1 files changed, 310 insertions, 0 deletions

diff --git a/language-web/src/main/js/xtext/UpdateService.ts b/language-web/src/main/js/xtext/UpdateService.ts
new file mode 100644
index 00000000..9b672e79
--- /dev/null
+++ b/language-web/src/main/js/xtext/UpdateService.ts
@@ -0,0 +1,310 @@
+import {
+  ChangeDesc,
+  ChangeSet,
+  Transaction,
+} from '@codemirror/state';
+import { nanoid } from 'nanoid';
+
+import type { EditorStore } from '../editor/EditorStore';
+import type { XtextWebSocketClient } from './XtextWebSocketClient';
+import { ConditionVariable } from '../utils/ConditionVariable';
+import { getLogger } from '../utils/logger';
+import { Timer } from '../utils/Timer';
+import {
+  IContentAssistEntry,
+  isContentAssistResult,
+  isDocumentStateResult,
+  isInvalidStateIdConflictResult,
+} from './xtextServiceResults';
+
+const UPDATE_TIMEOUT_MS = 500;
+
+const WAIT_FOR_UPDATE_TIMEOUT_MS = 1000;
+
+const log = getLogger('xtext.UpdateService');
+
+export interface IAbortSignal {
+  aborted: boolean;
+}
+
+export class UpdateService {
+  resourceName: string;
+
+  xtextStateId: string | null = null;
+
+  private readonly store: EditorStore;
+
+  /**
+   * The changes being synchronized to the server if a full or delta text update is running,
+   * `null` otherwise.
+   */
+  private pendingUpdate: ChangeDesc | null = null;
+
+  /**
+   * Local changes not yet sychronized to the server and not part of the running update, if any.
+   */
+  private dirtyChanges: ChangeDesc;
+
+  private readonly webSocketClient: XtextWebSocketClient;
+
+  private readonly updatedCondition = new ConditionVariable(
+    () => this.pendingUpdate === null && this.xtextStateId !== null,
+    WAIT_FOR_UPDATE_TIMEOUT_MS,
+  );
+
+  private readonly idleUpdateTimer = new Timer(() => {
+    this.handleIdleUpdate();
+  }, UPDATE_TIMEOUT_MS);
+
+  constructor(store: EditorStore, webSocketClient: XtextWebSocketClient) {
+    this.resourceName = `${nanoid(7)}.problem`;
+    this.store = store;
+    this.dirtyChanges = this.newEmptyChangeDesc();
+    this.webSocketClient = webSocketClient;
+  }
+
+  onReconnect(): void {
+    this.xtextStateId = null;
+    this.updateFullText().catch((error) => {
+      log.error('Unexpected error during initial update', error);
+    });
+  }
+
+  onTransaction(transaction: Transaction): void {
+    if (transaction.docChanged) {
+      this.dirtyChanges = this.dirtyChanges.composeDesc(transaction.changes.desc);
+      this.idleUpdateTimer.reschedule();
+    }
+  }
+
+  /**
+   * Computes the summary of any changes happened since the last complete update.
+   *
+   * The result reflects any changes that happened since the `xtextStateId`
+   * version was uploaded to the server.
+   *
+   * @return the summary of changes since the last update
+   */
+  computeChangesSinceLastUpdate(): ChangeDesc {
+    return this.pendingUpdate?.composeDesc(this.dirtyChanges) || this.dirtyChanges;
+  }
+
+  private handleIdleUpdate() {
+    if (!this.webSocketClient.isOpen || this.dirtyChanges.empty) {
+      return;
+    }
+    if (this.pendingUpdate === null) {
+      this.update().catch((error) => {
+        log.error('Unexpected error during scheduled update', error);
+      });
+    }
+    this.idleUpdateTimer.reschedule();
+  }
+
+  private newEmptyChangeDesc() {
+    const changeSet = ChangeSet.of([], this.store.state.doc.length);
+    return changeSet.desc;
+  }
+
+  async updateFullText(): Promise<void> {
+    await this.withUpdate(() => this.doUpdateFullText());
+  }
+
+  private async doUpdateFullText(): Promise<[string, void]> {
+    const result = await this.webSocketClient.send({
+      resource: this.resourceName,
+      serviceType: 'update',
+      fullText: this.store.state.doc.sliceString(0),
+    });
+    if (isDocumentStateResult(result)) {
+      return [result.stateId, undefined];
+    }
+    log.error('Unexpected full text update result:', result);
+    throw new Error('Full text update failed');
+  }
+
+  /**
+   * Makes sure that the document state on the server reflects recent
+   * local changes.
+   *
+   * Performs either an update with delta text or a full text update if needed.
+   * If there are not local dirty changes, the promise resolves immediately.
