1 files changed, 116 insertions, 0 deletions

diff --git a/language-web/src/main/js/xtext/OccurrencesService.ts b/language-web/src/main/js/xtext/OccurrencesService.ts
new file mode 100644
index 00000000..804f5ba2
--- /dev/null
+++ b/language-web/src/main/js/xtext/OccurrencesService.ts
@@ -0,0 +1,116 @@
+import { Transaction } from '@codemirror/state';
+
+import type { EditorStore } from '../editor/EditorStore';
+import type { IOccurrence } from '../editor/findOccurrences';
+import type { UpdateService } from './UpdateService';
+import { getLogger } from '../utils/logger';
+import { Timer } from '../utils/Timer';
+import { XtextWebSocketClient } from './XtextWebSocketClient';
+import {
+  isOccurrencesResult,
+  isServiceConflictResult,
+  ITextRegion,
+} from './xtextServiceResults';
+
+const FIND_OCCURRENCES_TIMEOUT_MS = 1000;
+
+// Must clear occurrences asynchronously from `onTransaction`,
+// because we must not emit a conflicting transaction when handling the pending transaction.
+const CLEAR_OCCURRENCES_TIMEOUT_MS = 10;
+
+const log = getLogger('xtext.OccurrencesService');
+
+function transformOccurrences(regions: ITextRegion[]): IOccurrence[] {
+  const occurrences: IOccurrence[] = [];
+  regions.forEach(({ offset, length }) => {
+    if (length > 0) {
+      occurrences.push({
+        from: offset,
+        to: offset + length,
+      });
+    }
+  });
+  return occurrences;
+}
+
+export class OccurrencesService {
+  private store: EditorStore;
+
+  private webSocketClient: XtextWebSocketClient;
+
+  private updateService: UpdateService;
+
+  private hasOccurrences = false;
+
+  private findOccurrencesTimer = new Timer(() => {
+    this.handleFindOccurrences();
+  }, FIND_OCCURRENCES_TIMEOUT_MS);
+
+  private clearOccurrencesTimer = new Timer(() => {
+    this.clearOccurrences();
+  }, CLEAR_OCCURRENCES_TIMEOUT_MS);
+
+  constructor(
+    store: EditorStore,
+    webSocketClient: XtextWebSocketClient,
+    updateService: UpdateService,
+  ) {
+    this.store = store;
+    this.webSocketClient = webSocketClient;
+    this.updateService = updateService;
+  }
+
+  onTransaction(transaction: Transaction): void {
+    if (transaction.docChanged) {
+      this.clearOccurrencesTimer.schedule();
+      this.findOccurrencesTimer.reschedule();
+    }
+    if (transaction.isUserEvent('select')) {
+      this.findOccurrencesTimer.reschedule();
+    }
+  }
+
+  private handleFindOccurrences() {
+    this.clearOccurrencesTimer.cancel();
+    this.updateOccurrences().catch((error) => {
+      log.error('Unexpected error while updating occurrences', error);
+      this.clearOccurrences();
+    });
+  }
+
+  private async updateOccurrences() {
+    await this.updateService.update();
+    const result = await this.webSocketClient.send({
+      resource: this.updateService.resourceName,
+      serviceType: 'occurrences',
+      expectedStateId: this.updateService.xtextStateId,
+      caretOffset: this.store.state.selection.main.head,
+    });
+    const allChanges = this.updateService.computeChangesSinceLastUpdate();
+    if (!allChanges.empty
+      || (isServiceConflictResult(result) && result.conflict === 'canceled')) {
+      // Stale occurrences result, the user already made some changes.
+      // We can safely ignore the occurrences and schedule a new find occurrences call.
+      this.clearOccurrences();
+      this.findOccurrencesTimer.schedule();
+      return;
+    }
+    if (!isOccurrencesResult(result) || result.stateId !== this.updateService.xtextStateId) {
+      log.error('Unexpected occurrences result', result);
+      this.clearOccurrences();
+      return;
+    }
+    const write = transformOccurrences(result.writeRegions);
+    const read = transformOccurrences(result.readRegions);
+    this.hasOccurrences = write.length > 0 || read.length > 0;
+    log.debug('Found', write.length, 'write and', read.length, 'read occurrences');
+    this.store.updateOccurrences(write, read);
+  }
+
+  private clearOccurrences() {
+    if (this.hasOccurrences) {
+      this.store.updateOccurrences([], []);
+      this.hasOccurrences = false;
+    }
+  }
+}