• Automatically download book covers when preview panel opens
• Implement 24-hour cooldown for failed cover download attempts
• Create .not-available marker files for unavailable covers
• Add comprehensive test suite for cover fetcher functionality

Add cooldown and failure tracking for cover downloads

• Added 24-hour cooldown mechanism using .not-available marker files
• Implemented timeSincePreviousAttempt() to check file modification timestamps
• Added flagAsNotAvailable() to create/update marker files on download failure
• Added deleteNotAvailableFileIfExists() to clean up markers after successful downloads
• Enhanced error handling to distinguish between client/server errors and other exceptions
• Modified image fallback URL suffix to include ?default=false parameter
• Added imports for time/duration handling and exception types

jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java

Trigger background cover download on preview open

• Modified update() method to trigger cover download after preview generation
• Added downloadCoverAndRefresh() method to download covers in background task
• Integrated preference check for shouldDownloadCovers() setting
• Refresh preview text after successful cover download if entry is still current

jabgui/src/main/java/org/jabref/gui/preview/PreviewViewer.java

Add comprehensive BookCoverFetcher test suite

• Created comprehensive test suite with 7 test cases covering core functionality
• Tests cover: not-available file creation, empty directory handling, existing cover retrieval
• Tests verify 24-hour cooldown behavior with modification time checks
• Tests confirm deletion of marker files after successful downloads
• Uses mocked Directories and ExternalApplicationsPreferences with temporary directories
• Tests use real ISBNs (9780141036144 for valid, 1234567881 for invalid covers)

jabgui/src/test/java/org/jabref/gui/importer/BookCoverFetcherTest.java

Description

New code uses Optional.isEmpty() checks followed by Optional.get(), which is discouraged and can
lead to less readable and more error-prone control flow. The compliance rule requires using
idiomatic Optional APIs (map/filter/ifPresentOrElse/orElseThrow) instead.

Code

jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[R64-66]

+            Optional<Duration> timeSincePreviousAttempt = timeSincePreviousAttempt(name, directory);
+            if (!timeSincePreviousAttempt.isEmpty() && timeSincePreviousAttempt.get().toHours() < IMAGE_DOWNLOAD_COOLDOWN_HOURS) {
+                LOGGER.info("Skipped download attempt for {}, attempted less than 24 hours ago", name);

Evidence

PR Compliance ID 24 forbids presence checks (isEmpty/isPresent) followed by get() in
new/modified code; the added cooldown logic does exactly that when inspecting
timeSincePreviousAttempt.

jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[64-66]
Best Practice: Learned patterns

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`BookCoverFetcher` uses `Optional.isEmpty()` + `Optional.get()` in new code paths, which violates the project's Optional style guidelines.
## Issue Context
The cooldown logic should use `Optional` idioms such as `filter`, `map`, `ifPresentOrElse`, or `orElseThrow` instead of presence checks + `get()`.
## Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[64-66]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

Description

The newly added tests call downloadCoversForEntry(...), which performs real HTTP downloads
(URLDownload), making tests slow and potentially flaky in CI/offline environments. Compliance
requires tests to remain deterministic and fast unless clearly justified and controlled.

Code

jabgui/src/test/java/org/jabref/gui/importer/BookCoverFetcherTest.java[R76-81]

+    void createNotAvailableFileAfterFailedDownload() throws Exception {
+        bookCoverFetcher.downloadCoversForEntry(badEntry);
+
+        assertTrue(Files.notExists(badCoverPath));
+        assertTrue(Files.exists(badNotAvailablePath));
+    }

Evidence

PR Compliance ID 17 requires tests to be deterministic and fast; the new test directly triggers
cover downloading without mocking network access, and the implementation performs network requests
via URLDownload.

