(import scheme)
(import (chicken base))
(import (chicken bitwise))
(import (chicken format))
(import (chicken time posix))
(import (srfi 1))
(import (rename format (format cl-format)))
(import (prefix glfw3 glfw:))
(import (prefix epoxy gl:))
(import (prefix nuklear-glfw3-opengl2 nk:))
(import (prefix nuklear nk:))

(define width 1200)
(define height 800)

(glfw:init)
(glfw:make-window width height "Overview")
(glfw:make-context-current (glfw:window))
(set!-values (width height) (glfw:get-window-size (glfw:window)))

(define ctx (nk:init (glfw:window)))
(nk:init-default-font ctx)

(define ->flag bitwise-ior)
(define (flag? flag flags) (not (zero? (bitwise-and flag flags))))

(define bg (nk:make-color 0.1 0.18 0.24 1.0))

(define show-menu? #t)
(define titlebar? #t)

(define border? #t)
(define resize? #t)
(define movable? #t)
(define no-scrollbar? #f)
(define scale-left? #f)
(define minimizable? #t)

(define menu-progress 60)
(define menu-slider 10)
(define menu-check #t)

(define menu/none 0)
(define menu/file 1)
(define menu/edit 2)
(define menu/view 3)
(define menu/chart 4)
(define menu-state menu/none)

(define progress 40)
(define slider 10)
(define check #t)

(define A 0)
(define B 1)
(define C 2)

(define checkbox #f)
(define option 0)

(define int-slider 5)
(define float-slider 2.5)
(define prog-value 40)
(define property-float 2)
(define property-int 10)
(define property-neg 10)

(define range-float-min 0)
(define range-float-max 100)
(define range-float-value 50)
(define range-int-min 0)
(define range-int-value 2048)
(define range-int-max 4096)
(define ratio '(120 150))

(define selected-list (make-vector 4 #f))
(define selected-grid (make-vector 16 #f))

(define (vector-for-each proc vec)
  (let loop ((i 0))
    (when (< i (vector-length vec))
      (proc i (vector-ref vec i))
      (loop (add1 i)))))

(define (vector-toggle! vec n)
  (let ((value (vector-ref vec n)))
    (vector-set! vec n (not value))))

(define chart-selection 8)
(define check-values (make-list 4 #f))
(define position '(0 0 0))
(define combo-color (nk:make-color 130 50 50 255))
(define combo-color2 (nk:rgba-f->colorf 0.509 0.705 0.2 1.0))
(define use-hsva? #f)
(define prog-a 20)
(define prog-b 40)
(define prog-c 10)
(define prog-d 90)
(define weapons '("Fist" "Pistol" "Shotgun" "Plasma" "BFG"))
(define weapon-idx 0)

(define time-selected? #f)
(define date-selected? #f)
(define selected-time #f)
(define selected-date #f)

(define text (make-vector 8 ""))
(define field-buffer "")
(define box-buffer "")

(define (mask-text text)
  (make-string (string-length text) #\*))

(define pi (* 2 (asin 1)))
(define col-index -1)
(define line-index -1)

(define selected (make-list 4 #f))
(define color (nk:make-color 255 0 0 255))
(define popup-active? #f)

(define group-titlebar? #f)
(define group-border? #t)
(define group-no-scrollbar? #f)

(define (group-flags)
  (->flag (if group-titlebar? nk:window/title 0)
          (if group-border? nk:window/border 0)
          (if group-no-scrollbar? nk:window/no-scrollbar 0)))

(define group-width 320)
(define group-height 200)

(define selected-group (make-list 16 #f))
(define root-selected #f)
(define selected-leaves (make-list 8 #f))
(define selected-nodes (make-list 4 #f))

(define left-selected-group (make-list 32 #f))
(define top-right-selected-group (make-list 4 #f))
(define center-right-selected-group (make-list 4 #f))
(define bottom-right-selected-group (make-list 4 #f))

(define vertical-a 100)
(define vertical-b 100)
(define vertical-c 100)

(define horizontal-a 100)
(define horizontal-b 100)
(define horizontal-c 100)

(define (window-flags)
  (->flag (if border? nk:window/border 0)
          (if resize? nk:window/scalable 0)
          (if movable? nk:window/movable 0)
          (if no-scrollbar? nk:window/no-scrollbar 0)
          (if scale-left? nk:window/scale-left 0)
          (if minimizable? nk:window/minimizable 0)))

(nk:style-window-header-align-set! (nk:context-style ctx) nk:header/right)

(define show-app-about? #f)

(let loop ()
  (when (and (not (glfw:window-should-close (glfw:window))))
    (glfw:poll-events)
    (nk:new-frame)

    (when (nk:window-begin ctx "Overview"
                           (nk:make-rect 10 10 400 600)
                           (window-flags))
      (when show-menu?
        ;; menubar
        (nk:menubar-begin ctx)
        ;; menu #1
        (nk:layout-row-begin ctx nk:layout/static 25 5)
        (nk:layout-row-push ctx 45)
        (when (nk:menu-begin-label ctx "MENU" nk:text/left (nk:make-vec2 120 200))
          (nk:layout-row-dynamic ctx 25 1)
          (when (nk:menu-item-label ctx "Hide" nk:text/left)
            (set! show-menu? #f))
          (when (nk:menu-item-label ctx "About" nk:text/left)
            (set! show-app-about? #t))
          (receive (val changed?) (nk:progress ctx progress 100 nk:modify/modifiable)
            (when changed? (set! progress val)))
          (set! slider (nk:slider-int ctx 0 slider 16 1))
          (set! check (nk:check-label ctx "check" check))
          (nk:menu-end ctx))

        ;; menu #2
        (nk:layout-row-push ctx 60)
        (when (nk:menu-begin-label ctx "ADVANCED" nk:text/left (nk:make-vec2 200 600))
          (let ((state 0))
            (set! state (if (= menu-state menu/file) nk:collapse/maximized nk:collapse/minimized))
            (receive (open? state) (nk:tree-state-push ctx nk:tree/tab "FILE" state)
              (if open?
                  (begin
                    (set! menu-state menu/file)
                    (for-each
                     (lambda (label)
                       (nk:menu-item-label ctx label nk:text/left))
                     '("New" "Open" "Save" "Close" "Exit"))
                    (nk:tree-pop ctx))
                  (when (= menu-state menu/file)
                    (set! menu-state menu/none))))

            (set! state (if (= menu-state menu/edit) nk:collapse/maximized nk:collapse/minimized))
            (receive (open? state) (nk:tree-state-push ctx nk:tree/tab "EDIT" state)
              (if open?
                  (begin
                    (set! menu-state menu/edit)
                    (for-each
                     (lambda (label)
                       (nk:menu-item-label ctx label nk:text/left))
                     '("Copy" "Delete" "Cut" "Paste"))
                    (nk:tree-pop ctx))
                  (when (= menu-state menu/edit)
                    (set! menu-state menu/none))))

