From 1a3e8e7ecf70f70d34ac4f35dbf7268edac04ce6 Mon Sep 17 00:00:00 2001
From: ConnorYoh <40631091+ConnorYoh@users.noreply.github.com>
Date: Tue, 2 Sep 2025 15:09:05 +0100
Subject: [PATCH] Undo Button -> review state. Result files added to recents
 (#4337)

Produced PDFs go into recent files
Undo button added to review state
Undo causes undoConsume which replaces result files with source files.
Removes result files from recent files too

---------

Co-authored-by: Connor Yoh <connor@stirlingpdf.com>
---
 .claude/settings.local.json                   |   5 +-
 frontend/package.json                         |   1 +
 .../public/locales/en-GB/translation.json     |   5 +-
 .../tools/shared/ReviewToolStep.tsx           |  86 ++++++---
 .../tools/shared/createToolFlow.tsx           |   4 +-
 frontend/src/contexts/FileContext.tsx         |  14 +-
 frontend/src/contexts/file/FileReducer.ts     |  79 ++++----
 frontend/src/contexts/file/fileActions.ts     | 178 ++++++++++++++++--
 frontend/src/contexts/file/fileHooks.ts       |   7 +-
 .../useAddPasswordOperation.test.ts           |   1 +
 .../useChangePermissionsOperation.test.ts     |   1 +
 .../useRemovePasswordOperation.test.ts        |   1 +
 .../src/hooks/tools/shared/useBaseTool.ts     |   7 +
 .../hooks/tools/shared/useToolOperation.ts    | 102 +++++++++-
 frontend/src/tools/AddPassword.tsx            |   6 +
 frontend/src/tools/AddWatermark.tsx           |   6 +
 frontend/src/tools/Automate.tsx               |   8 +-
 frontend/src/tools/ChangePermissions.tsx      |   1 +
 frontend/src/tools/Compress.tsx               |   1 +
 frontend/src/tools/Convert.tsx                |   6 +
 frontend/src/tools/OCR.tsx                    |   6 +
 frontend/src/tools/RemoveCertificateSign.tsx  |   1 +
 frontend/src/tools/RemovePassword.tsx         |   1 +
 frontend/src/tools/Repair.tsx                 |   1 +
 frontend/src/tools/Sanitize.tsx               |   1 +
 frontend/src/tools/SingleLargePage.tsx        |   1 +
 frontend/src/tools/Split.tsx                  |   1 +
 frontend/src/tools/UnlockPdfForms.tsx         |   1 +
 frontend/src/types/fileContext.ts             |   4 +-
 29 files changed, 440 insertions(+), 96 deletions(-)

diff --git a/.claude/settings.local.json b/.claude/settings.local.json
index 54c5f7b19..877d932ef 100644
--- a/.claude/settings.local.json
+++ b/.claude/settings.local.json
@@ -13,9 +13,10 @@
       "Bash(npx tsc:*)",
       "Bash(node:*)",
       "Bash(npm run dev:*)",
-      "Bash(sed:*)"
+      "Bash(sed:*)",
+      "Bash(npm run typecheck:*)"
     ],
     "deny": [],
     "defaultMode": "acceptEdits"
   }
-}
+}
\ No newline at end of file
diff --git a/frontend/package.json b/frontend/package.json
index 13c795fc2..160c96c18 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -42,6 +42,7 @@
     "prebuild": "npm run generate-icons",
     "build": "npx tsc --noEmit && vite build",
     "preview": "vite preview",
+    "typecheck": "tsc --noEmit",
     "generate-licenses": "node scripts/generate-licenses.js",
     "generate-icons": "node scripts/generate-icons.js",
     "generate-icons:verbose": "node scripts/generate-icons.js --verbose",
diff --git a/frontend/public/locales/en-GB/translation.json b/frontend/public/locales/en-GB/translation.json
index 70aeefbf4..637ab59e1 100644
--- a/frontend/public/locales/en-GB/translation.json
+++ b/frontend/public/locales/en-GB/translation.json
@@ -41,6 +41,9 @@
   "save": "Save",
   "saveToBrowser": "Save to Browser",
   "download": "Download",
+  "undoOperationTooltip": "Click to undo the last operation and restore the original files",
+  "undo": "Undo",
+  "moreOptions": "More Options",
   "editYourNewFiles": "Edit your new file(s)",
   "close": "Close",
   "fileSelected": "Selected: {{filename}}",
@@ -2382,4 +2385,4 @@
       "processImagesDesc": "Converts multiple image files into a single PDF document, then applies OCR technology to extract searchable text from the images."
     }
   }
-}
\ No newline at end of file
+}
diff --git a/frontend/src/components/tools/shared/ReviewToolStep.tsx b/frontend/src/components/tools/shared/ReviewToolStep.tsx
index 475715704..364077e4f 100644
--- a/frontend/src/components/tools/shared/ReviewToolStep.tsx
+++ b/frontend/src/components/tools/shared/ReviewToolStep.tsx
@@ -1,27 +1,48 @@
-import React, { useEffect, useRef } from 'react';
-import { Button, Stack, Text } from '@mantine/core';
-import { useTranslation } from 'react-i18next';
-import DownloadIcon from '@mui/icons-material/Download';
-import ErrorNotification from './ErrorNotification';
-import ResultsPreview from './ResultsPreview';
-import { SuggestedToolsSection } from './SuggestedToolsSection';
-import { ToolOperationHook } from '../../../hooks/tools/shared/useToolOperation';
+import React, { useEffect, useRef, useState } from "react";
+import { Button, Group, Stack } from "@mantine/core";
+import { useTranslation } from "react-i18next";
+import DownloadIcon from "@mui/icons-material/Download";
+import UndoIcon from "@mui/icons-material/Undo";
+import ErrorNotification from "./ErrorNotification";
+import ResultsPreview from "./ResultsPreview";
+import { SuggestedToolsSection } from "./SuggestedToolsSection";
+import { ToolOperationHook } from "../../../hooks/tools/shared/useToolOperation";
+import { Tooltip } from "../../shared/Tooltip";
 
 export interface ReviewToolStepProps<TParams = unknown> {
   isVisible: boolean;
   operation: ToolOperationHook<TParams>;
   title?: string;
   onFileClick?: (file: File) => void;
+  onUndo: () => void;
 }
 
