9 files changed, 457 insertions, 4 deletions

diff --git a/bsie/utils/__init__.py b/bsie/utils/__init__.py
index bd22236..9cb60ed 100644
--- a/bsie/utils/__init__.py
+++ b/bsie/utils/__init__.py
@@ -4,19 +4,24 @@ Part of the bsie module.
 A copy of the license is provided with the project.
 Author: Matthias Baumgartner, 2022
 """
-# imports
+# standard imports
 import typing
 
 # inner-module imports
 from . import bsfs
+from . import filematcher
 from . import namespaces as ns
 from . import node
+from .loading import safe_load, unpack_qualified_name
 
 # exports
 __all__: typing.Sequence[str] = (
     'bsfs',
+    'filematcher',
     'node',
     'ns',
+    'safe_load',
+    'unpack_qualified_name',
     )
 
 ## EOF ##
diff --git a/bsie/utils/bsfs.py b/bsie/utils/bsfs.py
index 0b88479..ef5db31 100644
--- a/bsie/utils/bsfs.py
+++ b/bsie/utils/bsfs.py
@@ -4,7 +4,7 @@ Part of the bsie module.
 A copy of the license is provided with the project.
 Author: Matthias Baumgartner, 2022
 """
-# imports
+# standard imports
 import typing
 