            (set! state (if (= menu-state menu/view) nk:collapse/maximized nk:collapse/minimized))
            (receive (open? state) (nk:tree-state-push ctx nk:tree/tab "VIEW" state)
              (if open?
                  (begin
                    (set! menu-state menu/view)
                    (for-each
                     (lambda (label)
                       (nk:menu-item-label ctx label nk:text/left))
                     '("About" "Options" "Customize"))
                    (nk:tree-pop ctx))
                  (when (= menu-state menu/view)
                    (set! menu-state menu/none))))

            (set! state (if (= menu-state menu/chart) nk:collapse/maximized nk:collapse/minimized))
            (receive (open? state) (nk:tree-state-push ctx nk:tree/tab "CHART" state)
              (if open?
                  (let ((values '(26 13 30 15 25 10 20 40 12 8 22 28)))
                    (set! menu-state menu/chart)
                    (nk:layout-row-dynamic ctx 150 1)
                    (nk:chart-begin ctx nk:chart/column (length values) 0 50)
                    (for-each
                     (lambda (value)
                       (nk:chart-push ctx value))
                     values)
                    (nk:chart-end ctx)
                    (nk:tree-pop ctx))
                  (when (= menu-state menu/chart)
                    (set! menu-state menu/none)))))
          (nk:menu-end ctx))

        ;; menu widgets
        (nk:layout-row-push ctx 70)
        (set! menu-progress (nk:progress ctx menu-progress 100 nk:modify/modifiable))
        (set! menu-slider (nk:slider-int ctx 0 menu-slider 16 1))
        (set! menu-check (nk:check-label ctx "check" menu-check))
        (nk:menubar-end ctx))

      (when show-app-about?
        ;; about popup
        (if (nk:popup-begin ctx nk:popup/static "About" nk:window/closable (nk:make-rect 20 100 300 190))
            (begin
              (nk:layout-row-dynamic ctx 20 1)
              (nk:label ctx "Nuklear" nk:text/left)
              (nk:label ctx "By Micha Mettke" nk:text/left)
              (nk:label ctx "nuklear is licensed under the public domain License" nk:text/left)
              (nk:popup-end ctx))
            (set! show-app-about? #f)))

      (when (nk:tree-push ctx nk:tree/tab "Window" nk:collapse/minimized)
        (nk:layout-row-dynamic ctx 30 2)
        (set! titlebar? (nk:check-label ctx "Titlebar" titlebar?))
        (set! show-menu? (nk:check-label ctx "Menu" show-menu?))
        (set! border? (nk:check-label ctx "Border" border?))
        (set! resize? (nk:check-label ctx "Resizable" resize?))
        (set! movable? (nk:check-label ctx "Movable" movable?))
        (set! no-scrollbar? (nk:check-label ctx "No Scrollbar" no-scrollbar?))
        (set! minimizable? (nk:check-label ctx "Minimizable" minimizable?))
        (set! scale-left? (nk:check-label ctx "Scale Left" scale-left?))
        (nk:tree-pop ctx))

      (when (nk:tree-push ctx nk:tree/tab "Widgets" nk:collapse/minimized)
        (when (nk:tree-push ctx nk:tree/node "Text" nk:collapse/minimized)
          (nk:layout-row-dynamic ctx 20 1)
          (nk:label ctx "Label aligned left" nk:text/left)
          (nk:label ctx "Label aligned centered" nk:text/centered)
          (nk:label ctx "Label aligned right" nk:text/right)
          (nk:label-colored ctx "Blue text" nk:text/left (nk:rgb->color 0 0 255))
          (nk:label-colored ctx "Yellow text" nk:text/left (nk:rgb->color 255 255 0))
          (nk:text ctx "Text with \x00 ASCII NUL in it" nk:text/right)

          (nk:layout-row-static ctx 100 200 1)
          (nk:label-wrap ctx "This is a very long line to hopefully get this text to be wrapped into multiple lines to show line wrapping")
          (nk:layout-row-dynamic ctx 100 1)
          (nk:label-wrap ctx "This is another long text to show dynamic window changes on multiline text")

          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Button" nk:collapse/minimized)
          (nk:layout-row-static ctx 30 100 3)
          (when (nk:button-label ctx "Button")
            (print "Button pressed!"))
          (nk:button-behavior-set! ctx nk:button/repeater)
          (when (nk:button-label ctx "Repeater")
            (print "Repeater is being pressed!"))
          (nk:button-behavior-set! ctx nk:button/default)
          (nk:button-color ctx (nk:rgb->color 0 0 255))

          (nk:layout-row-static ctx 25 25 8)
          (nk:button-symbol ctx nk:symbol/circle-solid)
          (nk:button-symbol ctx nk:symbol/circle-outline)
          (nk:button-symbol ctx nk:symbol/rect-solid)
          (nk:button-symbol ctx nk:symbol/rect-outline)
          (nk:button-symbol ctx nk:symbol/triangle-up)
          (nk:button-symbol ctx nk:symbol/triangle-down)
          (nk:button-symbol ctx nk:symbol/triangle-left)
          (nk:button-symbol ctx nk:symbol/triangle-right)

          (nk:layout-row-static ctx 30 100 2)
          (nk:button-symbol-label ctx nk:symbol/triangle-left "prev" nk:text/right)
          (nk:button-symbol-label ctx nk:symbol/triangle-right "next" nk:text/left)

          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Basic" nk:collapse/minimized)
          (nk:layout-row-static ctx 30 100 1)
          (set! checkbox (nk:check-label ctx "Checkbox" checkbox))

          (nk:layout-row-static ctx 30 80 3)
          (set! option (if (nk:option-label ctx "optionA" (= option A)) A option))
          (set! option (if (nk:option-label ctx "optionB" (= option B)) B option))
          (set! option (if (nk:option-label ctx "optionC" (= option C)) C option))

          (nk:layout-row ctx nk:layout/static 30 ratio)
          (nk:label ctx "Slider int" nk:text/left)
          (set! int-slider (nk:slider-int ctx 0 int-slider 10 1))
          (nk:label ctx "Slider float" nk:text/left)
          (set! float-slider (nk:slider-float ctx 0 float-slider 5 0.5))
          (nk:label ctx (format "Progressbar: ~a" prog-value) nk:text/left)
          (set! prog-value (nk:progress ctx prog-value 100 nk:modify/modifiable))

