#lang racket/base
(require 
 racket/bool
 racket/function
 xml
 xexpr-path
 "layer2.rkt")

(define logger (make-logger 'ebus-layer7 (current-logger)))

(define definition
 (parameterize ([collapse-whitespace #t]
                [xexpr-drop-empty-attributes #t])
  (xml->xexpr (document-element (read-xml (open-input-file "../ebus-xml/ebus.xml"))))))

(define (paket ebus-paket)
  (define primaryCommand (number->string (layer2-ebus-paket-primaryCommand ebus-paket)))
  (define secondaryCommand (number->string (layer2-ebus-paket-secondaryCommand ebus-paket)))
  (xexpr-path-first (list 'packets 'packet (list 'primary primaryCommand)
                                           (list 'secondary secondaryCommand)) definition))

(define (paket-name xexpr)
    (xexpr-path-first '((name)) xexpr))

(define (paket-fields paket-definition)
    (filter 
     (lambda (i) (and (pair? i) (member (car i) '(bit bcd data1b data1c byte data2b data2c word byteEnum))))
     (xexpr-path-list '(fields *) paket-definition)))

;; returns the full device-definition
(define (device address)
  (xexpr-path-first (list 'devices 'device (list 'address (number->string address))) definition))

;; returns device-name in a list or empty-list
(define (device-name address)
  (xexpr-path-first (list 'devices 'device (list 'address (number->string address)) '(name)) definition))

(define (paket-parse ebus-paket)
  (define paket-definition (paket ebus-paket))
  (define source-device-name (device-name (layer2-ebus-paket-source ebus-paket)))
  (cond ((and (not (false? paket-definition)) (not (false? source-device-name)))
         (define paket-id (string-append source-device-name "." (paket-name paket-definition)))
         (define decoders (map (lambda (field) (create-decoder paket-id field)) (paket-fields paket-definition)))
         (define payload (layer2-ebus-paket-payload ebus-paket))
         (for/list ([decoder decoders])
          (decoder payload)))
   (else (void (log-message logger 'warning 
                (format "Unknown Paket from source ~s: ~s" (layer2-ebus-paket-source ebus-paket) ebus-paket) #t)))))


(define (create-decoder paket-id field)
  (define type (car field))
  (define name (string-append paket-id "." (xexpr-path-first '((name)) field)))
  (define offset (string->number (xexpr-path-first '((offset)) field)))
  (define decoder (hash-ref decoder-table type #f))
  (cond ((false? decoder) (void (log-message logger 'warning (format "No decoder for type ~s" type))))
   (else (curry (car decoder) name field offset))))

(define decoder-table
 (make-hash (list
             (list 'bit (lambda (name field offset payload)
                         (list name 'bit (field-decoder-bit (list-ref payload offset)))))
             (list 'bcd (lambda (name field offset payload)
                         (list name 'bcd (field-decoder-bcd (list-ref payload offset)))))
             (list 'data1b (lambda (name field offset payload)
                            (list name 'data1b (field-decoder-data1b (list-ref payload offset)))))
             (list 'data1c (lambda (name field offset payload)
                            (list name 'data1b (field-decoder-data1c (list-ref payload offset)))))
             (list 'byte (lambda (name field offset payload)
                          (list name 'byte offset (list-ref payload offset))))
             (list 'data2b (lambda (name field offset payload)
                            (list name 'data2b (field-decoder-data2b 
                                                       (list-ref payload offset)
                                                       (list-ref payload (+ offset 1))))))
             (list 'data2c (lambda (name field offset payload)
              (list name 'data2c offset 
               (field-decoder-data2c (list-ref payload offset) (list-ref payload (+ offset 1))))))
            (list 'word (lambda (name field offset payload)
                         (list name 'word (field-decoder-word (list-ref payload offset) (list-ref payload (+ offset 1))))))
            (list 'byteEnum (lambda (name field offset payload)
                         (list name 'byteEnum (field-decoder-byteEnum (list-ref payload offset) field))))
            )))

;; 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
 ;;    Beispiel für die Berechnung:
 ;;    if ((x & 8000h) == 8000h) // y negativ
 ;;    y = - [dez(High_Byte(!x)) 16 + dez(High_Nibble (Low_Byte (!x)))
 ;;    + (dez(Low_Nibble (Low_Byte (!x))) +1 ) / 16]
 ;;    else                       // y positiv
 ;;    y = dez(High_Byte(x)) 16 + dez(High_ Nibble (Low Byte (x)))
 ;;    + dez(Low_ Nibble (Low Byte (x))) / 16
(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
	  (+ (arithmetic-shift (u-not highByte) 4)
	     (highNibble (u-not lowByte))
             (/ (+ (lowNibble (u-not lowByte)) 1)
                16.0)))
      (+ (arithmetic-shift highByte 4)
         (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 (xexpr-path-list '(option) field-definition)])
				(list (string->number (xexpr-path-first '((value)) option)) ;; '(value name)
				      (xexpr-path-first '((name)) option))))
  (define options (filter pred all-options))
  (cond ((= (length options) 1)
	 (list-ref (car options) 1))
	(else (format "<undefined:~a>" value))))

;; 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-parse paket))
	(else paket)))

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