diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index a7ec5ba..88d69fb 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -19,7 +19,7 @@ project(${APP_NAME}
     LANGUAGES C
 )
 
-add_executable(${APP_NAME} main.c utils.c buffer.c backtrace.c)
+add_executable(${APP_NAME} wm.c utils.c buffer.c backtrace.c monitor.c client.c)
 
 # use C23
 set_property(TARGET ${APP_NAME} PROPERTY C_STANDARD 23)
@@ -31,6 +31,9 @@ pkg_check_modules(deps REQUIRED
 
     xcb
     xcb-aux
+    xcb-randr
+    xcb-xfixes
+    xcb-xinerama
 )
 
 target_include_directories(${APP_NAME} SYSTEM
@@ -63,8 +66,8 @@ else()
     message(STATUS "checking for execinfo -- not found")
 endif()
 
-configure_file("${SOURCE_DIR}/config.h.in"
-    "${BUILD_DIR}/config.h"
+configure_file("${SOURCE_DIR}/app.h.in"
+    "${BUILD_DIR}/app.h"
     ESCAPE_QUOTES
     @ONLY
 )
diff --git a/src/config.h.in b/src/app.h.in
similarity index 100%
rename from src/config.h.in
rename to src/app.h.in
diff --git a/src/backtrace.c b/src/backtrace.c
index 26ca326..4fbbe65 100644
--- a/src/backtrace.c
+++ b/src/backtrace.c
@@ -1,7 +1,7 @@
 #include "backtrace.h"
 
+#include "app.h"
 #include "buffer.h"
-#include "config.h"
 
 #ifdef HAS_EXECINFO
 #include <execinfo.h>
@@ -9,7 +9,6 @@
 
 #define MAX_STACK_SIZE 32
 
-
 /**
  * Get a backtrace.
  * @param buffer The buffer to fill with backtrace.
diff --git a/src/bar.h b/src/bar.h
new file mode 100644
index 0000000..3f59c93
--- /dev/null
+++ b/src/bar.h
@@ -0,0 +1,2 @@
+#pragma once
+
diff --git a/src/base.h b/src/base.h
new file mode 100644
index 0000000..a748914
--- /dev/null
+++ b/src/base.h
@@ -0,0 +1,13 @@
+#pragma once
+
+#include <stdint.h>
+
+typedef struct area_t {
+  int16_t x, y;
+  uint16_t width, height;
+} area_t;
+
+typedef struct extent_in_bar_t {
+  int16_t start;
+  int16_t end;
+} extent_in_bar_t;
diff --git a/src/client.c b/src/client.c
new file mode 100644
index 0000000..f679c0d
--- /dev/null
+++ b/src/client.c
@@ -0,0 +1 @@
+#include "client.h"
diff --git a/src/client.h b/src/client.h
new file mode 100644
index 0000000..9943dda
--- /dev/null
+++ b/src/client.h
@@ -0,0 +1,45 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "color.h"
+#include "types.h"
+
+void client_manage(xcb_window_t window);
+
+void client_send_to_tag(client_t *client, uint32_t tag_mask);
+void client_send_to_monitor(client_t *client, monitor_t *monitor);
+
+void client_move_to(client_t *client, int16_t x, int16_t y);
+void client_resize(client_t *client, uint16_t width, uint16_t height);
+void client_change_border_color(client_t *client, color_t *color);
+void client_change_border_width(client_t *client, uint16_t border_width);
+
+void client_set_floating(client_t *client, bool floating);
+void client_set_fullscreen(client_t *client, bool fullscreen);
+void client_set_maximize(client_t *client, bool maximize);
+void client_set_minimize(client_t *client, bool minimize);
+void client_set_sticky(client_t *client, bool sticky);
+void client_set_urgent(client_t *client, bool urgent);
+
+void client_set_class_instance(client_t *client, const char *class,
+                               const char *instance);
+
+void client_set_name(client_t *client, char *name);
+void client_set_icon_name(client_t *client, char *icon_name);
+void client_set_net_name(client_t *client, char *name);
+void client_set_net_icon_name(client_t *client, char *icon_name);
+
+void client_set_role(client_t *client, char *role);
+
+void client_set_transient_for_window(client_t *client,
+                                     xcb_window_t transient_for_window);
+void client_set_leader_window(client_t *client, xcb_window_t leader_window);
+
+void client_kill(client_t *client);
+void client_unmanage(client_t *client);
+
+void client_focus(client_t *client);
+void client_stack_raise(client_t *client);
+
+bool client_is_visible(client_t *client);
diff --git a/src/color.h b/src/color.h
new file mode 100644
index 0000000..746261c
--- /dev/null
+++ b/src/color.h
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+typedef struct color_t {
+  uint32_t rgba; /* use for human reading */
+  uint32_t argb; /* use for xcb */
+
+  /* channels of color, use for cairo */
+  double red;   /* red channel */
+  double green; /* green channel */
+  double blue;  /* blue channel */
+  double alpha; /* alpha channel */
+} color_t;
+
+/**
+ * @brief parsing color represented in hexadecimal format
+ * @param hex color represented in hexadecimal format, the supported format
+   have: RGB/RGBA/RRGGBB/RRGGBBAA/#RGB/#RGBA/#RRGGBB/#RRGGBBAA
+ * @param color return the parsed color
+ */
+void parse_color(const char *hex, color_t *const color);
diff --git a/src/draw.h b/src/draw.h
new file mode 100644
index 0000000..45dcbb0
--- /dev/null
+++ b/src/draw.h
@@ -0,0 +1,3 @@
+#pragma once
+
+
diff --git a/src/monitor.c b/src/monitor.c
new file mode 100644
index 0000000..3ac0a1c
--- /dev/null
+++ b/src/monitor.c
@@ -0,0 +1,3 @@
+#include "monitor.h"
+
+
diff --git a/src/monitor.h b/src/monitor.h
new file mode 100644
index 0000000..e43f315
--- /dev/null
+++ b/src/monitor.h
@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "types.h"
+
+void monitor_select_tag(monitor_t *monitor, uint32_t tag_mask);
diff --git a/src/types.h b/src/types.h
index 00e6320..e9effce 100644
--- a/src/types.h
+++ b/src/types.h
@@ -1,16 +1,74 @@
 #pragma once
 
