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# standard imports
import typing
# external imports
import pyparsing
from pyparsing import printables, alphas8bit, punc8bit, QuotedString, Word, \
delimitedList, Or, CaselessKeyword, Group, oneOf, Optional
# inner-module imports
from . import matcher
from .. import errors
# exports
__all__: typing.Sequence[str] = (
'parse',
)
## code ##
class FileMatcherParser():
"""
EXPR := RULES | RULES "|" RULES
RULESET := RULE | RULE, RULE
RULE := CRITERION OP VALUE | CRITERION OP {VALUES} | VALUELESS
OP := != | =
VALUES := VALUE | VALUE, VALUE
VALUE := [word]
CRITERION := mime | extension | ...
"""
# criteria matcher nodes w/ arguments
_CRITERIA: typing.Dict[str, typing.Type[matcher.Matcher]] = {
'extension': matcher.Extension,
'mime': matcher.Mime,
}
# criteria matcher nodes w/o arguments
_VALUELESS: typing.Dict[str, typing.Type[matcher.Matcher]] = {
'any': matcher.Any,
'nothing': matcher.Nothing,
'exists': matcher.Exists,
'isfile': matcher.IsFile,
'isdir': matcher.IsDir,
'islink': matcher.IsLink,
'isabs': matcher.IsAbs,
'isrel': matcher.IsRel,
'ismount': matcher.IsMount,
'emtpy': matcher.IsEmpty,
'readable': matcher.IsReadable,
'writable': matcher.IsWritable,
'executable': matcher.IsExecutable,
}
# pyparsing parser instance.
_parser: pyparsing.ParseExpression
def __init__(self):
# build the parser
# VALUE := [word]
alphabet = (printables + alphas8bit + punc8bit).translate(str.maketrans('', '', ',{}|='))
value = QuotedString(quoteChar='"', escChar='\\') ^ Word(alphabet)
# CRITERION := mime | extension | ...
criterion = Or([CaselessKeyword(p) for p in self._CRITERIA]).setResultsName('criterion')
valueless = Or([CaselessKeyword(p) for p in self._VALUELESS]).setResultsName('criterion')
# VALUES := VALUE | VALUE, VALUE
values = delimitedList(value, delim=',').setResultsName('value')
# OP := '=' | '!='
eqop = oneOf('= !=').setResultsName('op')
# RULE := CRITERION OP VALUE | CRITERION OP {VALUES} | VALUELESS
rule_none = Group(Optional('!').setResultsName('op') + valueless).setResultsName('rule_none')
rule_one = Group(criterion + eqop + value.setResultsName('value')).setResultsName('rule_one')
rule_few = Group(criterion + eqop + '{' + values + '}').setResultsName('rule_few')
# RULESET := RULE | RULE, RULE
ruleset = Group(delimitedList(rule_none ^ rule_one ^ rule_few, delim=','))
# EXPR := RULESET | RULESET \| RULESET
self._parser = delimitedList(ruleset, delim='|')
def parse(self, query: str) -> matcher.Matcher: # pylint: disable=too-many-branches
"""Build a file matcher from a rule definition."""
# preprocess the query
query = query.strip()
# empty query
if len(query) == 0:
return matcher.Any()
try:
parsed = self._parser.parseString(query, parseAll=True)
except pyparsing.ParseException as err:
raise errors.ParserError(f'Cannot parse query {err}')
# convert to Matcher
rules = []
for exp in parsed:
tokens = []
for rule in exp:
# fetch accepted values
if rule.getName() == 'rule_none':
accepted = []
elif rule.getName() == 'rule_one':
accepted = [rule.value]
elif rule.getName() == 'rule_few':
accepted = list(rule.value)
else: # prevented by grammar
raise errors.UnreachableError('Invalid rule definition')
# build criterion
if rule.criterion in self._VALUELESS:
cls = self._VALUELESS[rule.criterion]
if rule.op == '!':
tokens.append(matcher.NOT(cls()))
else:
tokens.append(cls())
elif rule.criterion in self._CRITERIA:
cls = self._CRITERIA[rule.criterion]
if rule.op == '!=':
tokens.append(matcher.NOT(cls(accepted)))
else:
tokens.append(cls(accepted))
else: # prevented by grammar
raise errors.UnreachableError(f'Invalid condition "{rule.criterion}"')
# And-aggregate rules in one ruleset (if needed)
tokens = matcher.And(tokens) if len(tokens) > 1 else tokens[0]
rules.append(tokens)
# Or-aggregate rulesets
expr = matcher.Or(rules) if len(rules) > 1 else rules[0]
return expr
# build default instance
file_match_parser = FileMatcherParser()
def parse(query: str) -> matcher.Matcher:
"""Shortcut for FileMatcherParser()(query)."""
return file_match_parser.parse(query)
## EOF ##
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