-function ReviewStepContent<TParams = unknown>({ operation, onFileClick }: { operation: ToolOperationHook<TParams>; onFileClick?: (file: File) => void }) {
+function ReviewStepContent<TParams = unknown>({
+  operation,
+  onFileClick,
+  onUndo,
+}: {
+  operation: ToolOperationHook<TParams>;
+  onFileClick?: (file: File) => void;
+  onUndo: () => void;
+}) {
   const { t } = useTranslation();
   const stepRef = useRef<HTMLDivElement>(null);
 
-  const previewFiles = operation.files?.map((file, index) => ({
-    file,
-    thumbnail: operation.thumbnails[index]
-  })) || [];
+  const handleUndo = async () => {
+    try {
+      onUndo();
+    } catch (error) {
+      // Error is already handled by useToolOperation, just reset loading state
+      console.error("Undo operation failed:", error);
+    }
+  };
+
+  const previewFiles =
+    operation.files?.map((file, index) => ({
+      file,
+      thumbnail: operation.thumbnails[index],
+    })) || [];
 
   // Auto-scroll to bottom when content appears
   useEffect(() => {
@@ -31,7 +52,7 @@ function ReviewStepContent<TParams = unknown>({ operation, onFileClick }: { oper
         setTimeout(() => {
           scrollableContainer.scrollTo({
             top: scrollableContainer.scrollHeight,
-            behavior: 'smooth'
+            behavior: "smooth",
           });
         }, 100); // Small delay to ensure content is rendered
       }
@@ -40,10 +61,7 @@ function ReviewStepContent<TParams = unknown>({ operation, onFileClick }: { oper
 
   return (
     <Stack gap="sm" ref={stepRef}>
-      <ErrorNotification
-        error={operation.errorMessage}
-        onClose={operation.clearError}
-      />
+      <ErrorNotification error={operation.errorMessage} onClose={operation.clearError} />
 
       {previewFiles.length > 0 && (
         <ResultsPreview
@@ -53,7 +71,18 @@ function ReviewStepContent<TParams = unknown>({ operation, onFileClick }: { oper
         />
       )}
 
-       {operation.downloadUrl && (
+      <Tooltip content={t("undoOperationTooltip", "Click to undo the last operation and restore the original files")}>
+        <Button
+          leftSection={<UndoIcon />}
+          variant="outline"
+          color="var(--mantine-color-gray-6)"
+          onClick={handleUndo}
+          fullWidth
+        >
+          {t("undo", "Undo")}
+        </Button>
+      </Tooltip>
+      {operation.downloadUrl && (
         <Button
           component="a"
           href={operation.downloadUrl}
@@ -78,14 +107,13 @@ export function createReviewToolStep<TParams = unknown>(
 ): React.ReactElement {
   const { t } = useTranslation();
 
-  return createStep(t("review", "Review"), {
-    isVisible: props.isVisible,
-    _excludeFromCount: true,
-    _noPadding: true
-  }, (
-    <ReviewStepContent 
-      operation={props.operation} 
-      onFileClick={props.onFileClick}
-    />
-  ));
+  return createStep(
+    t("review", "Review"),
+    {
+      isVisible: props.isVisible,
+      _excludeFromCount: true,
+      _noPadding: true,
+    },
+    <ReviewStepContent operation={props.operation} onFileClick={props.onFileClick} onUndo={props.onUndo} />
+  );
 }
diff --git a/frontend/src/components/tools/shared/createToolFlow.tsx b/frontend/src/components/tools/shared/createToolFlow.tsx
index da2503b4e..b6a7594c6 100644
--- a/frontend/src/components/tools/shared/createToolFlow.tsx
+++ b/frontend/src/components/tools/shared/createToolFlow.tsx
@@ -43,6 +43,7 @@ export interface ReviewStepConfig {
   operation: ToolOperationHook<any>;
   title: string;
   onFileClick?: (file: File) => void;
+  onUndo: () => void;
   testId?: string;
 }
 
@@ -105,7 +106,8 @@ export function createToolFlow(config: ToolFlowConfig) {
           isVisible: config.review.isVisible,
           operation: config.review.operation,
           title: config.review.title,
-          onFileClick: config.review.onFileClick
+          onFileClick: config.review.onFileClick,
+          onUndo: config.review.onUndo
         })}
       </ToolStepProvider>
     </Stack>
diff --git a/frontend/src/contexts/FileContext.tsx b/frontend/src/contexts/FileContext.tsx
index 0698310b4..39faa0643 100644
--- a/frontend/src/contexts/FileContext.tsx
+++ b/frontend/src/contexts/FileContext.tsx
@@ -25,7 +25,7 @@ import {
 // Import modular components
 import { fileContextReducer, initialFileContextState } from './file/FileReducer';
 import { createFileSelectors } from './file/fileSelectors';
-import { AddedFile, addFiles, consumeFiles, createFileActions } from './file/fileActions';
+import { AddedFile, addFiles, consumeFiles, undoConsumeFiles, createFileActions } from './file/fileActions';
 import { FileLifecycleManager } from './file/lifecycle';
 import { FileStateContext, FileActionsContext } from './file/contexts';
 import { IndexedDBProvider, useIndexedDB } from './IndexedDBContext';
@@ -121,9 +121,13 @@ function FileContextInner({
   const baseActions = useMemo(() => createFileActions(dispatch), []);
 
