_row;
  term_cols = ws.ws_col;

  gettimeofday(&last_blink, 0);
  gettimeofday(&last_refresh, 0);

  if (!(terminal_buffer = calloc(term_rows, sizeof(char *))) ||
      !(color_buffer = calloc(term_rows, sizeof(unsigned long *))) ||
      !(attr_buffer = calloc(term_rows, sizeof(int *))) ||
      !(bg_color_buffer = calloc(term_rows, sizeof(unsigned long *))))
    return 1;

  for (int i = 0; i < term_rows; i++) {
    if (!(terminal_buffer[i] = calloc(term_cols, sizeof(char))) ||
        !(color_buffer[i] = calloc(term_cols, sizeof(unsigned long))) ||
        !(attr_buffer[i] = calloc(term_cols, sizeof(int))) ||
        !(bg_color_buffer[i] = calloc(term_cols, sizeof(unsigned long))))
      return 1;
    memset(terminal_buffer[i], ' ', term_cols);
  }

  if (!(display = XOpenDisplay(0)))
    return 1;
  XInitThreads();

  current_color = XWhitePixel(display, DefaultScreen(display));
  current_bg_color = XBlackPixel(display, DefaultScreen(display));

  for (int i = 0; i < term_rows; i++)
    for (int j = 0; j < term_cols; j++) {
      bg_color_buffer[i][j] = current_bg_color;
      color_buffer[i][j] = current_color;
    }

  XSizeHints hints = {.flags = PResizeInc | PMinSize,
                      .width_inc = CHAR_WIDTH,
                      .height_inc = CHAR_HEIGHT,
                      .min_width = CHAR_WIDTH * 4,
                      .min_height = CHAR_HEIGHT};

  Window win = XCreateSimpleWindow(
      display, DefaultRootWindow(display), 0, 0, term_cols * CHAR_WIDTH,
      term_rows * CHAR_HEIGHT, 0, XBlackPixel(display, DefaultScreen(display)),
      XBlackPixel(display, DefaultScreen(display)));

  buffer_pixmap = XCreatePixmap(display, DefaultRootWindow(display),
                                term_cols * CHAR_WIDTH, term_rows * CHAR_HEIGHT,
                                DefaultDepth(display, DefaultScreen(display)));

  XSetWMNormalHints(display, win, &hints);
  XStoreName(display, win, window_name);
  XSelectInput(display, win,
               KeyPressMask | ExposureMask | StructureNotifyMask |
                   FocusChangeMask);
  XMapWindow(display, win);

  if (openpty(&master, &slave, 0, 0, &ws) == -1)
    return 1;

  master_fd = master;

  if ((child_pid = fork()) == -1)
    return 1;

  if (!child_pid) {
    close(master);
    for (int i = 0; i < 3; i++)
      close(i);

    setsid();
    for (int i = 0; i < 3; i++)
      if (dup2(slave, i) == -1)
        return 1;

    if (slave > 2)
      close(slave);

    char *sh = getenv("SHELL");
    setenv("TERM", "xterm-256color", 1);
    execl(sh ? sh : "/bin/sh", sh ? sh : "sh", 0);
    return 1;
  }

  close(slave);

  struct {
    Display *display;
    Window window;
  } ctx = {display, win};

  XEvent ev;
  fd_set fds;
  struct timeval tv = {0, 1000};

  for (;;) {
    if (waitpid(child_pid, 0, WNOHANG) == child_pid) {
      destroy_cb(display, win);
      return 0;
    }

    while (XPending(display)) {
      XNextEvent(display, &ev);
      switch (ev.type) {
      case ConfigureNotify: {
        XConfigureEvent *ce = &ev.xconfigure;
        int nr = ce->height / CHAR_HEIGHT;
        int nc = ce->width / CHAR_WIDTH;
        if (nr != term_rows || nc != term_cols) {
          resize_buffers(nr, nc);
          ws.ws_row = term_rows;
          ws.ws_col = term_cols;
          ws.ws_xpixel = term_cols * CHAR_WIDTH;
          ws.ws_ypixel = term_rows * CHAR_HEIGHT;
          ioctl(master, TIOCSWINSZ, &ws);
        }
        break;
      }
      case FocusIn:
        window_focused = needs_refresh = 1;
        break;
      case FocusOut:
        window_focused = 0;
        needs_refresh = 1;
        break;
      case KeyPress:
        if (ev.xkey.keycode < 128) {
          key_press_cb(&ev.xkey, &master);
        }
        break;
      case Expose:
        needs_refresh = 1;
        check_refresh(display, win);
        break;
      }
    }

    FD_ZERO(&fds);
    FD_SET(master, &fds);
    if (select(master + 1, &fds, 0, 0, &tv) > 0)
      master_cb(master, &ctx, win);

    check_refresh(display, win);
    update_cursor_state(display, win);
  }
}