(in-package #:cl-tty.container)

(defclass scroll-box (dirty-mixin)
  ((children :initform nil :initarg :children
             :accessor scroll-box-children :type list)
   (scroll-y :initform 0 :initarg :scroll-y
             :accessor scroll-box-scroll-y :type fixnum)
   (scroll-x :initform 0 :initarg :scroll-x
             :accessor scroll-box-scroll-x :type fixnum)
   (sticky-scroll-p :initform t :initarg :sticky-scroll-p
                    :accessor sticky-scroll-p :type boolean)
   (layout-node :initform (make-layout-node) :accessor scroll-box-layout-node)))

(defun make-scroll-box (&key (children nil) (scroll-y 0) (scroll-x 0)
                          sticky-scroll-p)
  (make-instance 'scroll-box
    :children children
    :scroll-y scroll-y
    :scroll-x scroll-x
    :sticky-scroll-p (if (null sticky-scroll-p) t sticky-scroll-p)))

(defmethod component-children ((sb scroll-box))
  (scroll-box-children sb))

(defmethod component-layout-node ((sb scroll-box))
  (scroll-box-layout-node sb))

(defun clamp-scroll (sb)
  "Clamp scroll offsets to valid range."
  (let* ((ln (scroll-box-layout-node sb))
         (viewport-height (if ln (layout-node-height ln) 0))
         (viewport-width  (if ln (layout-node-width ln) 0))
         (content-height (scroll-box-content-height sb))
         (content-width  (scroll-box-content-width sb)))
    (setf (scroll-box-scroll-y sb)
          (max 0 (min (scroll-box-scroll-y sb)
                      (- content-height viewport-height))))
    (setf (scroll-box-scroll-x sb)
          (max 0 (min (scroll-box-scroll-x sb)
                      (- content-width viewport-width))))))

(defun scroll-by (sb dy dx)
  "Scroll by DY rows and DX columns. Clamps to valid range."
  (incf (scroll-box-scroll-y sb) dy)
  (incf (scroll-box-scroll-x sb) dx)
  (clamp-scroll sb)
  (mark-dirty sb))

(defun scroll-box-content-height (sb)
  "Total height of all children."
  (reduce #'+ (scroll-box-children sb)
          :key (lambda (c)
                 (let ((ln (component-layout-node c)))
                   (if ln (max 1 (layout-node-height ln)) 1)))
          :initial-value 0))

(defun scroll-box-content-width (sb)
  "Maximum width among children."
  (reduce #'max (scroll-box-children sb)
          :key (lambda (c)
                 (let ((ln (component-layout-node c)))
                   (if ln (max 1 (layout-node-width ln)) 1)))
          :initial-value 0))

(defmethod render ((sb scroll-box) backend)
  "Render visible children with scroll offset applied.
Delegates to each child's `render` method, temporarily offsetting
its layout-node position for the scroll offset. Children outside
the viewport are clipped out."
  (let* ((ln (scroll-box-layout-node sb))
         (vx 0) (vy 0)
         (vw (if ln (layout-node-width ln) 80))
         (vh (if ln (layout-node-height ln) 24))
         (sy (scroll-box-scroll-y sb))
         (sx (scroll-box-scroll-x sb)))
    (dolist (child (scroll-box-children sb))
      (let* ((cln (component-layout-node child))
             (ch (if cln (layout-node-height cln) 1))
             (cy vy))
        ;; Only render children that are visible in the viewport
        (when (and (< (- cy sy) vh)
                   (> (+ (- cy sy) ch) 0))
          ;; Temporarily offset child's layout-node position for rendering
          (let ((orig-x (if cln (layout-node-x cln) 0))
                (orig-y (if cln (layout-node-y cln) 0)))
            (when cln
              (setf (layout-node-x cln) (- vx sx)
                    (layout-node-y cln) (- vy sy)))
            (unwind-protect
                 (render child backend)
              (when cln
                (setf (layout-node-x cln) orig-x
                      (layout-node-y cln) orig-y)))))
        (incf vy ch)))
    (draw-scrollbars sb backend vw vh)))

(defun update-sticky-scroll (sb)
  "If sticky-scroll-p is active and at bottom, keep at bottom."
  (when (sticky-scroll-p sb)
    (let* ((content-h (scroll-box-content-height sb))
           (ln (scroll-box-layout-node sb))
           (viewport-h (if ln (layout-node-height ln) 24)))
      (when (>= (scroll-box-scroll-y sb) (- content-h viewport-h 1))
        (setf (scroll-box-scroll-y sb)
              (max 0 (- content-h viewport-h)))))))

(defun scrollbar-thumb (scroll-pos viewport-size content-size)
  "Return the thumb position for a scrollbar (0.0 to 1.0)."
  (if (> content-size viewport-size)
      (/ (float scroll-pos) (- content-size viewport-size))
      0.0))

(defun draw-scrollbars (sb backend viewport-w viewport-h)
  "Draw scrollbars if content exceeds viewport."
  (let* ((content-h (scroll-box-content-height sb))
         (content-w (scroll-box-content-width sb))
         (sy (scroll-box-scroll-y sb))
         (sx (scroll-box-scroll-x sb))
         (ln (scroll-box-layout-node sb))
         (ox (if ln (layout-node-x ln) 0))
         (oy (if ln (layout-node-y ln) 0)))
    ;; Vertical scrollbar
    (when (> content-h viewport-h)
      (let* ((thumb (scrollbar-thumb sy viewport-h content-h))
             (thumb-pos (round (* thumb viewport-h))))
        (draw-rect backend (+ ox (1- viewport-w)) oy 1 viewport-h :bg :scrollbar-bg)
        (draw-text backend (+ ox (1- viewport-w)) (+ oy thumb-pos) "█" nil nil)))
    ;; Horizontal scrollbar
    (when (> content-w viewport-w)
      (let* ((thumb (scrollbar-thumb sx viewport-w content-w))
             (thumb-pos (round (* thumb viewport-w))))
        (draw-rect backend ox (+ oy (1- viewport-h)) viewport-w 1 :bg :scrollbar-bg)
        (draw-text backend (+ ox thumb-pos) (+ oy (1- viewport-h)) "█" nil nil)))))