 #include <glib.h>
+#include <stdint.h>
 #include <xcb/xcb.h>
 #include <xcb/xproto.h>
 
-typedef struct global_state_t {
-  bool need_restart;
-  GMainLoop *loop;
+#include "base.h"
+#include "color.h"
 
-  xcb_connection_t *xcb_conn;
-  xcb_screen_t *screen;
-  int default_screen;
-} global_state_t;
+typedef struct client_t client_t;
+typedef struct monitor_t monitor_t;
+typedef struct tag_t tag_t;
+typedef struct task_in_tag_t task_in_tag_t;
 
-extern global_state_t global_state;
+typedef struct layout_t {
+  char *symbol;
+  void (*arrange)(tag_t *tag);
+} layout_t;
+
+struct client_t {
+  client_t *stack_next;
+  client_t *next;
+
+  monitor_t *monitor;
+  uint32_t tags;
+
+  area_t geometry;
+  color_t *border_color;
+  uint16_t border_width;
+
+  bool floating;
+  bool fullscreen;
+  bool maximize;
+  bool minimize;
+  bool sticky;
+  bool urgent;
+
+  char *class, *instance;
+  char *name, *icon_name, *net_name, *net_icon_name;
+  char *role;
+
+  xcb_window_t transient_for_window;
+  xcb_window_t leader_window;
+  xcb_window_t frame_window;
+  xcb_window_t window;
+};
+
+struct monitor_t {
+  monitor_t *next;
+  area_t geometry;
+  area_t workarea;
+  tag_t *tag_list;
+  tag_t *selected_tag;
+
+  xcb_window_t bar_window;
+};
+
+struct tag_t {
+  uint32_t index; /* index in all tags */
+  uint32_t mask;
+  extent_in_bar_t bar_extent;
+  tag_t *next;
+  char *name;
+  layout_t *layout;
+  task_in_tag_t *task_list;
+};
+
+struct task_in_tag_t {
+  client_t *client;
+  task_in_tag_t *next;
+  area_t geometry;
+  extent_in_bar_t bar_extent;
+};
diff --git a/src/utils.c b/src/utils.c
index ece8992..9154906 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -5,7 +5,7 @@
 #include <stdlib.h>
 #include <time.h>
 