          (nk:layout-row ctx nk:layout/static 25 ratio)
          (nk:label ctx "Property float:" nk:text/left)
          (set! property-float (nk:property-float ctx "Float:" 0 property-float 64 0.1 0.2))
          (nk:label ctx "Property int:" nk:text/left)
          (set! property-int (nk:property-int ctx "Int:" 0 property-int 100 1 1))
          (nk:label ctx "Property neg:" nk:text/left)
          (set! property-neg (nk:property-int ctx "Neg:" -10 property-neg 10 1 1))

          (nk:layout-row-dynamic ctx 25 1)
          (nk:label ctx "Range:" nk:text/left)
          (nk:layout-row-dynamic ctx 25 3)
          (set! range-float-min (nk:property-float ctx "#min:" 0 range-float-min range-float-max 1 0.2))
          (set! range-float-value (nk:property-float ctx "#float:" range-float-min range-float-value range-float-max 1 0.2))
          (set! range-float-max (nk:property-float ctx "#max:" range-float-min range-float-max 100 1 0.2))

          (set! range-int-min (nk:property-int ctx "#min:" -32767 range-int-min range-int-max 1 10))
          (set! range-int-value (nk:property-int ctx "#neg:" range-int-min range-int-value range-int-max 1 10))
          (set! range-int-max (nk:property-int ctx "#max:" range-int-min range-int-max 32767 1 10))

          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Inactive" nk:collapse/minimized)
          ;; TODO
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Selectable" nk:collapse/minimized)
          (when (nk:tree-push ctx nk:tree/node "List" nk:collapse/minimized)
            (nk:layout-row-static ctx 18 100 1)
            (vector-set! selected-list 0 (nk:selectable-label ctx "Selectable" nk:text/left (vector-ref selected-list 0)))
            (vector-set! selected-list 1 (nk:selectable-label ctx "Selectable" nk:text/left (vector-ref selected-list 1)))
            (nk:label ctx "Not selectable" nk:text/left)
            (vector-set! selected-list 2 (nk:selectable-label ctx "Selectable" nk:text/left (vector-ref selected-list 2)))
            (vector-set! selected-list 3 (nk:selectable-label ctx "Selectable" nk:text/left (vector-ref selected-list 3)))
            (nk:tree-pop ctx))

          (when (nk:tree-push ctx nk:tree/node "Grid" nk:collapse/minimized)
            (nk:layout-row-static ctx 50 50 4)
            (vector-for-each
             (lambda (i x)
               (let* ((value (nk:selectable-label ctx "Z" nk:text/centered x))
                      (clicked? (not (eqv? x value))))
                 (when clicked?
                   (vector-set! selected-grid i value)
                   (let ((x (modulo i 4))
                         (y (quotient i 4)))
                     (when (> x 0)
                       (vector-toggle! selected-grid (sub1 i)))
                     (when (< x 3)
                       (vector-toggle! selected-grid (add1 i)))
                     (when (> y 0)
                       (vector-toggle! selected-grid (- i 4)))
                     (when (< y 3)
                       (vector-toggle! selected-grid (+ i 4)))))))
             selected-grid)
            (nk:tree-pop ctx))

          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Combo" nk:collapse/minimized)
          ;; Combobox Widgets
          ;; In this library comboboxes are not limited to being a popup
          ;; list of selectable text. Instead it is a abstract concept of
          ;; having something that is *selected* or displayed, a popup window
          ;; which opens if something needs to be modified and the content
          ;; of the popup which causes the *selected* or displayed value to
          ;; change or if wanted close the combobox.
          ;;
          ;; While strange at first handling comboboxes in a abstract way
          ;; solves the problem of overloaded window content. For example
          ;; changing a color value requires 4 value modifier (slider, property,...)
          ;; for RGBA then you need a label and ways to display the current color.
          ;; If you want to go fancy you even add rgb and hsv ratio boxes.
          ;; While fine for one color if you have a lot of them it because
          ;; tedious to look at and quite wasteful in space. You could add
          ;; a popup which modifies the color but this does not solve the
          ;; fact that it still requires a lot of cluttered space to do.
          ;;
          ;; In these kind of instance abstract comboboxes are quite handy. All
          ;; value modifiers are hidden inside the combobox popup and only
          ;; the color is shown if not open. This combines the clarity of the
          ;; popup with the ease of use of just using the space for modifiers.
          ;;
          ;; Other instances are for example time and especially date picker,
          ;; which only show the currently activated time/data and hide the
          ;; selection logic inside the combobox popup.

          ;; default combobox
          (nk:layout-row-static ctx 25 200 1)
          (set! weapon-idx (nk:combo ctx weapons weapon-idx 25 (nk:make-vec2 200 200)))

          ;; slider color combobox
          (when (nk:combo-begin-color ctx combo-color (nk:make-vec2 200 200))
            (nk:layout-row ctx nk:layout/dynamic 30 '(0.15 0.85))
            (nk:label ctx "R:" nk:text/left)
            (nk:color-r-set! combo-color (nk:slider-int ctx 0 (nk:color-r combo-color) 255 5))
            (nk:label ctx "G:" nk:text/left)
            (nk:color-g-set! combo-color (nk:slider-int ctx 0 (nk:color-g combo-color) 255 5))
            (nk:label ctx "B:" nk:text/left)
            (nk:color-b-set! combo-color (nk:slider-int ctx 0 (nk:color-b combo-color) 255 5))
            (nk:label ctx "A:" nk:text/left)
            (nk:color-a-set! combo-color (nk:slider-int ctx 0 (nk:color-a combo-color) 255 5))
            (nk:combo-end ctx))

          ;; complex color combobox
          (when (nk:combo-begin-color ctx (nk:colorf->color combo-color2) (nk:make-vec2 200 400))
            (nk:layout-row-dynamic ctx 120 1)
            (set! combo-color2 (nk:color-picker ctx combo-color2 nk:color/rgba))

            (nk:layout-row-dynamic ctx 25 2)
            (set! use-hsva? (if (nk:option-label ctx "RGB" (not use-hsva?)) #f use-hsva?))
            (set! use-hsva? (if (nk:option-label ctx "HSV" use-hsva?) #t use-hsva?))