 # bsfs imports
diff --git a/bsie/utils/errors.py b/bsie/utils/errors.py
new file mode 100644
index 0000000..8133cd4
--- /dev/null
+++ b/bsie/utils/errors.py
@@ -0,0 +1,48 @@
+"""Common BSIE exceptions.
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# standard imports
+import typing
+
+# exports
+__all__: typing.Sequence[str] = (
+    'BuilderError',
+    'ExtractorError',
+    'LoaderError',
+    'ReaderError',
+    )
+
+
+## code ##
+
+class _BSIEError(Exception):
+    """Generic BSIE error."""
+
+class BuilderError(_BSIEError):
+    """The Builder failed to create an instance."""
+
+class LoaderError(BuilderError):
+    """Failed to load a module or class."""
+
+class ExtractorError(_BSIEError):
+    """The Extractor failed to process the given content."""
+
+class ReaderError(_BSIEError):
+    """The Reader failed to read the given file."""
+
+class ProgrammingError(_BSIEError):
+    """An assertion-like error that indicates a code-base issue."""
+
+class UnreachableError(ProgrammingError):
+    """Bravo, you've reached a point in code that should logically not be reachable."""
+
+class ParserError(_BSIEError):
+    """Failed to parse due to invalid syntax or structures."""
+
+class UnsupportedFileFormatError(ReaderError):
+    """Failed to read a file format."""
+
+## EOF ##
diff --git a/bsie/utils/filematcher/__init__.py b/bsie/utils/filematcher/__init__.py
new file mode 100644
index 0000000..1e23e4e
--- /dev/null
+++ b/bsie/utils/filematcher/__init__.py
@@ -0,0 +1,20 @@
+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# standard imports
+import typing
+
+# inner-module imports
+from .matcher import Matcher
+from .parser import parse
+
+# exports
+__all__: typing.Sequence[str] = (
+    'Matcher',
+    'parse',
+    )
+
+## EOF ##
diff --git a/bsie/utils/filematcher/matcher.py b/bsie/utils/filematcher/matcher.py
new file mode 100644
index 0000000..a279a4b
--- /dev/null
+++ b/bsie/utils/filematcher/matcher.py
@@ -0,0 +1,179 @@
+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2021
+"""
+# standard imports
+from collections.abc import Callable, Collection, Hashable
+import abc
+import os
+import typing
+
+# external imports
+import magic
+
+# exports
+__all__: typing.Sequence[str] = []
+
+
+## code ##
+
+# abstract nodes
+
+class Matcher(abc.ABC, Hashable, Callable, Collection): # type: ignore [misc] # Invalid base class Callable
+    """Matcher node base class."""
+
+    # child expressions or terminals
+    _childs: typing.Set[typing.Any]
+
+    def __init__(self, *childs: typing.Any):
+        if len(childs) == 1 and isinstance(childs[0], (list, tuple, set)):
+            self._childs = set(childs[0])
+        else:
+            self._childs = set(childs)
+
+    def __contains__(self, needle: typing.Any) -> bool:
+        return needle in self._childs
+
+    def __iter__(self) -> typing.Iterator[typing.Any]:
+        return iter(self._childs)
+
+    def __len__(self) -> int:
+        return len(self._childs)
+
+    def __repr__(self) -> str:
+        return f'{type(self).__name__}({self._childs})'
+
+    def __hash__(self) -> int:
+        return hash((type(self), tuple(set(self._childs))))
+
+    def __eq__(self, other: typing.Any) -> bool:
+        return isinstance(other, type(self)) \
+           and self._childs == other._childs
+
+    @abc.abstractmethod
+    def __call__(self, path: str) -> bool: # pylint: disable=arguments-differ
+        """Check if *path* satisfies the conditions set by the Matcher instance."""
+
+class NOT(Matcher):
+    """Invert a matcher result."""
+    def __init__(self, expr: Matcher):
+        super().__init__(expr)
+    def __call__(self, path: str) -> bool:
+        return not next(iter(self._childs))(path)
+
+# aggregate nodes
+
+class Aggregate(Matcher): # pylint: disable=too-few-public-methods # Yeah, it's an interface...
+    """Aggregation function base class (And, Or)."""
+
+class And(Aggregate):
+    """Accept only if all conditions are satisfied."""
+    def __call__(self, path: str) -> bool:
+        for itm in self:
+            if not itm(path):
+                return False
+        return True
+
+class Or(Aggregate):
+    """Accept only if at least one condition is satisfied."""
+    def __call__(self, path: str) -> bool:
+        for itm in self:
+            if itm(path):
+                return True
+        return False
+
+
+# criteria nodes
+
+class Criterion(Matcher):
+    """Criterion base class. Limits acceptance to certain values."""
+    def accepted(self) -> typing.Set[typing.Any]:
+        """Return a set of accepted values."""
+        return self._childs
+
+# criteria w/o value (valueless)
+
+class Any(Criterion):
+    """Accepts anything."""
+    def __call__(self, path: str) -> bool:
+        return True
+
+class Nothing(Criterion):
+    """Accepts nothing."""
+    def __call__(self, path: str) -> bool:
+        return False
+
+class Exists(Criterion):
+    """Filters by existence."""
+    def __call__(self, path: str) -> bool:
+        return os.path.exists(path)
+
+class IsFile(Criterion):