   // Helper functions for pinned files
-  const consumeFilesWrapper = useCallback(async (inputFileIds: FileId[], outputFiles: File[]): Promise<void> => {
-    return consumeFiles(inputFileIds, outputFiles, stateRef, filesRef, dispatch);
-  }, []);
+  const consumeFilesWrapper = useCallback(async (inputFileIds: FileId[], outputFiles: File[]): Promise<FileId[]> => {
+    return consumeFiles(inputFileIds, outputFiles, stateRef, filesRef, dispatch, indexedDB);
+  }, [indexedDB]);
+
+  const undoConsumeFilesWrapper = useCallback(async (inputFiles: File[], inputFileRecords: FileRecord[], outputFileIds: FileId[]): Promise<void> => {
+    return undoConsumeFiles(inputFiles, inputFileRecords, outputFileIds, stateRef, filesRef, dispatch, indexedDB);
+  }, [indexedDB]);
 
   // Helper to find FileId from File object
   const findFileId = useCallback((file: File): FileId | undefined => {
@@ -206,6 +210,7 @@ function FileContextInner({
     pinFile: pinFileWrapper,
     unpinFile: unpinFileWrapper,
     consumeFiles: consumeFilesWrapper,
+    undoConsumeFiles: undoConsumeFilesWrapper,
     setHasUnsavedChanges,
     trackBlobUrl: lifecycleManager.trackBlobUrl,
     cleanupFile: (fileId: FileId) => lifecycleManager.cleanupFile(fileId, stateRef),
@@ -219,6 +224,7 @@ function FileContextInner({
     lifecycleManager,
     setHasUnsavedChanges,
     consumeFilesWrapper,
+    undoConsumeFilesWrapper,
     pinFileWrapper,
     unpinFileWrapper,
     indexedDB,
diff --git a/frontend/src/contexts/file/FileReducer.ts b/frontend/src/contexts/file/FileReducer.ts
index 969825505..93c06c4d2 100644
--- a/frontend/src/contexts/file/FileReducer.ts
+++ b/frontend/src/contexts/file/FileReducer.ts
@@ -25,6 +25,47 @@ export const initialFileContextState: FileContextState = {
   }
 };
 
+// Helper function for consume/undo operations
+function processFileSwap(
+  state: FileContextState,
+  filesToRemove: FileId[],
+  filesToAdd: FileRecord[]
+): FileContextState {
+  // Only remove unpinned files
+  const unpinnedRemoveIds = filesToRemove.filter(id => !state.pinnedFiles.has(id));
+  const remainingIds = state.files.ids.filter(id => !unpinnedRemoveIds.includes(id));
+
+  // Remove unpinned files from state
+  const newById = { ...state.files.byId };
+  unpinnedRemoveIds.forEach(id => {
+    delete newById[id];
+  });
+
+  // Add new files
+  const addedIds: FileId[] = [];
+  filesToAdd.forEach(record => {
+    if (!newById[record.id]) {
+      addedIds.push(record.id);
+      newById[record.id] = record;
+    }
+  });
+
+  // Clear selections that reference removed files
+  const validSelectedFileIds = state.ui.selectedFileIds.filter(id => !unpinnedRemoveIds.includes(id));
+
+  return {
+    ...state,
+    files: {
+      ids: [...addedIds, ...remainingIds],
+      byId: newById
+    },
+    ui: {
+      ...state.ui,
+      selectedFileIds: validSelectedFileIds
+    }
+  };
+}
+
 // Pure reducer function
 export function fileContextReducer(state: FileContextState, action: FileContextAction): FileContextState {
   switch (action.type) {
@@ -193,40 +234,12 @@ export function fileContextReducer(state: FileContextState, action: FileContextA
 
     case 'CONSUME_FILES': {
       const { inputFileIds, outputFileRecords } = action.payload;
+      return processFileSwap(state, inputFileIds, outputFileRecords);
+    }
 
-      // Only remove unpinned input files
-      const unpinnedInputIds = inputFileIds.filter(id => !state.pinnedFiles.has(id));
-      const remainingIds = state.files.ids.filter(id => !unpinnedInputIds.includes(id));
-
-      // Remove unpinned files from state
-      const newById = { ...state.files.byId };
-      unpinnedInputIds.forEach(id => {
-        delete newById[id];
-      });
-
-      // Add output files
-      const outputIds: FileId[] = [];
-      outputFileRecords.forEach(record => {
-        if (!newById[record.id]) {
-          outputIds.push(record.id);
-          newById[record.id] = record;
-        }
-      });
-
-      // Clear selections that reference removed files
-      const validSelectedFileIds = state.ui.selectedFileIds.filter(id => !unpinnedInputIds.includes(id));
-
-      return {
-        ...state,
-        files: {
-          ids: [...remainingIds, ...outputIds],
-          byId: newById
-        },
-        ui: {
-          ...state.ui,
-          selectedFileIds: validSelectedFileIds
-        }
-      };
+    case 'UNDO_CONSUME_FILES': {
+      const { inputFileRecords, outputFileIds } = action.payload;
+      return processFileSwap(state, outputFileIds, inputFileRecords);
     }
 
     case 'RESET_CONTEXT': {
diff --git a/frontend/src/contexts/file/fileActions.ts b/frontend/src/contexts/file/fileActions.ts
index 8d91f8855..e55108553 100644
--- a/frontend/src/contexts/file/fileActions.ts
+++ b/frontend/src/contexts/file/fileActions.ts
@@ -323,34 +323,28 @@ export async function addFiles(
 }
 
