274 lines
12 KiB
Swift
274 lines
12 KiB
Swift
//
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// Copyright 2022 New Vector Ltd
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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import DTCoreText
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import Foundation
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import LRUCache
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struct AttributedStringBuilder: AttributedStringBuilderProtocol {
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private let temporaryBlockquoteMarkingColor = UIColor.magenta
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private let temporaryCodeBlockMarkingColor = UIColor.cyan
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private let linkColor = UIColor.blue
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private let permalinkBaseURL: URL
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private static var cache = LRUCache<String, AttributedString>(countLimit: 1000)
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init(permalinkBaseURL: URL) {
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self.permalinkBaseURL = permalinkBaseURL
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}
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func fromPlain(_ string: String?) -> AttributedString? {
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guard let string else {
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return nil
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}
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if let cached = Self.cache.value(forKey: string) {
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return cached
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}
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let mutableAttributedString = NSMutableAttributedString(string: string)
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addLinks(mutableAttributedString)
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removeLinkColors(mutableAttributedString)
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let result = try? AttributedString(mutableAttributedString, including: \.elementX)
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Self.cache.setValue(result, forKey: string)
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return result
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}
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// Do not use the default HTML renderer of NSAttributedString because this method
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// runs on the UI thread which we want to avoid because renderHTMLString is called
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// most of the time from a background thread.
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// Use DTCoreText HTML renderer instead.
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// Using DTCoreText, which renders static string, helps to avoid code injection attacks
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// that could happen with the default HTML renderer of NSAttributedString which is a
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// webview.
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func fromHTML(_ htmlString: String?) -> AttributedString? {
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guard let htmlString else {
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return nil
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}
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if let cached = Self.cache.value(forKey: htmlString) {
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return cached
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}
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// Trick DTCoreText into preserving newlines
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let adjustedHTMLString = htmlString.replacingOccurrences(of: "\n", with: "<br>")
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guard let data = adjustedHTMLString.data(using: .utf8) else {
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return nil
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}
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let defaultFont = UIFont.preferredFont(forTextStyle: .body)
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let parsingOptions: [String: Any] = [
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DTUseiOS6Attributes: true,
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DTDefaultFontFamily: defaultFont.familyName,
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DTDefaultFontName: defaultFont.fontName,
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DTDefaultFontSize: defaultFont.pointSize,
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DTDefaultStyleSheet: DTCSSStylesheet(styleBlock: defaultCSS) as Any
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]
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guard let builder = DTHTMLAttributedStringBuilder(html: data, options: parsingOptions, documentAttributes: nil) else {
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return nil
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}
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builder.willFlushCallback = { element in
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element?.sanitize(font: defaultFont)
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}
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guard let attributedString = builder.generatedAttributedString() else {
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return nil
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}
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let mutableAttributedString = NSMutableAttributedString(attributedString: attributedString)
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removeDefaultForegroundColor(mutableAttributedString)
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addLinks(mutableAttributedString)
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detectPermalinks(mutableAttributedString)
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removeLinkColors(mutableAttributedString)
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replaceMarkedBlockquotes(mutableAttributedString)
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replaceMarkedCodeBlocks(mutableAttributedString)
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removeDTCoreTextArtifacts(mutableAttributedString)
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let result = try? AttributedString(mutableAttributedString, including: \.elementX)
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Self.cache.setValue(result, forKey: htmlString)
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return result
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}
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// MARK: - Private
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private func replaceMarkedBlockquotes(_ attributedString: NSMutableAttributedString) {
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// According to blockquotes in the string, DTCoreText can apply 2 policies:
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// - define a `DTTextBlocksAttribute` attribute on a <blockquote> block
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// - or, just define a `NSBackgroundColorAttributeName` attribute
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attributedString.enumerateAttribute(.DTTextBlocks, in: .init(location: 0, length: attributedString.length), options: []) { value, range, _ in
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guard let value = value as? NSArray,
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let dtTextBlock = value.firstObject as? DTTextBlock,
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dtTextBlock.backgroundColor == temporaryBlockquoteMarkingColor else {
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return
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}
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attributedString.addAttribute(.MatrixBlockquote, value: true, range: range)
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}
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attributedString.enumerateAttribute(.backgroundColor, in: .init(location: 0, length: attributedString.length), options: []) { value, range, _ in
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guard let value = value as? UIColor,
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value == temporaryBlockquoteMarkingColor else {
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return
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}
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attributedString.removeAttribute(.backgroundColor, range: range)
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attributedString.addAttribute(.MatrixBlockquote, value: true, range: range)
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}
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}
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func replaceMarkedCodeBlocks(_ attributedString: NSMutableAttributedString) {
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attributedString.enumerateAttribute(.backgroundColor, in: .init(location: 0, length: attributedString.length), options: []) { value, range, _ in
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if let value = value as? UIColor,
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value == temporaryCodeBlockMarkingColor {
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attributedString.addAttribute(.backgroundColor, value: UIColor.compound._bgCodeBlock as Any, range: range)
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}
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}
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}
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private func removeDTCoreTextArtifacts(_ attributedString: NSMutableAttributedString) {
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guard attributedString.length > 0 else {
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return
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}
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// DTCoreText adds a newline at the end of plain text ( https://github.com/Cocoanetics/DTCoreText/issues/779 )
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// or after a blockquote section.
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// Trim trailing whitespace and newlines in the string content
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while (attributedString.string as NSString).hasSuffixCharacter(from: .whitespacesAndNewlines) {
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attributedString.deleteCharacters(in: .init(location: attributedString.length - 1, length: 1))
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}
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}
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private func addLinks(_ attributedString: NSMutableAttributedString) {
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let string = attributedString.string
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var matches = MatrixEntityRegex.userIdentifierRegex.matches(in: string, options: [])
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matches.append(contentsOf: MatrixEntityRegex.roomIdentifierRegex.matches(in: string, options: []))
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// As of right now we do not handle event id links in any way so there is no need to add them as links
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// matches.append(contentsOf: MatrixEntityRegex.eventIdentifierRegex.matches(in: string, options: []))
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matches.append(contentsOf: MatrixEntityRegex.roomAliasRegex.matches(in: string, options: []))
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matches.append(contentsOf: MatrixEntityRegex.linkRegex.matches(in: string, options: []))
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guard matches.count > 0 else {
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return
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}
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// Sort the links by length so the longest one always takes priority
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matches.sorted { $0.range.length > $1.range.length }.forEach { match in
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guard let matchRange = Range(match.range, in: string) else {
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return
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}
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var hasLink = false
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attributedString.enumerateAttribute(.link, in: match.range, options: []) { value, _, stop in
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if value != nil {
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hasLink = true
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stop.pointee = true
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}
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}
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if hasLink {
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return
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}
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attributedString.addAttribute(.link, value: string[matchRange] as Any, range: match.range)
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}
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}
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private func detectPermalinks(_ attributedString: NSMutableAttributedString) {
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attributedString.enumerateAttribute(.link, in: .init(location: 0, length: attributedString.length), options: []) { value, range, _ in
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if value != nil {
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if let url = value as? URL {
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switch PermalinkBuilder.detectPermalink(in: url, baseURL: permalinkBaseURL) {
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case .userIdentifier(let identifier):
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attributedString.addAttributes([.MatrixUserID: identifier], range: range)
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case .roomIdentifier(let identifier):
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attributedString.addAttributes([.MatrixRoomID: identifier], range: range)
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case .roomAlias(let alias):
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attributedString.addAttributes([.MatrixRoomAlias: alias], range: range)
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case .event(let roomIdentifier, let eventIdentifier):
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attributedString.addAttributes([.MatrixEventID: EventIDAttributeValue(roomID: roomIdentifier, eventID: eventIdentifier)], range: range)
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case .none:
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break
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}
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}
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}
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}
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}
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private func removeDefaultForegroundColor(_ attributedString: NSMutableAttributedString) {
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attributedString.enumerateAttribute(.foregroundColor, in: .init(location: 0, length: attributedString.length), options: []) { value, range, _ in
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if value as? UIColor == UIColor.black {
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attributedString.removeAttribute(.foregroundColor, range: range)
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}
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}
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}
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private func removeLinkColors(_ attributedString: NSMutableAttributedString) {
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attributedString.enumerateAttribute(.link, in: .init(location: 0, length: attributedString.length), options: []) { value, range, _ in
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if value != nil {
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attributedString.removeAttribute(.foregroundColor, range: range)
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}
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}
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}
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private var defaultCSS: String {
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"""
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blockquote {
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background: \(temporaryBlockquoteMarkingColor.toHexString());
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display: block;
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}
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pre,code {
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background-color: \(temporaryCodeBlockMarkingColor.toHexString());
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display: inline;
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white-space: pre;
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font-size: 0.9em;
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-coretext-fontname: .AppleSystemUIFontMonospaced-Regular;
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}
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h1,h2,h3 {
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font-size: 1.2em;
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}
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"""
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}
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}
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extension UIColor {
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func toHexString() -> String {
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var red: CGFloat = 0.0
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var green: CGFloat = 0.0
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var blue: CGFloat = 0.0
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var alpha: CGFloat = 0.0
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getRed(&red, green: &green, blue: &blue, alpha: &alpha)
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let rgb = Int(red * 255) << 16 | Int(green * 255) << 8 | Int(blue * 255) << 0
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return NSString(format: "#%06x", rgb) as String
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}
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}
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extension NSAttributedString.Key {
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static let DTTextBlocks: NSAttributedString.Key = .init(rawValue: DTTextBlocksAttribute)
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static let MatrixBlockquote: NSAttributedString.Key = .init(rawValue: BlockquoteAttribute.name)
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static let MatrixUserID: NSAttributedString.Key = .init(rawValue: UserIDAttribute.name)
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static let MatrixRoomID: NSAttributedString.Key = .init(rawValue: RoomIDAttribute.name)
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static let MatrixRoomAlias: NSAttributedString.Key = .init(rawValue: RoomAliasAttribute.name)
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static let MatrixEventID: NSAttributedString.Key = .init(rawValue: EventIDAttribute.name)
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}
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