fix(importer): name a single-file audiobook from the audiobook file template (#2900)

[vavallee]

Closes #2900

Summary

With naming.audiobook_file_template set, a folder of tracks was renamed per track but a lone .m4b kept its download name. The template was only read inside if srcInfo.IsDir(); the single-file branch placed the file as filepath.Base(audiobookSource).

This takes option 1 from the issue (Readarr-style conditional part), with one adjustment the code forced:

• Single file, {Part} in a conditional group: the template renders with {Part} empty and the Feature: Conditional/optional text and width modifiers in naming templates #1127 renderer drops the whole group. {Author} - {Title}{ - Pt. Part:3}.{ext} gives Stephen King - The Shining.m4b, and Stephen King - Doctor Sleep - Pt. 001.m4b for each track of a multi-file book.
• Single file, bare {Part}: the glue sits outside the braces, so an empty part would leave The Shining - Part .m4b with the default {Title} - Part {Part:3}.{ext} (the issue's own repro template). That is worse than today, so such a template numbers the lone file as part 1: The Shining - Part 001.m4b. The rule reuses the renderer's own simple-group test (simpleGroupRe + widthThenLiteralRe), so it cannot drift from what actually collapses.
• No template: unchanged, source filename kept.

Same rendering function (applyWithExtra via a shared audiobookFileName) for single and multi-file, so the names differ only in the part. Extension is lowercased exactly as the multi-file flatten does.

Where it applies:

• Import, single-file branch (lone .m4b). The added "(2)" to dir on import when ebook import dir is the same as the audiobook import dir (regression?) #2686 shared-folder merge and its skip-on-collision now check the templated name.
• A folder holding one track (the flatten namer now receives the track count). Without this, the same audiobook would be The Shining.m4b from a manual file import and The Shining - Pt. 001.m4b from an auto-import of its folder. Multi-track folders are unchanged.
• Rename files: singleFileAudiobookDest from fix(importer): move single-file audiobooks into their folder on reorganize (#2894) #2901 calls the same helper, so preview and apply match the import. The Fix Match destination preview routes through it too.
• Settings validator: it checked for the substring {Part, which rejected every conditional form, so option 1 could not be saved. It now asks the renderer whether a group carries a Part token (importer.AudiobookTemplateHasPart). Still rejects templates with no part.

Not changed:

• Drop folder (External mode): placeDroppedFormat / dropPlaceAudiobook is a separate placement that never reads the file template, for multi-file either, so scouchman's report on Feature: Audiobook file-level renaming, including part-number naming (Readarr-style) #1126 is not covered here.
• The literal word Part inside a group is still read as the token ({ - Part Part:3} gives 1 001). Docs and the settings hint use Pt..
• Default template, no new settings.

Docs: docs/DEPLOYMENT.md explains single-file naming and how {Part} behaves; the settings hint says the same. Changelog fragment included.

How it was verified

• New tests in internal/importer/single_file_audiobook_template_test.go, plus validator cases in settings_handler_test.go. Run against origin/main sources (new-API unit tests excluded, they cannot compile there):
  • TestImport_SingleFileAudiobookUsesFileTemplate (hardlink/copy/move): folder holds [wwwwg_cd-rip.M4B], want [Jordan B. Peterson - We Who Wrestle with God.m4b]
  • TestImport_SingleFileAudiobookUnconditionalPartIsPartOne: folder holds [source.m4b]
  • TestImport_OneTrackFolderMatchesSingleFileName: got ... - Pt. 001.m4b
  • TestImport_SingleFileAudiobookTemplatedNameCollisionIsSkipped: file placed under its source name beside the seeded one, and move mode consumed the source
  • TestReorganize_SingleFileAudiobookUsesFileTemplate / TestPreviewImportDestination_SingleFileAudiobookUsesFileTemplate: proposed .../my_book_rip.m4b / .../rip.m4b
  • TestValidateSettingValue_AudiobookFileTemplate: {Title}{ - Pt. Part:3}.{ext} rejected
  • Guards that pass on both: ..WithoutTemplateKeepsSourceName, TestImport_MultiTrackFolderStillNumbersEveryTrack
• Mutations (each compiles under go vet, each fails a named test):
  • single-file template branch skipped: 5 tests fail incl. TestImport_SingleFileAudiobookUsesFileTemplate
  • empty-part collapse disabled (part forced to "1"): TestAudiobookSingleFileName and 5 more
  • bare {Part} left empty: TestAudiobookSingleFileName, ..UnconditionalPartIsPartOne
  • one-track folder uses multi naming: TestImport_OneTrackFolderMatchesSingleFileName
  • reorganize keeps source name: TestReorganize_SingleFileAudiobookUsesFileTemplate, preview test
• go build ./... && go vet ./..., GOOS=windows go build ./..., go test ./cmd/... ./internal/... (exit 0), golangci-lint run ./internal/importer/... ./internal/api/... (0 issues)
• web: npm run typecheck, npm run lint, vitest src/pages/settings (238 passed)

🤖 Generated with Claude Code

https://claude.ai/code/session_016fJcCVbNnKsmj2MAAMwWj9

[github-actions]

Clean fix. I traced through the regex logic and tested edge cases mentally — no issues found.

audiobookPartIsConditional / AudiobookTemplateHasPart correctness (internal/importer/renamer.go:193–222): the interaction between simpleGroupRe, widthThenLiteralRe, and groupWordRe is consistent with how renderGroup already classifies these groups. One minor observation: { - Part Series} (where "Part" is used as a label word, not a token) now passes AudiobookTemplateHasPart and could be saved as a template, whereas the old strings.Contains(value, "{Part") check would have rejected it (no {Part substring). The template would render oddly but wouldn't cause a crash or name collision. Edge case so obscure it's not worth blocking on.

singleAudiobookFileName path safety (scanner_handoff.go:183): the rendered == "" || "." || ".." guard is good. audiobookFileName already calls filepath.Base, so double protection.

One-track folder parity (scanner.go:1271): the count == 1 branch calling AudiobookSingleFileName is reached only inside the tmpl != "" gate, so the no-template path is unchanged.

singleFileAudiobookDest signature change (reorganize.go:220): the call site at line 167 passes author, seriesTitle, seriesNum that proposedPathFor already has in scope — no new DB calls.

Test suite is thorough: all three import modes, collision skip, one-track folder, reorganize preview/apply idempotency, and settings validator. The mutation list in the PR body cross-references named tests for each mutant.

— 🤖 Bindery triage bot (automated). Reply to correct me; a human will see it.

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/importer/scanner_handoff.go	80.00%	1 Missing and 1 partial ⚠️

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