1 files changed, 133 insertions, 0 deletions

diff --git a/language-web/src/main/js/xtext/ContentAssistService.ts b/language-web/src/main/js/xtext/ContentAssistService.ts
new file mode 100644
index 00000000..91789864
--- /dev/null
+++ b/language-web/src/main/js/xtext/ContentAssistService.ts
@@ -0,0 +1,133 @@
+import type {
+  Completion,
+  CompletionContext,
+  CompletionResult,
+} from '@codemirror/autocomplete';
+import type { ChangeSet, Transaction } from '@codemirror/state';
+
+import { getLogger } from '../logging';
+import type { UpdateService } from './UpdateService';
+
+const log = getLogger('xtext.ContentAssistService');
+
+export class ContentAssistService {
+  updateService: UpdateService;
+
+  lastCompletion: CompletionResult | null = null;
+
+  constructor(updateService: UpdateService) {
+    this.updateService = updateService;
+  }
+
+  onTransaction(transaction: Transaction): void {
+    if (this.shouldInvalidateCachedCompletion(transaction.changes)) {
+      this.lastCompletion = null;
+    }
+  }
+
+  async contentAssist(context: CompletionContext): Promise<CompletionResult> {
+    const tokenBefore = context.tokenBefore(['QualifiedName']);
+    let range: { from: number, to: number };
+    let selection: { selectionStart?: number, selectionEnd?: number };
+    if (tokenBefore === null) {
+      if (!context.explicit) {
+        return {
+          from: context.pos,
+          options: [],
+        };
+      }
+      range = {
+        from: context.pos,
+        to: context.pos,
+      };
+      selection = {};
+    } else {
+      range = {
+        from: tokenBefore.from,
+        to: tokenBefore.to,
+      };
+      selection = {
+        selectionStart: tokenBefore.from,
+        selectionEnd: tokenBefore.to,
+      };
+    }
+    if (!context.explicit && this.shouldReturnCachedCompletion(tokenBefore)) {
+      log.trace('Returning cached completion result');
+      // Postcondition of `shouldReturnCachedCompletion`: `lastCompletion !== null`
+      return {
+        ...this.lastCompletion as CompletionResult,
+        ...range,
+      };
+    }
+    this.lastCompletion = null;
+    const entries = await this.updateService.fetchContentAssist({
+      resource: this.updateService.resourceName,
+      serviceType: 'assist',
+      caretOffset: context.pos,
+      ...selection,
+    }, context);
+    if (context.aborted) {
+      return {
+        ...range,
+        options: [],
+      };
+    }
+    const options: Completion[] = [];
+    entries.forEach((entry) => {
+      options.push({
+        label: entry.proposal,
+        detail: entry.description,
+        info: entry.documentation,
+        type: entry.kind?.toLowerCase(),
+        boost: entry.kind === 'KEYWORD' ? -90 : 0,
+      });
+    });
+    log.debug('Fetched', options.length, 'completions from server');
+    this.lastCompletion = {
+      ...range,
+      options,
+      span: /^[a-zA-Z0-9_:]*$/,
+    };
+    return this.lastCompletion;
+  }
+
+  private shouldReturnCachedCompletion(
+    token: { from: number, to: number, text: string } | null,
+  ) {
+    if (token === null || this.lastCompletion === null) {
+      return false;
+    }
+    const { from, to, text } = token;
+    const { from: lastFrom, to: lastTo, span } = this.lastCompletion;
+    if (!lastTo) {
+      return true;
+    }
+    const [transformedFrom, transformedTo] = this.mapRangeInclusive(lastFrom, lastTo);
+    return from >= transformedFrom && to <= transformedTo && span && span.exec(text);
+  }
+
+  private shouldInvalidateCachedCompletion(changes: ChangeSet) {
+    if (changes.empty || this.lastCompletion === null) {
+      return false;
+    }
+    const { from: lastFrom, to: lastTo } = this.lastCompletion;
+    if (!lastTo) {
+      return true;
+    }
+    const [transformedFrom, transformedTo] = this.mapRangeInclusive(lastFrom, lastTo);
+    let invalidate = false;
+    changes.iterChangedRanges((fromA, toA) => {
+      if (fromA < transformedFrom || toA > transformedTo) {
+        invalidate = true;
+      }
+    });
+    return invalidate;
+  }
+
+  private mapRangeInclusive(lastFrom: number, lastTo: number): [number, number] {
+    const changes = this.updateService.computeChangesSinceLastUpdate();
+    const transformedFrom = changes.mapPos(lastFrom);
+    const transformedTo = changes.mapPos(lastTo, 1);
+    return [transformedFrom, transformedTo];
+  }
+}