trip-planner/docs/plans/2026-08-15-full-implementation.md

Полная реализация согласно спецификации docs/specification.md

Overview

Implement the complete multimodal trip planning service as specified in docs/specification.md, covering all four development stages from MVP through polish. The implementation follows the lazy graph expansion architecture due to Yandex.Schedules API limitations (no full timetable dump).

Problem solved: Users can find multimodal routes combining planes, trains, and buses with arbitrary transfer depth, automatic fallback to neighboring stations when main stations are closed, and map visualization — all within API quota constraints.

Key architectural decisions:

• Lazy graph expansion with hub stations (instead of full RAPTOR, which would exhaust API quota)
• BFS/Dijkstra with depth limiting (4-5 transfers max)
• On-demand /search requests only for relevant station pairs
• Multi-layer TTL caching strategy
• Pareto-front ranking (time, transfers, cost) rather than single "optimal" route
• Station closure detection with automatic fallback

Context (from discovery)

• Current state: Lazy graph expansion partially implemented (commit edfc567): hub station selection, on-demand /search, transfer depth limiting, synthetic edge fallback, ResetCircuitBreaker helper
• Files involved: internal/routing/graph.go, internal/routing/graph_test.go, internal/yandex/client.go, internal/yandex/client_test.go, internal/cache/, internal/storage/, cmd/api/, cmd/cron/
• Related patterns: cache-aside, circuit breaker, transfer rules, MCT calculation, GeoJSON assembly
• Dependencies: PostgreSQL with PostGIS (optional), Redis with TTL, Yandex.Schedules API

Development Approach

• Testing approach: TDD (tests first) — all new code must have corresponding tests; tests are a required deliverable of every task, not optional
• All tests must pass before starting the next task — no exceptions
• Update plan file when scope changes during implementation
• Run tests after each change
• Maintain backward compatibility

Testing Strategy

• Unit tests: Required for every task — write tests for all new/modified functions, including success and error scenarios
• Synthetic timetable fixtures: Test routing algorithm on synthetic data without real API calls
• Mock external API calls in all tests
• Test cache-aside patterns thoroughly
• Validate MCT (Minimum Connection Time) calculations

Progress Tracking

• Mark completed items with [x] immediately when done
• Add newly discovered tasks with ➕ prefix
• Document issues/blockers with ⚠️ prefix
• Keep plan in sync with actual work done

What Goes Where

• Implementation Steps ([ ] checkboxes): tasks achievable within this codebase
• Post-Completion (no checkboxes): items requiring external action
• Checkbox placement: Checkboxes belong only in Task sections (### Task N:). Do not put checkboxes in Success criteria, Overview, or Context

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Этап 1 — MVP (Minimum Viable Product)

Already partially implemented: lazy graph expansion, basic routing with single transport mode, basic caching

Implementation Steps

Task 1: Refactor hub station selection [ ]

• Remove Population field from HubStation struct in internal/routing/graph.go
• Simplify SelectHubStations to use only minOutgoingFlights criterion
• Update all test criteria to match new hub selection logic (remove minPopulation)
• Write tests: TestSelectHubStations with various minOutgoingFlights values
• Run tests - must pass before task 2

Task 2: Implement synthetic edge fallback in FindRoute [ ]

• Add synthetic edge fallback when lazy expansion fails in FindRoute method
• Create addSyntheticEdgesForNode function
• • Write tests: TestFindRouteWithSyntheticFallback
• Run tests - must pass before task 3

Task 3: Add ResetCircuitBreaker helper [ ]

• Add ResetCircuitBreaker function to internal/yandex/client.go
• Update tests to use the new reset function
• Write tests: TestResetCircuitBreaker
• Run tests - must pass before task 4

Task 4: Implement on-demand /search integration [ ]

• Integrate on-demand /search calls in lazy graph expansion
• Implement cache key generation and TTL policies
• Write tests: TestSearchRoutes_onDemand with circuit breaker reset
• Run tests - must pass before task 5