 /**
- * Consume files helper - replace unpinned input files with output files
+ * Helper function to process files into records with thumbnails and metadata
  */
-export async function consumeFiles(
-  inputFileIds: FileId[],
-  outputFiles: File[],
-  stateRef: React.MutableRefObject<FileContextState>,
-  filesRef: React.MutableRefObject<Map<FileId, File>>,
-  dispatch: React.Dispatch<FileContextAction>
-): Promise<void> {
-  if (DEBUG) console.log(`📄 consumeFiles: Processing ${inputFileIds.length} input files, ${outputFiles.length} output files`);
-
-  // Process output files through the 'processed' path to generate thumbnails
-  const outputFileRecords = await Promise.all(
-    outputFiles.map(async (file) => {
+async function processFilesIntoRecords(
+  files: File[],
+  filesRef: React.MutableRefObject<Map<FileId, File>>
+): Promise<Array<{ record: FileRecord; file: File; fileId: FileId; thumbnail?: string }>> {
+  return Promise.all(
+    files.map(async (file) => {
       const fileId = createFileId();
       filesRef.current.set(fileId, file);
 
-      // Generate thumbnail and page count for output file
+      // Generate thumbnail and page count
       let thumbnail: string | undefined;
       let pageCount: number = 1;
 
       try {
-        if (DEBUG) console.log(`📄 consumeFiles: Generating thumbnail for output file ${file.name}`);
+        if (DEBUG) console.log(`📄 Generating thumbnail for file ${file.name}`);
         const result = await generateThumbnailWithMetadata(file);
         thumbnail = result.thumbnail;
         pageCount = result.pageCount;
       } catch (error) {
-        if (DEBUG) console.warn(`📄 consumeFiles: Failed to generate thumbnail for output file ${file.name}:`, error);
+        if (DEBUG) console.warn(`📄 Failed to generate thumbnail for file ${file.name}:`, error);
       }
 
       const record = toFileRecord(file, fileId);
@@ -362,20 +356,168 @@ export async function consumeFiles(
         record.processedFile = createProcessedFile(pageCount, thumbnail);
       }
 
-      return record;
+      return { record, file, fileId, thumbnail };
     })
   );
+}
+
+/**
+ * Helper function to persist files to IndexedDB
+ */
+async function persistFilesToIndexedDB(
+  fileRecords: Array<{ file: File; fileId: FileId; thumbnail?: string }>,
+  indexedDB: { saveFile: (file: File, fileId: FileId, existingThumbnail?: string) => Promise<any> }
+): Promise<void> {
+  await Promise.all(fileRecords.map(async ({ file, fileId, thumbnail }) => {
+    try {
+      await indexedDB.saveFile(file, fileId, thumbnail);
+    } catch (error) {
+      console.error('Failed to persist file to IndexedDB:', file.name, error);
+    }
+  }));
+}
+
+/**
+ * Consume files helper - replace unpinned input files with output files
+ */
+export async function consumeFiles(
+  inputFileIds: FileId[],
+  outputFiles: File[],
+  stateRef: React.MutableRefObject<FileContextState>,
+  filesRef: React.MutableRefObject<Map<FileId, File>>,
+  dispatch: React.Dispatch<FileContextAction>,
+  indexedDB?: { saveFile: (file: File, fileId: FileId, existingThumbnail?: string) => Promise<any> } | null
+): Promise<FileId[]> {
+  if (DEBUG) console.log(`📄 consumeFiles: Processing ${inputFileIds.length} input files, ${outputFiles.length} output files`);
+
+  // Process output files with thumbnails and metadata
+  const outputFileRecords = await processFilesIntoRecords(outputFiles, filesRef);
+
+  // Persist output files to IndexedDB if available
+  if (indexedDB) {
+    await persistFilesToIndexedDB(outputFileRecords, indexedDB);
+  }
 
   // Dispatch the consume action
   dispatch({
     type: 'CONSUME_FILES',
     payload: {
       inputFileIds,
-      outputFileRecords
+      outputFileRecords: outputFileRecords.map(({ record }) => record)
     }
   });
 
