(module downstroke/entity
    *
  (import scheme
	  (chicken base)
	  (chicken keyword)
	  (only srfi-1 fold))

  ;; Entities = plists with shared keys (#:type, #:x, #:y, #:width, #:height, ...).

  (define (entity-ref entity key #!optional default)
    (get-keyword key entity (if (procedure? default) default (lambda () default))))

  (define (entity-type entity)
    (entity-ref entity #:type #f))

  (define (entity-set entity key val)
    (let ((cleaned (let loop ((lst entity) (acc '()))
                     (if (null? lst)
                         (reverse acc)
                         (let ((k (car lst))
                               (v (cadr lst)))
                           (if (eq? k key)
                               (loop (cddr lst) acc)
                               (loop (cddr lst) (cons v (cons k acc)))))))))
      (cons key (cons val cleaned))))

  (define (entity-update entity key proc #!optional default)
    (entity-set entity key (proc (entity-ref entity key default))))

  (define (make-player-entity x y width height)
    (list #:type 'player
	  #:x x
	  #:y y
	  #:width width
	  #:height height
	  #:vx 0
	  #:vy 0
	  #:gravity? #t
	  #:on-ground? #f
	  #:tile-id 29
	  #:input-map '((left  . (-2 .  0))
	                (right . ( 2 .  0))
	                (down  . ( 0 .  2)))))
)