AGENTS.md
jabgui/src/test/java/org/jabref/gui/importer/BookCoverFetcherTest.java[76-81]
jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[103-109]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`BookCoverFetcherTest` triggers real HTTP requests via `BookCoverFetcher.downloadCoversForEntry(...)`, which can make CI runs flaky/slow and fail in restricted network environments.
## Issue Context
`BookCoverFetcher` uses `new URLDownload(url)` to fetch content over the network. Tests should avoid real network by injecting a downloader abstraction or by mocking/stubbing the network layer.
## Fix Focus Areas
- jabgui/src/test/java/org/jabref/gui/importer/BookCoverFetcherTest.java[76-81]
- jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[103-109]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

Description

The PR adds substantial non-UI logic (download retry cooldown and .not-available state tracking)
inside the GUI module (org.jabref.gui). This increases coupling and violates the layering rule
that GUI should delegate business logic to the logic layer.

Code

jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[R74-91]

+    private Optional<Duration> timeSincePreviousAttempt(String name, Path directory) {
+        Optional<Path> notAvailablePathOptional = resolveNameWithType(directory, name, NOT_AVAILABLE_FILE_TYPE);
+        if (notAvailablePathOptional.isEmpty()) {
+            LOGGER.warn("Could not find not available file path for: {}", name);
+            return Optional.empty();
+        }
+        Path notAvailablePath = notAvailablePathOptional.get();
+        if (Files.exists(notAvailablePath)) {
+            try {
+                FileTime lastModifiedTimeStamp = Files.getLastModifiedTime(notAvailablePath);
+                Duration timeSinceLastModification = Duration.between(lastModifiedTimeStamp.toInstant(), Instant.now());
+                return Optional.of(timeSinceLastModification);
+            } catch (IOException e) {
+                LOGGER.warn("Could not read last modified time", e);
+            }
+        }
+        return Optional.empty();
+    }

Evidence

PR Compliance ID 12 requires the GUI layer to delegate complex non-UI behavior to
org.jabref.logic; the added method timeSincePreviousAttempt(...) implements filesystem-based
state tracking and cooldown logic directly in the GUI module.

AGENTS.md
jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[74-91]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
New cover download cooldown/state logic is implemented in the GUI module, rather than being delegated to the logic layer.
## Issue Context
`BookCoverFetcher` performs filesystem state tracking (`.not-available`) and cooldown calculation. Per layering guidelines, this kind of behavior should live in `org.jabref.logic` (e.g., as a service) with the GUI calling into it.
## Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[74-91]

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

Description

BookCoverFetcher flags a cover as “.not-available” for FetcherServerException (HTTP 5xx), so
transient server outages can suppress retries for 24 hours via the cooldown check. This can
incorrectly delay cover downloads long after the server has recovered.

Code

jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[R128-132]

+        } catch (FetcherClientException | FetcherServerException e) {
+            LOGGER.info("Remote book cover does not exist or server returned an error for URL: {}", url);
+            LOGGER.info("Flagging book cover as not available");
+            flagAsNotAvailable(name, directory);
      } catch (FetcherException e) {
-            LOGGER.error("Error while downloading cover image file", e);

Evidence

URLDownload throws FetcherServerException for HTTP status >= 500; BookCoverFetcher catches it
together with 4xx and writes a “not available” marker. Later, downloadCoverForISBN consults that
marker and skips retries for 24 hours.

jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[61-71]
jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[125-134]
jablib/src/main/java/org/jabref/logic/net/URLDownload.java[379-387]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`downloadCoverImage` treats HTTP 4xx (client) and 5xx (server) failures identically by creating/updating the `.not-available` marker. That marker then triggers a 24h cooldown, so temporary server failures can prevent retries for a day.
### Issue Context
`URLDownload.openConnection` throws `FetcherClientException` for 4xx and `FetcherServerException` for 5xx.
### Fix Focus Areas
- jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[61-71]
- jabgui/src/main/java/org/jabref/gui/importer/BookCoverFetcher.java[125-134]
### Suggested implementation direction
- Split the catch:
- On `FetcherClientException`: keep current behavior (create/update `.not-available`).
- On `FetcherServerException`: log and return without creating `.not-available` (or use a separate shorter-lived marker).
- (Optional) If you only want to mark “not available” on specific 4xx (e.g., 404), inspect `e.getHttpResponse().map(SimpleHttpResponse::statusCode)` via `FetcherException.getHttpResponse()` and gate marker creation accordingly.

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools