HTMLStreamer/Tests/HTMLStreamerTests/AttributedStringConverterTests.swift

//
//  AttributedStringConverterTests.swift
//  
//
//  Created by Shadowfacts on 11/24/23.
//

import XCTest
@testable import HTMLStreamer

final class AttributedStringConverterTests: XCTestCase {
    
    #if os(iOS)
    private let font = UIFont.systemFont(ofSize: 13)
    private let color = UIColor.black
    private lazy var italicFont = UIFont(descriptor: font.fontDescriptor.withSymbolicTraits([.traitItalic])!, size: 13)
    private lazy var boldFont = UIFont(descriptor: font.fontDescriptor.withSymbolicTraits([.traitBold])!, size: 13)
    private lazy var boldItalicFont = UIFont(descriptor: font.fontDescriptor.withSymbolicTraits([.traitBold, .traitItalic])!, size: 13)
    private let monospaceFont = UIFont.monospacedSystemFont(ofSize: 13, weight: .regular)
    #elseif os(macOS)
    private let font = NSFont.systemFont(ofSize: 13)
    private let color = NSColor.black
    private lazy var italicFont = NSFont(descriptor: font.fontDescriptor.withSymbolicTraits(.italic), size: 13)!
    private lazy var boldFont = NSFont(descriptor: font.fontDescriptor.withSymbolicTraits(.bold), size: 13)!
    private lazy var boldItalicFont = NSFont(descriptor: font.fontDescriptor.withSymbolicTraits([.bold, .italic]), size: 13)!
    private let monospaceFont = NSFont.monospacedSystemFont(ofSize: 13, weight: .regular)
    #endif
    private let blockquoteParagraphStyle: NSParagraphStyle = {
        let style = NSParagraphStyle.default.mutableCopy() as! NSMutableParagraphStyle
        style.headIndent = 32
        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)
    }
    
    private func convert<Callbacks: HTMLConversionCallbacks>(_ html: String, callbacks _: Callbacks.Type = Callbacks.self) -> NSAttributedString {
        #if os(iOS) || os(visionOS)
        let config = AttributedStringConverterConfiguration(
            font: font,
            monospaceFont: monospaceFont,
            fontMetrics: .default,
            color: color,
            paragraphStyle: .default
        )
        #else
        let config = AttributedStringConverterConfiguration(
            font: font,
            monospaceFont: monospaceFont,
            color: color,
            paragraphStyle: .default
        )
        #endif
        let converter = AttributedStringConverter<Callbacks>(configuration: config)
        return converter.convert(html: html)
    }

    func testConvertBR() {
        XCTAssertEqual(convert("a<br>b"), NSAttributedString(string: "a\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("a<br />b"), NSAttributedString(string: "a\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testConvertA() {
        XCTAssertEqual(convert("<a href='https://example.com'>link</a>"), NSAttributedString(string: "link", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
            .link: URL(string: "https://example.com")!,
        ]))
        XCTAssertEqual(convert("<a>link</a>"), NSAttributedString(string: "link", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testConvertP() {
        XCTAssertEqual(convert("<p>a</p><p>b</p>"), NSAttributedString(string: "a\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testConvertEm() {
        XCTAssertEqual(convert("<em>hello</em>"), NSAttributedString(string: "hello", attributes: [
            .font: italicFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<i>hello</i>"), NSAttributedString(string: "hello", attributes: [
            .font: italicFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testConvertStrong() {
        XCTAssertEqual(convert("<strong>hello</strong>"), NSAttributedString(string: "hello", attributes: [
            .font: boldFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<b>hello</b>"), NSAttributedString(string: "hello", attributes: [
            .font: boldFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testConvertBoldItalic() {
        XCTAssertEqual(convert("<strong><em>hello</em></strong>"), NSAttributedString(string: "hello", attributes: [
            .font: boldItalicFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testIncorrectNesting() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "bold ", attributes: [
            .font: boldFont,
        ]))
        result.append(NSAttributedString(string: "both", attributes: [
            .font: boldItalicFont,
        ]))
        result.append(NSAttributedString(string: " italic", attributes: [
            .font: italicFont,
        ]))
        result.addAttribute(.paragraphStyle, value: NSParagraphStyle.default, range: NSRange(location: 0, length: result.length))
        result.addAttribute(.foregroundColor, value: color, range: NSRange(location: 0, length: result.length))
        XCTAssertEqual(convert("<strong>bold <em>both</strong> italic</em>"), result)
    }
    