+   *
+   * @return a promise resolving when the update is completed
+   */
+  async update(): Promise<void> {
+    await this.prepareForDeltaUpdate();
+    const delta = this.computeDelta();
+    if (delta === null) {
+      return;
+    }
+    log.trace('Editor delta', delta);
+    await this.withUpdate(async () => {
+      const result = await this.webSocketClient.send({
+        resource: this.resourceName,
+        serviceType: 'update',
+        requiredStateId: this.xtextStateId,
+        ...delta,
+      });
+      if (isDocumentStateResult(result)) {
+        return [result.stateId, undefined];
+      }
+      if (isInvalidStateIdConflictResult(result)) {
+        return this.doFallbackToUpdateFullText();
+      }
+      log.error('Unexpected delta text update result:', result);
+      throw new Error('Delta text update failed');
+    });
+  }
+
+  private doFallbackToUpdateFullText() {
+    if (this.pendingUpdate === null) {
+      throw new Error('Only a pending update can be extended');
+    }
+    log.warn('Delta update failed, performing full text update');
+    this.xtextStateId = null;
+    this.pendingUpdate = this.pendingUpdate.composeDesc(this.dirtyChanges);
+    this.dirtyChanges = this.newEmptyChangeDesc();
+    return this.doUpdateFullText();
+  }
+
+  async fetchContentAssist(
+    params: Record<string, unknown>,
+    signal: IAbortSignal,
+  ): Promise<IContentAssistEntry[]> {
+    await this.prepareForDeltaUpdate();
+    if (signal.aborted) {
+      return [];
+    }
+    const delta = this.computeDelta();
+    if (delta !== null) {
+      log.trace('Editor delta', delta);
+      const entries = await this.withUpdate(async () => {
+        const result = await this.webSocketClient.send({
+          ...params,
+          requiredStateId: this.xtextStateId,
+          ...delta,
+        });
+        if (isContentAssistResult(result)) {
+          return [result.stateId, result.entries];
+        }
+        if (isInvalidStateIdConflictResult(result)) {
+          const [newStateId] = await this.doFallbackToUpdateFullText();
+          // We must finish this state update transaction to prepare for any push events
+          // before querying for content assist, so we just return `null` and will query
+          // the content assist service later.
+          return [newStateId, null];
+        }
+        log.error('Unextpected content assist result with delta update', result);
+        throw new Error('Unexpexted content assist result with delta update');
+      });
+      if (entries !== null) {
+        return entries;
+      }
+      if (signal.aborted) {
+        return [];
+      }
+    }
+    // Poscondition of `prepareForDeltaUpdate`: `xtextStateId !== null`
+    return this.doFetchContentAssist(params, this.xtextStateId as string);
+  }
+
+  private async doFetchContentAssist(params: Record<string, unknown>, expectedStateId: string) {
+    const result = await this.webSocketClient.send({
+      ...params,
+      requiredStateId: expectedStateId,
+    });
+    if (isContentAssistResult(result) && result.stateId === expectedStateId) {
+      return result.entries;
+    }
+    log.error('Unexpected content assist result', result);
+    throw new Error('Unexpected content assist result');
+  }
+
+  private computeDelta() {
+    if (this.dirtyChanges.empty) {
+      return null;
+    }
+    let minFromA = Number.MAX_SAFE_INTEGER;
+    let maxToA = 0;
+    let minFromB = Number.MAX_SAFE_INTEGER;
+    let maxToB = 0;
+    this.dirtyChanges.iterChangedRanges((fromA, toA, fromB, toB) => {
+      minFromA = Math.min(minFromA, fromA);
+      maxToA = Math.max(maxToA, toA);
+      minFromB = Math.min(minFromB, fromB);
+      maxToB = Math.max(maxToB, toB);
+    });
+    return {
+      deltaOffset: minFromA,
+      deltaReplaceLength: maxToA - minFromA,
+      deltaText: this.store.state.doc.sliceString(minFromB, maxToB),
+    };
+  }
+
+  /**
+   * Executes an asynchronous callback that updates the state on the server.
+   *
+   * Ensures that updates happen sequentially and manages `pendingUpdate`
+   * and `dirtyChanges` to reflect changes being synchronized to the server
+   * and not yet synchronized to the server, respectively.
+   *
+   * Optionally, `callback` may return a second value that is retured by this function.
+   *
+   * Once the remote procedure call to update the server state finishes
+   * and returns the new `stateId`, `callback` must return _immediately_
+   * to ensure that the local `stateId` is updated likewise to be able to handle
+   * push messages referring to the new `stateId` from the server.
+   * If additional work is needed to compute the second value in some cases,
+   * use `T | null` instead of `T` as a return type and signal the need for additional
+   * computations by returning `null`. Thus additional computations can be performed
+   * outside of the critical section.
+   *
+   * @param callback the asynchronous callback that updates the server state
+   * @return a promise resolving to the second value returned by `callback`
+   */
+  private async withUpdate<T>(callback: () => Promise<[string, T]>): Promise<T> {
+    if (this.pendingUpdate !== null) {
+      throw new Error('Another update is pending, will not perform update');
+    }
+    this.pendingUpdate = this.dirtyChanges;
+    this.dirtyChanges = this.newEmptyChangeDesc();
+    let newStateId: string | null = null;
+    try {
+      let result: T;
+      [newStateId, result] = await callback();
+      this.xtextStateId = newStateId;
+      this.pendingUpdate = null;
+      this.updatedCondition.notifyAll();
+      return result;
+    } catch (e) {
+      log.error('Error while update', e);
+      if (this.pendingUpdate === null) {
+        log.error('pendingUpdate was cleared during update');
+      } else {
+        this.dirtyChanges = this.pendingUpdate.composeDesc(this.dirtyChanges);
+      }
+      this.pendingUpdate = null;
+      this.webSocketClient.forceReconnectOnError();
+      this.updatedCondition.rejectAll(e);
+      throw e;
+    }
+  }
+
+  /**
+   * Ensures that there is some state available on the server (`xtextStateId`)
+   * and that there is not pending update.
+   *
+   * After this function resolves, a delta text update is possible.
+   *
+   * @return a promise resolving when there is a valid state id but no pending update
+   */
+  private async prepareForDeltaUpdate() {
+    // If no update is pending, but the full text hasn't been uploaded to the server yet,
+    // we must start a full text upload.
+    if (this.pendingUpdate === null && this.xtextStateId === null) {
+      await this.updateFullText();
+    }
+    await this.updatedCondition.waitFor();
+  }
+}