refactor: Create LocaleAffinityBiCalculatorBaseImpl

locales-common/src/main/java/com/spotify/i18n/locales/common/LocaleAffinityHelpersFactory.java

@@ -22,6 +22,7 @@
 
 import com.google.common.base.Preconditions;
 import com.ibm.icu.util.ULocale;
+import com.spotify.i18n.locales.common.impl.LocaleAffinityBiCalculatorBaseImpl;
 import com.spotify.i18n.locales.common.impl.LocaleAffinityCalculatorBaseImpl;
 import com.spotify.i18n.locales.common.impl.ReferenceLocalesCalculatorBaseImpl;
 import com.spotify.i18n.locales.common.model.LocaleAffinity;
@@ -125,7 +126,7 @@ public LocaleAffinityCalculator buildAffinityCalculatorForLanguageTags(
    * @see LocaleAffinityBiCalculator
    */
   public LocaleAffinityBiCalculator buildAffinityBiCalculator() {
-    return ReferenceLocalesCalculatorBaseImpl.builder().buildLocaleAffinityBiCalculator();
+    return LocaleAffinityBiCalculatorBaseImpl.builder().build();
   }
 
   /**

locales-common/src/main/java/com/spotify/i18n/locales/common/impl/LocaleAffinityBiCalculatorBaseImpl.java

