united-tattoo/docs/stories/ff-1-feature-flags-library-and-config.md

Feature Flags Library & Configuration — Brownfield Addition (FF-1)

Story ID: FF-1
Epic: Feature Flags Framework for Controlled Rollbacks — Brownfield Enhancement
Date: 2025-09-18
Owner: Product Manager (John)
Related Docs:

• docs/prd/epic-feature-flags-controlled-rollbacks.md
• docs/prd/rollback-strategy.md
• docs/brownfield-architecture-tech.md

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Story Title Feature Flags Library & Configuration — Brownfield Addition

User Story As an operator of the United Tattoo site, I want to control critical features via environment-driven flags, So that I can safely disable problematic areas without redeploying the application.

Story Context

Existing System Integration

• Integrates with: Next.js 14 App Router (server/client), route handlers under app/api, Cloudflare Pages/Workers runtime via OpenNext.
• Technology: TypeScript, environment variables via wrangler.toml ([env.preview.vars] / [env.production.vars]), Cloudflare bindings.
• Follows pattern: Centralized lib utilities (e.g., lib/utils.ts), environment validation in lib/env.ts, defensive configuration.
• Touch points:
  • New module lib/flags.ts (exporting typed, environment-driven booleans).
  • Documentation updates for wrangler env vars and operational usage.
  • Optional: non-breaking additions to lib/env.ts for boolean parsing.

Acceptance Criteria

Functional Requirements

1. A new module lib/flags.ts exports a typed Flags object (or individual exports) for the following keys with safe defaults that preserve current behavior:
   • ADMIN_ENABLED
   • ARTISTS_MODULE_ENABLED
   • UPLOADS_ADMIN_ENABLED
   • BOOKING_ENABLED
   • PUBLIC_APPOINTMENT_REQUESTS_ENABLED
   • REFERENCE_UPLOADS_PUBLIC_ENABLED
   • DEPOSITS_ENABLED
   • PUBLIC_DB_ARTISTS_ENABLED
   • ADVANCED_NAV_SCROLL_ANIMATIONS_ENABLED
   • STRICT_CI_GATES_ENABLED
   • ISR_CACHE_R2_ENABLED
2. Flags are derived from environment variables (string "true"/"false", case-insensitive) with robust parsing; missing or malformed values do not throw and fall back to defaults.
3. Server-side usage (route handlers, server components) and client-side usage (components) can import the same typed flags safely (tree-shakeable, no runtime errors).

Integration Requirements 4. Existing functionality remains unchanged by default when no flag variables are defined (defaults reflect current behavior). 5. The new module follows existing lib/* coding standards (TypeScript types, export conventions). 6. Documentation added to an operations note (append to docs/prd/rollback-strategy.md or new doc referenced by it) including:

• List of flags, default behavior, and how to toggle via wrangler dashboard/vars.
• Example wrangler.toml snippets for preview/production vars (non-secret).
• Post-toggle smoke checklist.

Quality Requirements 7. Unit tests cover boolean parsing and default behavior for at least three representative flags (true/false/undefined cases). 8. Typecheck, lint, and unit tests pass (no suppression added). 9. No regressions in existing functionality (smoke run of dev and preview builds).

Technical Notes

• Integration Approach:
  • Implement a pure-TS helper to parse env booleans: parseBool(str | undefined, defaultValue).
  • Export a const Flags object freezing evaluated booleans at module init time (OK for Workers model).
  • Client-side consumption: Ensure flags do not leak secrets (they are booleans only) and remain serializable if needed.
• Existing Pattern Reference:
  • Align with lib/utils.ts coding style and export patterns.
  • Reference docs/prd/rollback-strategy.md “Feature Flags Operations” for operator guidance.
• Key Constraints:
  • Do not introduce breaking changes or throw errors on missing envs.
  • Do not gate any routes/components in this story (wiring will be handled in a separate story).
  • Keep the module minimal; do not add runtime network calls or storage dependencies.

Definition of Done

• lib/flags.ts created with typed exports and safe defaults.
• Tests added (Vitest) verifying parsing and defaults.
• Documentation updated (rollback strategy ops section extended with flags list, toggling, smoke steps).
• Lint, typecheck, and unit tests pass locally (npm run test).
• Preview build succeeds (npm run pages:build && npm run preview).
• No functional changes observed when flags are absent (baseline preserved).

Risk and Compatibility Check

Minimal Risk Assessment

• Primary Risk: Misinterpretation of default behavior leading to unintended disablement.
• Mitigation: Defaults preserve current behavior; explicit console.warn on server when critical flags are undefined (non-fatal).
• Rollback: Delete or bypass imports of lib/flags.ts; defaults ensure no breakage when env flags are absent.

Compatibility Verification

• No breaking changes to existing APIs.
• No database changes.
• UI unchanged in this story (no gating yet).
• Negligible performance impact (constant boolean checks).

Validation Checklist

Scope Validation

• Single-session implementable (library + tests + docs).
• Straightforward integration (new lib module).
• Follows existing patterns exactly (lib/* utilities, env-based config).
• No design/architecture work required.

Clarity Check

• Requirements are unambiguous (module + keys + defaults + tests + docs).
• Integration points specified (lib, docs, env).
• Success criteria testable (unit tests, build/preview).
• Rollback approach simple (remove usage; defaults benign).

References

• Epic: docs/prd/epic-feature-flags-controlled-rollbacks.md
• Ops: docs/prd/rollback-strategy.md (Feature Flags Operations section to be updated in this story)