   if (DEBUG) console.log(`📄 consumeFiles: Successfully consumed files - removed ${inputFileIds.length} inputs, added ${outputFileRecords.length} outputs`);
+  
+  // Return the output file IDs for undo tracking
+  return outputFileRecords.map(({ fileId }) => fileId);
+}
+
+/**
+ * Helper function to restore files to filesRef and manage IndexedDB cleanup
+ */
+async function restoreFilesAndCleanup(
+  filesToRestore: Array<{ file: File; record: FileRecord }>,
+  fileIdsToRemove: FileId[],
+  filesRef: React.MutableRefObject<Map<FileId, File>>,
+  indexedDB?: { deleteFile: (fileId: FileId) => Promise<void> } | null
+): Promise<void> {
+  // Remove files from filesRef
+  fileIdsToRemove.forEach(id => {
+    if (filesRef.current.has(id)) {
+      if (DEBUG) console.log(`📄 Removing file ${id} from filesRef`);
+      filesRef.current.delete(id);
+    } else {
+      if (DEBUG) console.warn(`📄 File ${id} not found in filesRef`);
+    }
+  });
+
+  // Restore files to filesRef
+  filesToRestore.forEach(({ file, record }) => {
+    if (file && record) {
+      // Validate the file before restoring
+      if (file.size === 0) {
+        if (DEBUG) console.warn(`📄 Skipping empty file ${file.name}`);
+        return;
+      }
+      
+      // Restore the file to filesRef
+      if (DEBUG) console.log(`📄 Restoring file ${file.name} with id ${record.id} to filesRef`);
+      filesRef.current.set(record.id, file);
+    }
+  });
+
+  // Clean up IndexedDB
+  if (indexedDB) {
+    const indexedDBPromises = fileIdsToRemove.map(fileId =>
+      indexedDB.deleteFile(fileId).catch(error => {
+        console.error('Failed to delete file from IndexedDB:', fileId, error);
+        throw error; // Re-throw to trigger rollback
+      })
+    );
+    
+    // Execute all IndexedDB operations
+    await Promise.all(indexedDBPromises);
+  }
+}
+
+/**
+ * Undoes a previous consumeFiles operation by restoring input files and removing output files (unless pinned)
+ */
+export async function undoConsumeFiles(
+  inputFiles: File[],
+  inputFileRecords: FileRecord[],
+  outputFileIds: FileId[],
+  stateRef: React.MutableRefObject<FileContextState>,
+  filesRef: React.MutableRefObject<Map<FileId, File>>,
+  dispatch: React.Dispatch<FileContextAction>,
+  indexedDB?: { saveFile: (file: File, fileId: FileId, existingThumbnail?: string) => Promise<any>; deleteFile: (fileId: FileId) => Promise<void> } | null
+): Promise<void> {
+  if (DEBUG) console.log(`📄 undoConsumeFiles: Restoring ${inputFileRecords.length} input files, removing ${outputFileIds.length} output files`);
+
+  // Validate inputs
+  if (inputFiles.length !== inputFileRecords.length) {
+    throw new Error(`Mismatch between input files (${inputFiles.length}) and records (${inputFileRecords.length})`);
+  }
+
+  // Create a backup of current filesRef state for rollback
+  const backupFilesRef = new Map(filesRef.current);
+  
+  try {
+    // Prepare files to restore
+    const filesToRestore = inputFiles.map((file, index) => ({
+      file,
+      record: inputFileRecords[index]
+    }));
+
+    // Restore input files and clean up output files
+    await restoreFilesAndCleanup(
+      filesToRestore,
+      outputFileIds,
+      filesRef,
+      indexedDB
+    );
+
+    // Dispatch the undo action (only if everything else succeeded)
+    dispatch({
+      type: 'UNDO_CONSUME_FILES',
+      payload: {
+        inputFileRecords,
+        outputFileIds
+      }
+    });
+
+    if (DEBUG) console.log(`📄 undoConsumeFiles: Successfully undone consume operation - restored ${inputFileRecords.length} inputs, removed ${outputFileIds.length} outputs`);
+    
+  } catch (error) {
+    // Rollback filesRef to previous state
+    if (DEBUG) console.error('📄 undoConsumeFiles: Error during undo, rolling back filesRef', error);
+    filesRef.current.clear();
+    backupFilesRef.forEach((file, id) => {
+      filesRef.current.set(id, file);
+    });
+    throw error; // Re-throw to let caller handle
+  }
 }
 
 /**
diff --git a/frontend/src/contexts/file/fileHooks.ts b/frontend/src/contexts/file/fileHooks.ts
index c6fe6b466..e1b8e5cc4 100644
--- a/frontend/src/contexts/file/fileHooks.ts
+++ b/frontend/src/contexts/file/fileHooks.ts
@@ -165,6 +165,7 @@ export function useFileContext() {
     // File management
     addFiles: actions.addFiles,
     consumeFiles: actions.consumeFiles,
+    undoConsumeFiles: actions.undoConsumeFiles,
     recordOperation: (fileId: FileId, operation: any) => {}, // Operation tracking not implemented
     markOperationApplied: (fileId: FileId, operationId: string) => {}, // Operation tracking not implemented
     markOperationFailed: (fileId: FileId, operationId: string, error: string) => {}, // Operation tracking not implemented
@@ -187,7 +188,11 @@ export function useFileContext() {
     isFilePinned: selectors.isFilePinned,
 
     // Active files
-    activeFiles: selectors.getFiles()
+    activeFiles: selectors.getFiles(),
+
+    // Direct access to actions and selectors (for advanced use cases)
+    actions,
+    selectors
   }), [state, selectors, actions]);
 }
 
diff --git a/frontend/src/hooks/tools/addPassword/useAddPasswordOperation.test.ts b/frontend/src/hooks/tools/addPassword/useAddPasswordOperation.test.ts
index 76910bff6..93b55bc26 100644
--- a/frontend/src/hooks/tools/addPassword/useAddPasswordOperation.test.ts
+++ b/frontend/src/hooks/tools/addPassword/useAddPasswordOperation.test.ts
@@ -46,6 +46,7 @@ describe('useAddPasswordOperation', () => {
     resetResults: vi.fn(),
     clearError: vi.fn(),
     cancelOperation: vi.fn(),
+    undoOperation: vi.fn(),
   };
 
   beforeEach(() => {
diff --git a/frontend/src/hooks/tools/changePermissions/useChangePermissionsOperation.test.ts b/frontend/src/hooks/tools/changePermissions/useChangePermissionsOperation.test.ts
index 71a0500f6..682653e9e 100644
--- a/frontend/src/hooks/tools/changePermissions/useChangePermissionsOperation.test.ts
+++ b/frontend/src/hooks/tools/changePermissions/useChangePermissionsOperation.test.ts
@@ -45,6 +45,7 @@ describe('useChangePermissionsOperation', () => {
     resetResults: vi.fn(),
     clearError: vi.fn(),
     cancelOperation: vi.fn(),
+    undoOperation: vi.fn(),
   };
 
   beforeEach(() => {
diff --git a/frontend/src/hooks/tools/removePassword/useRemovePasswordOperation.test.ts b/frontend/src/hooks/tools/removePassword/useRemovePasswordOperation.test.ts
index be73ff1d3..cdaa7b416 100644
--- a/frontend/src/hooks/tools/removePassword/useRemovePasswordOperation.test.ts
+++ b/frontend/src/hooks/tools/removePassword/useRemovePasswordOperation.test.ts
@@ -44,6 +44,7 @@ describe('useRemovePasswordOperation', () => {
     resetResults: vi.fn(),
     clearError: vi.fn(),
     cancelOperation: vi.fn(),
+    undoOperation: vi.fn(),
   };
 
   beforeEach(() => {
diff --git a/frontend/src/hooks/tools/shared/useBaseTool.ts b/frontend/src/hooks/tools/shared/useBaseTool.ts
index c18444546..64e9af59e 100644
--- a/frontend/src/hooks/tools/shared/useBaseTool.ts
+++ b/frontend/src/hooks/tools/shared/useBaseTool.ts
@@ -21,6 +21,7 @@ interface BaseToolReturn<TParams> {
   handleExecute: () => Promise<void>;
   handleThumbnailClick: (file: File) => void;
   handleSettingsReset: () => void;
+  handleUndo: () => Promise<void>;
 