            (nk:layout-row-dynamic ctx 25 1)
            (if use-hsva?
                (let* ((hsva (nk:colorf->hsva-f combo-color2))
                       (h (nk:property-float ctx "#H:" 0 (car hsva) 1.0 0.01 0.005))
                       (s (nk:property-float ctx "#S:" 0 (cadr hsva) 1.0 0.01 0.005))
                       (v (nk:property-float ctx "#V:" 0 (list-ref hsva 2) 1.0 0.01 0.005))
                       (a (nk:property-float ctx "#A:" 0 (list-ref hsva 3) 1.0 0.01 0.005)))
                  (set! combo-color2 (nk:hsva-f->colorf h s v a)))
                (begin
                  (nk:color-r-set! combo-color2 (nk:property-float ctx "#R:" 0 (nk:color-r combo-color2) 1.0 0.01 0.005))
                  (nk:color-g-set! combo-color2 (nk:property-float ctx "#G:" 0 (nk:color-g combo-color2) 1.0 0.01 0.005))
                  (nk:color-b-set! combo-color2 (nk:property-float ctx "#B:" 0 (nk:color-b combo-color2) 1.0 0.01 0.005))
                  (nk:color-a-set! combo-color2 (nk:property-float ctx "#A:" 0 (nk:color-a combo-color2) 1.0 0.01 0.005))))
            (nk:combo-end ctx))

          ;; progressbar combobox
          (let ((sum (+ prog-a prog-b prog-c prog-d)))
            (when (nk:combo-begin-label ctx (number->string sum) (nk:make-vec2 200 200))
              (nk:layout-row-dynamic ctx 30 1)
              (set! prog-a (nk:progress ctx prog-a 100 nk:modify/modifiable))
              (set! prog-b (nk:progress ctx prog-b 100 nk:modify/modifiable))
              (set! prog-c (nk:progress ctx prog-c 100 nk:modify/modifiable))
              (set! prog-d (nk:progress ctx prog-d 100 nk:modify/modifiable))
              (nk:combo-end ctx)))

          ;; checkbox combobox
          (let ((sum (count identity check-values)))
            (when (nk:combo-begin-label ctx (number->string sum) (nk:make-vec2 200 200))
              (nk:layout-row-dynamic ctx 30 1)
              (set! check-values
                    (map-in-order
                     (lambda (checked? weapon)
                       (nk:check-label ctx weapon checked?))
                     check-values weapons))
              (nk:combo-end ctx)))

          ;; complex text combobox
          (let ((label (cl-format #f "~{~,2f~^, ~}" position)))
            (when (nk:combo-begin-label ctx label (nk:make-vec2 200 200))
              (nk:layout-row-dynamic ctx 25 1)
              (set! position
                    (map-in-order
                     (lambda (component label)
                       (nk:property-float ctx label -1024 component 1024 1 0.5))
                     position '("#X:" "#Y:" "#Z:")))
              (nk:combo-end ctx)))

          ;; chart combobox
          (let ((label (cl-format #f "~,2f" chart-selection)))
            (when (nk:combo-begin-label ctx label (nk:make-vec2 200 250))
              (nk:layout-row-dynamic ctx 150 1)
              (let* ((values #(26 13 30 15 25 10 20 40 12 8 22 28 5))
                     (size (vector-length values)))
                (nk:chart-begin ctx nk:chart/column size 0 50)
                (vector-for-each
                 (lambda (_i x)
                   (let ((events (nk:chart-push ctx x)))
                     (when (flag? nk:chart/clicked events)
                       (set! chart-selection x)
                       (nk:combo-close ctx))))
                 values)
                (nk:chart-end ctx))
              (nk:combo-end ctx)))

          (when (not time-selected?)
            (set! selected-time (seconds->local-time)))
          (when (not date-selected?)
            (set! selected-date (seconds->local-time)))

          ;; time combobox
          (let ((label (time->string selected-time "%H:%M:%S")))
            (when (nk:combo-begin-label ctx label (nk:make-vec2 200 250))
              (set! time-selected? #t)
              (nk:layout-row-dynamic ctx 25 1)
              (vector-set! selected-time 0 (nk:property-int ctx "#S:" 0 (vector-ref selected-time 0) 59 1 1))
              (vector-set! selected-time 1 (nk:property-int ctx "#M:" 0 (vector-ref selected-time 1) 59 1 1))
              (vector-set! selected-time 2 (nk:property-int ctx "#S:" 0 (vector-ref selected-time 2) 23 1 1))
              (nk:combo-end ctx)))

          ;; date combobox
          (let ((label (time->string selected-date "%d-%m-%Y")))
            (when (nk:combo-begin-label ctx label (nk:make-vec2 350 400))
              (let* ((month (vector-ref selected-date 4))
                     (months #("January" "February" "March" "April" "May" "June" "July" "August" "September" "October" "November" "December"))
                     (month-label (vector-ref months month))
                     (week-days #("SUN" "MON" "TUE" "WED" "THU" "FRI" "SAT"))
                     (month-days #(31 28 31 30 31 30 31 31 30 31 30 31))
                     (year (+ (vector-ref selected-date 5) 1900))
                     (leap-year? (or (and (zero? (modulo year 4))
                                          (not (zero? (modulo year 100))))
                                     (zero? (modulo year 400))))
                     (days (vector-ref month-days month))
                     (days (if (and (= month 1) leap-year?)
                               (add1 days)
                               days)))

                ;; header with month and year
                (set! date-selected? #t)
                (nk:layout-row-begin ctx nk:layout/dynamic 20 3)
                (nk:layout-row-push ctx 0.05)
                (when (nk:button-symbol ctx nk:symbol/triangle-left)
                  (if (zero? month)
                      (begin
                        (vector-set! selected-date 4 11)
                        (vector-set! selected-date 5 (max 0 (sub1 (vector-ref selected-date 5)))))
                      (vector-set! selected-date 4 (sub1 month))))
                (nk:layout-row-push ctx 0.9)
                (nk:label ctx (format "~a ~a" month-label year) nk:text/centered)
                (nk:layout-row-push ctx 0.05)
                (when (nk:button-symbol ctx nk:symbol/triangle-right)
                  (if (= month 11)
                      (begin
                        (vector-set! selected-date 4 0)
                        (vector-set! selected-date 5 (add1 (vector-ref selected-date 5))))
                      (vector-set! selected-date 4 (add1 month))))
                (nk:layout-row-end ctx)

                ;; good old week day formula
                (let* ((year-n (if (< month 2) (sub1 year) year))
                       (y (modulo year-n 100))
                       (c (quotient year-n 100))
                       (y4 (floor (/ y 4)))
                       (c4 (floor (/ c 4)))
                       (m (floor (- (* 2.6 (add1 (modulo (+ month 10) 12))) 0.2)))
                       (week-day (modulo (+ (modulo (- (+ 1 m y y4 c4) (* 2 c)) 7) 7) 7)))

                  ;; weekdays
                  (nk:layout-row-dynamic ctx 35 7)
                  (vector-for-each
                   (lambda (_i x)
                     (nk:label ctx x nk:text/centered))
                   week-days)

                  ;; days
                  (when (> week-day 0)
                    (nk:spacing ctx (inexact->exact week-day)))
                  (let loop ((i 1))
                    (when (<= i days)
                      (when (nk:button-label ctx (number->string i))
                        (vector-set! selected-date 3 i)
                        (nk:combo-close ctx))
                      (loop (add1 i))))))
              (nk:combo-end ctx)))

