Add pull-down gesture to expand from collapsed week view back to month view

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

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

@@ -74,6 +74,32 @@ class CalendarViewModel(private val coroutineScope: CoroutineScope) {
         }
     }
 
+    // 折叠状态下下拉恢复：delta 为负值（向下拖）推动 progress 向 0
+    fun onExpandDrag(delta: Float) {
+        coroutineScope.launch {
+            val new = (_collapseAnimatable.value + delta).coerceIn(0f, 1f)
+            _collapseAnimatable.snapTo(new)
+        }
+    }
+
+    // 下拉超过 50% 时自动展开到月视图，否则回弹到周视图
+    fun onExpandDragEnd() {
+        coroutineScope.launch {
+            if (_collapseAnimatable.value < 0.5f) {
+                _collapseAnimatable.animateTo(
+                    targetValue = 0f,
+                    animationSpec = spring(dampingRatio = 0.8f, stiffness = 400f)
+                )
+                isCollapsed = false
+            } else {
+                _collapseAnimatable.animateTo(
+                    targetValue = 1f,
+                    animationSpec = spring(dampingRatio = 0.8f, stiffness = 400f)
+                )
+            }
+        }
+    }
+
     /**
      * 计算给定日期的 ISO 8601 周号。
      *

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

@@ -38,7 +38,17 @@ fun BottomCard(
         modifier = modifier
             .fillMaxWidth()
             .pointerInput(viewModel.isCollapsed) {
-                if (viewModel.isCollapsed) return@pointerInput
+                if (viewModel.isCollapsed) {
+                    // 折叠状态：下拉恢复到月视图
+                    detectVerticalDragGestures(
+                        onDragEnd = { viewModel.onExpandDragEnd() },
+                        onDragCancel = { viewModel.onExpandDragEnd() }
+                    ) { _, dragAmount ->
+                        val delta = -dragAmount / dragRange
+                        viewModel.onExpandDrag(delta)
+                    }
+                } else {
+                    // 展开状态：上拉折叠到周视图
                     detectVerticalDragGestures(
                         onDragEnd = { viewModel.onDragEnd() },
                         onDragCancel = { viewModel.onDragEnd() }
@@ -46,6 +56,7 @@ fun BottomCard(
                         val delta = -dragAmount / dragRange
                         viewModel.onDrag(delta)
                     }
+                }
             },
         shape = RoundedCornerShape(topStart = 16.dp, topEnd = 16.dp),
         color = MaterialTheme.colorScheme.surfaceVariant,

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

@@ -106,7 +106,8 @@ fun CalendarMonthView(
                     weekdayHeaderHeightPx = size.height
                 }
             )
-            if (viewModel.isCollapsed) {
+            // 完全折叠且无动画时显示 WeekPager，否则显示 CalendarPager（含下拉恢复过程）
+            if (viewModel.isCollapsed && viewModel.collapseProgress >= 1f) {
                 WeekPager(
                     selectedDate = viewModel.selectedDate,
                     today = today,