    func testMisnestedLink() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "hello ", attributes: [
            .font: font,
        ]))
        result.append(NSAttributedString(string: "world", attributes: [
            .font: boldFont,
        ]))
        result.addAttribute(.link, value: URL(string: "https://example.com")!, range: NSRange(location: 0, length: result.length))
        result.addAttribute(.paragraphStyle, value: NSParagraphStyle.default, range: NSRange(location: 0, length: result.length))
        result.addAttribute(.foregroundColor, value: color, range: NSRange(location: 0, length: result.length))
        XCTAssertEqual(convert("<a href='https://example.com'>hello <b>world</a></b>"), result)
    }
    
    func testDel() {
        XCTAssertEqual(convert("<del>blah</del>"), NSAttributedString(string: "blah", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
            .strikethroughStyle: NSUnderlineStyle.single.rawValue,
        ]))
    }
    
    func testCode() {
        XCTAssertEqual(convert("<code>wee</code>"), NSAttributedString(string: "wee", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testPre() {
        XCTAssertEqual(convert("<pre>wee</pre>"), NSAttributedString(string: "wee", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testBlockquote() {
        XCTAssertEqual(convert("<blockquote>hello</blockquote>"), NSAttributedString(string: "hello", attributes: [
            .font: italicFont,
            .paragraphStyle: blockquoteParagraphStyle,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<blockquote><b>hello</b></blockquote>"), NSAttributedString(string: "hello", attributes: [
            .font: boldItalicFont,
            .paragraphStyle: blockquoteParagraphStyle,
            .foregroundColor: color,
        ]))
    }
    
    func testTextAfterBlockquote() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "wee", attributes: [
            .font: italicFont,
            .paragraphStyle: blockquoteParagraphStyle,
        ]))
        result.append(NSAttributedString(string: "\n\nafter", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
        ]))
        result.addAttribute(.foregroundColor, value: color, range: NSRange(location: 0, length: result.length))
        XCTAssertEqual(convert("<blockquote>wee</blockquote>after"), result)
    }
    
    func testMultipleBlockElements() {
        let result = NSAttributedString(string: "a\n\nb", attributes: [
            .font: italicFont,
            .paragraphStyle: blockquoteParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<blockquote>a</blockquote><blockquote>b</blockquote>"), result)
    }
    
    func testSelfClosing() {
        XCTAssertEqual(convert("<b />asdf"), NSAttributedString(string: "asdf", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testMakeURLCallback() {
        struct Callbacks: HTMLConversionCallbacks {
            static func makeURL(string: String) -> URL? {
                URL(string: "https://apple.com")
            }
        }
        let result = convert("<a href='https://example.com'>test</a>", callbacks: Callbacks.self)
        XCTAssertEqual(result, NSAttributedString(string: "test", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .link: URL(string: "https://apple.com")!,
            .foregroundColor: color,
        ]))
    }
    
    func testElementActionCallback() {
        struct Callbacks: HTMLConversionCallbacks {
            static func elementAction(name: String, attributes: [Attribute]) -> ElementAction {
                let clazz = attributes.attributeValue(for: "class")
                if clazz == "skip" {
                    return .skip
                } else if clazz == "replace" {
                    return .replace("…")
                } else if clazz == "append" {
                    return .append("…")
                } else {
                    return .default
                }
            }
        }
        let skipped = convert("<span class='skip'>test</span>", callbacks: Callbacks.self)
        XCTAssertEqual(skipped, NSAttributedString())
        let skipNested = convert("<span class='skip'><b>test</b></span>", callbacks: Callbacks.self)
        XCTAssertEqual(skipNested, NSAttributedString())
        let skipNestped2 = convert("<b><span class='skip'>test</span></b>", callbacks: Callbacks.self)
        XCTAssertEqual(skipNestped2, NSAttributedString())
        let replaced = convert("<span class='replace'>test</span>", callbacks: Callbacks.self)
        XCTAssertEqual(replaced, NSAttributedString(string: "…", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        let replaceNested = convert("<span class='replace'><b>a</b></span>", callbacks: Callbacks.self)
        XCTAssertEqual(replaceNested, NSAttributedString(string: "…", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        let appended = convert("<span class='append'>test</span>", callbacks: Callbacks.self)
        XCTAssertEqual(appended, NSAttributedString(string: "test…", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        let appended2 = convert("<span class='append'>test <span>blah</span></span>", callbacks: Callbacks.self)
        XCTAssertEqual(appended2, NSAttributedString(string: "test blah…", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    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,
            .foregroundColor: color,
        ]))
    }
    
