UI Designer

class UIDesignerActivity : BaseIDEActivity() {
  private val viewModel by viewModels<WorkspaceViewModel>()
  
  companion object {
    const val EXTRA_FILE = "layout_file"
    
    fun launch(context: Context, layoutFile: File) {
      val intent = Intent(context, UIDesignerActivity::class.java)
      intent.putExtra(EXTRA_FILE, layoutFile)
      context.startActivity(intent)
    }
  }
}

class DesignerWorkspaceFragment : Fragment() {
  val workspaceView: ViewGroup
    get() = binding.designerCanvas
  
  private fun setupWorkspace() {
    // Setup canvas
    workspaceView.setOnDragListener(WidgetDragListener())
    
    // Enable touch interactions
    enableViewSelection()
    enableViewDragging()
  }
  
  fun addView(widget: View, params: ViewGroup.LayoutParams) {
    workspaceView.addView(widget, params)
    refreshHierarchy()
  }
}

class WidgetsItemAdapter(
  private val widgets: List<WidgetInfo>
) : RecyclerView.Adapter<WidgetViewHolder>() {
  
  override fun onBindViewHolder(holder: WidgetViewHolder, position: Int) {
    val widget = widgets[position]
    holder.bind(widget)
    
    // Setup drag behavior
    holder.itemView.setOnLongClickListener {
      val dragData = ClipData.newPlainText("widget", widget.className)
      val shadowBuilder = WidgetDragShadowBuilder(it)
      it.startDragAndDrop(dragData, shadowBuilder, widget, 0)
      true
    }
  }
}

class WidgetTouchListener(
  private val workspace: ViewGroup
) : View.OnTouchListener {
  
  override fun onTouch(view: View, event: MotionEvent): Boolean {
    return when (event.action) {
      MotionEvent.ACTION_DOWN -> {
        // Prepare for drag
        val dragShadow = WidgetDragShadowBuilder(view)
        val data = ClipData.newPlainText("view_id", view.id.toString())
        view.startDragAndDrop(data, dragShadow, view, 0)
        true
      }
      else -> false
    }
  }
}

class WidgetDragListener(
  private val workspace: ViewGroup
) : View.OnDragListener {
  
  override fun onDrag(view: View, event: DragEvent): Boolean {
    return when (event.action) {
      DragEvent.ACTION_DRAG_STARTED -> true
      
      DragEvent.ACTION_DRAG_ENTERED -> {
        // Highlight drop target
        view.background = highlightDrawable
        true
      }
      
      DragEvent.ACTION_DROP -> {
        // Handle drop
        val widget = createWidget(event.clipData)
        val params = calculateLayoutParams(event.x, event.y)
        workspace.addView(widget, params)
        true
      }
      
      DragEvent.ACTION_DRAG_ENDED -> {
        view.background = null
        true
      }
      
      else -> false
    }
  }
}

class WidgetDragShadowBuilder(
  view: View
) : View.DragShadowBuilder(view) {
  
  private val shadow = ColorDrawable(Color.LTGRAY)
  
  override fun onProvideShadowMetrics(
    outShadowSize: Point,
    outShadowTouchPoint: Point
  ) {
    val width = view.width / 2
    val height = view.height / 2
    
    outShadowSize.set(width, height)
    outShadowTouchPoint.set(width / 2, height / 2)
  }
  
  override fun onDrawShadow(canvas: Canvas) {
    shadow.setBounds(0, 0, view.width, view.height)
    shadow.draw(canvas)
  }
}

class ViewInfoFragment : Fragment() {
  private var selectedView: View? = null
  
  fun setSelectedView(view: View) {
    selectedView = view
    displayAttributes(view)
  }
  
  private fun displayAttributes(view: View) {
    val attrs = extractAttributes(view)
    binding.attributeList.adapter = ViewAttrListAdapter(attrs) { attr, value ->
      applyAttribute(view, attr, value)
    }
  }
  
  private fun applyAttribute(view: View, attr: String, value: String) {
    when (attr) {
      "android:text" -> (view as? TextView)?.text = value
      "android:textSize" -> (view as? TextView)?.textSize = value.toFloat()
      "android:layout_width" -> updateLayoutParam(view, "width", value)
      "android:layout_height" -> updateLayoutParam(view, "height", value)
      // ... more attributes
    }
  }
}

class ViewAttrListAdapter(
  private val attributes: List<Attribute>,
  private val onAttributeChanged: (String, String) -> Unit
) : RecyclerView.Adapter<AttrViewHolder>() {
  
  override fun onBindViewHolder(holder: AttrViewHolder, position: Int) {
    val attr = attributes[position]
    holder.nameText.text = attr.name
    holder.valueInput.setText(attr.value)
    
    holder.valueInput.addTextChangedListener { text ->
      onAttributeChanged(attr.name, text.toString())
    }
  }
}

