personalization: add get_typical_input_len() to ConfigurableParameter

The aim is to tell a user interface how wide an input text field should
be chosen to be convenient -- ideally showing the entire value in all
cases, but not too huge for fields that have no sane size limit.

Change-Id: I2568a032167a10517d4d75d8076a747be6e21890

pySim/esim/saip/personalization.py

@@ -250,6 +250,13 @@ class ConfigurableParameter(abc.ABC, metaclass=ClassVarMeta):
             return (None, None)
         return (min(vals), max(vals))
 
+    @classmethod
+    def get_typical_input_len(cls):
+        '''return a good length to use as the visible width of a user interface input field.
+           May be overridden by subclasses.
+           This default implementation returns the maximum allowed value length -- a good fit for most subclasses.
+           '''
+        return cls.get_len_range()[1] or 16
 
 class DecimalParam(ConfigurableParameter):
     """Decimal digits. The input value may be a string of decimal digits like '012345', or an int. The output of
@@ -352,6 +359,16 @@ class BinaryParam(ConfigurableParameter):
         val = super().validate_val(val)
         return bytes(val)
 
+    @classmethod
+    def get_typical_input_len(cls):
+        # override to return twice the length, because of hex digits.
+        min_len, max_len = cls.get_len_range()
+        if max_len is None:
+            return None
+        # two hex characters per value octet.
+        # (maybe *3 to also allow for spaces?)
+        return max_len * 2
+
 
 class EnumParam(ConfigurableParameter):
     value_map = {