@@ -0,0 +1,226 @@
+/*-
+ * -\-\-
+ * locales-common
+ * --
+ * Copyright (C) 2016 - 2025 Spotify AB
+ * --
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * -/-/-
+ */
+
+package com.spotify.i18n.locales.common.impl;
+
+import static com.spotify.i18n.locales.utils.hierarchy.LocalesHierarchyUtils.isSameLocale;
+import static com.spotify.i18n.locales.utils.language.LanguageUtils.getSpokenLanguageLocale;
+import static com.spotify.i18n.locales.utils.languagetag.LanguageTagUtils.parse;
+
+import com.google.auto.value.AutoValue;
+import com.ibm.icu.impl.locale.LSR;
+import com.ibm.icu.impl.locale.LikelySubtags;
+import com.ibm.icu.impl.locale.LocaleDistance;
+import com.ibm.icu.util.LocaleMatcher.Direction;
+import com.ibm.icu.util.LocaleMatcher.FavorSubtag;
+import com.ibm.icu.util.ULocale;
+import com.spotify.i18n.locales.common.LocaleAffinityBiCalculator;
+import com.spotify.i18n.locales.common.LocaleAffinityCalculator;
+import com.spotify.i18n.locales.common.model.LocaleAffinity;
+import com.spotify.i18n.locales.common.model.LocaleAffinityResult;
+import com.spotify.i18n.locales.utils.available.AvailableLocalesUtils;
+import edu.umd.cs.findbugs.annotations.Nullable;
+import java.util.Optional;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * Base implementation of {@link LocaleAffinityBiCalculator} that calculates the locale affinity
+ * between two given language tags.
+ *
+ * <p>This class is not intended for public subclassing. New object instances must be created using
+ * the builder pattern, starting with the {@link #builder()} method.
+ *
+ * @author Eric Fjøsne
+ */
+@AutoValue
+public abstract class LocaleAffinityBiCalculatorBaseImpl implements LocaleAffinityBiCalculator {
+
+  // Set containing all available language codes in CLDR.
+  private static final Set<String> AVAILABLE_LANGUAGE_CODES =
+      AvailableLocalesUtils.getReferenceLocales().stream()
+          .map(ULocale::getLanguage)
+          .collect(Collectors.toSet());
+
+  // LocaleDistance.INSTANCE is commented as VisibleForTesting, so not ideal ... but this is the
+  // only way to make use of this class, which provides the features we need here.
+  private static final LocaleDistance LOCALE_DISTANCE_INSTANCE = LocaleDistance.INSTANCE;
+
+  // LocaleDistance best distance method arguments, all assigned to their default as per icu
+  // implementation.
+  private static final int LOCALE_DISTANCE_SHIFTED =
+      LocaleDistance.shiftDistance(LOCALE_DISTANCE_INSTANCE.getDefaultScriptDistance());
+  private static final int LOCALE_DISTANCE_SUPPORTED_LSRS_LENGTH = 1;
+  private static final FavorSubtag LOCALE_DISTANCE_FAVOR_SUBTAG = FavorSubtag.LANGUAGE;
+  private static final Direction LOCALE_DISTANCE_DIRECTION = Direction.WITH_ONE_WAY;
+
+  // LikelySubtags.INSTANCE is commented as VisibleForTesting, so not ideal ... but this is the
+  // only way to make use of this class, which provides the features we need here.
+  private static final LikelySubtags LIKELY_SUBTAGS_INSTANCE = LikelySubtags.INSTANCE;
+
+  // LikelySubtags method arguments, all assigned to their default as per icu implementation.
+  private static final boolean LIKELY_SUBTAGS_RETURNS_INPUT_IF_UNMATCH = false;
+
+  // Distance threshold: Anything above this value will be scored 0.
+  private static final double DISTANCE_THRESHOLD = 224.0;
+
+  // Score to affinity thresholds
+  private static final int SCORE_THRESHOLD_MUTUALLY_INTELLIGIBLE = 65;
+  private static final int SCORE_THRESHOLD_HIGH = 30;
+  private static final int SCORE_THRESHOLD_LOW = 0;
+
+  // Language codes for which we need some manual tweaks
+  private static final String LANGUAGE_CODE_CROATIAN = "hr";
+  private static final String LANGUAGE_CODE_BOSNIAN = "bs";
+
+  /**
+   * Returns the calculated {@link LocaleAffinityResult} for the given two language tags
+   *
+   * @return the locale affinity result
+   */
+  @Override
+  public LocaleAffinityResult calculate(
+      @Nullable final String languageTag1, @Nullable final String languageTag2) {
+    return LocaleAffinityResult.builder().affinity(getAffinity(languageTag1, languageTag2)).build();
+  }
+
+  private LocaleAffinity getAffinity(
+      @Nullable final String languageTag1, @Nullable final String languageTag2) {
+    // We parse the language tags, and filter out locales with a language unavailable in CLDR.
+    final Optional<ULocale> locale1 =
+        parse(languageTag1).filter(locale -> isAvailableLanguage(locale));
+    final Optional<ULocale> locale2 =
+        parse(languageTag2).filter(locale -> isAvailableLanguage(locale));
+