          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Input" nk:collapse/minimized)
          (nk:layout-row ctx nk:layout/static 25 '(120 150))
          (nk:label ctx "Default:" nk:text/left)
          (vector-set! text 0 (nk:edit-string ctx nk:edit/simple (vector-ref text 0) 8))
          (nk:label ctx "Int:" nk:text/left)
          (vector-set! text 1 (nk:edit-string ctx nk:edit/simple (vector-ref text 1) 64 nk:filter-decimal))
          (nk:label ctx "Float:" nk:text/left)
          (vector-set! text 2 (nk:edit-string ctx nk:edit/simple (vector-ref text 2) 64 nk:filter-float))
          (nk:label ctx "Hex:" nk:text/left)
          (vector-set! text 3 (nk:edit-string ctx nk:edit/simple (vector-ref text 3) 64 nk:filter-hex))
          (nk:label ctx "Octal:" nk:text/left)
          (vector-set! text 4 (nk:edit-string ctx nk:edit/simple (vector-ref text 4) 64 nk:filter-oct))
          (nk:label ctx "Binary:" nk:text/left)
          (vector-set! text 5 (nk:edit-string ctx nk:edit/simple (vector-ref text 5) 64 nk:filter-binary))

          (nk:label ctx "Password:" nk:text/left)
          (let* ((password (vector-ref text 6))
                 (buffer (mask-text password))
                 (old-length (string-length buffer))
                 (buffer (nk:edit-string ctx nk:edit/field buffer 64))
                 (new-length (string-length buffer)))
            (cond
             ((> new-length old-length)
              (vector-set! text 6 (string-append password (substring buffer old-length new-length))))
             ((< new-length old-length)
              (vector-set! text 6 (substring password 0 new-length)))))

          (nk:label ctx "Field:" nk:text/left)
          (set! field-buffer (nk:edit-string ctx nk:edit/field field-buffer 64))

          (nk:label ctx "Box:" nk:text/left)
          (nk:layout-row-static ctx 180 278 1)
          (set! box-buffer (nk:edit-string ctx nk:edit/box box-buffer 512))

          (nk:layout-row ctx nk:layout/static 25 '(120 150))
          (receive (value edit-events) (nk:edit-string* ctx (->flag nk:edit/field nk:edit/sig-enter) (vector-ref text 7) 64 nk:filter-ascii)
            (vector-set! text 7 value)
            (when (or (nk:button-label ctx "Submit")
                      (flag? nk:edit/committed edit-events))
              (set! box-buffer (string-append box-buffer value "\n"))
              (vector-set! text 7 "")))
          (nk:tree-pop ctx))

        (nk:tree-pop ctx))

      (when (nk:tree-push ctx nk:tree/tab "Chart" nk:collapse/minimized)
        (let ((step (/ (* 2 pi) 32)))
          ;; line chart
          (nk:layout-row-dynamic ctx 100 1)
          (let ((id 0)
                (index -1))
            (when (nk:chart-begin ctx nk:chart/lines 32 -1 1)
              (let loop ((i 0))
                (when (< i 32)
                  (let ((events (nk:chart-push ctx (cos id))))
                    (when (flag? nk:chart/hovering events)
                      (set! index (floor i)))
                    (when (flag? nk:chart/clicked events)
                      (set! line-index (floor i)))
                    (set! id (+ id step)))
                  (loop (add1 i))))
              (nk:chart-end ctx))

            (when (not (= index -1))
              (let ((value (cos (* index step))))
                (nk:tooltip ctx (cl-format #f "Value: ~,2f" value))))
            (when (not (= line-index -1))
              (nk:layout-row-dynamic ctx 20 1)
              (let ((value (cos (* line-index step))))
                (nk:label ctx (cl-format #f "Selected value: ~,2f" value) nk:text/left))))

          ;; column chart
          (nk:layout-row-dynamic ctx 100 1)
          (let ((id 0)
                (index -1))
            (when (nk:chart-begin ctx nk:chart/column 32 0 1)
              (let loop ((i 0))
                (when (< i 32)
                  (let ((events (nk:chart-push ctx (abs (sin id)))))
                    (when (flag? nk:chart/hovering events)
                      (set! index (floor i)))
                    (when (flag? nk:chart/clicked events)
                      (set! col-index (floor i)))
                    (set! id (+ id step)))
                  (loop (add1 i))))
              (nk:chart-end ctx))
            (when (not (= index -1))
              (let ((value (abs (sin (* step index)))))
                (nk:tooltip ctx (cl-format "Value: ~,2f" value))))
            (when (not (= col-index -1))
              (nk:layout-row-dynamic ctx 20 1)
              (let ((value (abs (sin (* step col-index)))))
                (nk:label ctx (cl-format "Selected value: ~,2f" value) nk:text/left))))

          ;; mixed chart
          (nk:layout-row-dynamic ctx 100 1)
          (when (nk:chart-begin ctx nk:chart/column 32 0 1)
            (nk:chart-add-slot ctx nk:chart/lines 32 -1 1)
            (nk:chart-add-slot ctx nk:chart/lines 32 -1 1)
            (let loop ((i 0)
                       (id 0))
              (when (< i 32)
                (nk:chart-push-slot ctx (abs (sin id)) 0)
                (nk:chart-push-slot ctx (cos id) 1)
                (nk:chart-push-slot ctx (sin id) 2)
                (loop (add1 i) (+ id step)))))
          (nk:chart-end ctx)

          ;; mixed colored chart
          (nk:layout-row-dynamic ctx 100 1)
          (when (nk:chart-begin-colored ctx nk:chart/lines (nk:rgb->color 255 0 0) (nk:rgb->color 150 0 0) 32 0 1)
            (nk:chart-add-slot-colored ctx nk:chart/lines (nk:rgb->color 0 0 255) (nk:rgb->color 0 0 150) 32 -1 1)
            (nk:chart-add-slot-colored ctx nk:chart/lines (nk:rgb->color 0 255 0) (nk:rgb->color 0 150 0) 32 -1 1)
            (let loop ((i 0)
                       (id 0))
              (when (< i 32)
                (nk:chart-push-slot ctx (abs (sin id)) 0)
                (nk:chart-push-slot ctx (cos id) 1)
                (nk:chart-push-slot ctx (sin id) 2)
                (loop (add1 i) (+ id step)))))
          (nk:chart-end ctx))
        (nk:tree-pop ctx))

      (when (nk:tree-push ctx nk:tree/tab "Popup" nk:collapse/minimized)
        (let ((bounds #f))
          ;; menu contextual
          (nk:layout-row-static ctx 30 150 1)
          (set! bounds (nk:widget-bounds ctx))
          (nk:label ctx "Right click me for menu" nk:text/left)

