feat(feed): 랭킹 강조 텍스트 계약을 추가한다

app/src/main/java/kr/co/vividnext/sodalive/v2/widget/feed/FeedRankHighlight.kt

@@ -0,0 +1,13 @@
+package kr.co.vividnext.sodalive.v2.widget.feed
+
+data class FeedRankHighlight(
+    val start: Int,
+    val endExclusive: Int
+) {
+    fun coerceIn(text: CharSequence): FeedRankHighlight? {
+        if (text.isEmpty()) return null
+        val safeStart = start.coerceIn(0, text.length)
+        val safeEnd = endExclusive.coerceIn(0, text.length)
+        return if (safeStart < safeEnd) FeedRankHighlight(safeStart, safeEnd) else null
+    }
+}

app/src/main/java/kr/co/vividnext/sodalive/v2/widget/feed/FeedRankTextStyler.kt

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+package kr.co.vividnext.sodalive.v2.widget.feed
+
+import android.text.SpannableString
+import android.text.Spanned
+import android.text.style.ForegroundColorSpan
+
+object FeedRankTextStyler {
+    fun style(
+        text: String,
+        highlightRanges: List<FeedRankHighlight>,
+        highlightColor: Int
+    ): SpannableString {
+        val spannable = SpannableString(text)
+        highlightRanges.mapNotNull { it.coerceIn(text) }.forEach { range ->
+            spannable.setSpan(
+                ForegroundColorSpan(highlightColor),
+                range.start,
+                range.endExclusive,
+                Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
+            )
+        }
+        return spannable
+    }
+}

app/src/test/java/kr/co/vividnext/sodalive/v2/widget/feed/FeedRankHighlightTest.kt

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+package kr.co.vividnext.sodalive.v2.widget.feed
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class FeedRankHighlightTest {
+
+    @Test
+    fun `valid range remains unchanged`() {
+        val range = FeedRankHighlight(start = 3, endExclusive = 6).coerceIn("abc12위def")
+
+        assertEquals(3, range?.start)
+        assertEquals(6, range?.endExclusive)
+    }
+
+    @Test
+    fun `range larger than text is clamped`() {
+        val range = FeedRankHighlight(start = 2, endExclusive = 99).coerceIn("abc12위")
+
+        assertEquals(2, range?.start)
+        assertEquals(6, range?.endExclusive)
+    }
+
+    @Test
+    fun `empty range is ignored`() {
+        val range = FeedRankHighlight(start = 4, endExclusive = 4).coerceIn("abc12위")
+
+        assertNull(range)
+    }
+
+    @Test
+    fun `range starting after text is ignored`() {
+        val range = FeedRankHighlight(start = 99, endExclusive = 100).coerceIn("abc12위")
+
+        assertNull(range)
+    }
+}

app/src/test/java/kr/co/vividnext/sodalive/v2/widget/feed/FeedRankTextStylerTest.kt

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+package kr.co.vividnext.sodalive.v2.widget.feed
+
+import android.app.Application
+import android.graphics.Color
+import android.text.Spanned
+import android.text.style.ForegroundColorSpan
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+@RunWith(RobolectricTestRunner::class)
+@Config(sdk = [28], application = Application::class)
+class FeedRankTextStylerTest {
+
+    @Test
+    fun `applies highlight color only to rank range`() {
+        val text = "크리에이터님이 12위를 차지하였어요!"
+        val styled = FeedRankTextStyler.style(
+            text = text,
+            highlightRanges = listOf(FeedRankHighlight(start = 8, endExclusive = 11)),
+            highlightColor = Color.CYAN
+        )
+
+        val spans = styled.getSpans(0, styled.length, ForegroundColorSpan::class.java)
+
+        assertEquals(1, spans.size)
+        assertEquals(Color.CYAN, spans[0].foregroundColor)
+        assertEquals(8, styled.getSpanStart(spans[0]))
+        assertEquals(11, styled.getSpanEnd(spans[0]))
+        assertEquals(Spanned.SPAN_EXCLUSIVE_EXCLUSIVE, styled.getSpanFlags(spans[0]))
+    }
+}