class AddAttrFragment : DialogFragment() {
  
  private fun showAttributePicker() {
    val availableAttrs = listOf(
      "android:id",
      "android:text",
      "android:textColor",
      "android:textSize",
      "android:background",
      "android:padding",
      "android:margin",
      "android:layout_width",
      "android:layout_height",
      "android:gravity",
      // ... more attributes
    )
    
    binding.attrList.adapter = AddAttrListAdapter(availableAttrs) { attr ->
      addAttributeToView(attr)
      dismiss()
    }
  }
}

class ShowHierarchyAction : UiDesignerAction() {
  override fun execAction(data: ActionData): Boolean {
    val hierarchy = buildHierarchy(workspace.rootView)
    showHierarchyDialog(hierarchy)
    return true
  }
  
  private fun buildHierarchy(view: View): TreeNode {
    val node = TreeNode(view)
    if (view is ViewGroup) {
      for (i in 0 until view.childCount) {
        node.addChild(buildHierarchy(view.getChildAt(i)))
      }
    }
    return node
  }
}

ConstraintLayout
├── Toolbar
│   └── TextView (title)
├── LinearLayout
│   ├── ImageView
│   ├── TextView
│   └── Button
└── FloatingActionButton

object ViewToXml {
  fun generateXml(
    context: Context,
    view: View,
    onSuccess: (String) -> Unit,
    onError: (Result<String>, Throwable?) -> Unit
  ) {
    try {
      val xml = StringBuilder()
      xml.append("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n")
      
      writeView(view, xml, 0)
      
      onSuccess(formatXml(xml.toString()))
    } catch (e: Exception) {
      onError(Result.failure(e), e)
    }
  }
  
  private fun writeView(view: View, xml: StringBuilder, indent: Int) {
    val tag = getXmlTag(view)
    val attrs = extractAttributes(view)
    
    xml.append("  ".repeat(indent))
    xml.append("<$tag")
    
    // Write attributes
    attrs.forEach { (name, value) ->
      xml.append("\n")
      xml.append("  ".repeat(indent + 1))
      xml.append("$name=\"$value\"")
    }
    
    // Write children
    if (view is ViewGroup && view.childCount > 0) {
      xml.append(">\n")
      
      for (i in 0 until view.childCount) {
        writeView(view.getChildAt(i), xml, indent + 1)
      }
      
      xml.append("  ".repeat(indent))
      xml.append("</$tag>\n")
    } else {
      xml.append(" />\n")
    }
  }
}

class UndoAction : UiDesignerAction() {
  override fun execAction(data: ActionData): Boolean {
    val viewModel = data.get(WorkspaceViewModel::class.java)
    return viewModel.undo()
  }
}

class RedoAction : UiDesignerAction() {
  override fun execAction(data: ActionData): Boolean {
    val viewModel = data.get(WorkspaceViewModel::class.java)
    return viewModel.redo()
  }
}

class ShowXmlAction : UiDesignerAction() {
  override fun execAction(data: ActionData): Boolean {
    val workspace = getWorkspace(data)
    
    ViewToXml.generateXml(
      context = data.requireContext(),
      view = workspace.workspaceView,
      onSuccess = { xml ->
        showXmlPreview(xml)
      },
      onError = { _, error ->
        showError("Failed to generate XML: ${error?.message}")
      }
    )
    
    return true
  }
}

class UiViewLayeredForeground : Drawable() {
  private val borderPaint = Paint().apply {
    style = Paint.Style.STROKE
    strokeWidth = 4f
    color = Color.BLUE
  }
  
  private val cornerPaint = Paint().apply {
    style = Paint.Style.FILL
    color = Color.BLUE
  }
  
  override fun draw(canvas: Canvas) {
    // Draw border
    canvas.drawRect(bounds, borderPaint)
    
    // Draw corner handles
    val handleSize = 16f
    canvas.drawCircle(bounds.left.toFloat(), bounds.top.toFloat(), 
                     handleSize, cornerPaint)
    canvas.drawCircle(bounds.right.toFloat(), bounds.top.toFloat(), 
                     handleSize, cornerPaint)
    canvas.drawCircle(bounds.left.toFloat(), bounds.bottom.toFloat(), 
                     handleSize, cornerPaint)
    canvas.drawCircle(bounds.right.toFloat(), bounds.bottom.toFloat(), 
                     handleSize, cornerPaint)
  }
}

// 1. Open layout file in designer
val layoutFile = File(projectDir, "app/src/main/res/layout/activity_main.xml")
UIDesignerActivity.launch(context, layoutFile)

// 2. User designs layout with drag-and-drop
// - Drag LinearLayout from palette
// - Drop onto canvas
// - Drag TextView and Button into LinearLayout
// - Edit attributes in property panel

// 3. Generate XML
ViewToXml.generateXml(context, rootView) { xml ->
  // 4. Save to file
  layoutFile.writeText(xml)
  
  // 5. Return to editor
  finish()
}