          (when (nk:contextual-begin ctx 0 (nk:make-vec2 100 300) bounds)
            (nk:layout-row-dynamic ctx 25 1)
            (set! show-menu? (nk:check-label ctx "Menu" show-menu?))
            (set! progress (nk:progress ctx progress 100 nk:modify/modifiable))
            (set! slider (nk:slider-int ctx 0 slider 16 1))
            (when (nk:contextual-item-label ctx "About" nk:text/centered)
              (set! show-app-about? #t))
            (set! selected
                  (map-in-order
                   (lambda (value)
                     (nk:selectable-label ctx (if value "Unselect" "Select") nk:text/left value))
                   selected))
            (nk:contextual-end ctx))

          ;; color contextual
          (nk:layout-row-begin ctx nk:layout/static 30 2)
          (nk:layout-row-push ctx 100)
          (nk:label ctx "Right Click here:" nk:text/left)
          (nk:layout-row-push ctx 50)
          (set! bounds (nk:widget-bounds ctx))
          (nk:button-color ctx color)
          (nk:layout-row-end ctx)

          (when (nk:contextual-begin ctx 0 (nk:make-vec2 350 60) bounds)
            (nk:layout-row-dynamic ctx 30 4)
            (nk:color-r-set! color (nk:property-int ctx "#r:" 0 (nk:color-r color) 255 1 1))
            (nk:color-g-set! color (nk:property-int ctx "#g:" 0 (nk:color-g color) 255 1 1))
            (nk:color-b-set! color (nk:property-int ctx "#b:" 0 (nk:color-b color) 255 1 1))
            (nk:color-a-set! color (nk:property-int ctx "#a:" 0 (nk:color-a color) 255 1 1))
            (nk:contextual-end ctx))

          ;; popup
          (nk:layout-row-begin ctx nk:layout/static 30 2)
          (nk:layout-row-push ctx 100)
          (nk:label ctx "Popup:" nk:text/left)
          (nk:layout-row-push ctx 50)
          (when (nk:button-label ctx "Popup")
            (set! popup-active? #t))
          (nk:layout-row-end ctx)

          (if popup-active?
              (when (nk:popup-begin ctx nk:popup/static "Error" 0
                                    (nk:make-rect 20 100 220 150))
                (nk:layout-row-dynamic ctx 25 1)
                (nk:label ctx "A terrible error has occurred" nk:text/left)
                (nk:layout-row-dynamic ctx 25 2)
                (when (nk:button-label ctx "OK")
                  (set! popup-active? #f)
                  (nk:popup-close ctx))
                (when (nk:button-label ctx "Cancel")
                  (set! popup-active? #f)
                  (nk:popup-close ctx))
                (nk:popup-end ctx))
              (set! popup-active? #f))

          ;; tooltip
          (nk:layout-row-static ctx 30 150 1)
          (set! bounds (nk:widget-bounds ctx))
          (nk:label ctx "Hover me for tooltip" nk:text/left)
          (when (nk:input-mouse-hovering-in-rect? (nk:context-input ctx) bounds)
            (nk:tooltip ctx "This is a tooltip")))
        (nk:tree-pop ctx))

      (when (nk:tree-push ctx nk:tree/tab "Layout" nk:collapse/minimized)
        (when (nk:tree-push ctx nk:tree/node "Widget" nk:collapse/minimized)
          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "Dynamic fixed column layout with generated position and size:" nk:text/left)
          (nk:layout-row-dynamic ctx 30 3)
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")

          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "static fixed column layout with generated position and size:" nk:text/left)
          (nk:layout-row-static ctx 30 100 3)
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")

          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "Dynamic list-based custom column layout with generated position and custom size:" nk:text/left)
          (nk:layout-row ctx nk:layout/dynamic 30 '(0.2 0.6 0.2))
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")

          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "Static list-based custom column layout with generated position and custom size:" nk:text/left)
          (nk:layout-row ctx nk:layout/static 30 '(100 200 50))
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")
          (nk:button-label ctx "button")

          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "Dynamic immediate mode custom column layout with generated position and custom size:" nk:text/left)
          (nk:layout-row-begin ctx nk:layout/dynamic 30 3)
          (nk:layout-row-push ctx 0.2)
          (nk:button-label ctx "button")
          (nk:layout-row-push ctx 0.6)
          (nk:button-label ctx "button")
          (nk:layout-row-push ctx 0.2)
          (nk:button-label ctx "button")
          (nk:layout-row-end ctx)

          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "Static immediate mode custom column layout with generated position and custom size:" nk:text/left)
          (nk:layout-row-begin ctx nk:layout/static 30 3)
          (nk:layout-row-push ctx 100)
          (nk:button-label ctx "button")
          (nk:layout-row-push ctx 200)
          (nk:button-label ctx "button")
          (nk:layout-row-push ctx 50)
          (nk:button-label ctx "button")
          (nk:layout-row-end ctx)

          (nk:layout-row-dynamic ctx 30 1)
          (nk:label ctx "Static free space with custom position and custom size:" nk:text/left)
          (nk:layout-space-begin ctx nk:layout/static 120 4)
          (nk:layout-space-push ctx (nk:make-rect 100 0 100 30))
          (nk:button-label ctx "button")
          (nk:layout-space-push ctx (nk:make-rect 0 15 100 30))
          (nk:button-label ctx "button")
          (nk:layout-space-push ctx (nk:make-rect 200 15 100 30))
          (nk:button-label ctx "button")
          (nk:layout-space-push ctx (nk:make-rect 100 30 100 30))
          (nk:button-label ctx "button")
          (nk:layout-space-end ctx)
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Group" nk:collapse/minimized)
          (nk:layout-row-dynamic ctx 30 3)
          (set! group-titlebar? (nk:check-label ctx "Titlebar" group-titlebar?))
          (set! group-border? (nk:check-label ctx "Border" group-border?))
          (set! group-no-scrollbar? (nk:check-label ctx "No Scrollbar" group-no-scrollbar?))