    func testMultiScalar() {
        XCTAssertEqual(convert("🇺🇸"), NSAttributedString(string: "🇺🇸", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
    }
    
    func testEmptyBlockElements() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "inside\nquote", attributes: [
            .font: italicFont,
            .paragraphStyle: blockquoteParagraphStyle,
            .foregroundColor: color,
        ]))
        result.append(NSAttributedString(string: "\n\nafter", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<p></p><blockquote><span>inside<br>quote</span></blockquote><span>after</span><p></p>"), result)
    }
    
    func testFollowedByList() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "a", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        result.append(NSAttributedString(string: "\n\n\t1.\tb\n\t2.\tc", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<p>a</p><ol><li>b</li><li>c</li></ol>"), result)
        XCTAssertEqual(convert("<span>a</span><ol><li>b</li><li>c</li></ol>"), result)
        XCTAssertEqual(convert("a<ol><li>b</li><li>c</li></ol>"), result)
    }
    
    func testListItemOutsideList() {
        let result = NSAttributedString(string: "a", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<li>a</li>"), result)
    }
    
    func testSkipElementActionFollowingUnfinishedRun() {
        struct Callbacks: HTMLConversionCallbacks {
            static func elementAction(name: String, attributes: [Attribute]) -> ElementAction {
                attributes.attributeValue(for: "class") == "invisible" ? .skip : .default
            }
        }
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "example.com", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
            .link: URL(string: "https://example.com")!,
        ]))
        XCTAssertEqual(convert(#"<a href="https://example.com"><span class="invisible">https://</span><span>example.com</span><span class="invisible"></span></a>"#, callbacks: Callbacks.self), result)
    }
    
    func testMalformedOnlyClosingTag() {
        XCTAssertEqual(convert("</span>"), .init())
    }
    
    func testMultipleClosingBlockTagsBeforeOpeningBlockTag() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "a", attributes: [
            .font: italicFont,
            .paragraphStyle: blockquoteParagraphStyle,
            .foregroundColor: color,
        ]))
        result.append(NSAttributedString(string: "\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert(#"<blockquote><p>a</p></blockquote><p>b</p>"#), result)
    }
    
    func testNewlineBetweenClosingAndOpeningBlockTag() {
        let result = NSAttributedString(string: "a\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a</p>\n<p>b</p>"), result)
        XCTAssertEqual(convert("<p>a</p><p>\nb</p>"), result)
    }
    
    func testEndAfterNewlineInBlockContent() {
        let result = NSAttributedString(string: "a", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a\n\n</p>"), result)
        XCTAssertEqual(convert("<p>a\n\n</p>\n"), result)
        XCTAssertEqual(convert("<p>\n\na</p>"), result)
        XCTAssertEqual(convert("<p>\n\na</p>\n"), result)
        let result2 = NSAttributedString(string: "a\n\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a\n\n\nb</p>"), result2)
    }
    
    func testBRAtBlockElementBoundary() {
        let two = NSAttributedString(string: "a\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a<br></p><p>b</p>"), two)
        let three = NSAttributedString(string: "a\n\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a</p><p><br>b</p>"), three)
    }
    
    func testPreFollowedByP() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "a", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        result.append(NSAttributedString(string: "\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<pre>a<br></pre><p>b</p>"), result)
    }
    
    func testPreFollowedByPre() {
        let result = NSAttributedString(string: "a\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>a</pre><pre>b</pre>"), result)
    }
    
    func testBRAtPreBoundary() {
        let two = NSAttributedString(string: "a\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>a<br></pre><pre>b</pre>"), two)
        let three = NSAttributedString(string: "a\n\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>a</pre><pre><br>b</pre>"), three)
    }
    
    func testNestedPre() {
        let one = NSAttributedString(string: "a", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre><pre>a</pre></pre>"), one)
        let two = NSAttributedString(string: "a\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>a<pre>b</pre></pre>"), two)
        XCTAssertEqual(convert("<pre>a<br><pre>b</pre></pre>"), two)
        let three = NSAttributedString(string: "a\n\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>a<pre><br>b</pre></pre>"), three)
    }
    
    func testIgnoreLeadingNewlineInPre() {
        let one = NSAttributedString(string: "a", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>\na</pre>"), one)
        let two = NSMutableAttributedString()
        two.append(NSAttributedString(string: "a", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        two.append(NSAttributedString(string: "\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("a<pre>\nb</pre>"), two)
    }
    
    func testPreFollowingChar() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "a", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        result.append(NSAttributedString(string: "\n\nb", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("a<pre>b</pre>"), result)
    }
    
