Implement filtering and sorting functionality

- Add getItemsByFilter server action with support for:
  - Priority filtering (low, medium, high)
  - Completed status filtering
  - Tag filtering with compound AND logic
  - Due date range filtering
  - Sorting by createdAt, dueDate, priority, and title
  - Ascending and descending sort order
- Handle null due dates in sorting (placed at end)
- Implement compound filter logic with AND conditions
- Requirements: 6.1, 6.2, 6.3, 6.5

lib/actions.ts

@@ -178,8 +178,8 @@ export async function searchItems(query: string, listId?: string) {
 
   const tagMatches = allItems.filter((item) => {
     const tags = Array.isArray(item.tags) ? item.tags : []
-    return tags.some((tag: string) =>
-      tag.toLowerCase().includes(searchTerm)
+    return tags.some((tag) =>
+      typeof tag === 'string' && tag.toLowerCase().includes(searchTerm)
     )
   })
 
@@ -190,4 +190,106 @@ export async function searchItems(query: string, listId?: string) {
   )
 
   return uniqueResults
+}
+
+export async function getItemsByFilter(
+  listId: string | null,
+  filters: {
+    priority?: 'low' | 'medium' | 'high' | null
+    completed?: boolean | null
+    tags?: string[]
+    dueDateRange?: { start: Date | null; end: Date | null }
+    sortBy?: 'createdAt' | 'dueDate' | 'priority' | 'title'
+    sortOrder?: 'asc' | 'desc'
+  } = {}
+) {
+  // Build the where clause with compound filters (AND logic)
+  const whereClause: any = {}
+
+  // Add list scope if specified
+  if (listId) {
+    whereClause.listId = listId
+  }
+
+  // Filter by priority
+  if (filters.priority) {
+    whereClause.priority = filters.priority
+  }
+
+  // Filter by completed status
+  if (filters.completed !== undefined && filters.completed !== null) {
+    whereClause.completed = filters.completed
+  }
+
+  // Filter by due date range
+  if (filters.dueDateRange) {
+    const { start, end } = filters.dueDateRange
+    if (start || end) {
+      whereClause.dueDate = {}
+      if (start) {
+        whereClause.dueDate.gte = start
+      }
+      if (end) {
+        whereClause.dueDate.lte = end
+      }
+    }
+  }
+
+  // Fetch items from database
+  const items = await prisma.item.findMany({
+    where: whereClause,
+    include: {
+      list: true,
+    },
+  })
+
+  // Filter by tags (client-side since tags are stored as JSON)
+  let filteredItems = items
+  if (filters.tags && filters.tags.length > 0) {
+    filteredItems = items.filter((item) => {
+      const itemTags = Array.isArray(item.tags) ? item.tags : []
+      return filters.tags!.every((filterTag) =>
+        itemTags.some((itemTag) => typeof itemTag === 'string' && itemTag === filterTag)
+      )
+    })
+  }
+
+  // Sort items
+  const sortBy = filters.sortBy || 'createdAt'
+  const sortOrder = filters.sortOrder || 'desc'
+
+  const sortedItems = [...filteredItems].sort((a, b) => {
+    let comparison = 0
+
+    switch (sortBy) {
+      case 'createdAt':
+        comparison = a.createdAt.getTime() - b.createdAt.getTime()
+        break
+      case 'dueDate':
+        // Handle null due dates - place at end
+        if (a.dueDate === null && b.dueDate === null) {
+          comparison = 0
+        } else if (a.dueDate === null) {
+          comparison = 1 // a goes after b
+        } else if (b.dueDate === null) {
+          comparison = -1 // b goes after a
+        } else {
+          comparison = a.dueDate.getTime() - b.dueDate.getTime()
+        }
+        break
+      case 'priority':
+        const priorityOrder = { low: 1, medium: 2, high: 3 }
+        const aPriority = priorityOrder[a.priority as keyof typeof priorityOrder] || 2
+        const bPriority = priorityOrder[b.priority as keyof typeof priorityOrder] || 2
+        comparison = aPriority - bPriority
+        break
+      case 'title':
+        comparison = a.title.localeCompare(b.title)
+        break
+    }
+
+    return sortOrder === 'asc' ? comparison : -comparison
+  })
+
+  return sortedItems
 }