;; Inset blend - fade a smaller frame into a larger background
;; Uses distance-based alpha for smooth transition (no hard edges)

(require-primitives "xector")

(define-effect xector_inset_blend
  :params (
    (x :type int :default 0 :desc "X position of inset")
    (y :type int :default 0 :desc "Y position of inset")
    (fade-width :type int :default 50 :desc "Width of fade region in pixels")
    (overlay :type frame :default nil :desc "The smaller frame to inset")
  )
  (let* (
         ;; Get dimensions
         (bg-h (first (list (nth (list (red frame)) 0))))  ;; TODO: need image:height
         (bg-w bg-h)  ;; placeholder

         ;; For now, create a simple centered circular blend
         ;; Distance from center of overlay position
         (cx (+ x (/ (- bg-w (* 2 x)) 2)))
         (cy (+ y (/ (- bg-h (* 2 y)) 2)))

         ;; Get coordinates as xectors
         (px (x-coords frame))
         (py (y-coords frame))

         ;; Distance from center
         (dx (α- px cx))
         (dy (α- py cy))
         (dist (αsqrt (α+ (α* dx dx) (α* dy dy))))

         ;; Inner radius (fully overlay) and outer radius (fully background)
         (inner-r (- (/ bg-w 2) x fade-width))
         (outer-r (- (/ bg-w 2) x))

         ;; Blend factor: 1.0 inside inner-r, 0.0 outside outer-r, linear between
         (t (α/ (α- dist inner-r) fade-width))
         (blend (α- 1 (αclamp t 0 1)))

         ;; Extract channels from both frames
         (bg-r (red frame))
         (bg-g (green frame))
         (bg-b (blue frame)))

    ;; If overlay provided, blend it
    (if overlay
        (let* ((ov-r (red overlay))
               (ov-g (green overlay))
               (ov-b (blue overlay))
               ;; Linear blend: result = bg * (1-blend) + overlay * blend
               (r-out (α+ (α* bg-r (α- 1 blend)) (α* ov-r blend)))
               (g-out (α+ (α* bg-g (α- 1 blend)) (α* ov-g blend)))
               (b-out (α+ (α* bg-b (α- 1 blend)) (α* ov-b blend))))
          (rgb r-out g-out b-out))
        ;; No overlay - just show the blend mask for debugging
        (let ((mask-vis (α* blend 255)))
          (rgb mask-vis mask-vis mask-vis)))))