#lang r7rs

(#%require (only racket/base random))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;                                Key ADT                                    ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; The key is placed at a random coin position in the maze. When Pac-Man
;; picks it up, doors can be opened. Contains NO graphics code.

(define-library (pacman-project adt key)
  (import (scheme base)
          (pacman-project constants)
          (pacman-project adt position))
  (export make-key)

  (begin

    ;; make-key :: maze -> key
    ;; Creates a key and places it at a random coin position.
    (define (make-key maze)
      (let ((position #f)
            (taken? #f))

        ;; place-random! :: -> /
        ;; Places the key on a random cell that contains a coin.
        (define (place-random!)
          (let loop ((attempts 0))
            (if (>= attempts max-placement-attempts)
                (error "No valid position found for key")
                (let ((col (random 0 (maze 'cols)))
                      (row (random 0 (maze 'rows))))
                  (if ((maze 'coin?) row col)
                      (begin
                        (set! position (make-position row col))
                        ((maze 'cell-set!) row col cell-type-key))
                      (loop (+ attempts 1)))))))

        ;; take! :: -> /
        ;; Marks the key as taken.
        (define (take!)
          (set! taken? #t))

        ;; Initialization: place the key immediately on creation.
        (place-random!)

        ;; dispatch-key :: symbol -> any
        (define (dispatch-key msg)
          (cond ((eq? msg 'position) position)
                ((eq? msg 'taken?) taken?)
                ((eq? msg 'take!) take!)
                (else (error "Key ADT -- Unknown message:" msg))))

        dispatch-key))))