Fix #6430, #6431: Preserve worked example list spacing

utility/src/main/java/org/oppia/android/util/parser/html/HtmlParser.kt

@@ -220,20 +220,21 @@ class HtmlParser private constructor(
    * renders ordered lists as bullets rather than as numbers).
    */
   private fun replaceListTags(html: String): String {
-    var adjustedHtml = html
-    if ("<li>" in adjustedHtml) {
-      adjustedHtml = adjustedHtml.replace("<li>", "<$CUSTOM_LIST_LI_TAG>")
-        .replace("</li>", "</$CUSTOM_LIST_LI_TAG>")
-    }
-    if ("<ul>" in adjustedHtml) {
-      adjustedHtml = adjustedHtml.replace("<ul>", "<$CUSTOM_LIST_UL_TAG>")
-        .replace("</ul>", "</$CUSTOM_LIST_UL_TAG>")
-    }
-    if ("<ol>" in adjustedHtml) {
-      adjustedHtml = adjustedHtml.replace("<ol>", "<$CUSTOM_LIST_OL_TAG>")
-        .replace("</ol>", "</$CUSTOM_LIST_OL_TAG>")
-    }
-    return adjustedHtml
+    return html
+      .replaceListTag(originalTag = "li", replacementTag = CUSTOM_LIST_LI_TAG)
+      .replaceListTag(originalTag = "ul", replacementTag = CUSTOM_LIST_UL_TAG)
+      .replaceListTag(originalTag = "ol", replacementTag = CUSTOM_LIST_OL_TAG)
+  }
+
+  /**
+   * Replaces opening and closing [originalTag] tags while preserving attributes such as the XHTML
+   * namespace included by Oppia's rich-text editor.
+   */
+  private fun String.replaceListTag(originalTag: String, replacementTag: String): String {
+    return replace(
+      Regex("""<(/?)$originalTag(?=[\s>])""", RegexOption.IGNORE_CASE),
+      "<$1$replacementTag"
+    )
   }
 
   private fun trimSpannable(spannable: SpannableStringBuilder): SpannableStringBuilder {

utility/src/test/java/org/oppia/android/util/parser/html/HtmlParserTest.kt

@@ -10,6 +10,7 @@ import android.text.style.BulletSpan
 import android.text.style.ClickableSpan
 import android.text.style.ImageSpan
 import android.text.style.LeadingMarginSpan
+import android.text.style.URLSpan
 import android.view.View
 import android.widget.TextView
 import androidx.appcompat.app.AppCompatActivity
@@ -30,6 +31,7 @@ import com.google.common.truth.Truth.assertThat
 import dagger.Component
 import org.hamcrest.CoreMatchers
 import org.hamcrest.Matchers.not
+import org.json.JSONObject
 import org.junit.After
 import org.junit.Before
 import org.junit.Rule
@@ -984,6 +986,68 @@ class HtmlParserTest {
     )
   }
 
+  @Test
+  fun testHtmlContent_withWorkedExampleNamespacedList_preservesBlockSpacing() {
+    val htmlParser = htmlParserFactory.create(
+      resourceBucketName,
+      entityType = "",
+      entityId = "",
+      imageCenterAlign = false,
+      displayLocale = appLanguageLocaleHandler.getDisplayLocale()
+    )
+    val textView = TextView(context)
+    val workedExampleMarkup = createWorkedExampleMarkup(
+      questionHtml = "Where should the content be separated?",
+      answerHtml =
+        "<ol xmlns=\"http://www.w3.org/1999/xhtml\"><li>Outer item one:<ul>" +
+          "<li>Inner item one.</li><li>Inner item two.</li></ul></li>" +
+          "<li>Outer item two.</li></ol><p>Following paragraph.</p>"
+    )
+
+    val htmlResult = htmlParser.parseOppiaHtml(
+      workedExampleMarkup,
+      textView,
+      workedExampleLabels = WORKED_EXAMPLE_LABELS
+    )
+
+    assertThat(htmlResult.getSpansFromWholeString(ListItemLeadingMarginSpan.OlSpan::class))
+      .hasLength(2)
+    assertThat(htmlResult.getSpansFromWholeString(ListItemLeadingMarginSpan.UlSpan::class))
+      .hasLength(2)
+    assertThat(htmlResult.toString()).contains("Inner item two.\nOuter item two.")
+    assertThat(htmlResult.toString()).contains("Outer item two.\n\nFollowing paragraph.")
+  }
+
+  @Test
+  fun testHtmlContent_withWorkedExampleNamespacedList_doesNotCreateFalseLinks() {
+    val htmlParser = htmlParserFactory.create(
+      resourceBucketName,
+      entityType = "",
+      entityId = "",
+      imageCenterAlign = false,
+      displayLocale = appLanguageLocaleHandler.getDisplayLocale()
+    )
+    val textView = TextView(context)
+    val workedExampleMarkup = createWorkedExampleMarkup(
+      questionHtml = "Add the decimals.",
+      answerHtml =
+        "<ul xmlns=\"http://www.w3.org/1999/xhtml\">" +
+          "<li>Add a decimal point before the tenths place.</li>" +
+          "<li>Now add the place value digits.</li>" +
+          "<li>The answer is 5.682.</li></ul>"
+    )
+
+    val htmlResult = htmlParser.parseOppiaHtml(
+      workedExampleMarkup,
+      textView,
+      workedExampleLabels = WORKED_EXAMPLE_LABELS
+    )
+
+    assertThat(htmlResult.toString()).contains("place.\nNow")
+    assertThat(htmlResult.toString()).contains("digits.\nThe")
+    assertThat(htmlResult.getSpansFromWholeString(URLSpan::class)).isEmpty()
+  }
+
   @Test
   fun testHtmlContent_withUrl_hasClickableSpanAndCorrectText() {
     val htmlParser = htmlParserFactory.create(
@@ -1430,6 +1494,21 @@ class HtmlParserTest {
     return DisplayLocaleImpl(context, formattingLocale, machineLocale, formatterFactory)
   }
 
+  private fun createWorkedExampleMarkup(questionHtml: String, answerHtml: String): String {
+    return "<$CUSTOM_WORKED_EXAMPLE_TAG " +
+      "question-with-value=\"${questionHtml.encodeAsWorkedExampleAttribute()}\" " +
+      "answer-with-value=\"${answerHtml.encodeAsWorkedExampleAttribute()}\">" +
+      "</$CUSTOM_WORKED_EXAMPLE_TAG>"
+  }
+
+  private fun String.encodeAsWorkedExampleAttribute(): String {
+    return JSONObject.quote(this)
+      .replace("&", "&amp;amp;")
+      .replace("\"", "&amp;quot;")
+      .replace("<", "&amp;lt;")
+      .replace(">", "&amp;gt;")
+  }
+
   private fun Spannable.getTextForSpan(span: Any): String =
     subSequence(getSpanStart(span), getSpanEnd(span)).toString()