Show Cursor Events as Range Highlighter

When the ethersync client sends cursor events, the Intellij plugin will
highlight the cursors of remote ethersync clients as range highlights in
the editor.

Author: schrieveslaach

src/main/kotlin/io/github/ethersync/EthersyncService.kt

@@ -2,5 +2,5 @@ package io.github.ethersync
 
 interface EthersyncService {
 
-   fun connectToPeer(multiAddress: String)
-}
+   fun connectToPeer(peer: String)
+}

src/main/kotlin/io/github/ethersync/EthersyncServiceImpl.kt

@@ -7,7 +7,6 @@ import com.intellij.openapi.project.Project
 import com.intellij.util.io.awaitExit
 import com.intellij.util.io.readLineAsync
 import io.github.ethersync.protocol.EthersyncEditorProtocol
-import io.github.ethersync.protocol.EthersyncEditorProtocolImpl
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.launch
 import org.eclipse.lsp4j.jsonrpc.Launcher
@@ -87,7 +86,7 @@ class EthersyncServiceImpl(
                clientProcess.outputStream,
                Executors.newCachedThreadPool(),
                { c -> c },
-               { gsonBuilder -> {} }
+               { _ -> run {} }
          )
 
          val listening = launcher.startListening()

src/main/kotlin/io/github/ethersync/protocol/EthersyncEditorProtocolImpl.kt

@@ -1,18 +1,65 @@
 package io.github.ethersync.protocol
 
+import com.intellij.openapi.application.ApplicationManager
+import com.intellij.openapi.application.ModalityState
 import com.intellij.openapi.components.Service
+import com.intellij.openapi.editor.LogicalPosition
+import com.intellij.openapi.editor.markup.HighlighterLayer
+import com.intellij.openapi.editor.markup.HighlighterTargetArea
+import com.intellij.openapi.editor.markup.RangeHighlighter
+import com.intellij.openapi.editor.markup.TextAttributes
 import com.intellij.openapi.fileEditor.FileEditorManager
+import com.intellij.openapi.fileEditor.TextEditor
 import com.intellij.openapi.project.Project
+import com.intellij.ui.JBColor
+import java.util.LinkedList
 
 @Service(Service.Level.PROJECT)
 class EthersyncEditorProtocolImpl(private val project: Project) : EthersyncEditorProtocol {
+
+   private val highlighter = LinkedList<RangeHighlighter>()
+
    override fun cursor(cursorEvent: CursorEvent) {
-      System.out.printf("Cursor: %s, %s\n", cursorEvent.documentUri, cursorEvent.ranges)
 
-      val fileEditorManager = FileEditorManager.getInstance(project);
-      val editor = fileEditorManager.allEditors
-         .find { editor -> editor.file.url == cursorEvent.documentUri } ?: return
+      val fileEditorManager = FileEditorManager.getInstance(project)
+
+      val fileEditor = fileEditorManager.allEditors
+         .first { editor -> editor.file.url == cursorEvent.documentUri } ?: return
+
+      if (fileEditor is TextEditor) {
+         val editor = fileEditor.editor
+         ApplicationManager.getApplication().invokeLater({
+            synchronized(highlighter) {
+            val markupModel = editor.markupModel
+
+            for (hl in highlighter) {
+               markupModel.removeHighlighter(hl)
+            }
+            highlighter.clear()
+
+            for(range in cursorEvent.ranges) {
+               val startPosition = editor.logicalPositionToOffset(LogicalPosition(range.start.line, range.start.character))
+               val endPosition = editor.logicalPositionToOffset(LogicalPosition(range.end.line, range.end.character))
+
+               val textAttributes = TextAttributes().apply {
+                  backgroundColor = JBColor(JBColor.YELLOW, JBColor.DARK_GRAY)
+                  // TODO: unclear which is the best effect type
+                  // effectType = EffectType.LINE_UNDERSCORE
+                  // effectColor = JBColor(JBColor.YELLOW, JBColor.DARK_GRAY)
+               }
+
+               val hl = markupModel.addRangeHighlighter(
+                  startPosition,
+                  endPosition + 1,
+                  HighlighterLayer.ADDITIONAL_SYNTAX,
+                  textAttributes,
+                  HighlighterTargetArea.EXACT_RANGE
+               )
 
-      // TODO find a way how to create an additional cursor
+               highlighter.add(hl)
+            }
+               }
+         }, ModalityState.nonModal())
+      }
    }
-}
+}