feat(banner): 배너 자동 전환 동작을 추가한다

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

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

@@ -52,6 +52,12 @@ class BannerAdapter(
 
     fun toRealIndex(position: Int): Int = if (items.isEmpty()) 0 else position % items.size
 
+    fun startPosition(realIndex: Int): Int {
+        if (items.size <= 1) return realIndex
+        val center = VIRTUAL_ITEM_COUNT / 2
+        return center - (center % items.size) + realIndex
+    }
+
     inner class BannerViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
         private val imageView: ImageView = itemView.findViewById(R.id.iv_banner)
 

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

@@ -1,6 +1,8 @@
 package kr.co.vividnext.sodalive.v2.widget.banner
 
 import android.content.Context
+import android.os.Handler
+import android.os.Looper
 import android.util.AttributeSet
 import android.view.LayoutInflater
 import android.view.View
@@ -8,6 +10,7 @@ import android.widget.FrameLayout
 import android.widget.ImageView
 import android.widget.TextView
 import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.LinearSmoothScroller
 import androidx.recyclerview.widget.PagerSnapHelper
 import androidx.recyclerview.widget.RecyclerView
 import kr.co.vividnext.sodalive.R
@@ -28,8 +31,23 @@ class BannerView @JvmOverloads constructor(
     private val snapHelper = PagerSnapHelper()
     private var items: List<BannerItem> = emptyList()
     private var currentIndex: Int = 0
+    private var currentAdapterPosition: Int = 0
     private var itemSpacingPx: Int = 0
     private var spacingDecoration: RecyclerView.ItemDecoration? = null
+    private val autoScrollHandler = Handler(Looper.getMainLooper())
+    private val autoScrollRunnable = Runnable { moveToNextBanner() }
+    private var hasWindowAttachmentForAutoScroll = false
+    private val bannerScrollListener = object : RecyclerView.OnScrollListener() {
+        override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
+            when (newState) {
+                RecyclerView.SCROLL_STATE_DRAGGING -> stopAutoScroll()
+                RecyclerView.SCROLL_STATE_IDLE -> {
+                    updateCurrentIndexFromSnap()
+                    startAutoScrollIfNeeded()
+                }
+            }
+        }
+    }
 
     init {
         clipToPadding = false
@@ -44,6 +62,18 @@ class BannerView @JvmOverloads constructor(
         updateCounter()
     }
 
+    override fun onAttachedToWindow() {
+        super.onAttachedToWindow()
+        hasWindowAttachmentForAutoScroll = true
+        startAutoScrollIfNeeded()
+    }
+
+    override fun onDetachedFromWindow() {
+        stopAutoScroll()
+        hasWindowAttachmentForAutoScroll = false
+        super.onDetachedFromWindow()
+    }
+
     override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
         super.onSizeChanged(w, h, oldw, oldh)
         if (w > 0) applyLayoutSize(w)
@@ -53,9 +83,12 @@ class BannerView @JvmOverloads constructor(
         this.items = items
         currentIndex = BannerState.from(items.size, currentIndex).currentIndex
         visibility = if (items.isEmpty()) GONE else VISIBLE
+        stopAutoScroll()
         adapter.submitItems(items)
+        scrollToCurrentBanner()
         if (width > 0) applyLayoutSize(width)
         updateCounter()
+        startAutoScrollIfNeeded()
     }
 
     fun setOnBannerClickListener(listener: ((BannerItem) -> Unit)?) {
@@ -73,11 +106,7 @@ class BannerView @JvmOverloads constructor(
             clipToPadding = false
             clipChildren = false
             if (onFlingListener == null) snapHelper.attachToRecyclerView(this)
-            addOnScrollListener(object : RecyclerView.OnScrollListener() {
-                override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
-                    if (newState == RecyclerView.SCROLL_STATE_IDLE) updateCurrentIndexFromSnap()
-                }
-            })
+            addOnScrollListener(bannerScrollListener)
         }
     }
 
@@ -95,10 +124,44 @@ class BannerView @JvmOverloads constructor(
         }
     }
 
+    private fun scrollToCurrentBanner() {
+        val recyclerView = requireNotNull(recyclerView)
+        currentAdapterPosition = if (items.size > 1) {
+            adapter.startPosition(currentIndex)
+        } else {
+            currentIndex
+        }
+        recyclerView.scrollToPosition(currentAdapterPosition)
+    }
+
+    private fun moveToNextBanner() {
+        if (BannerState.from(items.size, currentIndex).displayMode != BannerDisplayMode.Carousel) return
+        val recyclerView = requireNotNull(recyclerView)
+        val layoutManager = recyclerView.layoutManager as? LinearLayoutManager ?: return
+        val nextPosition = currentAdapterPosition + 1
+        currentAdapterPosition = nextPosition
+        currentIndex = adapter.toRealIndex(nextPosition)
+        layoutManager.startSmoothScroll(BannerSmoothScroller(context).apply { targetPosition = nextPosition })
+        updateCounter()
+        startAutoScrollIfNeeded()
+    }
+
+    private fun startAutoScrollIfNeeded() {
+        stopAutoScroll()
+        if (!hasWindowAttachmentForAutoScroll) return
+        if (BannerState.from(items.size, currentIndex).displayMode != BannerDisplayMode.Carousel) return
+        autoScrollHandler.postDelayed(autoScrollRunnable, AUTO_SCROLL_INTERVAL_MS)
+    }
+
+    private fun stopAutoScroll() {
+        autoScrollHandler.removeCallbacks(autoScrollRunnable)
+    }
+
     private fun updateCurrentIndexFromSnap() {
         val layoutManager = requireNotNull(recyclerView).layoutManager ?: return
         val snapView = snapHelper.findSnapView(layoutManager) ?: return
         val position = layoutManager.getPosition(snapView)
+        currentAdapterPosition = position
         currentIndex = adapter.toRealIndex(position)
         updateCounter()
     }
@@ -118,6 +181,17 @@ class BannerView @JvmOverloads constructor(
 
     private fun Int.dpToPx(): Int = (this * resources.displayMetrics.density).roundToInt()
 
+    companion object {
+        private const val AUTO_SCROLL_INTERVAL_MS = 5_000L
+        private const val SCROLL_ANIMATION_DURATION_MS = 350
+
+        fun scrollAnimationDurationMsForTest(): Int = SCROLL_ANIMATION_DURATION_MS
+    }
+
+    private class BannerSmoothScroller(context: Context) : LinearSmoothScroller(context) {
+        override fun calculateTimeForScrolling(dx: Int): Int = SCROLL_ANIMATION_DURATION_MS
+    }
+
     private class BannerSpacingDecoration(
         private val spacingPx: Int
     ) : RecyclerView.ItemDecoration() {