          (nk:layout-row-begin ctx nk:layout/static 22 3)
          (nk:layout-row-push ctx 50)
          (nk:label ctx "size:" nk:text/left)
          (nk:layout-row-push ctx 130)
          (set! group-width (nk:property-int ctx "#Width:" 100 group-width 500 10 1))
          (nk:layout-row-push ctx 130)
          (set! group-height (nk:property-int ctx "#Height:" 100 group-height 500 10 1))
          (nk:layout-row-end ctx)

          (nk:layout-row-static ctx group-height group-width 2)
          (when (nk:group-begin ctx "Group" (group-flags))
            (nk:layout-row-static ctx 18 100 1)
            (set! selected-group
                  (map-in-order
                   (lambda (value)
                     (nk:selectable-label ctx (if value "Selected" "Unselected") nk:text/centered value))
                   selected-group))
            (nk:group-end ctx))
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Tree" nk:collapse/minimized)
          (let ((sel root-selected))
            (receive (open? sel) (nk:tree-element-push ctx nk:tree/node "Root" nk:collapse/minimized sel)
              (when open?
                (let ((node-select (car selected-leaves)))
                  (when (not (eqv? sel root-selected))
                    (set! root-selected sel)
                    (set! selected-leaves (make-list 8 sel)))
                  (receive (open? node-select) (nk:tree-element-push ctx nk:tree/node "Node" nk:collapse/minimized node-select)
                    (when open?
                      (when (not (eqv? node-select (car selected-leaves)))
                        (set-car! selected-leaves node-select)
                        (set! selected-nodes (make-list node-select 4)))
                      (nk:layout-row-static ctx 18 100 1)
                      (set! selected-nodes
                            (map-in-order
                             (lambda (selected-node)
                               (nk:selectable-symbol-label ctx nk:symbol/circle-solid (if selected-node "Selected" "Unselected") nk:text/right selected-node))
                             selected-nodes))
                      (nk:tree-element-pop ctx)))
                  (nk:layout-row-static ctx 18 100 1)
                  (set! selected-leaves
                        (map-in-order
                         (lambda (selected-leaf)
                           (nk:selectable-symbol-label ctx nk:symbol/circle-solid (if selected-leaf "Selected" "Unselected") nk:text/right selected-leaf))
                         selected-leaves)))
                (nk:tree-element-pop ctx))))
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Notebook" nk:collapse/minimized)
          ;; TODO
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Simple" nk:collapse/minimized)
          (nk:layout-row-dynamic ctx 300 2)
          (when (nk:group-begin ctx "Group_Without_Border" 0)
            (nk:layout-row-static ctx 18 150 1)
            (let loop ((i 0))
              (when (< i 64)
                (nk:label ctx (cl-format #f "0x~2,'0x: scrollable region" i) nk:text/left)
                (loop (add1 i))))
            (nk:group-end ctx))

          (when (nk:group-begin ctx "Group_With_Border" nk:window/border)
            (nk:layout-row-dynamic ctx 25 2)
            (let loop ((i 0))
              (when (< i 64)
                (let ((x (+ (bitwise-xor (* (modulo i 7) 10) 32)
                            64 (* (modulo i 2) 2))))
                  (nk:button-label ctx (cl-format #f "~8,'0d" x))
                (loop (add1 i)))))
            (nk:group-end ctx))
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Complex" nk:collapse/minimized)
          (nk:layout-space-begin ctx nk:layout/static 500 64)
          (nk:layout-space-push ctx (nk:make-rect 0 0 150 500))
          (when (nk:group-begin ctx "Group_left" nk:window/border)
            (nk:layout-row-static ctx 18 100 1)
            (set! left-selected-group
                  (map-in-order
                   (lambda (value)
                     (nk:selectable-label ctx (if value "Selected" "Unselected") nk:text/centered value))
                   left-selected-group))
            (nk:group-end ctx))

          (nk:layout-space-push ctx (nk:make-rect 160 0 150 240))
          (when (nk:group-begin ctx "Group_top" nk:window/border)
            (nk:layout-row-dynamic ctx 25 1)
            (nk:button-label ctx "#FFAA")
            (nk:button-label ctx "#FFBB")
            (nk:button-label ctx "#FFCC")
            (nk:button-label ctx "#FFDD")
            (nk:button-label ctx "#FFEE")
            (nk:button-label ctx "#FFFF")
            (nk:group-end ctx))

          (nk:layout-space-push ctx (nk:make-rect 160 250 150 250))
          (when (nk:group-begin ctx "Group_bottom" nk:window/border)
            (nk:layout-row-dynamic ctx 25 1)
            (nk:button-label ctx "#FFAA")
            (nk:button-label ctx "#FFBB")
            (nk:button-label ctx "#FFCC")
            (nk:button-label ctx "#FFDD")
            (nk:button-label ctx "#FFEE")
            (nk:button-label ctx "#FFFF")
            (nk:group-end ctx))

          (nk:layout-space-push ctx (nk:make-rect 320 0 150 150))
          (when (nk:group-begin ctx "Group_right_top" nk:window/border)
            (nk:layout-row-static ctx 18 100 1)
            (set! top-right-selected-group
                  (map-in-order
                   (lambda (value)
                     (nk:selectable-label ctx (if value "Selected" "Unselected") nk:text/centered value))
                   top-right-selected-group))
            (nk:group-end ctx))

          (nk:layout-space-push ctx (nk:make-rect 320 160 150 150))
          (when (nk:group-begin ctx "Group_right_center" nk:window/border)
            (nk:layout-row-static ctx 18 100 1)
            (set! center-right-selected-group
                  (map-in-order
                   (lambda (value)
                     (nk:selectable-label ctx (if value "Selected" "Unselected") nk:text/centered value))
                   center-right-selected-group))
            (nk:group-end ctx))

          (nk:layout-space-push ctx (nk:make-rect 320 320 150 150))
          (when (nk:group-begin ctx "Group_right_bottom" nk:window/border)
            (nk:layout-row-static ctx 18 100 1)
            (set! bottom-right-selected-group
                  (map-in-order
                   (lambda (value)
                     (nk:selectable-label ctx (if value "Selected" "Unselected") nk:text/centered value))
                   bottom-right-selected-group))
            (nk:group-end ctx))

          (nk:layout-space-end ctx)
          (nk:tree-pop ctx))

        (when (nk:tree-push ctx nk:tree/node "Splitter" nk:collapse/minimized)
          (let ((input (nk:context-input ctx)))
            (nk:layout-row-static ctx 20 310 1)
            (nk:label ctx "Use slider and spinner to change tile size" nk:text/left)
            (nk:label ctx "Drag the space between tiles to change tile ratio" nk:text/left)
            (when (nk:tree-push ctx nk:tree/node "Vertical" nk:collapse/minimized)
              (let ((row-layout (list vertical-a 8 vertical-b 8 vertical-c))
                    (bounds #f))
                ;; header
                (nk:layout-row-static ctx 30 100 2)
                (nk:label ctx "left:" nk:text/left)
                (set! vertical-a (nk:slider-float ctx 10 vertical-a 200 10))

                (nk:label ctx "middle:" nk:text/left)
                (set! vertical-b (nk:slider-float ctx 10 vertical-b 200 10))

                (nk:label ctx "right:" nk:text/left)
                (set! vertical-c (nk:slider-float ctx 10 vertical-c 200 10))

                ;; tiles
                (nk:layout-row ctx nk:layout/static 200 row-layout)

