Add pattern matcher wrapper

The utility functions “adjust_patterns” and “exclude_path” produce
respectively use a standard list object containing pattern objects.
With the forthcoming introduction of patterns for filtering files
to be extracted it's better to move the logic of these classes into
a single class.

The wrapper allows adding any number of patterns to an internal list
together with a value to be returned if a match function finds that
one of the patterns matches. A fallback value is returned otherwise.

borg/helpers.py

@@ -274,6 +274,27 @@ def exclude_path(path, patterns):
     return False
 
 
+class PatternMatcher:
+    def __init__(self, fallback=None):
+        self._items = []
+
+        # Value to return from match function when none of the patterns match.
+        self.fallback = fallback
+
+    def add(self, patterns, value):
+        """Add list of patterns to internal list. The given value is returned from the match function when one of the
+        given patterns matches.
+        """
+        self._items.extend((i, value) for i in patterns)
+
+    def match(self, path):
+        for (pattern, value) in self._items:
+            if pattern.match(path):
+                return value
+
+        return self.fallback
+
+
 def normalized(func):
     """ Decorator for the Pattern match methods, returning a wrapper that
     normalizes OSX paths to match the normalized pattern on OSX, and

borg/testsuite/helpers.py

@@ -12,7 +12,7 @@ import msgpack.fallback
 from ..helpers import exclude_path, Location, format_file_size, format_timedelta, PathPrefixPattern, FnmatchPattern, make_path_safe, \
     prune_within, prune_split, get_cache_dir, Statistics, is_slow_msgpack, yes, RegexPattern, \
     StableDict, int_to_bigint, bigint_to_int, parse_timestamp, CompressionSpec, ChunkerParams, \
-    ProgressIndicatorPercent, ProgressIndicatorEndless, load_excludes, parse_pattern
+    ProgressIndicatorPercent, ProgressIndicatorEndless, load_excludes, parse_pattern, PatternMatcher
 from . import BaseTestCase, environment_variable, FakeInputs
 
 
@@ -374,6 +374,29 @@ def test_parse_pattern_error(pattern):
         parse_pattern(pattern)
 
 
+def test_pattern_matcher():
+    pm = PatternMatcher()
+
+    assert pm.fallback is None
+
+    for i in ["", "foo", "bar"]:
+        assert pm.match(i) is None
+
+    pm.add([RegexPattern("^a")], "A")
+    pm.add([RegexPattern("^b"), RegexPattern("^z")], "B")
+    pm.add([RegexPattern("^$")], "Empty")
+    pm.fallback = "FileNotFound"
+
+    assert pm.match("") == "Empty"
+    assert pm.match("aaa") == "A"
+    assert pm.match("bbb") == "B"
+    assert pm.match("ccc") == "FileNotFound"
+    assert pm.match("xyz") == "FileNotFound"
+    assert pm.match("z") == "B"
+
+    assert PatternMatcher(fallback="hey!").fallback == "hey!"
+
+
 def test_compression_specs():
     with pytest.raises(ValueError):
         CompressionSpec('')