   // Standard computed state
   hasFiles: boolean;
@@ -88,6 +89,11 @@ export function useBaseTool<TParams>(
     onPreviewFile?.(null);
   }, [operation, onPreviewFile]);
 
+  const handleUndo = useCallback(async () => {
+    await operation.undoOperation();
+    onPreviewFile?.(null);
+  }, [operation, onPreviewFile]);
+
   // Standard computed state
   const hasFiles = selectedFiles.length > 0;
   const hasResults = operation.files.length > 0 || operation.downloadUrl !== null;
@@ -109,6 +115,7 @@ export function useBaseTool<TParams>(
     handleExecute,
     handleThumbnailClick,
     handleSettingsReset,
+    handleUndo,
 
     // State
     hasFiles,
diff --git a/frontend/src/hooks/tools/shared/useToolOperation.ts b/frontend/src/hooks/tools/shared/useToolOperation.ts
index 6e2ce6404..d8d35176d 100644
--- a/frontend/src/hooks/tools/shared/useToolOperation.ts
+++ b/frontend/src/hooks/tools/shared/useToolOperation.ts
@@ -1,4 +1,4 @@
-import { useCallback } from 'react';
+import { useCallback, useRef, useEffect } from 'react';
 import axios from 'axios';
 import { useTranslation } from 'react-i18next';
 import { useFileContext } from '../../../contexts/FileContext';
@@ -9,6 +9,7 @@ import { extractErrorMessage } from '../../../utils/toolErrorHandler';
 import { createOperation } from '../../../utils/toolOperationTracker';
 import { ResponseHandler } from '../../../utils/toolResponseProcessor';
 import { FileId } from '../../../types/file';
+import { FileRecord } from '../../../types/fileContext';
 
 // Re-export for backwards compatibility
 export type { ProcessingProgress, ResponseHandler };
@@ -107,6 +108,7 @@ export interface ToolOperationHook<TParams = void> {
   resetResults: () => void;
   clearError: () => void;
   cancelOperation: () => void;
+  undoOperation: () => Promise<void>;
 }
 
 // Re-export for backwards compatibility
@@ -128,13 +130,20 @@ export const useToolOperation = <TParams>(
   config: ToolOperationConfig<TParams>
 ): ToolOperationHook<TParams> => {
   const { t } = useTranslation();
-  const { recordOperation, markOperationApplied, markOperationFailed, addFiles, consumeFiles, findFileId } = useFileContext();
+  const { recordOperation, markOperationApplied, markOperationFailed, addFiles, consumeFiles, undoConsumeFiles, findFileId, actions: fileActions, selectors } = useFileContext();
 
   // Composed hooks
   const { state, actions } = useToolState();
   const { processFiles, cancelOperation: cancelApiCalls } = useToolApiCalls<TParams>();
   const { generateThumbnails, createDownloadInfo, cleanupBlobUrls, extractZipFiles, extractAllZipFiles } = useToolResources();
 
+  // Track last operation for undo functionality
+  const lastOperationRef = useRef<{
+    inputFiles: File[];
+    inputFileRecords: FileRecord[];
+    outputFileIds: FileId[];
+  } | null>(null);
+
   const executeOperation = useCallback(async (
     params: TParams,
     selectedFiles: File[]
@@ -232,8 +241,33 @@ export const useToolOperation = <TParams>(
         actions.setDownloadInfo(downloadInfo.url, downloadInfo.filename);
 
         // Replace input files with processed files (consumeFiles handles pinning)
-        const inputFileIds = validFiles.map(file => findFileId(file)).filter(Boolean) as FileId[];
-        await consumeFiles(inputFileIds, processedFiles);
+        const inputFileIds: FileId[] = [];
+        const inputFileRecords: FileRecord[] = [];
+        
+        // Build parallel arrays of IDs and records for undo tracking
+        for (const file of validFiles) {
+          const fileId = findFileId(file);
+          if (fileId) {
+            const record = selectors.getFileRecord(fileId);
+            if (record) {
+              inputFileIds.push(fileId);
+              inputFileRecords.push(record);
+            } else {
+              console.warn(`No file record found for file: ${file.name}`);
+            }
+          } else {
+            console.warn(`No file ID found for file: ${file.name}`);
+          }
+        }
+        
+        const outputFileIds = await consumeFiles(inputFileIds, processedFiles);
+        
+        // Store operation data for undo (only store what we need to avoid memory bloat)
+        lastOperationRef.current = {
+          inputFiles: validFiles, // Keep original File objects for undo
+          inputFileRecords: inputFileRecords.map(record => ({ ...record })), // Deep copy to avoid reference issues
+          outputFileIds
+        };
 
         markOperationApplied(fileId, operationId);
       }
@@ -259,8 +293,65 @@ export const useToolOperation = <TParams>(
   const resetResults = useCallback(() => {
     cleanupBlobUrls();
     actions.resetResults();
+    // Clear undo data when results are reset to prevent memory leaks
+    lastOperationRef.current = null;
   }, [cleanupBlobUrls, actions]);
 