                ;; left space
                (when (nk:group-begin ctx "left" (->flag nk:window/border nk:window/no-scrollbar))
                  (nk:layout-row-dynamic ctx 25 1)
                  (nk:button-label ctx "#FFAA")
                  (nk:button-label ctx "#FFBB")
                  (nk:button-label ctx "#FFCC")
                  (nk:button-label ctx "#FFDD")
                  (nk:button-label ctx "#FFEE")
                  (nk:button-label ctx "#FFFF")
                  (nk:group-end ctx))

                ;; scaler
                (set! bounds (nk:widget-bounds ctx))
                (nk:spacing ctx 1)
                (when (and (or (nk:input-mouse-hovering-in-rect? input bounds)
                               (nk:input-mouse-previously-hovering-in-rect? input bounds))
                           (nk:input-mouse-down? input nk:button/left))
                  (let ((delta (nk:mouse-delta (nk:input-mouse input))))
                    (set! vertical-a (+ (car row-layout) (nk:vec2-x delta)))
                    (set! vertical-b (- (list-ref row-layout 2) (nk:vec2-x delta)))))

                ;; middle space
                (when (nk:group-begin ctx "center" (->flag nk:window/border nk:window/no-scrollbar))
                  (nk:layout-row-dynamic ctx 25 1)
                  (nk:button-label ctx "#FFAA")
                  (nk:button-label ctx "#FFBB")
                  (nk:button-label ctx "#FFCC")
                  (nk:button-label ctx "#FFDD")
                  (nk:button-label ctx "#FFEE")
                  (nk:button-label ctx "#FFFF")
                  (nk:group-end ctx))

                ;; scaler
                (set! bounds (nk:widget-bounds ctx))
                (nk:spacing ctx 1)
                (when (and (or (nk:input-mouse-hovering-in-rect? input bounds)
                               (nk:input-mouse-previously-hovering-in-rect? input bounds))
                           (nk:input-mouse-down? input nk:button/left))
                  (let ((delta (nk:vec2-x (nk:mouse-delta (nk:input-mouse input)))))
                    (set! vertical-b (+ (list-ref row-layout 2) delta))
                    (set! vertical-c (- (list-ref row-layout 4) delta))))

                ;; right space
                (when (nk:group-begin ctx "right" (->flag nk:window/border nk:window/no-scrollbar))
                  (nk:layout-row-dynamic ctx 25 1)
                  (nk:button-label ctx "#FFAA")
                  (nk:button-label ctx "#FFBB")
                  (nk:button-label ctx "#FFCC")
                  (nk:button-label ctx "#FFDD")
                  (nk:button-label ctx "#FFEE")
                  (nk:button-label ctx "#FFFF")
                  (nk:group-end ctx)))
              (nk:tree-pop ctx))

            (when (nk:tree-push ctx nk:tree/node "Horizontal" nk:collapse/minimized)
              (let ((bounds #f))
                ;; header
                (nk:layout-row-static ctx 30 100 2)
                (nk:label ctx "top:" nk:text/left)
                (set! horizontal-a (nk:slider-float ctx 10 horizontal-a 200 10))

                (nk:label ctx "middle:" nk:text/left)
                (set! horizontal-b (nk:slider-float ctx 10 horizontal-b 200 10))

                (nk:label ctx "bottom:" nk:text/left)
                (set! horizontal-c (nk:slider-float ctx 10 horizontal-c 200 10))

                ;; top space
                (nk:layout-row-dynamic ctx horizontal-a 1)
                (when (nk:group-begin ctx "top" (->flag nk:window/border nk:window/no-scrollbar))
                  (nk:layout-row-dynamic ctx 25 3)
                  (nk:button-label ctx "#FFAA")
                  (nk:button-label ctx "#FFBB")
                  (nk:button-label ctx "#FFCC")
                  (nk:button-label ctx "#FFDD")
                  (nk:button-label ctx "#FFEE")
                  (nk:button-label ctx "#FFFF")
                  (nk:group-end ctx))

                ;; scaler
                (nk:layout-row-dynamic ctx 8 1)
                (set! bounds (nk:widget-bounds ctx))
                (nk:spacing ctx 1)
                (when (and (or (nk:input-mouse-hovering-in-rect? input bounds)
                               (nk:input-mouse-previously-hovering-in-rect? input bounds))
                           (nk:input-mouse-down? input nk:button/left))
                  (let ((delta (nk:vec2-y (nk:mouse-delta (nk:input-mouse input)))))
                    (set! horizontal-a (+ horizontal-a delta))
                    (set! horizontal-b (- horizontal-b delta))))

                ;; middle space
                (nk:layout-row-dynamic ctx horizontal-b 1)
                (when (nk:group-begin ctx "middle" (->flag nk:window/border nk:window/no-scrollbar))
                  (nk:layout-row-dynamic ctx 25 3)
                  (nk:button-label ctx "#FFAA")
                  (nk:button-label ctx "#FFBB")
                  (nk:button-label ctx "#FFCC")
                  (nk:button-label ctx "#FFDD")
                  (nk:button-label ctx "#FFEE")
                  (nk:button-label ctx "#FFFF")
                  (nk:group-end ctx))

                ;; scaler
                (nk:layout-row-dynamic ctx 8 1)
                (set! bounds (nk:widget-bounds ctx))
                (when (and (or (nk:input-mouse-hovering-in-rect? input bounds)
                               (nk:input-mouse-previously-hovering-in-rect? input bounds))
                           (nk:input-mouse-down? input nk:button/left))
                  (let ((delta (nk:vec2-y (nk:mouse-delta (nk:input-mouse input)))))
                    (set! horizontal-b (+ horizontal-b delta))
                    (set! horizontal-c (- horizontal-c delta))))

                ;; bottom space
                (nk:layout-row-dynamic ctx horizontal-c 1)
                (when (nk:group-begin ctx "bottom" (->flag nk:window/border nk:window/no-scrollbar))
                  (nk:layout-row-dynamic ctx 25 3)
                  (nk:button-label ctx "#FFAA")
                  (nk:button-label ctx "#FFBB")
                  (nk:button-label ctx "#FFCC")
                  (nk:button-label ctx "#FFDD")
                  (nk:button-label ctx "#FFEE")
                  (nk:button-label ctx "#FFFF")
                  (nk:group-end ctx)))
              (nk:tree-pop ctx)))
          (nk:tree-pop ctx))
        (nk:tree-pop ctx)))
    (nk:window-end ctx)

    (let-values (((width height) (glfw:get-window-size (glfw:window))))
      (gl:viewport 0 0 width height))
    (gl:clear gl:+color-buffer-bit+)
    (gl:clear-color (nk:color-r bg) (nk:color-g bg) (nk:color-b bg) (nk:color-a bg))
    (nk:render nk:anti-aliasing/on)
    (glfw:swap-buffers (glfw:window))
    (loop)))

(nk:shutdown)
(glfw:terminate)