Gemtext: add a sweet streaming parser

app/src/main/java/dev/lowrespalmtree/comet/Gemtext.kt

@@ -0,0 +1,64 @@
+package dev.lowrespalmtree.comet
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.launch
+import java.nio.ByteBuffer
+import java.nio.CharBuffer
+import java.nio.charset.Charset
+
+open class Line
+
+class EmptyLine : Line()
+class ParagraphLine(val text: String) : Line()
+class TitleLine(val level: Int, val text: String) : Line()
+class LinkLine(val url: String, val label: String) : Line()
+class PreFenceLine(val caption: String) : Line()
+class PreTextLine(val text: String) : Line()
+class BlockquoteLine(val text: String) : Line()
+class ListItemLine(val text: String) : Line()
+
+fun parseData(
+    inChannel: Channel<ByteArray>,
+    charset: Charset,
+    scope: CoroutineScope
+): Channel<Line> {
+    val channel = Channel<Line>()
+    scope.launch {
+        var isPref = false
+        var buffer = ByteArray(0)
+        for (data in inChannel) {
+            buffer += data
+            var nextLineFeed: Int = -1
+            while (buffer.isNotEmpty() && buffer.indexOf(0x0A).also { nextLineFeed = it } > -1) {
+                val lineData = buffer.sliceArray(0 until nextLineFeed)
+                buffer = buffer.sliceArray(nextLineFeed + 1 until buffer.size)
+                val lineString = charset.decode(ByteBuffer.wrap(lineData))
+                val line = parseLine(lineString, isPref)
+                when (line) {
+                    is PreFenceLine -> isPref = !isPref
+                }
+                channel.send(line)
+            }
+        }
+    }
+    return channel
+}
+
+private fun parseLine(line: CharBuffer, isPreformatted: Boolean): Line =
+    when {
+        line.isEmpty() -> EmptyLine()
+        line.startsWith("###") -> TitleLine(3, getCharsFrom(line, 3))
+        line.startsWith("##") -> TitleLine(2, getCharsFrom(line, 2))
+        line.startsWith("#") -> TitleLine(1, getCharsFrom(line, 1))
+        line.startsWith(">") -> BlockquoteLine(getCharsFrom(line, 1))
+        line.startsWith("```") -> PreFenceLine(getCharsFrom(line, 3))
+        line.startsWith("* ") -> ListItemLine(getCharsFrom(line, 2))
+        line.startsWith("=>") -> getCharsFrom(line, 2).split(" ", limit = 2)
+            .run { LinkLine(get(0), if (size == 2) get(1) else "") }
+        else -> if (isPreformatted) PreTextLine(line.toString()) else ParagraphLine(line.toString())
+    }
+
+private fun getCharsFrom(line: CharBuffer, index: Int) = line.substring(index).removePrefix(" ")
+
+private const val TAG = "Gemtext"

app/src/main/java/dev/lowrespalmtree/comet/MainActivity.kt

@@ -89,9 +89,17 @@ class MainActivity : AppCompatActivity() {
 
         private suspend fun handleRequestSuccess(response: Response) {
             val charset = Charset.defaultCharset()
-            for (data in response.data) {
-                val decoded = charset.decode(ByteBuffer.wrap(data)).toString()
-                source += decoded
+            for (line in parseData(response.data, charset, viewModelScope)) {
+                when (line) {
+                    is EmptyLine -> { source += "\n" }
+                    is ParagraphLine -> { source += line.text + "\n" }
+                    is TitleLine -> { source += "TTL-${line.level} ${line.text}\n" }
+                    is LinkLine -> { source += "LNK ${line.url} + ${line.label}\n" }
+                    is PreFenceLine -> { source += "PRE ${line.caption}\n" }
+                    is PreTextLine -> { source += line.text + "\n" }
+                    is BlockquoteLine -> { source += "QUO ${line.text}\n" }
+                    is ListItemLine -> { source += "LST ${line.text}\n" }
+                }
                 sourceLiveData.postValue(source)
             }
         }