Add fling velocity threshold to collapse/expand drag gesture

Quick swipe now snaps to the target state regardless of progress position,
matching the behavior of HorizontalPager's fling logic. Uses VelocityTracker
to measure release velocity and a 800 dp/s threshold (FLING_VELOCITY_THRESHOLD_DP).
Slow drags still use the positional COLLAPSE_THRESHOLD (50%) as before.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

shared/src/commonMain/kotlin/plus/rua/project/CalendarViewModel.kt

@@ -17,6 +17,7 @@ import kotlinx.datetime.plus
 import kotlinx.datetime.todayIn
 import kotlin.time.Clock
 import plus.rua.project.ui.COLLAPSE_THRESHOLD
+import plus.rua.project.ui.FLING_VELOCITY_THRESHOLD_DP
 
 data class CalendarDay(
     val date: LocalDate,
@@ -61,10 +62,16 @@ class CalendarViewModel(
     }
 
     // 拖拽超过阈值时自动折叠到周视图，否则回弹到月视图
-    fun onDragEnd() {
+    // velocityDpPerSec: 松手时的 fling 速度 (dp/s)，正值=上滑（折叠方向），负值=下滑（展开方向）
+    fun onDragEnd(velocityDpPerSec: Float = 0f) {
         coroutineScope.launch {
-            val current = _collapseAnimatable.value
+            val progress = _collapseAnimatable.value
-            if (current > COLLAPSE_THRESHOLD) {
+            val shouldCollapse = when {
+                velocityDpPerSec > FLING_VELOCITY_THRESHOLD_DP -> true   // 快速上滑→折叠
+                velocityDpPerSec < -FLING_VELOCITY_THRESHOLD_DP -> false // 快速下滑→展开
+                else -> progress > COLLAPSE_THRESHOLD                    // 慢速按 progress 判断
+            }
+            if (shouldCollapse) {
                 _collapseAnimatable.animateTo(
                     targetValue = 1f,
                     animationSpec = spring(dampingRatio = 0.8f, stiffness = 400f)
@@ -88,10 +95,16 @@ class CalendarViewModel(
     }
 
     // 下拉超过阈值时自动展开到月视图，否则回弹到周视图
-    fun onExpandDragEnd() {
+    // velocityDpPerSec: 同上，正值=上滑，负值=下滑
+    fun onExpandDragEnd(velocityDpPerSec: Float = 0f) {
         coroutineScope.launch {
-            val current = _collapseAnimatable.value
+            val progress = _collapseAnimatable.value
-            if (current < COLLAPSE_THRESHOLD) {
+            val shouldExpand = when {
+                velocityDpPerSec < -FLING_VELOCITY_THRESHOLD_DP -> true  // 快速下滑→展开
+                velocityDpPerSec > FLING_VELOCITY_THRESHOLD_DP -> false  // 快速上滑→保持折叠
+                else -> progress < COLLAPSE_THRESHOLD                    // 慢速按 progress 判断
+            }
+            if (shouldExpand) {
                 _collapseAnimatable.animateTo(
                     targetValue = 0f,
                     animationSpec = spring(dampingRatio = 0.8f, stiffness = 400f)

shared/src/commonMain/kotlin/plus/rua/project/ui/BottomCard.kt

@@ -11,11 +11,13 @@ import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.unit.dp
 import plus.rua.project.CalendarViewModel
 
@@ -33,20 +35,27 @@ fun BottomCard(
     dragRangePx: Float,
     modifier: Modifier = Modifier
 ) {
+    val density = LocalDensity.current
+
     Surface(
         modifier = modifier
             .fillMaxWidth()
             .pointerInput(viewModel.isCollapsed) {
+                val velocityTracker = androidx.compose.ui.input.pointer.util.VelocityTracker()
                 if (viewModel.isCollapsed) {
                     // 折叠状态：下拉恢复到月视图
                     detectVerticalDragGestures(
                         onDragEnd = {
-                            viewModel.onExpandDragEnd()
+                            val velocity = velocityTracker.calculateVelocity()
+                            // 上滑为正（折叠方向），下拉为负（展开方向）
+                            val velocityDpPerSec = with(density) { -velocity.y.toDp().value }
+                            viewModel.onExpandDragEnd(velocityDpPerSec)
                         },
                         onDragCancel = {
                             viewModel.onExpandDragEnd()
                         }
-                    ) { _, dragAmount ->
+                    ) { change, dragAmount ->
+                        velocityTracker.addPosition(change.uptimeMillis, change.position)
                         val delta = -dragAmount / dragRangePx
                         viewModel.onExpandDrag(delta)
                     }
@@ -54,12 +63,16 @@ fun BottomCard(
                     // 展开状态：上拉折叠到周视图
                     detectVerticalDragGestures(
                         onDragEnd = {
-                            viewModel.onDragEnd()
+                            val velocity = velocityTracker.calculateVelocity()
+                            // 上滑为正（折叠方向），下拉为负（展开方向）
+                            val velocityDpPerSec = with(density) { -velocity.y.toDp().value }
+                            viewModel.onDragEnd(velocityDpPerSec)
                         },
                         onDragCancel = {
                             viewModel.onDragEnd()
                         }
-                    ) { _, dragAmount ->
+                    ) { change, dragAmount ->
+                        velocityTracker.addPosition(change.uptimeMillis, change.position)
                         val delta = -dragAmount / dragRangePx
                         viewModel.onDrag(delta)
                     }

shared/src/commonMain/kotlin/plus/rua/project/ui/CalendarUtils.kt

@@ -24,6 +24,9 @@ const val HORIZONTAL_PADDING_DP = 16
 /** BottomCard 拖拽手势范围最小值 (dp)，防止行数少时 dragRange 过小 */
 const val DRAG_RANGE_MIN_DP = 100
 
+/** fling 速度阈值 (dp/s)，超过此速度按方向直接折叠/展开，不受 progress 阈值限制 */
+const val FLING_VELOCITY_THRESHOLD_DP = 800
+
 /** 日历与 BottomCard 之间的间距 (dp)：展开时 */
 const val CARD_GAP_EXPANDED_DP = 24