fix(MAJORLEA-013): 6 review findings across 3 files

[flamingo]

Closes 6 review findings across 3 files.

Draft — this is a starting point, not a finished change. The fix required judgment, so read it before trusting it.

#	Fix confidence	Finding	Location
1	🟡 72 medium	RegionService.getRegionById() and getRegionByName() return null instead of Optional or throwing	backend/src/main/java/cx/flamingo/analysis/service/RegionService.java:113
2	🟢 95 high	RegionService uses @Autowired field injection instead of @requiredargsconstructor	backend/src/main/java/cx/flamingo/analysis/service/RegionService.java:28
3	🟡 88 medium	RegionService.getRegionTotalPopulation() performs a full scan of all cities for every region during autocomplete sorting — O(n*m) complexity	backend/src/main/java/cx/flamingo/analysis/service/RegionService.java:80
4	🟡 72 medium	StateService.getStateById() and getStateByCode() return null instead of Optional or throwing	backend/src/main/java/cx/flamingo/analysis/service/StateService.java:107
5	🟢 90 high	StateService.getStateTotalPopulation() performs a full scan of all cities for every state during autocomplete sorting — O(n*m) complexity	backend/src/main/java/cx/flamingo/analysis/service/StateService.java:72
6	🟡 72 medium	LanguageService.getLanguageById() returns null instead of Optional or throwing	backend/src/main/java/cx/flamingo/analysis/service/LanguageService.java:62

What changed — and what was deliberately left — is explained per finding as inline review comments on the lines each finding touched.

---

Run: https://product-hub.flamingo.so/admin/code-review
Run id: 8f1c6ef6-6b61-4dcd-bb0e-59bc6a7d37e8

Merging this PR is recorded as acceptance of the rule that produced it;
closing it unmerged is recorded as rejection. Both feed rule health, so
closing a wrong suggestion is useful rather than merely tidy.

[flamingo]

🦩 What this fix changed, finding by finding

6 finding(s) fixed in this draft — 6 explained inline on the diff.

[flamingo]

🦩 🔴 RegionService.getRegionById() and getRegionByName() return null instead of Optional or throwing

Changed getRegionById(String id) and getRegionByName(String name) to return Optional<Region> instead of Region, replacing .orElse(null) with .findFirst() directly (which already returns Optional<Region>). Added import java.util.Optional;. The return-type change is correct and complete within this file, but callers of these methods in other files (not visible here) will now receive Optional<Region> and must be updated to call .get(), .orElseThrow(), or similar — those callers will fail to compile until updated. A reviewer must check all call sites before merging.

🤖 Prompt for AI agents

In backend/src/main/java/cx/flamingo/analysis/service/RegionService.java around line 113, review and complete this code-review fix: RegionService.getRegionById() and getRegionByName() return null instead of Optional or throwing.
What the draft fix changed: Changed `getRegionById(String id)` and `getRegionByName(String name)` to return `Optional<Region>` instead of `Region`, replacing `.orElse(null)` with `.findFirst()` directly (which already returns `Optional<Region>`). Added `import java.util.Optional;`. The return-type change is correct and complete within this file, but callers of these methods in other files (not visible here) will now receive `Optional<Region>` and must be updated to call `.get()`, `.orElseThrow()`, or similar — those callers will fail to compile until updated. A reviewer must check all call sites before merging.
Verify the change is correct and complete; do not refactor unrelated code.

fix confidence: 🟡 72 medium — react 👍/👎 to teach the reviewer

[flamingo]

🦩 🟠 RegionService uses @Autowired field injection instead of @requiredargsconstructor

Removed both @Autowired annotations from stateService and cityService fields, changed them to private final, added @RequiredArgsConstructor to the class annotation, and removed the import org.springframework.beans.factory.annotation.Autowired; import. Added import lombok.RequiredArgsConstructor;. This is a mechanical, low-risk change consistent with Lombok constructor injection conventions.

