(core) add more detail to /compare endpoint

Summary:
 * Extends `/api/docs/docId1/compare/docId2` endpoint with a `detail=1` option to include details of what changed in the document content.
 * Adds an `/api/docs/docId/compare?left=HASH&right=HASH` endpoint for comparing two versions of a single document. This is needed to implement the extension to `/api/docs/docId1/compare/docId2`.
 * Adds a `HashUtil` class to allow hash aliases like `HEAD` and `HEAD~`.

Everything is a bit crude:
 * Changes are expressed as ActionSummary objects, which aren't fully fleshed out.
 * Extra data about formula columns is inserted in an inflexible way.

This is extracted and cleaned up from https://phab.getgrist.com/D2600.

Test Plan: added tests

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2614

app/common/ActionSummary.ts

@@ -1,5 +1,6 @@
 import {CellDelta, TabularDiff, TabularDiffs} from 'app/common/TabularDiff';
 import toPairs = require('lodash/toPairs');
+import { RowRecord } from 'app/plugin/GristData';
 
 /**
  * An ActionSummary represents the overall effect of changes that took place
@@ -90,6 +91,13 @@ export interface TableDelta {
   /** Partial record of cell-level changes - large bulk changes not included. */
   columnDeltas: {[colId: string]: ColumnDelta};
   columnRenames: LabelDelta[];  /** a list of column renames/additions/removals */
+
+  /*
+   * A snapshot of row content for added and updated rows, including formula columns.
+   * Not included in regular summaries, but used in comparisons.  Hopefully this
+   * can evaporate in future.
+   */
+  finalRowContent?: {[rowId: number]: RowRecord};
 }
 
 /**

app/common/UserAPI.ts

@@ -1,3 +1,4 @@
+import {ActionSummary} from 'app/common/ActionSummary';
 import {ApplyUAResult} from 'app/common/ActiveDocAPI';
 import {BaseAPI, IOptions} from 'app/common/BaseAPI';
 import {BillingAPI, BillingAPIImpl} from 'app/common/BillingAPI';
@@ -218,6 +219,18 @@ export interface DocStateComparison {
   //        both: both documents have changes (possible divergence)
   //   unrelated: no common history found
   summary: 'same' | 'left' | 'right' | 'both' | 'unrelated';
+  // optionally, details of what changed may be included.
+  details?: DocStateComparisonDetails;
+}
+
+/**
+ * Detailed comparison between document versions.  For now, this
+ * is provided as a pair of ActionSummary objects, relative to
+ * the most recent common ancestor.
+ */
+export interface DocStateComparisonDetails {
+  leftChanges: ActionSummary;
+  rightChanges: ActionSummary;
 }
 
 export {UserProfile} from 'app/common/LoginSessionAPI';
@@ -289,7 +302,13 @@ export interface DocAPI {
   replace(source: DocReplacementOptions): Promise<void>;
   getSnapshots(): Promise<DocSnapshots>;
   forceReload(): Promise<void>;
-  compareState(remoteDocId: string): Promise<DocStateComparison>;
+  // Compare two documents, optionally including details of the changes.
+  compareDoc(remoteDocId: string, options?: { detail: boolean }): Promise<DocStateComparison>;
+  // Compare two versions within a document, including details of the changes.
+  // Versions are identified by action hashes, or aliases understood by HashUtil.
+  // Currently, leftHash is expected to be an ancestor of rightHash.  If rightHash
+  // is HEAD, the result will contain a copy of any rows added or updated.
+  compareVersion(leftHash: string, rightHash: string): Promise<DocStateComparison>;
 }
 
 // Operations that are supported by a doc worker.
@@ -676,7 +695,17 @@ export class DocAPIImpl extends BaseAPI implements DocAPI {
     });
   }
 
