Add a service layer abstraction for fetching feature collections

[rm-hull]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @rm-hull, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a dedicated service layer for fetching geographic feature collections, specifically postcode polygons. By abstracting the data access and caching mechanisms behind a PolygonsRepo interface, these changes enhance the application's modularity, maintainability, and testability. The PolygonSearch API endpoint now leverages this new abstraction, decoupling its logic from the underlying data storage and caching implementation details.

Highlights

• Service Layer Abstraction: I've introduced a new PolygonsRepo interface and its CachedPolygonsRepo implementation within the internal package. This abstracts the logic for retrieving geojson.FeatureCollection objects, including file decompression and caching, centralizing data access concerns.
• Dependency Inversion: The PolygonSearch handler in the routes package has been refactored to depend on the new PolygonsRepo interface instead of directly on the memoize.Memoizer cache and raw file system operations. This promotes a cleaner architecture and better separation of concerns.
• Improved Testability: The introduction of the PolygonsRepo interface allows for easier mocking of the data retrieval layer in unit tests. Correspondingly, a mockPolygonsRepo has been added to routes/search_test.go, and existing tests were updated, along with a new success test case for PolygonSearch.

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[github-actions]

	Tests	Passed ✅	Skipped	Failed
JUnit Test Report	36 ran	36 passed	0 skipped	0 failed

Test	Result
JUnit Test Report
postcode-polygons/internal.TestDecompressFeatureCollection_Success	✅ passed
postcode-polygons/internal.TestDecompressFeatureCollection_FileNotFound	✅ passed
postcode-polygons/internal.TestDecompressFeatureCollection_InvalidBZ2	✅ passed
postcode-polygons/internal.TestCompressFeatureCollection_Success	✅ passed
postcode-polygons/internal.TestCompressFeatureCollection_ErrorOnCreate	✅ passed
postcode-polygons/internal.TestCompressFeatureCollection_And_DecompressFeatureCollection_RoundTrip	✅ passed
postcode-polygons/routes.TestCodePointSearch_BadBBox	✅ passed
postcode-polygons/routes.TestCodePointSearch_TooBig	✅ passed
postcode-polygons/routes.TestCodePointSearch_InternalError	✅ passed
postcode-polygons/routes.TestCodePointSearch_Success	✅ passed
postcode-polygons/routes.TestPolygonSearch_BadBBox	✅ passed
postcode-polygons/routes.TestPolygonSearch_InternalError	✅ passed
postcode-polygons/routes.TestPolygonSearch_Success	✅ passed
postcode-polygons/routes.TestPolygonSearch_PolygonNotFound	✅ passed
postcode-polygons/routes.TestPolygonSearch_PolygonRepoError	✅ passed
postcode-polygons/routes.TestParseBBox/valid	✅ passed
postcode-polygons/routes.TestParseBBox/too_few_parts	✅ passed
postcode-polygons/routes.TestParseBBox/not_numbers	✅ passed
postcode-polygons/routes.TestParseBBox/min_greater_than_max	✅ passed
postcode-polygons/routes.TestParseBBox	✅ passed
postcode-polygons/routes.TestIsTooBig/not_too_big	✅ passed
postcode-polygons/routes.TestIsTooBig/too_wide	✅ passed
postcode-polygons/routes.TestIsTooBig/too_high	✅ passed
postcode-polygons/routes.TestIsTooBig	✅ passed
postcode-polygons/spatial-index.TestNewCodePointSpatialIndex_Success	✅ passed
postcode-polygons/spatial-index.TestNewCodePointSpatialIndex_BadZip	✅ passed
postcode-polygons/spatial-index.TestSearch	✅ passed
postcode-polygons/spatial-index.TestSearchIter_InvalidBounds	✅ passed
postcode-polygons/spatial-index.TestLen	✅ passed
postcode-polygons/spatial-index.Test_fromCodePointCSV	✅ passed
postcode-polygons/spatial-index.TestParseCSV_WithHeader_Success	✅ passed
postcode-polygons/spatial-index.TestParseCSV_WithoutHeader_Success	✅ passed
postcode-polygons/spatial-index.TestParseCSV_ParseError	✅ passed
postcode-polygons/spatial-index.TestParseCSV_MalformedLine	✅ passed
postcode-polygons/spatial-index.TestParseCSV_HeaderReadError	✅ passed
postcode-polygons/spatial-index.TestParseCSV_YieldStopsEarly	✅ passed

• View JUnit Test Report

[gemini-code-assist]

Code Review

This pull request successfully introduces a service layer abstraction for fetching feature collections, which is a great step towards improving the modularity and testability of the application. The PolygonsRepo interface and its CachedPolygonsRepo implementation correctly encapsulate the data retrieval logic, and the updates to the routes/search.go handler and associated tests are well-executed, demonstrating a clear separation of concerns.

[coveralls]

Pull Request Test Coverage Report for Build 15949163788

Details

• 5 of 17 (29.41%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+4.9%) to 51.907%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/api_server.go	0	3	0.0%
internal/polygons_repo.go	0	9	0.0%

Totals
Change from base Build 15948796983:	4.9%
Covered Lines:	245
Relevant Lines:	472

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💛 - Coveralls