🤖 Prompt for AI agents

In backend/src/main/java/cx/flamingo/analysis/service/RegionService.java around line 28, review and complete this code-review fix: RegionService uses @Autowired field injection instead of @RequiredArgsConstructor.
What the draft fix changed: Removed both `@Autowired` annotations from `stateService` and `cityService` fields, changed them to `private final`, added `@RequiredArgsConstructor` to the class annotation, and removed the `import org.springframework.beans.factory.annotation.Autowired;` import. Added `import lombok.RequiredArgsConstructor;`. This is a mechanical, low-risk change consistent with Lombok constructor injection conventions.
Verify the change is correct and complete; do not refactor unrelated code.

fix confidence: 🟢 95 high — react 👍/👎 to teach the reviewer

[flamingo]

🦩 🟠 RegionService.getRegionTotalPopulation() performs a full scan of all cities for every region during autocomplete sorting — O(n*m) complexity

Added a private Map<String, Integer> regionPopulationCache field and a buildPopulationCache() method that pre-computes regionId → total population by iterating all cities once (O(C)) and accumulating via Map.merge. buildPopulationCache() is called at the end of @PostConstruct init(). getRegionTotalPopulation(Region) now does a single O(1) map lookup via regionPopulationCache.getOrDefault(region.getId(), 0) instead of a full city scan. Added import java.util.HashMap; and import java.util.Map;. Risk: the cache is built once at startup and is not invalidated if cities are updated at runtime; if cityService data is mutable after init, the cache could become stale. Based on the visible code this appears to be static CSV-loaded data, so this is acceptable.

🤖 Prompt for AI agents

In backend/src/main/java/cx/flamingo/analysis/service/RegionService.java around line 80, review and complete this code-review fix: RegionService.getRegionTotalPopulation() performs a full scan of all cities for every region during autocomplete sorting — O(n*m) complexity.
What the draft fix changed: Added a `private Map<String, Integer> regionPopulationCache` field and a `buildPopulationCache()` method that pre-computes regionId → total population by iterating all cities once (O(C)) and accumulating via `Map.merge`. `buildPopulationCache()` is called at the end of `@PostConstruct init()`. `getRegionTotalPopulation(Region)` now does a single O(1) map lookup via `regionPopulationCache.getOrDefault(region.getId(), 0)` instead of a full city scan. Added `import java.util.HashMap;` and `import java.util.Map;`. Risk: the cache is built once at startup and is not invalidated if cities are updated at runtime; if `cityService` data is mutable after init, the cache could become stale. Based on the visible code this appears to be static CSV-loaded data, so this is acceptable.
Verify the change is correct and complete; do not refactor unrelated code.

fix confidence: 🟡 88 medium — react 👍/👎 to teach the reviewer

[flamingo]

🦩 🔴 StateService.getStateById() and getStateByCode() return null instead of Optional or throwing

Changed getStateById() and getStateByCode() to return Optional<State> instead of State, replacing .orElse(null) with .findFirst() directly (which already returns Optional<State>). Added import java.util.Optional;. The return-type change is correct and complete within this file, but callers in other files (not visible here) that previously received a State directly will now receive Optional<State> and will fail to compile until updated. The reviewer must locate all callers (e.g. via getStateById(...) and getStateByCode(...) usages across the codebase) and update them to use .orElseThrow(...) or .orElse(...) as appropriate. This is a breaking API change that cannot be fully resolved in this file alone.