+  // Cleanup on unmount to prevent memory leaks
+  useEffect(() => {
+    return () => {
+      lastOperationRef.current = null;
+    };
+  }, []);
+
+  const undoOperation = useCallback(async () => {
+    if (!lastOperationRef.current) {
+      actions.setError(t('noOperationToUndo', 'No operation to undo'));
+      return;
+    }
+
+    const { inputFiles, inputFileRecords, outputFileIds } = lastOperationRef.current;
+
+    // Validate that we have data to undo
+    if (inputFiles.length === 0 || inputFileRecords.length === 0) {
+      actions.setError(t('invalidUndoData', 'Cannot undo: invalid operation data'));
+      return;
+    }
+
+    if (outputFileIds.length === 0) {
+      actions.setError(t('noFilesToUndo', 'Cannot undo: no files were processed in the last operation'));
+      return;
+    }
+
+    try {
+      // Undo the consume operation
+      await undoConsumeFiles(inputFiles, inputFileRecords, outputFileIds);
+      
+      // Clear results and operation tracking
+      resetResults();
+      lastOperationRef.current = null;
+      
+      // Show success message
+      actions.setStatus(t('undoSuccess', 'Operation undone successfully'));
+      
+    } catch (error: any) {
+      let errorMessage = extractErrorMessage(error);
+      
+      // Provide more specific error messages based on error type
+      if (error.message?.includes('Mismatch between input files')) {
+        errorMessage = t('undoDataMismatch', 'Cannot undo: operation data is corrupted');
+      } else if (error.message?.includes('IndexedDB')) {
+        errorMessage = t('undoStorageError', 'Undo completed but some files could not be saved to storage');
+      } else if (error.name === 'QuotaExceededError') {
+        errorMessage = t('undoQuotaError', 'Cannot undo: insufficient storage space');
+      }
+      
+      actions.setError(`${t('undoFailed', 'Failed to undo operation')}: ${errorMessage}`);
+      
+      // Don't clear the operation data if undo failed - user might want to try again
+    }
+  }, [undoConsumeFiles, resetResults, actions, t]);
+
   return {
     // State
     files: state.files,
@@ -277,6 +368,7 @@ export const useToolOperation = <TParams>(
     executeOperation,
     resetResults,
     clearError: actions.clearError,
-    cancelOperation
+    cancelOperation,
+    undoOperation
   };
 };
diff --git a/frontend/src/tools/AddPassword.tsx b/frontend/src/tools/AddPassword.tsx
index b12598e26..adbc25b5a 100644
--- a/frontend/src/tools/AddPassword.tsx
+++ b/frontend/src/tools/AddPassword.tsx
@@ -60,6 +60,11 @@ const AddPassword = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
     onPreviewFile?.(null);
   };
 
+  const handleUndo = async () => {
+    await addPasswordOperation.undoOperation();
+    onPreviewFile?.(null);
+  };
+
   const hasFiles = selectedFiles.length > 0;
   const hasResults = addPasswordOperation.files.length > 0 || addPasswordOperation.downloadUrl !== null;
   const passwordsCollapsed = !hasFiles || hasResults;
@@ -110,6 +115,7 @@ const AddPassword = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
       operation: addPasswordOperation,
       title: t("addPassword.results.title", "Encrypted PDFs"),
       onFileClick: handleThumbnailClick,
+      onUndo: handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/AddWatermark.tsx b/frontend/src/tools/AddWatermark.tsx
index 1638ceb1c..7065b2a5b 100644
--- a/frontend/src/tools/AddWatermark.tsx
+++ b/frontend/src/tools/AddWatermark.tsx
@@ -79,6 +79,11 @@ const AddWatermark = ({ onPreviewFile, onComplete, onError }: BaseToolProps) =>
     onPreviewFile?.(null);
   };
 
+  const handleUndo = async () => {
+    await watermarkOperation.undoOperation();
+    onPreviewFile?.(null);
+  };
+
   const hasFiles = selectedFiles.length > 0;
   const hasResults = watermarkOperation.files.length > 0 || watermarkOperation.downloadUrl !== null;
 
@@ -203,6 +208,7 @@ const AddWatermark = ({ onPreviewFile, onComplete, onError }: BaseToolProps) =>
       operation: watermarkOperation,
       title: t("watermark.results.title", "Watermark Results"),
       onFileClick: handleThumbnailClick,
+      onUndo: handleUndo,
     },
     forceStepNumbers: true,
   });
diff --git a/frontend/src/tools/Automate.tsx b/frontend/src/tools/Automate.tsx
index 15e5ea3fa..589c38678 100644
--- a/frontend/src/tools/Automate.tsx
+++ b/frontend/src/tools/Automate.tsx
@@ -43,6 +43,11 @@ const Automate = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
     setStepData({ step: AUTOMATION_STEPS.SELECTION });
   };
 
+  const handleUndo = async () => {
+    await automateOperation.undoOperation();
+    onPreviewFile?.(null);
+  };
+
   // Register reset function with the tool workflow context - only once on mount
   React.useEffect(() => {
     const stableResetFunction = () => {
@@ -224,7 +229,8 @@ const Automate = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
       onFileClick: (file: File) => {
         onPreviewFile?.(file);
         actions.setWorkbench('viewer');
-      }
+      },
+      onUndo: handleUndo
     }
   });
 };
diff --git a/frontend/src/tools/ChangePermissions.tsx b/frontend/src/tools/ChangePermissions.tsx
index 5f6582a76..3982d1520 100644
--- a/frontend/src/tools/ChangePermissions.tsx
+++ b/frontend/src/tools/ChangePermissions.tsx
@@ -50,6 +50,7 @@ const ChangePermissions = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("changePermissions.results.title", "Modified PDFs"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/Compress.tsx b/frontend/src/tools/Compress.tsx
index bb57e70a4..6fbc92b09 100644
--- a/frontend/src/tools/Compress.tsx
+++ b/frontend/src/tools/Compress.tsx
@@ -50,6 +50,7 @@ const Compress = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("compress.title", "Compression Results"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/Convert.tsx b/frontend/src/tools/Convert.tsx
index f0612ea83..5ced39670 100644
--- a/frontend/src/tools/Convert.tsx
+++ b/frontend/src/tools/Convert.tsx
@@ -93,6 +93,11 @@ const Convert = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
     onPreviewFile?.(null);
   };
 