-  public async compareState(remoteDocId: string): Promise<DocStateComparison> {
-    return this.requestJson(`${this._url}/compare/${remoteDocId}`);
+  public async compareDoc(remoteDocId: string, options: {
+    detail?: boolean
+  } = {}): Promise<DocStateComparison> {
+     const q = options.detail ? '?detail=true' : '';
+     return this.requestJson(`${this._url}/compare/${remoteDocId}${q}`);
+  }
+
+  public async compareVersion(leftHash: string, rightHash: string): Promise<DocStateComparison> {
+    const  url = new URL(`${this._url}/compare`);
+    url.searchParams.append('left', leftHash);
+    url.searchParams.append('right', rightHash);
+    return this.requestJson(url.href);
   }
 }

app/server/lib/ActiveDoc.ts

@@ -184,6 +184,15 @@ export class ActiveDoc extends EventEmitter {
     return this._actionHistory.getRecentStates(maxStates);
   }
 
+  /**
+   * Access specific actions identified by actionNum.
+   * TODO: for memory reasons on large docs, would be best not to hold many actions
+   * in memory at a time, so should e.g. fetch them one at a time.
+   */
+  public getActions(actionNums: number[]): Promise<Array<LocalActionBundle|undefined>> {
+    return this._actionHistory.getActions(actionNums);
+  }
+
   /**
    * Get the most recent actions from the history.  Results are ordered by
    * earliest actions first, later actions later.  If `summarize` is set,

app/server/lib/DocApi.ts

@@ -1,12 +1,12 @@
-import { Application, NextFunction, Request, RequestHandler, Response } from "express";
-
+import { ActionSummary, createEmptyActionSummary } from "app/common/ActionSummary";
 import { ApiError } from 'app/common/ApiError';
 import { BrowserSettings } from "app/common/BrowserSettings";
-import { fromTableDataAction, TableColValues } from 'app/common/DocActions';
-import { arrayRepeat } from "app/common/gutil";
+import { fromTableDataAction, RowRecord, TableColValues } from 'app/common/DocActions';
+import { arrayRepeat, isAffirmative } from "app/common/gutil";
 import { SortFunc } from 'app/common/SortFunc';
 import { DocReplacementOptions, DocState, DocStateComparison, DocStates, NEW_DOCUMENT_CODE} from 'app/common/UserAPI';
 import { HomeDBManager, makeDocAuthResult } from 'app/gen-server/lib/HomeDBManager';
+import { concatenateSummaries, summarizeAction } from "app/server/lib/ActionSummary";
 import { ActiveDoc } from "app/server/lib/ActiveDoc";
 import { assertAccess, getOrSetDocAuth, getTransitiveHeaders, getUserId, isAnonymousUser,
          RequestWithLogin } from 'app/server/lib/Authorizer';
@@ -15,12 +15,15 @@ import { docSessionFromRequest, makeExceptionalDocSession, OptDocSession } from
 import { DocWorker } from "app/server/lib/DocWorker";
 import { expressWrap } from 'app/server/lib/expressWrap';
 import { GristServer } from 'app/server/lib/GristServer';
+import { HashUtil } from 'app/server/lib/HashUtil';
 import { makeForkIds } from "app/server/lib/idUtils";
+import * as log from 'app/server/lib/log';
 import { getDocId, getDocScope, integerParam, isParameterOn, optStringParam,
-         sendOkReply, sendReply } from 'app/server/lib/requestUtils';
+  sendOkReply, sendReply, stringParam } from 'app/server/lib/requestUtils';
 import { SandboxError } from "app/server/lib/sandboxUtil";
 import { handleOptionalUpload, handleUpload } from "app/server/lib/uploads";
 import * as contentDisposition from 'content-disposition';
+import { Application, NextFunction, Request, RequestHandler, Response } from "express";
 import fetch from 'node-fetch';
 import * as path from 'path';
 