-#include "config.h"
+#include "app.h"
 
 const char *current_time_str(void) {
   static char buffer[25];
diff --git a/src/main.c b/src/wm.c
similarity index 60%
rename from src/main.c
rename to src/wm.c
index 18dbf8a..856fc49 100644
--- a/src/main.c
+++ b/src/wm.c
@@ -1,20 +1,32 @@
+#include "wm.h"
+
 #include <glib-unix.h>
 #include <glib.h>
 #include <glibconfig.h>
 #include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <xcb/randr.h>
 #include <xcb/xcb.h>
 #include <xcb/xcb_aux.h>
+#include <xcb/xfixes.h>
+#include <xcb/xinerama.h>
 #include <xcb/xproto.h>
 
 #include "backtrace.h"
 #include "buffer.h"
-#include "types.h"
 #include "utils.h"
 
-global_state_t global_state;
+static void wm_setup_signal(void);
+static void wm_check_other_wm(void);
+static void wm_check_xcb_extensions(void);
+static void wm_detect_monitor(void);
+static void wm_scan_clients(void);
+
+wm_t wm;
 
 /** argv used to run wm */
 static char **cmd_argv;
@@ -22,13 +34,7 @@ static char **cmd_argv;
 /** A pipe that is used to asynchronously handle SIGCHLD */
 static int sigchld_pipe[2];
 
-static void wm_atexit(bool restart) { global_state.need_restart = restart; }
-
-static void wm_restart(void) {
-  wm_atexit(true);
-  execvp(cmd_argv[0], cmd_argv);
-  fatal("execv() failed: %s", strerror(errno));
-}
+static void wm_atexit(bool restart) { wm.need_restart = restart; }
 
 static gboolean restart_on_signal(gpointer data) {
   wm_restart();
@@ -36,7 +42,7 @@ static gboolean restart_on_signal(gpointer data) {
 }
 
 static gboolean exit_on_signal(gpointer data) {
-  g_main_loop_quit(global_state.loop);
+  g_main_loop_quit(wm.loop);
   return TRUE;
 }
 
@@ -54,7 +60,26 @@ static void signal_child(int signum) {
   assert(res == 1);
 }
 
-static void check_other_wm(void) {
+void wm_setup_signal(void) {
+  g_unix_signal_add(SIGINT, exit_on_signal, NULL);
+  g_unix_signal_add(SIGTERM, exit_on_signal, NULL);
+  g_unix_signal_add(SIGHUP, restart_on_signal, NULL);
+
+  struct sigaction sa = {.sa_handler = signal_fatal, .sa_flags = SA_RESETHAND};
+  sigemptyset(&sa.sa_mask);
+  sigaction(SIGABRT, &sa, 0);
+  sigaction(SIGBUS, &sa, 0);
+  sigaction(SIGFPE, &sa, 0);
+  sigaction(SIGILL, &sa, 0);
+  sigaction(SIGSEGV, &sa, 0);
+  signal(SIGPIPE, SIG_IGN);
+
+  sa.sa_handler = signal_child;
+  sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
+  sigaction(SIGCHLD, &sa, 0);
+}
+
+void wm_check_other_wm(void) {
   /* connect X server */
   int default_screen;
   xcb_connection_t *conn = xcb_connect(NULL, &default_screen);
@@ -77,41 +102,58 @@ static void check_other_wm(void) {
       "SubstructureRedirect)");
   }
 
