Convert lists to attributed strings

Sources/HTMLStreamer/AttributedStringConverter.swift

@@ -99,6 +99,28 @@ struct AttributedStringConverter<Callbacks: AttributedStringCallbacks> {
             styleStack.append(.blockquote)
         case "p":
             startBlockElement()
+        case "ol":
+            startBlockElement()
+            finishRun()
+            styleStack.append(.orderedList(nextElementOrdinal: 1))
+        case "ul":
+            startBlockElement()
+            finishRun()
+            styleStack.append(.unorderedList)
+        case "li":
+            if str.length != 0 || !currentRun.isEmpty {
+                currentRun.append("\n")
+            }
+            let marker: String
+            if case .orderedList(let nextElementOrdinal) = styleStack.last {
+                marker = orderedTextList.marker(forItemNumber: nextElementOrdinal)
+                styleStack[styleStack.count - 1] = .orderedList(nextElementOrdinal: nextElementOrdinal + 1)
+            } else if case .unorderedList = styleStack.last {
+                marker = unorderedTextList.marker(forItemNumber: 0)
+            } else {
+                break
+            }
+            currentRun.append("\t\(marker)\t")
         default:
             break
         }
@@ -135,6 +157,14 @@ struct AttributedStringConverter<Callbacks: AttributedStringCallbacks> {
         case "blockquote":
             finishRun()
             removeLastStyle(.blockquote)
+        case "ol":
+            finishRun()
+            removeLastStyle(.orderedList)
+        case "ul":
+            finishRun()
+            removeLastStyle(.unorderedList)
+        case "li":
+            finishRun()
         default:
             break
         }
@@ -159,6 +189,19 @@ struct AttributedStringConverter<Callbacks: AttributedStringCallbacks> {
         return style
     }()
     
+    private lazy var listParagraphStyle: NSParagraphStyle = {
+        let style = configuration.paragraphStyle.mutableCopy() as! NSMutableParagraphStyle
+        // I don't like that I can't just use paragraphStyle.textLists, because it makes the list markers
+        // not use the monospace digit font (it seems to just use whatever font attribute is set for the whole thing),
+        // and it doesn't right align the list markers.
+        // Unfortunately, doing it manually means the list markers are incldued in the selectable text.
+        style.headIndent = 32
+        style.firstLineHeadIndent = 0
+        // Use 2 tab stops, one for the list marker, the second for the content.
+        style.tabStops = [NSTextTab(textAlignment: .right, location: 28), NSTextTab(textAlignment: .natural, location: 32)]
+        return style
+    }()
+    
     private mutating func finishRun() {
         guard !currentRun.isEmpty else {
             return
@@ -190,6 +233,8 @@ struct AttributedStringConverter<Callbacks: AttributedStringCallbacks> {
             case .blockquote:
                 attributes[.paragraphStyle] = blockquoteParagraphStyle
                 currentFontTraits.insert(.italic)
+            case .orderedList, .unorderedList:
+                attributes[.paragraphStyle] = listParagraphStyle
             }
         }
         
@@ -290,6 +335,8 @@ private enum Style {
     case link(URL?)
     case strikethrough
     case blockquote
+    case orderedList(nextElementOrdinal: Int)
+    case unorderedList
     
     var type: StyleType {
         switch self {
@@ -305,11 +352,22 @@ private enum Style {
             return .strikethrough
         case .blockquote:
             return .blockquote
+        case .orderedList(nextElementOrdinal: _):
+            return .orderedList
+        case .unorderedList:
+            return .unorderedList
         }
     }
     
-    enum StyleType {
+    enum StyleType: Equatable {
-        case bold, italic, monospace, link, strikethrough, blockquote
+        case bold
+        case italic
+        case monospace
+        case link
+        case strikethrough
+        case blockquote
+        case orderedList
+        case unorderedList
     }
 }
 
@@ -318,3 +376,12 @@ extension Collection where Element == Attribute {
         first(where: { $0.name == name })?.value
     }
 }
+
+private let orderedTextList = OrderedNumberTextList(markerFormat: .decimal, options: 0)
+private let unorderedTextList = NSTextList(markerFormat: .disc, options: 0)
+
+private class OrderedNumberTextList: NSTextList {
+    override func marker(forItemNumber itemNumber: Int) -> String {
+        "\(super.marker(forItemNumber: itemNumber))."
+    }
+}

Tests/HTMLStreamerTests/AttributedStringConverterTests.swift

@@ -26,6 +26,13 @@ final class AttributedStringConverterTests: XCTestCase {
         style.firstLineHeadIndent = 32
         return style
     }()
+    private let listParagraphStyle: NSParagraphStyle = {
+        let style = NSParagraphStyle.default.mutableCopy() as! NSMutableParagraphStyle
+        style.headIndent = 32
+        style.firstLineHeadIndent = 0
+        style.tabStops = [NSTextTab(textAlignment: .right, location: 28), NSTextTab(textAlignment: .natural, location: 32)]
+        return style
+    }()
     
     private func convert(_ html: String) -> NSAttributedString {
         convert(html, callbacks: DefaultCallbacks.self)
@@ -192,4 +199,12 @@ final class AttributedStringConverterTests: XCTestCase {
         ]))
     }
     
+    func testOrderedList() {
+        let result = convert("<ol><li>a</li><li>b</li></ol>")
+        XCTAssertEqual(result, NSAttributedString(string: "\t1.\ta\n\t2.\tb", attributes: [
+            .font: font,
+            .paragraphStyle: listParagraphStyle,
+        ]))
+    }
+    
 }