@@ -281,6 +284,7 @@ export class DocWorkerApi {
     }));
 
     this._app.get('/api/docs/:docId/compare/:docId2', canView, withDoc(async (activeDoc, req, res) => {
+      const showDetails = isAffirmative(req.query.detail);
       const docSession = docSessionFromRequest(req);
       const {states} = await this._getStates(docSession, activeDoc);
       const ref = await fetch(this._grist.getHomeUrl(req, `/api/docs/${req.params.docId2}/states`), {
@@ -305,9 +309,37 @@ export class DocWorkerApi {
       const comparison: DocStateComparison = {
         left, right, parent, summary
       };
+      if (showDetails && parent) {
+        // Calculate changes from the parent to the current version of this document.
+        const leftChanges = (await this._getChanges(docSession, activeDoc, states, parent.h,
+                                                    'HEAD')).details!.rightChanges;
+
+        // Calculate changes from the (common) parent to the current version of the other document.
+        const url = `/api/docs/${req.params.docId2}/compare?left=${parent.h}`;
+        const rightChangesReq = await fetch(this._grist.getHomeUrl(req, url), {
+          headers: {
+            ...getTransitiveHeaders(req),
+            'Content-Type': 'application/json',
+          }
+        });
+        const rightChanges = (await rightChangesReq.json()).details!.rightChanges;
+
+        // Add the left and right changes as details to the result.
+        comparison.details = { leftChanges, rightChanges };
+      }
       res.json(comparison);
     }));
 
+    // Give details about what changed between two versions of a document.
+    this._app.get('/api/docs/:docId/compare', canView, withDoc(async (activeDoc, req, res) => {
+      // This could be a relatively slow operation if actions are large.
+      const left = stringParam(req.query.left || 'HEAD');
+      const right = stringParam(req.query.right || 'HEAD');
+      const docSession = docSessionFromRequest(req);
+      const {states} = await this._getStates(docSession, activeDoc);
+      res.json(await this._getChanges(docSession, activeDoc, states, left, right));
+    }));
+
     // Do an import targeted at a specific workspace. Although the URL fits ApiServer, this
     // endpoint is handled only by DocWorker, so is handled here. (Note: this does not handle
     // actual file uploads, so no worries here about large request bodies.)
@@ -437,6 +469,94 @@ export class DocWorkerApi {
     };
   }
 