🤖 Prompt for AI agents

In backend/src/main/java/cx/flamingo/analysis/service/StateService.java around line 107, review and complete this code-review fix: StateService.getStateById() and getStateByCode() return null instead of Optional or throwing.
What the draft fix changed: Changed `getStateById()` and `getStateByCode()` to return `Optional<State>` instead of `State`, replacing `.orElse(null)` with `.findFirst()` directly (which already returns `Optional<State>`). Added `import java.util.Optional;`. The return-type change is correct and complete within this file, but callers in other files (not visible here) that previously received a `State` directly will now receive `Optional<State>` and will fail to compile until updated. The reviewer must locate all callers (e.g. via `getStateById(...)` and `getStateByCode(...)` usages across the codebase) and update them to use `.orElseThrow(...)` or `.orElse(...)` as appropriate. This is a breaking API change that cannot be fully resolved in this file alone.
Verify the change is correct and complete; do not refactor unrelated code.

fix confidence: 🟡 72 medium — react 👍/👎 to teach the reviewer

[flamingo]

🦩 🟠 StateService.getStateTotalPopulation() performs a full scan of all cities for every state during autocomplete sorting — O(n*m) complexity

Added buildPopulationCache() called from @PostConstruct init() after loadStates(). Added field private Map<String, Integer> statePopulationCache and method buildPopulationCache() which iterates all cities once and accumulates population per stateId using Map.merge. Changed getStateTotalPopulation(State) to do an O(1) statePopulationCache.getOrDefault(state.getId(), 0) lookup instead of a full city scan. Added import java.util.HashMap; and import java.util.Map;. The cache is built once at startup; if city data changes at runtime the cache would be stale, but given the existing @PostConstruct-only loading pattern this is consistent with the rest of the service.

🤖 Prompt for AI agents

In backend/src/main/java/cx/flamingo/analysis/service/StateService.java around line 72, review and complete this code-review fix: StateService.getStateTotalPopulation() performs a full scan of all cities for every state during autocomplete sorting — O(n*m) complexity.
What the draft fix changed: Added `buildPopulationCache()` called from `@PostConstruct init()` after `loadStates()`. Added field `private Map<String, Integer> statePopulationCache` and method `buildPopulationCache()` which iterates all cities once and accumulates population per `stateId` using `Map.merge`. Changed `getStateTotalPopulation(State)` to do an O(1) `statePopulationCache.getOrDefault(state.getId(), 0)` lookup instead of a full city scan. Added `import java.util.HashMap;` and `import java.util.Map;`. The cache is built once at startup; if city data changes at runtime the cache would be stale, but given the existing `@PostConstruct`-only loading pattern this is consistent with the rest of the service.
Verify the change is correct and complete; do not refactor unrelated code.

fix confidence: 🟢 90 high — react 👍/👎 to teach the reviewer

[flamingo]

🦩 🔴 LanguageService.getLanguageById() returns null instead of Optional or throwing

Changed getLanguageById(String id) return type from Language to Optional<Language> and replaced .orElse(null) with .findFirst() directly (line 62-65). Added import java.util.Optional; at line 10. The method itself is now null-safe. RISK: Any callers of getLanguageById() in other files (controllers, services, etc.) that previously used the returned Language directly will now receive an Optional<Language> and will fail to compile until updated to call .get(), .orElseThrow(), or similar. Those callers are not visible in this file and must be updated separately. A reviewer should search the codebase for all usages of getLanguageById before merging.

🤖 Prompt for AI agents

In backend/src/main/java/cx/flamingo/analysis/service/LanguageService.java around line 62, review and complete this code-review fix: LanguageService.getLanguageById() returns null instead of Optional or throwing.
What the draft fix changed: Changed `getLanguageById(String id)` return type from `Language` to `Optional<Language>` and replaced `.orElse(null)` with `.findFirst()` directly (line 62-65). Added `import java.util.Optional;` at line 10. The method itself is now null-safe. RISK: Any callers of `getLanguageById()` in other files (controllers, services, etc.) that previously used the returned `Language` directly will now receive an `Optional<Language>` and will fail to compile until updated to call `.get()`, `.orElseThrow()`, or similar. Those callers are not visible in this file and must be updated separately. A reviewer should search the codebase for all usages of `getLanguageById` before merging.
Verify the change is correct and complete; do not refactor unrelated code.

fix confidence: 🟡 72 medium — react 👍/👎 to teach the reviewer