#!/usr/bin/env python3

import serial
import json
import re

class Usv(object):
    def __init__(self, device, baudrate, json_file):
        self._serial_port = serial.Serial(device,
                baudrate=baudrate,
                timeout=10)

        # force a clean prompt
        self._serial_port.write(b"\r")
        self._read_until_prompt()
        #print("cleaned prompt")
        with open(json_file) as fhandle:
            self.json_params = json.load(fhandle)


    def _read_until_prompt(self):
        # match on "\n=>"
        prompt = False
        inbuf = []
        while not prompt:
            inbuf.append(self._serial_port.read(1))
            if len(inbuf) > 2:
                if inbuf[-3] == b"\n" and \
                        inbuf[-2] == b"=" and inbuf[-1] == b">":
                    prompt = True
        return inbuf
    
    def get_parameters(self):
        # [{'name': 'acvoltsin', 'index': 1}, 
        results = {}

        for parameter in self.json_params:
            outbuf = "d %s\r" % parameter['num']
            self._serial_port.write(outbuf.encode())
            inbuf = self._read_until_prompt()
            
            sbuf = ""
            for char in inbuf:
                sbuf += char.decode("utf-8")
            #print("-->%s<--" % sbuf)

            regex = parameter['regex']
            match = re.search(regex, sbuf, re.MULTILINE)
            
            if match:
                name = parameter['name']
                value = float(match.group(1))

                results.setdefault(name, value)
                #print("MATCH: %s: %f" % (name,value))

        return results
          


if __name__ == "__main__":
    import pprint

    usv = Usv("/dev/ttyU0", 600, "usv_param.json")
    parameters = usv.get_parameters()
    pprint.pprint(parameters)