;;;
;;; RULE
;;;
;;; (make-rule prereqs wants-build? build-func) ---> rule
;;;
;;; prereqs: '(#{:rule} ...)
;;; wants-build?: (lambda (res-p0 res-p1 ... res-pN init-state) body ...)
;;;               res-pX: result of prerequisite-rule no. X
;;;   (wants-build? res-p0 ... res-pN init-state) 
;;;      ---> (res-wants-build? . cooked-state)
;;; build-func: 
;;;   (lambda (res-wants-build? res-p0 ... res-pN cooked-state) 
;;;      ---> (res-build-func . end-state)
;;;
(define-record-type :rule
  (make-rule prereqs wants-build? build-func)
  is-rule?
  (prereqs rule-prereqs)
  (wants-build? rule-wants-build?)
  (build-func rule-build-func))

;;;
;;; RULE-SET
;;;
;;; (make-empty-rule-set) ---> rule-set
;;; (rule-set-add rule rule-set) ---> rule-set
;;;
(define-record-type :rule-set
  (make-rule-set rules)
  is-rule-set?
  (rules rule-set-rules))

(define (make-empty-rule-set) 
  (make-rule-set '()))

(define (rule-set-add rule rule-set)
  (let ((listen-ch (collect&reply/make-channel)))
    (if (not (assq rule (rule-set-rules rule-set)))
	(make-rule-set (alist-cons rule listen-ch (rule-set-rules rule-set)))
	(error "make-rule: rule already exists."))))

(define (rule-set-get-listen-ch rule rule-set)
  (let ((maybe-rule (assoc rule (rule-set-rules rule-set))))
    (if (and maybe-rule 
	     (pair? maybe-rule) 
	     (is-collect&reply-channel? (cdr maybe-rule)))
	(cdr maybe-rule)
	(error "rule not found in rule-set."))))

;;;
;;; RULE-RESULT
;;; 
;;; (rule-result-wants-build? rule-result) --->  
;;;    (wants-build?-result . cooked-state) oder (#f . cooked-state) 
;;; 
;;; (rule-result-build-func rule-result) --->  
;;;    (build-func-result . end-state) oder #f 
;;; 
;;; (rule-make rule init-state rule-set) ---> rule-result 
;;; 
(define-record-type :rule-result
  (make-rule-result wants-build?-result build-func-result)
  is-rule-result?
  (wants-build?-result rule-result-wants-build?)
  (build-func-result rule-result-build-func))

(define (rule-make rule init-state rule-set)
  ;;
  ;; this could be rewritten in future
  ;; 
  ;; check for unused threads -> dont start them
  ;;
  (map (lambda (r) 
	 (rule-node r (rule-set-get-listen-ch r rule-set) init-state rule-set))
       (map car (rule-set-rules rule-set)))
  (let* ((server (rule-set-get-listen-ch rule rule-set))
	 (client (send&collect/make-channel))
	 (recipient (make-link client server)))
    (send&collect/send client (make-tagged-msg recipient (rule-cmd make)))
    (tagged-msg-stripped (send&collect/receive client))))

(define-enumerated-type rule-cmd :rule-cmd
  is-rule-cmd?
  the-rule-cmds
  rule-cmd-name
  rule-cmd-index
  (make link shutdown))

(define (position< maybe-lesser maybe-greater objects)
  (if (null? objects) 
      (error "position< has empty objects-list.")
      (let search-objects ((current (car objects))
			   (todo (cdr objects)))
	(cond
	 ((= (tagged-msg-tag maybe-lesser) current) #t)
	 ((= (tagged-msg-tag maybe-greater) current) #f)
	 ((null? todo) 
	  (error "position< maybe-lesser or maybe-greater not found."))
	 (else (search-objects (car todo) (cdr todo)))))))

(define (rule-node/sort-msgs unsorted to-order)
  (map tagged-msg-stripped
       (sort (lambda (maybe-lesser maybe-greater) 
	       (position< maybe-lesser maybe-greater to-order))
	     unsorted (list))))

(define (rule-node/prereqs-results rule connect-ch recipients)
  (let ((unsorted-msgs (map (lambda (recipient) 
			      (let ((tmsg (make-tagged-msg recipient
							   (rule-cmd make))))
				(send&collect/send connect-ch tmsg)
				(send&collect/receive connect-ch)))
			    recipients)))
    (rule-node/sort-msgs unsorted-msgs recipients)))

(define (rule-node/make rule listen-ch connect-ch recipients init-state)
  (let ((prereqs-results (rule-node/prereqs-results rule connect-ch recipients)))
    (let ((wants-build?-result (if (null? prereqs-results)
				   ((rule-wants-build? rule) init-state)
				   (apply (rule-wants-build? rule)
					  (append prereqs-results 
						  (list init-state))))))
      (let ((build-required? (car wants-build?-result))
	    (cooked-state (cdr wants-build?-result)))
	(if build-required? 
	    (let* ((build-func (rule-build-func rule))
		   (build-func-result (if (null? prereqs-results)
					  (build-func build-required? cooked-state)
					  (apply build-func
						 (append (list build-required?)
							 prereqs-results 
							 (list cooked-state)))))
		   (end-state (cdr build-func-result)))
	      (make-rule-result wants-build?-result build-func-result))
	    (make-rule-result wants-build?-result #f))))))

(define (rule-node/make-links rule connect-ch rule-set)
  (let ((listen-chs (map (lambda (r) 
                           (cdr (assq r (rule-set-rules rule-set))))
                         (rule-prereqs rule))))
    (map (lambda (listen-ch)
           (make-link connect-ch listen-ch))
         listen-chs)))

(define (rule-node rule listen-ch init-state rule-set)
  (let ((connect-ch (send&collect/make-channel)))
    (spawn
      (lambda () 
	;; 
	;; wait for anything on the listen-ch
	;; check if it is a known command
	;; if so: process this command
	;; otherwise it was noise
	;; 
	;; if its the first time the make command drops in
	;; initially make the connections to every prereq-listen-ch
	;; 
	(let node-loop ((tmsg (collect&reply/receive listen-ch))
			(maybe-recipients #f))
	  (let ((sender (tagged-msg-tag tmsg))
		(cmd (tagged-msg-stripped tmsg)))
	    (cond
	     ((eq? (rule-cmd-name cmd) 'make)
	      (if (not maybe-recipients) 
		  (set! maybe-recipients 
			(rule-node/make-links rule connect-ch rule-set)))
	      (let ((res (rule-node/make rule listen-ch connect-ch 
					 maybe-recipients init-state)))
		(collect&reply/send listen-ch (make-tagged-msg sender res))))
	     ((eq? (rule-cmd-name cmd) 'shutdown) (terminate-current-thread))))
	  (node-loop (collect&reply/receive listen-ch) maybe-recipients)))
      'rule-node)))