#lang racket/base
(require racket/list
         (planet lizorkin/sxml:2:1/sxml)
         (planet lizorkin/ssax:2:0/ssax)
         "layer2.rkt")

(define definition
  (ssax:xml->sxml (open-input-file "../ebus-xml/ebus.xml")
                  '[(#f . "http://xapek.org/ebus/0.1")]))


(define (paket ebus-paket)
  (define primaryCommand (layer2-ebus-paket-primaryCommand ebus-paket))
  (define secondaryCommand (layer2-ebus-paket-secondaryCommand ebus-paket))
  ((sxpath (string-append "//packet[@primary=" (number->string primaryCommand)
			  " and @secondary=" (number->string secondaryCommand) "]"))
   definition))

;; returns the full device-definition
(define (device address)
  ((sxpath (string-append "//devices/device[@address=" (number->string address) "]"))
   definition))

;; returns device-name in a list or empty-list
(define (device-name address)
  ((sxpath "@name/text()") (device address)))


(define (paket-fields ebus-paket)
  (define paket-definition (paket ebus-paket))
  (cond ((> (length paket-definition) 0)
	 (let* 
	     ([paket-name (first ((sxpath "@name/text()") paket-definition))]
	      [fields ((sxpath "fields/*") paket-definition)]
	      [values 
	       (for/list ([field fields]) (paket-fields-dispatch-decoder ebus-paket field paket-name))])
	   ;; filter invalid values
	   (for/list ([value values] #:when (not (void? value)))
		     value)))
	(else (display (format "Unknown Paket: ~s~n" ebus-paket))
	      (void))))

(define (paket-fields-dispatch-decoder ebus-paket field paket-name)
  (define datatype ((sxpath "name()") field))
  (define name (string-append paket-name "." (first ((sxpath "@name/text()") field))))
  (define offset (string->number (first ((sxpath "@offset/text()") field))))
  (define payload (layer2-ebus-paket-payload ebus-paket))
  (cond ((string=? "bit" datatype)
	 (list name datatype offset
	       (field-decoder-bit (list-ref payload offset))))
	((string=? "bcd" datatype)
	 (list name datatype offset
	       (field-decoder-bcd (list-ref payload offset))))
	((string=? "data1b" datatype)
	 (list name datatype offset
	       (field-decoder-data1b (list-ref payload offset))))
	((string=? "data1c" datatype)
	 (list name datatype offset
	       (field-decoder-data1c (list-ref (layer2-ebus-paket-payload ebus-paket) offset))))
	((string=? "byte" datatype)
	 (list name datatype offset (list-ref payload offset)))
	((string=? "data2b" datatype)
	 (list name datatype offset
	       (field-decoder-data2b (list-ref payload offset)
				     (list-ref payload (+ offset 1)))))
	((string=? "data2c" datatype)
	 (list name datatype offset
	       (field-decoder-data2c (list-ref payload offset)
				     (list-ref payload (+ offset 1)))))
	((string=? "word" datatype)
	 (list name datatype offset
	       (field-decoder-word (list-ref payload offset)
				   (list-ref payload (+ offset 1)))))
	((string=? "byteEnum" datatype)
	 (list name datatype offset
	       (field-decoder-byteEnum (list-ref payload offset) field)))
	(else (display (string-append "unknown datatype: " datatype "\n"))
	      (void))))

;; type bit
(define (field-decoder-bit value)
  (cond ((= value 1) 1)
        (else 0)))

;; type data1b
(define (field-decoder-data1b value)
  value)

;; type data1c
(define (field-decoder-data1c value)
  (/ value 2.0))

;; type data2b
(define (field-decoder-data2b lowByte highByte)
  (if (= (bitwise-and highByte 128) 128)
      (* -1 
	 (+ (+ 256 (bitwise-not highByte))
	    (/ (+ 256 (bitwise-not (+ lowByte 1))) 256.0)))
      (+ highByte (/ lowByte 256.0))))

;; type data2c
(define (field-decoder-data2c lowByte highByte)
  (define (lowNibble v)
    (bitwise-and v #x0f))
  (define (highNibble v)
    (arithmetic-shift v -4))
  (define (u-not v)
    (+ 256 (bitwise-not v)))
  (if (= (bitwise-and highByte 128) 128)
      (* -1
	 (+ (* 16 (u-not highByte))
	    (highNibble (u-not lowByte))
	    (/ (lowNibble (u-not lowByte) 16))))
      (+ (* 16 (u-not highByte))
	 (highNibble lowByte)
	 (/ (lowNibble lowByte) 16))))

;; type byteEnum
(define (field-decoder-byteEnum value field-definition)
  (define (pred l)
    (= value (list-ref l 0)))
  (define all-options (for/list ([option ((sxpath "option") field-definition)])
				(list (string->number (first ((sxpath "@value/text()") option))) ;; value, name
				      (first ((sxpath "@name/text()") option)))))
  (define options (filter pred all-options))
  (cond ((= (length options) 1)
	 (list-ref (first options) 1))
	(else "<undefined>")))

;; type word
(define (field-decoder-word lowByte highByte)
  (+ lowByte
     (arithmetic-shift highByte 8)))

;; type bcd
(define (field-decoder-bcd value)
  (+ (bitwise-and value #x0f)
     (arithmetic-shift value -4)))
  
;; read one ebus-paket or eof from input-port
;; or return #<eof>
(define (read-ebus input-port)
  (define paket (layer2-read-ebus input-port))
  (cond ((layer2-ebus-paket? paket)
	 (paket-fields paket))
	(else paket)))

(provide (prefix-out layer7- paket)
         (prefix-out layer7- paket-fields)
         (prefix-out layer7- device)
         (prefix-out layer7- device-name)
	 ;; read ebus from port an return fields from next paket
	 (prefix-out layer7- read-ebus))