Add plain text representation of messages (#1850)

* Add plain text representation of messages.

This is used in the room list as the last message in a room, in the message summary when a message is selected, in the 'replying to' block, in the 'replied to' block in a message in the timeline, and in notifications.

libraries/matrixui/src/main/kotlin/io/element/android/libraries/matrix/ui/messages/ToHtmlDocument.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2023 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.
+ */
+
+package io.element.android.libraries.matrix.ui.messages
+
+import io.element.android.libraries.matrix.api.permalink.PermalinkData
+import io.element.android.libraries.matrix.api.permalink.PermalinkParser
+import io.element.android.libraries.matrix.api.timeline.item.event.FormattedBody
+import io.element.android.libraries.matrix.api.timeline.item.event.MessageFormat
+import org.jsoup.Jsoup
+import org.jsoup.nodes.Document
+
+/**
+ * Converts the HTML string [FormattedBody.body] to a [Document] by parsing it.
+ * If the message is not formatted or the format is not [MessageFormat.HTML] we return `null`.
+ *
+ * This will also make sure mentions are prefixed with `@`.
+ *
+ * @param prefix if not null, the prefix will be inserted at the beginning of the message.
+ */
+fun FormattedBody.toHtmlDocument(prefix: String? = null): Document? {
+    return takeIf { it.format == MessageFormat.HTML }?.body?.let { formattedBody ->
+        val dom = if (prefix != null) {
+            Jsoup.parse("$prefix $formattedBody")
+        } else {
+            Jsoup.parse(formattedBody)
+        }
+
+        // Prepend `@` to mentions
+        fixMentions(dom)
+
+        dom
+    }
+}
+
+private fun fixMentions(dom: Document) {
+    val links = dom.getElementsByTag("a")
+    links.forEach {
+        if (it.hasAttr("href")) {
+            val link = PermalinkParser.parse(it.attr("href"))
+            if (link is PermalinkData.UserLink && !it.text().startsWith("@")) {
+                it.prependText("@")
+            }
+        }
+    }
+}

libraries/matrixui/src/main/kotlin/io/element/android/libraries/matrix/ui/messages/ToPlainText.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2023 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.
+ */
+
+package io.element.android.libraries.matrix.ui.messages
+
+import io.element.android.libraries.matrix.api.timeline.item.event.FormattedBody
+import io.element.android.libraries.matrix.api.timeline.item.event.TextMessageType
+import io.element.android.libraries.matrix.api.timeline.item.event.MessageFormat
+import org.jsoup.nodes.Document
+import org.jsoup.nodes.Element
+import org.jsoup.nodes.Node
+import org.jsoup.nodes.TextNode
+import org.jsoup.select.NodeVisitor
+
+/**
+ * Converts the HTML string in [TextMessageType.formatted] to a plain text representation by parsing it and removing all formatting.
+ * If the message is not formatted or the format is not [MessageFormat.HTML], the [TextMessageType.body] is returned instead.
+ */
+fun TextMessageType.toPlainText() = formatted?.toPlainText() ?: body
+
+/**
+ * Converts the HTML string in [FormattedBody.body] to a plain text representation by parsing it and removing all formatting.
+ * If the message is not formatted or the format is not [MessageFormat.HTML] we return `null`.
+ * @param prefix if not null, the prefix will be inserted at the beginning of the message.
+ */
+fun FormattedBody.toPlainText(prefix: String? = null): String? {
+    return this.toHtmlDocument(prefix)?.toPlainText()
+}
+
+/**
+ * Converts the HTML [Document] to a plain text representation by parsing it and removing all formatting.
+ */
+fun Document.toPlainText(): String {
+    val visitor = PlainTextNodeVisitor()
+    traverse(visitor)
+    return visitor.build()
+}
+
+private class PlainTextNodeVisitor : NodeVisitor {
+    private val builder = StringBuilder()
+
+    override fun head(node: Node, depth: Int) {
+        if (node is TextNode && node.text().isNotBlank()) {
+            builder.append(node.text())
+        } else if (node is Element && node.tagName() == "li") {
+            val index = node.elementSiblingIndex()
+            val isOrdered = node.parent()?.nodeName()?.lowercase() == "ol"
+            if (isOrdered) {
+                builder.append("${index + 1}. ")
+            } else {
+                builder.append("• ")
+            }
+        } else if (node is Element && node.isBlock && builder.lastOrNull() != '\n') {
+            builder.append("\n")
+        }
+    }
+
+    override fun tail(node: Node, depth: Int) {
+        fun nodeIsBlockButNotLastOne(node: Node) = node is Element && node.isBlock && node.lastElementSibling() !== node
+        fun nodeIsLineBreak(node: Node) = node.nodeName().lowercase() == "br"
+        if (nodeIsBlockButNotLastOne(node) || nodeIsLineBreak(node)) {
+            builder.append("\n")
+        }
+    }
+
+    fun build(): String {
+        return builder.toString().trim()
+    }
+}