+    """Checks if the path is a regular file."""
+    def __call__(self, path: str) -> bool:
+        return os.path.isfile(path)
+
+class IsDir(Criterion):
+    """Checks if the path is a directory."""
+    def __call__(self, path: str) -> bool:
+        return os.path.isdir(path)
+
+class IsLink(Criterion):
+    """Checks if the path is a link."""
+    def __call__(self, path: str) -> bool:
+        return os.path.islink(path)
+
+class IsAbs(Criterion):
+    """Checks if the path is an absolute path."""
+    def __call__(self, path: str) -> bool:
+        return os.path.isabs(path)
+
+class IsRel(Criterion):
+    """Checks if the path is a relative path."""
+    def __call__(self, path: str) -> bool:
+        return not os.path.isabs(path)
+
+class IsMount(Criterion):
+    """Checks if the path is a mount point."""
+    def __call__(self, path: str) -> bool:
+        return os.path.ismount(path)
+
+class IsEmpty(Criterion):
+    """Checks if the path is an empty file."""
+    def __call__(self, path: str) -> bool:
+        return os.path.exists(path) and os.stat(path).st_size == 0
+
+class IsReadable(Criterion):
+    """Checks if the path is readable."""
+    def __call__(self, path: str) -> bool:
+        return os.path.exists(path) and os.access(path, os.R_OK)
+
+class IsWritable(Criterion):
+    """Checks if the path is writable."""
+    def __call__(self, path: str) -> bool:
+        return os.path.exists(path) and os.access(path, os.W_OK)
+
+class IsExecutable(Criterion):
+    """Checks if the path is executable."""
+    def __call__(self, path: str) -> bool:
+        return os.path.exists(path) and os.access(path, os.X_OK)
+
+# criteria w/ value
+
+class Extension(Criterion):
+    """Filters by file extension (without the dot)."""
+    def __call__(self, path: str) -> bool:
+        _, ext = os.path.splitext(path)
+        return ext[1:] in self.accepted()
+
+class Mime(Criterion):
+    """Filters by mime type."""
+    def __call__(self, path: str) -> bool:
+        try:
+            return magic.from_file(path, mime=True).lower() in self.accepted()
+        except FileNotFoundError:
+            return False
+
+## EOF ##
diff --git a/bsie/utils/filematcher/parser.py b/bsie/utils/filematcher/parser.py
new file mode 100644
index 0000000..2f82875
--- /dev/null
+++ b/bsie/utils/filematcher/parser.py
@@ -0,0 +1,146 @@
+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2021
+"""
+# 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 ##
diff --git a/bsie/utils/loading.py b/bsie/utils/loading.py
new file mode 100644
index 0000000..eb05c35
--- /dev/null
+++ b/bsie/utils/loading.py
@@ -0,0 +1,54 @@
+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# standard imports
+import importlib
+import typing
+
+# inner-module imports
+from . import errors
+
+# exports
+__all__: typing.Sequence[str] = (
+    'safe_load',
+    'unpack_qualified_name',
+    )
+
+
+## code ##
+
+def safe_load(module_name: str, class_name: str):
+    """Get a class from a module. Raise BuilderError if anything goes wrong."""
+    try:
+        # load the module
+        module = importlib.import_module(module_name)
+    except Exception as err:
+        # cannot import module
+        raise errors.LoaderError(f'cannot load module {module_name}') from err
+
+    try:
+        # get the class from the module
+        cls = getattr(module, class_name)
+    except Exception as err:
+        # cannot find the class
+        raise errors.LoaderError(f'cannot load class {class_name} from module {module_name}') from err
+
+    return cls
+
+
+def unpack_qualified_name(name):
+    """Split a name into its module and class component (dot-separated)."""
+    if not isinstance(name, str):
+        raise TypeError(name)
+    if '.' not in name:
+        raise ValueError('name must be a qualified class name.')
+    module_name, class_name = name[:name.rfind('.')], name[name.rfind('.')+1:]
+    if module_name == '':
+        raise ValueError('name must be a qualified class name.')
+    return module_name, class_name
+
+
+## EOF ##
diff --git a/bsie/utils/namespaces.py b/bsie/utils/namespaces.py
index a29fc1b..393b436 100644
--- a/bsie/utils/namespaces.py
+++ b/bsie/utils/namespaces.py
@@ -4,7 +4,7 @@ Part of the bsie module.
 A copy of the license is provided with the project.
 Author: Matthias Baumgartner, 2022
 """
-# imports
+# standard imports
 import typing
 
 # inner-module imports
@@ -15,6 +15,7 @@ bse = _bsfs.Namespace('http://bsfs.ai/schema/Entity')
 bsfs = _bsfs.Namespace('http://bsfs.ai/schema', fsep='/')
 bsm = _bsfs.Namespace('http://bsfs.ai/schema/Meta')
 xsd = _bsfs.Namespace('http://www.w3.org/2001/XMLSchema')
+bsf = _bsfs.Namespace('http://ie.bsfs.ai/schema/Feature')
 
 # export
 __all__: typing.Sequence[str] = (
diff --git a/bsie/utils/node.py b/bsie/utils/node.py
index ecf39cd..91e4f37 100644
--- a/bsie/utils/node.py
+++ b/bsie/utils/node.py
@@ -4,7 +4,7 @@ Part of the bsie module.
 A copy of the license is provided with the project.
 Author: Matthias Baumgartner, 2022
 """
-# imports
+# standard imports
 import typing
 
 # bsie imports