feat(banner): 배너 레이아웃 계산 계약을 추가한다

app/src/main/java/kr/co/vividnext/sodalive/v2/widget/banner/BannerLayoutCalculator.kt

@@ -0,0 +1,23 @@
+package kr.co.vividnext.sodalive.v2.widget.banner
+
+object BannerLayoutCalculator {
+    private const val SIDE_INSET_DP = 20
+    private const val ITEM_SPACING_DP = 8
+
+    fun calculate(screenWidthDp: Int, density: Float): BannerLayoutSize {
+        val itemSizeDp = screenWidthDp - (SIDE_INSET_DP * 2)
+        return BannerLayoutSize(
+            itemWidthDp = itemSizeDp,
+            itemHeightDp = itemSizeDp,
+            sideInsetDp = SIDE_INSET_DP,
+            itemSpacingDp = ITEM_SPACING_DP
+        )
+    }
+}
+
+data class BannerLayoutSize(
+    val itemWidthDp: Int,
+    val itemHeightDp: Int,
+    val sideInsetDp: Int,
+    val itemSpacingDp: Int
+)

app/src/test/java/kr/co/vividnext/sodalive/v2/widget/banner/BannerLayoutCalculatorTest.kt

@@ -0,0 +1,40 @@
+package kr.co.vividnext.sodalive.v2.widget.banner
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class BannerLayoutCalculatorTest {
+
+    @Test
+    fun `화면 폭 402dp이면 배너 아이템 크기는 362dp다`() {
+        val size = BannerLayoutCalculator.calculate(
+            screenWidthDp = 402,
+            density = 1f
+        )
+
+        assertEquals(362, size.itemWidthDp)
+        assertEquals(362, size.itemHeightDp)
+    }
+
+    @Test
+    fun `화면 폭 360dp이면 배너 아이템 크기는 320dp다`() {
+        val size = BannerLayoutCalculator.calculate(
+            screenWidthDp = 360,
+            density = 1f
+        )
+
+        assertEquals(320, size.itemWidthDp)
+        assertEquals(320, size.itemHeightDp)
+    }
+
+    @Test
+    fun `배너 레이아웃은 고정 좌우 여백과 아이템 간격을 사용한다`() {
+        val size = BannerLayoutCalculator.calculate(
+            screenWidthDp = 402,
+            density = 1f
+        )
+
+        assertEquals(20, size.sideInsetDp)
+        assertEquals(8, size.itemSpacingDp)
+    }
+}