Lucene Suggestions using phonetic algorithms

PhoneticFstTests.java

package de.spinscale.prt;

import org.apache.lucene.analysis.custom.CustomAnalyzer;
import org.apache.lucene.analysis.phonetic.PhoneticFilterFactory;
import org.apache.lucene.search.suggest.FileDictionary;
import org.apache.lucene.search.suggest.Lookup;
import org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.NIOFSDirectory;
import org.junit.jupiter.api.Test;

import java.io.StringReader;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import static org.assertj.core.api.Assertions.assertThat;

public class PhoneticFstTests {

    @Test
    public void testPhoneticSuggester() throws Exception {
        Map<String, String> args = new HashMap<>();
        args.put("encoder", "ColognePhonetic");
        CustomAnalyzer analyzer = CustomAnalyzer.builder()
                .addTokenFilter(PhoneticFilterFactory.class, args)
                .withTokenizer("standard")
                .build();

        Directory directory = new NIOFSDirectory(Paths.get("/tmp/"));
        AnalyzingSuggester suggester = new AnalyzingSuggester(directory, "lucene-tmp", analyzer);
        // payloads are optional
        String input = """
spülmaschine\t10\tspülmaschine
spüle\t1\tspüle
speer\t5\tspeer
gabel\t100\tgabel
""";
        FileDictionary dictionary = new FileDictionary(new StringReader(input));
        suggester.build(dictionary);

        assertLookup("sp", suggester, "spülmaschine/10", "speer/5", "spüle/1");
        assertLookup("spul", suggester, "spülmaschine/10", "spüle/1");
        assertLookup("spöl", suggester, "spülmaschine/10", "spüle/1");
        assertLookup("spln", suggester, "spülmaschine/10");
        // this is why you shouldnt use this as your default suggester
        assertLookup("spe", suggester, "spülmaschine/10", "speer/5", "spüle/1");
        assertLookup("spee", suggester, "spülmaschine/10", "speer/5", "spüle/1");
        // back to normal
        assertLookup("speer", suggester, "speer/5");

        assertLookup("gabel", suggester, "gabel/100");
        assertLookup("gabbel", suggester, "gabel/100");
        assertLookup("gobel", suggester, "gabel/100");
        assertLookup("ggobel", suggester, "gabel/100");
    }

    private void assertLookup(String input, AnalyzingSuggester suggester, String ... expectedOutcomesWithScore) {
        List<Lookup.LookupResult> results = suggester.lookup(input, null, false, 10);
        assertThat(results).map(Lookup.LookupResult::toString).containsExactly(expectedOutcomesWithScore);
    }
}