+    if (locale1.isPresent() && locale2.isPresent()) {
+      // We attempt to match based on corresponding spoken language first, and make use of the
+      // score-based affinity calculation as fallback.
+      if (hasSameSpokenLanguageAffinity(locale1.get(), locale2.get())) {
+        return LocaleAffinity.SAME;
+      } else {
+        return calculateScoreBasedAffinity(locale1.get(), locale2.get());
+      }
+    } else {
+      return LocaleAffinity.NONE;
+    }
+  }
+
+  private boolean hasSameSpokenLanguageAffinity(final ULocale locale1, final ULocale locale2) {
+    final Optional<ULocale> spoken1 = getSpokenLanguageLocale(locale1.toLanguageTag());
+    final Optional<ULocale> spoken2 = getSpokenLanguageLocale(locale2.toLanguageTag());
+    return spoken1.isPresent() && spoken2.isPresent() && isSameLocale(spoken1.get(), spoken2.get());
+  }
+
+  static LocaleAffinity calculateScoreBasedAffinity(final ULocale l1, final ULocale l2) {
+    int bestDistance = getBestDistanceBetweenLocales(l1, l2);
+    int correspondingScore = convertDistanceToAffinityScore(bestDistance);
+    return convertScoreToLocaleAffinity(correspondingScore);
+  }
+
+  static boolean isAvailableLanguage(final ULocale locale) {
+    return AVAILABLE_LANGUAGE_CODES.contains(locale.getLanguage().toLowerCase());
+  }
+
+  private static int getBestDistanceBetweenLocales(final ULocale locale1, final ULocale locale2) {
+    final LSR lsr1 = getMaximizedLanguageScriptRegion(locale1);
+    final LSR lsr2 = getMaximizedLanguageScriptRegion(locale2);
+    return getBestDistanceBetweenLSR(lsr1, lsr2);
+  }
+
+  static int getBestDistanceBetweenLSR(final LSR lsr1, final LSR lsr2) {
+    // Croatian should be matched with Bosnian. This is the case for Bosnian written in Latin
+    // script, but not Cyrillic, because the ICU implementation enforces script matching. We
+    // created a workaround to ensure that we return a MUTUALLY_INTELLIGIBLE affinity when
+    // encountering this locale.
+    if (calculatingDistanceBetweenCroatianAndBosnian(lsr1, lsr2)) {
+      return 0;
+    } else {
+      // We calculate distances both ways, and return the minimum value (= best distance).
+      return Math.min(calculateDistance(lsr1, lsr2), calculateDistance(lsr2, lsr1));
+    }
+  }
+
+  private static int calculateDistance(final LSR lsr1, final LSR lsr2) {
+    return Math.abs(
+        LOCALE_DISTANCE_INSTANCE.getBestIndexAndDistance(
+            lsr1,
+            new LSR[] {lsr2},
+            LOCALE_DISTANCE_SUPPORTED_LSRS_LENGTH,
+            LOCALE_DISTANCE_SHIFTED,
+            LOCALE_DISTANCE_FAVOR_SUBTAG,
+            LOCALE_DISTANCE_DIRECTION));
+  }
+
+  static int convertDistanceToAffinityScore(final int distance) {
+    if (distance > DISTANCE_THRESHOLD) {
+      return 0;
+    } else {
+      return (int) ((DISTANCE_THRESHOLD - distance) / DISTANCE_THRESHOLD * 100.0);
+    }
+  }
+
+  static LocaleAffinity convertScoreToLocaleAffinity(final int score) {
+    if (score > SCORE_THRESHOLD_MUTUALLY_INTELLIGIBLE) {
+      return LocaleAffinity.MUTUALLY_INTELLIGIBLE;
+    } else if (score > SCORE_THRESHOLD_HIGH) {
+      return LocaleAffinity.HIGH;
+    } else if (score > SCORE_THRESHOLD_LOW) {
+      return LocaleAffinity.LOW;
+    } else {
+      return LocaleAffinity.NONE;
+    }
+  }
+
+  private static boolean calculatingDistanceBetweenCroatianAndBosnian(
+      final LSR lsr1, final LSR lsr2) {
+    return (lsr1.language.equals(LANGUAGE_CODE_CROATIAN)
+            && lsr2.language.equals(LANGUAGE_CODE_BOSNIAN))
+        || (lsr1.language.equals(LANGUAGE_CODE_BOSNIAN)
+            && lsr2.language.equals(LANGUAGE_CODE_CROATIAN));
+  }
+
+  static LSR getMaximizedLanguageScriptRegion(final ULocale locale) {
+    return LIKELY_SUBTAGS_INSTANCE.makeMaximizedLsrFrom(
+        locale, LIKELY_SUBTAGS_RETURNS_INPUT_IF_UNMATCH);
+  }
+
+  /**
+   * Returns a {@link Builder} instance that will allow you to manually create a {@link
+   * LocaleAffinityBiCalculatorBaseImpl} instance.
+   *
+   * @return The builder
+   */
+  public static Builder builder() {
+    return new AutoValue_LocaleAffinityBiCalculatorBaseImpl.Builder();
+  }
+
+  /** A builder for a {@link LocaleAffinityBiCalculatorBaseImpl}. */
+  @AutoValue.Builder
+  public abstract static class Builder {
+    Builder() {} // package private constructor
+
+    abstract LocaleAffinityBiCalculatorBaseImpl autoBuild();
+
+    /** Builds a {@link LocaleAffinityCalculator} out of this builder. */
+    public final LocaleAffinityBiCalculator build() {
+      return autoBuild();
+    }
+  }
+}