;; Blend effect - combines two video streams
;; Multi-input effect: uses frame-a and frame-b
;; Params:
;;   mode - blend mode (add, multiply, screen, overlay, difference, lighten, darken, alpha)
;;   opacity - blend amount (0-1)
;;   resize-mode - how to resize frame-b to match frame-a (fit, crop, stretch)
;;   priority - which dimension takes priority (width, height)
;;   pad-color - color for padding in fit mode [r g b]

(define-effect blend
  :params (
    (mode :type string :default "overlay")
    (opacity :type float :default 0.5)
    (priority :type string :default "width")
    (list :type string :default 0 0 0)
  )
  )
  (let [a frame-a
        a-w (width a)
        a-h (height a)
        b-raw frame-b
        b-w (width b-raw)
        b-h (height b-raw)
        ;; Calculate scale based on resize mode and priority
        scale-w (/ a-w b-w)
        scale-h (/ a-h b-h)
        scale (if (= resize-mode "stretch")
                1  ;; Will use explicit dimensions
                (if (= resize-mode "crop")
                  (max scale-w scale-h)  ;; Scale to cover, then crop
                  (if (= priority "width")
                    scale-w
                    scale-h)))
        ;; For stretch, use target dimensions directly
        new-w (if (= resize-mode "stretch") a-w (round (* b-w scale)))
        new-h (if (= resize-mode "stretch") a-h (round (* b-h scale)))
        ;; Resize b
        b-resized (resize b-raw new-w new-h "linear")
        ;; Handle fit (pad) or crop to exact size
        b (if (= resize-mode "crop")
            ;; Crop to center
            (let [cx (/ (- new-w a-w) 2)
                  cy (/ (- new-h a-h) 2)]
              (crop b-resized cx cy a-w a-h))
            (if (and (= resize-mode "fit") (or (!= new-w a-w) (!= new-h a-h)))
              ;; Pad to center
              (let [pad-x (/ (- a-w new-w) 2)
                    pad-y (/ (- a-h new-h) 2)
                    canvas (make-image a-w a-h pad-color)]
                (paste canvas b-resized pad-x pad-y))
              b-resized))]
    (if (= mode "alpha")
      (blend-images a b opacity)
      (blend-images a (blend-mode a b mode) opacity)))