add Markdown surpport

android/sample-app/src/main/java/cn/learningpad/oraltrainer/sample/MarkdownText.kt

@@ -0,0 +1,130 @@
+package cn.learningpad.oraltrainer.sample
+
+import android.widget.TextView
+import androidx.core.text.HtmlCompat
+
+/** Renders common LLM Markdown into a TextView without extra libraries. */
+internal object MarkdownText {
+    private val heading = Regex("^(#{1,6})\\s*(.*)$")
+    private val unordered = Regex("^[-*+]\\s+(.*)$")
+    private val ordered = Regex("^\\d+[.)]\\s+(.*)$")
+    private val boldItalic = Regex("\\*\\*\\*(.+?)\\*\\*\\*")
+    private val bold = Regex("(\\*\\*|__)(.+?)\\1")
+    private val italic = Regex("(?<!\\*)\\*(?!\\*)(.+?)(?<!\\*)\\*(?!\\*)")
+    private val italicUnderscore = Regex("(?<!\\w)_(?!_)(.+?)(?<!_)_(?!\\w)")
+    private val inlineCode = Regex("`([^`]+)`")
+    private val image = Regex("!\\[([^\\]]*)]\\(([^)]+)\\)")
+    private val link = Regex("\\[([^\\]]+)]\\(([^)]+)\\)")
+
+    fun set(view: TextView, markdown: String) {
+        view.text = render(markdown)
+    }
+
+    fun render(markdown: String): CharSequence {
+        return HtmlCompat.fromHtml(toHtml(markdown), HtmlCompat.FROM_HTML_MODE_COMPACT)
+    }
+
+    internal fun toHtml(markdown: String): String {
+        val normalized = markdown.replace("\r\n", "\n").replace('\r', '\n')
+        val html = StringBuilder()
+        var inFence = false
+        val code = StringBuilder()
+        var listTag: String? = null
+
+        fun closeList() {
+            listTag?.let { html.append("</$it>") }
+            listTag = null
+        }
+
+        fun openList(tag: String) {
+            if (listTag != tag) {
+                closeList()
+                listTag = tag
+                html.append('<').append(tag).append('>')
+            }
+        }
+
+        for (line in normalized.split('\n')) {
+            val trimmed = line.trim()
+            if (trimmed.startsWith("```")) {
+                if (inFence) {
+                    html.append("<pre><code>").append(code).append("</code></pre>")
+                    code.setLength(0)
+                    inFence = false
+                } else {
+                    closeList()
+                    inFence = true
+                }
+                continue
+            }
+            if (inFence) {
+                if (code.isNotEmpty()) code.append('\n')
+                code.append(escape(line))
+                continue
+            }
+            if (trimmed.isEmpty()) {
+                closeList()
+                continue
+            }
+
+            val headingMatch = heading.matchEntire(trimmed)
+            if (headingMatch != null) {
+                closeList()
+                val level = headingMatch.groupValues[1].length
+                html.append("<h$level>").append(inline(headingMatch.groupValues[2])).append("</h$level>")
+                continue
+            }
+            val unorderedMatch = unordered.matchEntire(trimmed)
+            if (unorderedMatch != null) {
+                openList("ul")
+                html.append("<li>").append(inline(unorderedMatch.groupValues[1])).append("</li>")
+                continue
+            }
+            val orderedMatch = ordered.matchEntire(trimmed)
+            if (orderedMatch != null) {
+                openList("ol")
+                html.append("<li>").append(inline(orderedMatch.groupValues[1])).append("</li>")
+                continue
+            }
+            closeList()
+            if (trimmed.startsWith(">")) {
+                html.append("<blockquote>")
+                    .append(inline(trimmed.removePrefix(">").trimStart()))
+                    .append("</blockquote>")
+            } else {
+                html.append("<p>").append(inline(trimmed)).append("</p>")
+            }
+        }
+        if (inFence) {
+            html.append("<pre><code>").append(code).append("</code></pre>")
+        }
+        closeList()
+        return html.toString()
+    }
+
+    private fun inline(text: String): String {
+        val codes = mutableListOf<String>()
+        var current = escape(text)
+        current = inlineCode.replace(current) { match ->
+            codes += "<code>${match.groupValues[1]}</code>"
+            "%%MDCODE${codes.lastIndex}%%"
+        }
+        current = image.replace(current) { match -> escape(match.groupValues[1]) }
+        current = link.replace(current) { match ->
+            """<a href="${match.groupValues[2]}">${match.groupValues[1]}</a>"""
+        }
+        current = boldItalic.replace(current) { match -> "<b><i>${match.groupValues[1]}</i></b>" }
+        current = bold.replace(current) { match -> "<b>${match.groupValues[2]}</b>" }
+        current = italic.replace(current) { match -> "<i>${match.groupValues[1]}</i>" }
+        current = italicUnderscore.replace(current) { match -> "<i>${match.groupValues[1]}</i>" }
+        codes.forEachIndexed { index, value ->
+            current = current.replace("%%MDCODE$index%%", value)
+        }
+        return current
+    }
+
+    private fun escape(text: String): String =
+        text.replace("&", "&amp;")
+            .replace("<", "&lt;")
+            .replace(">", "&gt;")
+}

android/sample-app/src/main/java/cn/learningpad/oraltrainer/sample/SentenceExplanationOverlay.kt

@@ -123,8 +123,7 @@ internal class SentenceExplanationOverlay(
 
         val cached = store.load(mediaId, sentence.index)
         if (!cached.isNullOrBlank()) {
-            message.text = cached
-            message.setTextColor(SampleTheme.textDark)
+            showMarkdown(message, cached)
             markSaved(saveButton, saveHint)
             return
         }
@@ -145,8 +144,7 @@ internal class SentenceExplanationOverlay(
                 override fun onSuccess(result: SentenceExplanationResult) {
                     if (generation != requestGeneration) return
                     loadedExplanation = result.explanation
-                    message.text = result.explanation
-                    message.setTextColor(SampleTheme.textDark)
+                    showMarkdown(message, result.explanation)
                     saveButton.isEnabled = true
                     saveButton.alpha = 1f
                 }
@@ -176,6 +174,11 @@ internal class SentenceExplanationOverlay(
         api.release()
     }
 
+    private fun showMarkdown(message: TextView, explanation: String) {
+        message.setTextColor(SampleTheme.textDark)
+        MarkdownText.set(message, explanation)
+    }
+
     private fun markSaved(saveButton: TextView, saveHint: TextView) {
         saveButton.text = "已保存"
         saveButton.isEnabled = false