GH-666 Use reversed attrs for marked text

NvimView/NvimView/CellAttributesCollection.swift

@@ -8,6 +8,7 @@ import Foundation
 final class CellAttributesCollection {
 
   static let defaultAttributesId = 0
+  static let reversedDefaultAttributesId = Int.max
 
   private(set) var defaultAttributes = CellAttributes(
     fontTrait: [],
@@ -23,10 +24,20 @@ final class CellAttributesCollection {
   }
 
   func attributes(of id: Int) -> CellAttributes? {
-    guard let attrs = self.attributes[id] else {
+    if id == Int.max {
+      return self.defaultAttributes.reversed
+    }
+
+    let absId = abs(id)
+
+    guard let attrs = self.attributes[absId] else {
       return nil
     }
 
+    if id < 0 {
+      return attrs.replacingDefaults(with: self.defaultAttributes).reversed
+    }
+
     return attrs.replacingDefaults(with: self.defaultAttributes)
   }
 

NvimView/NvimView/NvimView+UiBridge.swift

@@ -234,6 +234,13 @@ extension NvimView {
         top: row, bottom: row, left: endCol, right: max(endCol, clearCol - 1)
       ))
     }
+
+    if row == self.markedPosition.row
+         && startCol <= self.markedPosition.column
+         && self.markedPosition.column <= endCol
+    {
+      self.ugrid.markCell(at: self.markedPosition)
+    }
   }
 
   private func doGoto(position: Position) {

NvimView/NvimView/UGrid.swift

@@ -23,6 +23,21 @@ final class UGrid {
     return !self.cells.isEmpty
   }
 
+  func markCell(at position: Position) {
+    let attrId = self.cells[position.row][position.column].attrId
+    let markedAttrId: Int
+    if attrId == CellAttributesCollection.defaultAttributesId {
+      markedAttrId = CellAttributesCollection.reversedDefaultAttributesId
+    } else {
+      markedAttrId = (-1) * attrId
+    }
+    self.cells[position.row][position.column].attrId = markedAttrId
+
+    if self.isNextCellEmpty(position) {
+      self.cells[position.row][position.column + 1].attrId = markedAttrId
+    }
+  }
+
   func position(from flattenedIndex: Int) -> Position {
     let row = min(
       self.size.height - 1,

NvimView/NvimViewTests/UGridTest.swift

@@ -13,6 +13,51 @@ class UGridTest: XCTestCase {
 
   private let ugrid = UGrid()
 
+  func testMarkPosition() {
+    self.ugrid.resize(Size(width: 20, height: 10))
+    self.ugrid.update(
+      row: 9,
+      startCol: 0,
+      endCol: 9,
+      clearCol: 0,
+      clearAttr: 0,
+      chunk: Array("0123456789".compactMap { String($0) }),
+      attrIds: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+    )
+    self.ugrid.markCell(at: Position(row: 9, column: 4))
+    expect(self.ugrid.cells[9][4].attrId).to(equal(-4))
+
+    self.ugrid.update(
+      row: 7,
+      startCol: 0,
+      endCol: 9,
+      clearCol: 0,
+      clearAttr: 0,
+      chunk: Array("23456789".compactMap { String($0) }) + ["하", ""],
+      attrIds: [0, 1, 2, 3, 4, 5, 6, 7, 8, 8]
+    )
+    self.ugrid.markCell(at: Position(row: 7, column: 8))
+    expect(self.ugrid.cells[7][8].attrId)
+      .to(equal(-8))
+    expect(self.ugrid.cells[7][9].attrId)
+      .to(equal(-8))
+
+    self.ugrid.update(
+      row: 8,
+      startCol: 0,
+      endCol: 9,
+      clearCol: 0,
+      clearAttr: 0,
+      chunk: ["하", ""] + Array("23456789".compactMap { String($0) }),
+      attrIds: [0, 0, 2, 3, 4, 5, 6, 7, 8, 9]
+    )
+    self.ugrid.markCell(at: Position(row: 8, column: 0))
+    expect(self.ugrid.cells[8][0].attrId)
+      .to(equal(CellAttributesCollection.reversedDefaultAttributesId))
+    expect(self.ugrid.cells[8][1].attrId)
+      .to(equal(CellAttributesCollection.reversedDefaultAttributesId))
+  }
+
   func testFlattenedIndex() {
     self.ugrid.resize(Size(width: 20, height: 10))
     expect(