Improve HTML formatter

Riot/Modules/MatrixKit/Utils/EventFormatter/HTMLFormatter.swift

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+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+import DTCoreText
+import UIKit
+
+@objcMembers
+class HTMLFormatter: NSObject {
+    /// Builds an attributed string from a string containing html.
+    ///
+    /// - Parameters:
+    ///   - htmlString: The html string to use.
+    ///   - allowedTags: The html tags that should be allowed.
+    ///   - imageHandler: The image handler for the formatted string
+    ///   - extraOptions: Extra options to apply for the format
+    ///   - font: The default font to use.
+    ///   - postFormatOperations: Optional block to provide operations to apply
+    /// - Returns: The built `NSAttributedString`.
+    /// - Note: It is recommended to include "p" and "body" tags in `allowedTags` as these are often added when parsing.
+    func formatHTML(_ htmlString: String,
+                    withAllowedTags allowedTags: [String],
+                    andImageHandler imageHandler: DTHTMLElement.ImageHandler? = nil,
+                    extraOptions: [AnyHashable: Any] = [:],
+                    font: UIFont,
+                    postFormatOperations: ((NSMutableAttributedString) -> Void)? = nil) -> NSAttributedString {
+        guard let data = htmlString.data(using: .utf8) else {
+            return NSAttributedString(string: htmlString)
+        }
+
+        let sanitizeCallback: DTHTMLAttributedStringBuilderWillFlushCallback = { [allowedTags, font] (element: DTHTMLElement?) in
+            element?.sanitize(with: allowedTags, bodyFont: font, imageHandler: imageHandler)
+        }
+
+        var options: [AnyHashable: Any] = [
+            DTUseiOS6Attributes: true,
+            DTDefaultFontFamily: font.familyName,
+            DTDefaultFontName: font.fontName,
+            DTDefaultFontSize: font.pointSize,
+            DTDefaultLinkDecoration: false,
+            DTWillFlushBlockCallBack: sanitizeCallback
+        ]
+        options.merge(extraOptions) { (_, new) in new }
+
+        guard let string = self.formatHTML(data, options: options) else {
+            return NSAttributedString(string: htmlString)
+        }
+
+        let mutableString = NSMutableAttributedString(attributedString: string)
+        MXKTools.removeDTCoreTextArtifacts(mutableString)
+        postFormatOperations?(mutableString)
+
+        return mutableString
+    }
+
+    /// Builds an attributed string by replacing a `%@` placeholder with the supplied link text and URL.
+    /// - Parameters:
+    ///   - string: The string to be formatted.
+    ///   - link: The link text to be inserted.
+    ///   - url: The URL to be linked to.
+    /// - Returns: An attributed string.
+    func format(_ string: String, with link: String, using url: URL) -> NSAttributedString {
+        let baseString = NSMutableAttributedString(string: string)
+        let attributedLink = NSAttributedString(string: link, attributes: [.link: url])
+        
+        let linkRange = (baseString.string as NSString).range(of: "%@")
+        baseString.replaceCharacters(in: linkRange, with: attributedLink)
+        
+        return baseString
+    }
+}
+
+extension HTMLFormatter {
+    /// This replicates DTCoreText's NSAttributedString `initWithHTMLData`.
+    /// It sets the sanitize callback on the builder from Swift to avoid EXC_BAD_ACCESS crashes.
+    ///
+    /// - Parameters:
+    ///   - data: The data in HTML format from which to create the attributed string.
+    ///   - options: Specifies how the document should be loaded.
+    /// - Returns: Returns an initialized object, or `nil` if the data can’t be decoded.
+    @objc func formatHTML(_ data: Data,
+                          options: [AnyHashable: Any]) -> NSAttributedString? {
+        guard !data.isEmpty else {
+            return nil
+        }
+
+        let stringBuilder = DTHTMLAttributedStringBuilder(html: data,
+                                                          options: options,
+                                                          // DTCoreText doesn't use document attributes anyway
+                                                          documentAttributes: nil)
+
+        if let willFlushCallback = options[DTWillFlushBlockCallBack] as? DTHTMLAttributedStringBuilderWillFlushCallback {
+            stringBuilder?.willFlushCallback = willFlushCallback
+        }
+
+        return stringBuilder?.generatedAttributedString()
+    }
+}