Refactor generateTSVString to use pure transformations and remove mutation

[SarthakJagota]

Summary

This PR refactors generateTSVString to remove mutation-based accumulation and adopt a functional transformation approach.

Changes

Replaced forEach + push with flatMap/map

Removed the TODO comment related to mutation

Eliminated @ts-expect-error by adding proper type narrowing

Preserved the existing TSV output format and column ordering

No behavioral changes

Motivation

The previous implementation relied on mutating an array (tsvRows) inside a loop. This refactor makes the function purely transformation-based, improving clarity and maintainability while maintaining identical output.

Testing

Verified that both labeled and URI TSV downloads produce identical output compared to the previous implementation.

No changes to UI behavior or data formatting.

#747

Summary by Sourcery

Refactor TSV generation in ResultContainer to use a pure transformation-based approach instead of mutating intermediate state.

Enhancements:

• Replace mutation-based TSV row accumulation with flatMap/map transformations while preserving the existing TSV format and column order.
• Introduce explicit type narrowing for subject_data to remove the need for TypeScript expectation errors.

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Refactors ResultContainer.generateTSVString to build the TSV output via pure array transformations (map/flatMap) instead of mutating an accumulator array, while preserving the existing TSV format and behavior and tightening type safety around subject_data.

Flow diagram for the refactored generateTSVString transformation pipeline

flowchart TD
  A[generateTSVString called with subjectsResponse and buttonIndex] --> B[Compute isFileWithLabels from buttonIndex]
  B --> C[Build headers as tab separated string]
  C --> D[Iterate with flatMap over subjectsResponse.responses]
  D --> E[For each subResp, find datasetMetadata in datasetsResponse.responses]
  E --> F[Destructure dataset fields with default values]
  F --> G{isProtected?}

  G -- Yes --> H[Build single TSV row for protected dataset]
  H --> I[Return array containing single row string]

  G -- No --> J{Is subResp.subject_data an array?}
  J -- No --> K[Return empty array for this subResp]
  J -- Yes --> L[Map subject_data to TSV row strings]
  L --> M[Return array of row strings for this subResp]

  I --> N[flatMap collects all row strings into dataRows]
  M --> N

  N --> O[Prepend headers to dataRows]
  O --> P[Join all rows with newline characters]
  P --> Q[Return final TSV string]

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File-Level Changes

Change	Details	Files
Refactor TSV generation from a mutating accumulator to a pure transformation pipeline.	Removed the mutable tsvRows accumulator and the forEach-based row construction Introduced dataRows computed via flatMap over subjectsResponse.responses to produce all TSV data rows Kept the header row composition logic but now combine headers and dataRows at the end into the final TSV string	src/components/ResultContainer.tsx
Tighten typing and control flow around protected vs unprotected subject data.	Replaced the ts-expect-error on subject_data with an explicit Array.isArray guard before iterating Used conditional branches to return a single row for protected datasets and multiple rows for unprotected datasets via map Ensured the TSV output structure uses the same columns and ordering for both protected and unprotected cases	src/components/ResultContainer.tsx
Remove obsolete TODO and clarify non-mutating approach.	Deleted the TODO about refactoring away from mutation since the function now uses pure transformations Kept comments minimal while relying on the new functional structure to convey intent	src/components/ResultContainer.tsx

Possibly linked issues

• Refactor generateTSVString to remove mutation and improve functional style #747: PR implements the requested generateTSVString refactor: replaces mutation with flatMap/map and removes @ts-expect-error, preserving output.
• Refactor generateTSVString to remove mutation and improve functional style #747: PR removes the @ts-expect-error on subject_data via Array.isArray type guard, restoring type safety as requested.

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