ros2namesgrako

#! /usr/bin/env python

# PoC Ros2Names parsing using EBNF and Grako (install from pypi)
# Tested with grako 3.14.0
#


import grako

POSITIVES = "foo", "abc123", "_foo", "Foo", "BAR", "~", "foo/bar", "~/foo", "{foo}_bar", "foo/{ping}/bar", "foo/_/bar", "rosservice:///foo", "rostopic://foo/bar"
NEGATIVES =  "123abc", "123", "__foo", "foo__bar", "foo bar", "foo__", "foo_", "foo//bar", "foo/", "~foo", "foo~", "foo~/bar", "foo/~bar", "/_/bar", "_", "_/_bar", "/~", "foo/~/bar", "{", "}", "}{"

TODO = "foo{x1}bar{x2}baz", "foo_/bar"



## Short EBNF Grako introduction
# [] optional element
# {} repetition
# (* *) comment
# | alternative  (order matters, first are tried first)
# '' token
# / / regex?
grammar = """

uriname
    =
    [ urischeme ] pathname $
    ;

urischeme
    =
    namecharp '://'
    ;

pathname
    =
    ['/' | '~/'] startpathsegment '/' { pathsegment '/' } endpathsegment
    |
    ['/' | '~/'] singlename
    |
    '~'
    ;

(* must not start with digit *)
startpathsegment
    =
    /[_A-Za-z][_A-Za-z0-9]+/
    |
    /[_A-Za-z][_A-Za-z0-9]*/ '{' namecharx '}' namecharx
    ;

pathsegment
    =
    namecharp
    |
    namecharx '{' namecharx '}' namecharx
    ;

(* must not finish with _ *)
endpathsegment
    =
    /[_A-Za-z0-9]*[A-Za-z0-9]/
    |
    namecharx '{' /[_A-Za-z0-9]*/ '}' { /[_A-Za-z0-9]*[A-Za-z0-9]/ }
    ;

(* must not start with digit, nor finish with _ *)
singlename
    =
    /[_A-Za-z][_A-Za-z0-9]*[A-Za-z0-9]/
    |
    [ /[_A-Za-z][_A-Za-z0-9]*/ ] '{' namecharx '}' { /[_A-Za-z0-9]*[A-Za-z0-9]/ }
    |
    /[A-Za-z]/
    ;

namecharp
    =
    /[_A-Za-z0-9]+/
    ;

namecharx
    =
    /[_A-Za-z0-9]*/
    ;

"""

def test_main():
    for s in POSITIVES:
        print("ACCEPTED: %s \t as %s " % (s, parse(s)))

    print('=' * 40)
        
    for s in NEGATIVES:
        thrown = False
        try:
            print("ERROR, SHOULD REFUSE: %s \t\t as %s" % (s, parse(s)))
        except Exception:
            print("REJECTED: " + s)
            thrown = True
        assert thrown

def parse(s):
    model = grako.genmodel("model", grammar)
    if ('__' in s):
        raise Exception("Must not cointain consecutive slashes")
    ast = model.parse(s, "uriname")

    return ast



if __name__ == '__main__':
    test_main()