-  global_state.xcb_conn = conn;
-  global_state.default_screen = default_screen;
-  global_state.screen = screen;
+  wm.xcb_conn = conn;
+  wm.default_screen = default_screen;
+  wm.screen = screen;
+}
+
+void wm_check_xcb_extensions(void) {
+  xcb_prefetch_extension_data(wm.xcb_conn, &xcb_xfixes_id);
+  xcb_prefetch_extension_data(wm.xcb_conn, &xcb_xinerama_id);
+  xcb_prefetch_extension_data(wm.xcb_conn, &xcb_randr_id);
+
+  const xcb_query_extension_reply_t *query;
+  query = xcb_get_extension_data(wm.xcb_conn, &xcb_xfixes_id);
+  wm.have_xfixes = query && query->present;
+
+  query = xcb_get_extension_data(wm.xcb_conn, &xcb_xinerama_id);
+  wm.have_xinerama = query && query->present;
+
+  query = xcb_get_extension_data(wm.xcb_conn, &xcb_randr_id);
+  wm.have_randr = query && query->present;
+}
+
+void wm_detect_monitor(void) {}
+void wm_scan_clients(void) {}
+
+void wm_restart(void) {
+  wm_atexit(true);
+  execvp(cmd_argv[0], cmd_argv);
+  fatal("execv() failed: %s", strerror(errno));
+}
+
+void wm_quit(void) {
+  if (g_main_loop_is_running(wm.loop)) {
+    g_main_loop_quit(wm.loop);
+  }
 }
 
 int main(int argc, char *argv[]) {
-  p_clear(&global_state, 1);
-
+  p_clear(&wm, 1);
   cmd_argv = argv;
+  wm_setup_signal();
 
-  g_unix_signal_add(SIGINT, exit_on_signal, NULL);
-  g_unix_signal_add(SIGTERM, exit_on_signal, NULL);
-  g_unix_signal_add(SIGHUP, restart_on_signal, NULL);
+  wm_check_other_wm();
+  wm_check_xcb_extensions();
 
-  struct sigaction sa = {.sa_handler = signal_fatal, .sa_flags = SA_RESETHAND};
-  sigemptyset(&sa.sa_mask);
-  sigaction(SIGABRT, &sa, 0);
-  sigaction(SIGBUS, &sa, 0);
-  sigaction(SIGFPE, &sa, 0);
-  sigaction(SIGILL, &sa, 0);
-  sigaction(SIGSEGV, &sa, 0);
-  signal(SIGPIPE, SIG_IGN);
+  wm_detect_monitor();
 
-  sa.sa_handler = signal_child;
-  sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
-  sigaction(SIGCHLD, &sa, 0);
-
-  check_other_wm();
-
-  if (global_state.loop == NULL) {
-    global_state.loop = g_main_loop_new(NULL, FALSE);
-    g_main_loop_run(global_state.loop);
+  if (wm.loop == NULL) {
+    wm.loop = g_main_loop_new(NULL, FALSE);
+    g_main_loop_run(wm.loop);
   }
-  g_main_loop_unref(global_state.loop);
-  global_state.loop = NULL;
+  g_main_loop_unref(wm.loop);
+  wm.loop = NULL;
 
   wm_atexit(false);
 
diff --git a/src/wm.h b/src/wm.h
new file mode 100644
index 0000000..7f9a29e
--- /dev/null
+++ b/src/wm.h
@@ -0,0 +1,26 @@
+#pragma once
+
+#include "types.h"
+
+typedef struct wm_t {
+  bool need_restart;
+  GMainLoop *loop;
+
+  client_t *client_list;
+  client_t *client_stack_list;
+  client_t *client_focused;
+  monitor_t *monitor_list;
+  monitor_t *current_monitor;
+
+  xcb_connection_t *xcb_conn;
+  xcb_screen_t *screen;
+  int default_screen;
+  bool have_xfixes;
+  bool have_xinerama;
+  bool have_randr;
+} wm_t;
+
+extern wm_t wm;
+
+void wm_restart(void);
+void wm_quit(void);
diff --git a/src/xwindow.h b/src/xwindow.h
new file mode 100644
index 0000000..6f70f09
--- /dev/null
+++ b/src/xwindow.h
@@ -0,0 +1 @@
+#pragma once