    func testSkipLeadingTrailingWhitespace() {
        let result = NSAttributedString(string: "a", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("  \n\ta"), result)
        XCTAssertEqual(convert("  \n\t<p>a</p>"), result)
        XCTAssertEqual(convert("a\n\t"), result)
        XCTAssertEqual(convert("<p>a</p>  \n\t"), result)
        let result2 = NSAttributedString(string: "a  ", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("a  \n\t"), result2)
        
        let pre = NSAttributedString(string: "a", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("  \n\t<pre>a</pre>"), pre)
        XCTAssertEqual(convert("<pre>a</pre>  \n\t"), pre)
    }
    
    func testDoesNotCollapseWhitespace() {
        let result = NSAttributedString(string: "a \t\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a \t\nb</p>"), result)
    }
    
    func testParagraphInsideListItem() {
        let result = NSAttributedString(string: "\t1.\ta\n\t2.\tb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li><p>a</p></li><li><p>b</p></li></ol>"), result)
    }
    
    func testMultipleParagraphsInsideListItem() {
        let result = NSAttributedString(string: "\t1.\ta\n\nb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li><p>a</p><p>b</p></li></ol>"), result)
    }
    
    func testBreakBetweenListItems() {
        let result = NSAttributedString(string: "\t1.\ta\n\n\t2.\tb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li>a</li><br><li>b</li></ol>"), result)
    }
    
    func testCharacterBetweenListItems() {
        let result = NSAttributedString(string: "\t1.\ta\n\t\tc\n\t2.\tb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li>a</li>c<li>b</li></ol>"), result)
        let result2 = NSAttributedString(string: "\t1.\ta\n\t\tc  \n\t2.\tb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li>a</li>c  <li>b</li></ol>"), result2)
    }
    
    func testWhitespaceCollapsingInTextBetweenListItems() {
        let result = NSAttributedString(string: "\t1.\ta\n\t\tc   d\n\t2.\tb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li>a</li>c   d<li>b</li></ol>"), result)
    }
    
    func testImplicitlyClosedListItem() {
        let result = NSAttributedString(string: "\t1.\ta\n\t2.\tb", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<ol><li>a<li>b</ol>"), result)
    }
    
    func testPreInsideListItem() {
        let result = NSMutableAttributedString()
        result.append(NSAttributedString(string: "\t1.\t", attributes: [
            .font: font,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ]))
        result.append(NSAttributedString(string: "a", attributes: [
            .font: monospaceFont,
            .paragraphStyle: listParagraphStyle,
            .foregroundColor: color,
        ]))
        XCTAssertEqual(convert("<ol><li><pre>a</pre></li></ol>"), result)
    }
    
    func testInvisibleAtBeginningOfParagraphDoesNotPreventParagraphBreak() {
        struct Invisible: HTMLConversionCallbacks {
            static func elementAction(name: String, attributes: [Attribute]) -> ElementAction {
                if attributes.attributeValue(for: "class") == "invisible" {
                    .skip
                } else {
                    .default
                }
            }
        }
        
        let result = NSAttributedString(string: "a\n\nc", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        let html = """
<p>a</p><p><span class="invisible">b</span><span class="ellipsis">c</span></p>
"""
        XCTAssertEqual(convert(html, callbacks: Invisible.self), result)
    }
    
    func testReplaceAtBeginningOfParagraphDoesNotPreventParagraphBreak() {
        struct Replace: HTMLConversionCallbacks {
            static func elementAction(name: String, attributes: [Attribute]) -> ElementAction {
                if attributes.attributeValue(for: "class") == "replace" {
                    .replace("c")
                } else {
                    .default
                }
            }
        }
        
        let result = NSAttributedString(string: "a\n\nc", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        let html = """
<p>a</p><p><span class="replace">b</span></p>
"""
        XCTAssertEqual(convert(html, callbacks: Replace.self), result)
    }
    
    func testLineBreakAtBeginningOfBlockElement() {
        let result = NSAttributedString(string: "a\n\n\n\nb", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a</p><p><br></p><p>b</p>"), result)
        
        let result2 = NSAttributedString(string: "a\n\n\nb\n\nc", attributes: [
            .font: font,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<p>a</p><p><br>b</p><p>c</p>"), result2)
    }

    func testWhitespaceAtEndOfPre() {
        let result = NSAttributedString(string: "a", attributes: [
            .font: monospaceFont,
            .paragraphStyle: NSParagraphStyle.default,
            .foregroundColor: color,
        ])
        XCTAssertEqual(convert("<pre>a </pre>"), result)
    }
    
}