split code into submodules

src/nominatim_db/tokenizer/token_analysis/config_variants.py

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+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# This file is part of Nominatim. (https://nominatim.org)
+#
+# Copyright (C) 2024 by the Nominatim developer community.
+# For a full list of authors see the git log.
+"""
+Parser for configuration for variants.
+"""
+from typing import Any, Iterator, Tuple, List, Optional, Set, NamedTuple
+from collections import defaultdict
+import itertools
+import re
+
+from nominatim_core.config import flatten_config_list
+from nominatim_core.errors import UsageError
+
+class ICUVariant(NamedTuple):
+    """ A single replacement rule for variant creation.
+    """
+    source: str
+    replacement: str
+
+
+def get_variant_config(in_rules: Any,
+                       normalizer: Any) -> Tuple[List[Tuple[str, List[str]]], str]:
+    """ Convert the variant definition from the configuration into
+        replacement sets.
+
+        Returns a tuple containing the replacement set and the list of characters
+        used in the replacements.
+    """
+    immediate = defaultdict(list)
+    chars: Set[str] = set()
+
+    if in_rules:
+        vset: Set[ICUVariant] = set()
+        rules = flatten_config_list(in_rules, 'variants')
+
+        vmaker = _VariantMaker(normalizer)
+
+        for section in rules:
+            for rule in (section.get('words') or []):
+                vset.update(vmaker.compute(rule))
+
+        # Intermediate reorder by source. Also compute required character set.
+        for variant in vset:
+            if variant.source[-1] == ' ' and variant.replacement[-1] == ' ':
+                replstr = variant.replacement[:-1]
+            else:
+                replstr = variant.replacement
+            immediate[variant.source].append(replstr)
+            chars.update(variant.source)
+
+    return list(immediate.items()), ''.join(chars)
+
+
+class _VariantMaker:
+    """ Generator for all necessary ICUVariants from a single variant rule.
+
+        All text in rules is normalized to make sure the variants match later.
+    """
+
+    def __init__(self, normalizer: Any) -> None:
+        self.norm = normalizer
+
+
+    def compute(self, rule: Any) -> Iterator[ICUVariant]:
+        """ Generator for all ICUVariant tuples from a single variant rule.
+        """
+        parts = re.split(r'(\|)?([=-])>', rule)
+        if len(parts) != 4:
+            raise UsageError(f"Syntax error in variant rule: {rule}")
+
+        decompose = parts[1] is None
+        src_terms = [self._parse_variant_word(t) for t in parts[0].split(',')]
+        repl_terms = (self.norm.transliterate(t).strip() for t in parts[3].split(','))
+
+        # If the source should be kept, add a 1:1 replacement
+        if parts[2] == '-':
+            for src in src_terms:
+                if src:
+                    for froms, tos in _create_variants(*src, src[0], decompose):
+                        yield ICUVariant(froms, tos)
+
+        for src, repl in itertools.product(src_terms, repl_terms):
+            if src and repl:
+                for froms, tos in _create_variants(*src, repl, decompose):
+                    yield ICUVariant(froms, tos)
+
+
+    def _parse_variant_word(self, name: str) -> Optional[Tuple[str, str, str]]:
+        name = name.strip()
+        match = re.fullmatch(r'([~^]?)([^~$^]*)([~$]?)', name)
+        if match is None or (match.group(1) == '~' and match.group(3) == '~'):
+            raise UsageError(f"Invalid variant word descriptor '{name}'")
+        norm_name = self.norm.transliterate(match.group(2)).strip()
+        if not norm_name:
+            return None
+
+        return norm_name, match.group(1), match.group(3)
+
+
+_FLAG_MATCH = {'^': '^ ',
+               '$': ' ^',
+               '': ' '}
+
+
+def _create_variants(src: str, preflag: str, postflag: str,
+                     repl: str, decompose: bool) -> Iterator[Tuple[str, str]]:
+    if preflag == '~':
+        postfix = _FLAG_MATCH[postflag]
+        # suffix decomposition
+        src = src + postfix
+        repl = repl + postfix
+
+        yield src, repl
+        yield ' ' + src, ' ' + repl
+
+        if decompose:
+            yield src, ' ' + repl
+            yield ' ' + src, repl
+    elif postflag == '~':
+        # prefix decomposition
+        prefix = _FLAG_MATCH[preflag]
+        src = prefix + src
+        repl = prefix + repl
+
+        yield src, repl
+        yield src + ' ', repl + ' '
+
+        if decompose:
+            yield src, repl + ' '
+            yield src + ' ', repl
+    else:
+        prefix = _FLAG_MATCH[preflag]
+        postfix = _FLAG_MATCH[postflag]
+
+        yield prefix + src + postfix, prefix + repl + postfix