+  const handleUndo = async () => {
+    await convertOperation.undoOperation();
+    onPreviewFile?.(null);
+  };
+
   return createToolFlow({
     files: {
       selectedFiles,
@@ -128,6 +133,7 @@ const Convert = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
       operation: convertOperation,
       title: t("convert.conversionResults", "Conversion Results"),
       onFileClick: handleThumbnailClick,
+      onUndo: handleUndo,
       testId: "conversion-results",
     },
   });
diff --git a/frontend/src/tools/OCR.tsx b/frontend/src/tools/OCR.tsx
index e2b56770e..fcfb96841 100644
--- a/frontend/src/tools/OCR.tsx
+++ b/frontend/src/tools/OCR.tsx
@@ -74,6 +74,11 @@ const OCR = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
     onPreviewFile?.(null);
   };
 
+  const handleUndo = async () => {
+    await ocrOperation.undoOperation();
+    onPreviewFile?.(null);
+  };
+
   const settingsCollapsed = expandedStep !== "settings";
 
   return createToolFlow({
@@ -132,6 +137,7 @@ const OCR = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
       operation: ocrOperation,
       title: t("ocr.results.title", "OCR Results"),
       onFileClick: handleThumbnailClick,
+      onUndo: handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/RemoveCertificateSign.tsx b/frontend/src/tools/RemoveCertificateSign.tsx
index 8583b34c6..195fc11f1 100644
--- a/frontend/src/tools/RemoveCertificateSign.tsx
+++ b/frontend/src/tools/RemoveCertificateSign.tsx
@@ -34,6 +34,7 @@ const RemoveCertificateSign = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("removeCertSign.results.title", "Certificate Removal Results"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/RemovePassword.tsx b/frontend/src/tools/RemovePassword.tsx
index 9e8b1f5f4..970eb324b 100644
--- a/frontend/src/tools/RemovePassword.tsx
+++ b/frontend/src/tools/RemovePassword.tsx
@@ -50,6 +50,7 @@ const RemovePassword = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("removePassword.results.title", "Decrypted PDFs"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/Repair.tsx b/frontend/src/tools/Repair.tsx
index 61d3986b6..c805592c5 100644
--- a/frontend/src/tools/Repair.tsx
+++ b/frontend/src/tools/Repair.tsx
@@ -34,6 +34,7 @@ const Repair = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("repair.results.title", "Repair Results"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/Sanitize.tsx b/frontend/src/tools/Sanitize.tsx
index d6f9bbe5d..f37c8fa0b 100644
--- a/frontend/src/tools/Sanitize.tsx
+++ b/frontend/src/tools/Sanitize.tsx
@@ -48,6 +48,7 @@ const Sanitize = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("sanitize.sanitizationResults", "Sanitization Results"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/SingleLargePage.tsx b/frontend/src/tools/SingleLargePage.tsx
index dc71c83cd..095428e70 100644
--- a/frontend/src/tools/SingleLargePage.tsx
+++ b/frontend/src/tools/SingleLargePage.tsx
@@ -34,6 +34,7 @@ const SingleLargePage = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("pdfToSinglePage.results.title", "Single Page Results"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/Split.tsx b/frontend/src/tools/Split.tsx
index 0c94b6cef..6a0cef697 100644
--- a/frontend/src/tools/Split.tsx
+++ b/frontend/src/tools/Split.tsx
@@ -48,6 +48,7 @@ const Split = (props: BaseToolProps) => {
       operation: base.operation,
       title: "Split Results",
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/tools/UnlockPdfForms.tsx b/frontend/src/tools/UnlockPdfForms.tsx
index 65445290f..332af5163 100644
--- a/frontend/src/tools/UnlockPdfForms.tsx
+++ b/frontend/src/tools/UnlockPdfForms.tsx
@@ -34,6 +34,7 @@ const UnlockPdfForms = (props: BaseToolProps) => {
       operation: base.operation,
       title: t("unlockPDFForms.results.title", "Unlocked Forms Results"),
       onFileClick: base.handleThumbnailClick,
+      onUndo: base.handleUndo,
     },
   });
 };
diff --git a/frontend/src/types/fileContext.ts b/frontend/src/types/fileContext.ts
index d9bd8751e..9210f9ce9 100644
--- a/frontend/src/types/fileContext.ts
+++ b/frontend/src/types/fileContext.ts
@@ -199,6 +199,7 @@ export type FileContextAction =
   | { type: 'PIN_FILE'; payload: { fileId: FileId } }
   | { type: 'UNPIN_FILE'; payload: { fileId: FileId } }
   | { type: 'CONSUME_FILES'; payload: { inputFileIds: FileId[]; outputFileRecords: FileRecord[] } }
+  | { type: 'UNDO_CONSUME_FILES'; payload: { inputFileRecords: FileRecord[]; outputFileIds: FileId[] } }
 
   // UI actions
   | { type: 'SET_SELECTED_FILES'; payload: { fileIds: FileId[] } }
@@ -228,7 +229,8 @@ export interface FileContextActions {
   unpinFile: (file: File) => void;
 
   // File consumption (replace unpinned files with outputs)
-  consumeFiles: (inputFileIds: FileId[], outputFiles: File[]) => Promise<void>;
+  consumeFiles: (inputFileIds: FileId[], outputFiles: File[]) => Promise<FileId[]>;
+  undoConsumeFiles: (inputFiles: File[], inputFileRecords: FileRecord[], outputFileIds: FileId[]) => Promise<void>;
   // Selection management
   setSelectedFiles: (fileIds: FileId[]) => void;
   setSelectedPages: (pageNumbers: number[]) => void;