+  /**
+   *
+   * Calculate changes between two document versions identified by leftHash and rightHash.
+   * If rightHash is the latest version of the document, the ActionSummary for it will
+   * contain a copy of updated and added rows.
+   *
+   * Currently will fail if leftHash is not an ancestor of rightHash (this restriction could
+   * be lifted, but is adequate for now).
+   *
+   */
+  private async _getChanges(docSession: OptDocSession, activeDoc: ActiveDoc, states: DocState[],
+                            leftHash: string, rightHash: string): Promise<DocStateComparison> {
+    const finder = new HashUtil(states);
+    const leftOffset = finder.hashToOffset(leftHash);
+    const rightOffset = finder.hashToOffset(rightHash);
+    if (rightOffset > leftOffset) {
+      throw new Error('Comparisons currently require left to be an ancestor of right');
+    }
+    const actionNums: number[] = states.slice(rightOffset, leftOffset).map(state => state.n);
+    const actions = (await activeDoc.getActions(actionNums)).reverse();
+    let totalAction = createEmptyActionSummary();
+    for (const action of actions) {
+      if (!action) { continue; }
+      const summary = summarizeAction(action);
+      totalAction = concatenateSummaries([totalAction, summary]);
+    }
+    const result: DocStateComparison = {
+      left: states[leftOffset],
+      right: states[rightOffset],
+      parent: states[leftOffset],
+      summary: (leftOffset === rightOffset) ? 'same' : 'right',
+      details: {
+        leftChanges: {tableRenames: [], tableDeltas: {}},
+        rightChanges: totalAction
+      }
+    };
+    // Currently, as a bit of a hack, the full final state of updated/added rows
+    // is included, including formula columns, by looking at the current state
+    // of the document.
+    if (rightOffset === 0) {
+      await this._addRowsToActionSummary(docSession, activeDoc, totalAction);
+    } else {
+      // In the future final row content may not be needed, if formula cells end
+      // up included in ActionSummary.
+      log.debug('cannot add rows when not comparing to current state of doc');
+    }
+    return result;
+  }
+
+  /**
+   * Adds the content of updated and added rows to an ActionSummary.
+   * For visualizing differences, currently there's no other way to get formula
+   * information.  This only makes sense for an ActionSummary between a previous
+   * version of the document and the current version, since it accesses the row
+   * content from the current version of the document.
+   */
+  private async _addRowsToActionSummary(docSession: OptDocSession, activeDoc: ActiveDoc,
+                                        summary: ActionSummary) {
+    for (const tableId of Object.keys(summary.tableDeltas)) {
+      const tableDelta = summary.tableDeltas[tableId];
+      const rowIds = new Set([...tableDelta.addRows, ...tableDelta.updateRows]);
+      try {
+        // Inefficient code that reads the entire table in order to pull out the few
+        // rows we need.
+        const [, , ids, columns] = await handleSandboxError(tableId, [], activeDoc.fetchQuery(
+          docSession, {tableId, filters: {}}, true));
+        const rows: {[key: number]: RowRecord} = {};
+        for (const rowId of rowIds) {
+          const rec: RowRecord = {id: rowId};
+          const idx = ids.indexOf(rowId);
+          if (idx >= 0) {
+            for (const colId of Object.keys(columns)) {
+              rec[colId] = columns[colId][idx];
+            }
+            rows[rowId] = rec;
+          }
+        }
+        tableDelta.finalRowContent = rows;
+      } catch (e) {
+        // ActionSummary has some rough spots - if there's some junk in it we just ignore
+        // that for now.
+        // TODO: add ids to doc actions and their undos so they can be aligned, so ActionSummary
+        // doesn't need to use heuristics.
+        log.error('_addRowsToChanges skipped a table');
+      }
+    }
+  }
+
   private async _removeDoc(req: Request, res: Response, permanent: boolean) {
     const scope = getDocScope(req);
     const docId = getDocId(req);

app/server/lib/HashUtil.ts

@@ -0,0 +1,46 @@
+import { DocState } from 'app/common/UserAPI';
+
+/**
+ *
+ * Helper class to support a small subset of git-style references for state hashes:
+ *   HEAD = the most recent state
+ *   [HASH]^1 = the parent of [HASH]
+ *   [HASH]~1 = the parent of [HASH]
+ *   [HASH]~2 = the grandparent of [HASH]
+ *   [HASH]^1^1 = the grandparent of [HASH]
+ *   [HASH]~3 = the great grandparent of [HASH]
+ * For git, where commits have multiple parents, "~" refers to the first parent,
+ * and "^1" also refers to the first parent.  For grist, there are only first parents
+ * (unless/until we start tracking history across merges).
+ *
+ */
+export class HashUtil {
+
+  /**
+   * To construct, provide a list of states, most recent first.
+   */
+  constructor(private _state: DocState[]) {}
+
+  /**
+   * Find the named hash in the list of states, allowing for aliases.
+   * Returns an index into the list of states provided in constructor.
+   */
+  public hashToOffset(hash: string): number {
+    const parts = hash.split(/([~^][0-9]*)/);
+    hash = parts.shift() || '';
+    let offset = hash === 'HEAD' ? 0 : this._state.findIndex(state => state.h === hash);
+    if (offset < 0) { throw new Error('Cannot read hash'); }
+    for (const part of parts) {
+      if (part === '^' || part === '^1') {
+        offset++;
+      } else if (part.startsWith('~')) {
+        offset += parseInt(part.slice(1) || '1', 10);
+      } else if (part === '') {
+        // pass
+      } else {
+        throw new Error('cannot parse hash');
+      }
+    }
+    return offset;
+  }
+}