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package org.egothor.stemmer;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertSame;

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;

/**
 * Unit tests for {@link DiacriticStripper}.
 */
@Tag("unit")
@Tag("diacritic")
@Tag("stemmer")
@Tag("normalization")
@DisplayName("DiacriticStripper")
class DiacriticStripperTest {

    /**
     * Verifies that pure ASCII input is returned unchanged and without allocating a
     * new string instance.
     */
    @Test
    @DisplayName("ASCII input is returned as-is")
    void asciiInputIsReturnedAsIs() {
        final String input = "plain-ascii-123";

        final String stripped = DiacriticStripper.strip(input);

        assertSame(input, stripped);
    }

    /**
     * Verifies direct-table replacements for Czech and other common diacritics.
     */
    @Test
    @DisplayName("Direct replacement table strips common diacritics")
    void directReplacementTableStripsCommonDiacritics() {
        assertEquals("prilis zlutoucky kun", DiacriticStripper.strip("příliš žluťoučký kůň"));
    }

    /**
     * Verifies explicit multi-character replacements for ligatures and sharp s.
     */
    @Test
    @DisplayName("Special replacements support multi-character ASCII output")
    void specialReplacementsSupportMultiCharacterAsciiOutput() {
        assertEquals("strasse AEsir and OEuvre", DiacriticStripper.strip("straße Æsir and Œuvre"));
        assertEquals("aether oeuvre", DiacriticStripper.strip("æther œuvre"));
    }

    /**
     * Verifies Unicode decomposition fallback for characters not in the direct
     * replacement table.
     */
    @Test
    @DisplayName("Unicode decomposition fallback strips combining marks")
    void unicodeDecompositionFallbackStripsCombiningMarks() {
        assertEquals("I", DiacriticStripper.strip("İ"));
    }

    /**
     * Verifies behavior for non-Latin letters that cannot be mapped to ASCII.
     */
    @Test
    @DisplayName("Unmappable non-Latin characters remain unchanged")
    void unmappableNonLatinCharactersRemainUnchanged() {
        assertEquals("abcЖxyz", DiacriticStripper.strip("abcЖxyz"));
    }

    /**
     * Verifies mixed input where normalization starts mid-string and subsequent
     * unchanged characters are preserved.
     */
    @Test
    @DisplayName("Mixed input preserves untouched characters after normalization starts")
    void mixedInputPreservesUntouchedCharactersAfterNormalizationStarts() {
        assertEquals("Cafe-123", DiacriticStripper.strip("Café-123"));
    }
}
