Print simple text or pizzas array

scontrini.rkt

@@ -0,0 +1,53 @@
+#lang racket
+
+(require racket/tcp)
+(require json)
+
+(define serial-port-device "/dev/ttyUSB0")
+(define port 4444)
+(define hostname "127.0.0.1")
+
+; Print the to-print string on the printer
+; TODO add synchronization to avoid race conditions
+(define (printer-print to-print)
+	(let ((file (open-output-file serial-port-device #:exists 'append)))
+		(display (string-replace to-print "\n" "\n\n") file) ; always add an extra newline because the printer is a little messed up
+		(close-output-port file)))
+
+; Format the pizzas array from the JSON in a human-readable way
+(define (format-pizza pizzas-list)
+	(let ((str ""))
+		(for-each (lambda (pizza-hashmap)
+			(set! str (string-append str (format "~a : ~s\n" (hash-ref pizza-hashmap 'quantity) (hash-ref pizza-hashmap 'name)))))
+			pizzas-list)
+		str))
+
+; Parse the commands given in the JSON
+(define (parse-json message)
+  	(let ((parsed-json (with-input-from-string message (lambda () (read-json))))) ; parse the JSON
+		(case (hash-ref parsed-json 'command)
+			(("print") (printer-print (hash-ref parsed-json 'text)))
+			(("pizza") (printer-print (format-pizza (hash-ref parsed-json 'pizzas)))))))
+
+; Receive the JSON message and execute the specified command
+(define (get-message input)
+	(let ((message ""))
+		(let loop-until-eof ((str (read-string 1 input)))
+			(if (eof-object? str)
+				(begin
+					(close-input-port input)
+					(parse-json message))
+				(begin
+					(set! message (string-append message str))
+					(loop-until-eof (read-string 1 input)))))))
+
+; Wait on a port and spawn new threads on each connection
+(define (wait-for-connection)
+  	(let ((listener (tcp-listen port 4 #t hostname)))
+	  	(let infinite-loop ()
+			(let-values (((input output) (tcp-accept listener)))
+				(close-output-port output) ; we don't need it
+				(thread (lambda () (get-message input)))
+				(infinite-loop)))))
+
+(wait-for-connection)