Task 5: Transfer depth limiting [ ]

• Implement depth limiting in BFS/Dijkstra (max 4-5 transfers)
• Add transfer depth tracking in search options
• Write tests: TestFindRouteWithDepthLimiting
• Run tests - must pass before task 6

Task 6: Pareto-front ranking [ ]

• Implement multi-criteria ranking (time, transfers, cost if available)
• Return set of non-dominated routes instead of single "optimal"
• Write tests: TestRouteParetoRanking
• Run tests - must pass before task 7

Task 7: Basic caching layer [ ]

• Implement cache-aside pattern for /search results
• Add TTL policies: 2-6 hours for near-term dates, 7 days for far-term
• Write tests: TestCacheAsideSearch
• Run tests - must pass before task 8

Task 8: Station status endpoint [ ]

• Implement GET /v1/stations/{id}/status endpoint
• Write tests: TestStationStatusEndpoint
• Run tests - must pass before task 9

✅ Stage 1 Complete — MVP ready (basic single-mode routing with lazy expansion)

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Этап 2 — Мультимодальность и MCT (Minimum Connection Time)

Add planes and buses, synthetic edges with MCT rules, manual neighboring airports

Implementation Steps

Task 9: Add bus transport type [ ]

• Add TransportType enum with values: plane, train, bus
• Update Edge struct to include TransportType
• Update routing algorithm to handle all three transport types
• Write tests: TestTransportTypesInGraph
• Run tests - must pass before task 10

Task 10: Synthetic edges "город↔аэропорт" [ ]

• Implement synthetic edges for airport-city transfers
• Add constants for transfer time estimation (section 7.4)
• Mark synthetic edges in GeoJSON output (dashed line)
• Write tests: TestSyntheticAirportCityEdges
• Run tests - must pass before task 11

Task 11: MCT rules implementation [ ]

• Create transfer_rules table migration
• Seed default MCT values (Section 7.4):
  • airport_internal/through → 30 min
  • airport_internal/separate → 60 min
  • station_internal → 30 min
  • airport_to_city/small → 60 min
  • airport_to_city/million_plus → 90 min
• Implement MinTransferTime function reading from transfer rules
• Use MCT in routing algorithm for transfer validation
• Write tests: TestMCTCalculation, TestTransferRules
• Run tests - must pass before task 12

Task 12: Manual neighboring stations [ ]

• Add station_neighbors table support
• Implement internal/airports package with geo + manual override
• Add source field (geo/manual) and is_excluded flag
• Update cities/{id}/stations endpoint to include neighbors when main station closed
• Write tests: TestNeighboringStations, TestStationNeighbors
• Run tests - must pass before task 13

Task 13: Admin station status override [ ]

• Implement POST /internal/admin/stations/{id}/status endpoint
• Add authentication protection
• Allow manual status setting with source: manual
• Write tests: TestAdminStationStatus, TestAdminAuth
• Run tests - must pass before task 14

✅ Stage 2 Complete — Multimodality + MCT operational

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Этап 3 — Глубокий поиск и автодетект (Deep Search + Closure Detection)

Lazy hub-based expansion to depth 4-5, Pareto ranking, auto-closure detection

Implementation Steps

Task 14: Lazy hub expansion depth 4-5 [ ]

• Implement BFS/Dijkstra with explicit depth limiting
• Track transfer count at each step; stop when depth > 5
• On expansion failure, add synthetic edges as fallback
• Write tests: TestLazyExpansionDepthLimit, TestFindRouteMaxTransfers
• Run tests - must pass before task 15

Task 15: Pareto-front ranking integration [ ]

• Integrate multi-criteria ranking into route search results
• Sort by default "быстрее всего" (fastest)
• Add UI controls to switch to "меньше пересадок" / "дешевле"
• Write tests: TestParetoFrontGeneration
• Run tests - must pass before task 16

Task 16: Auto station closure detection [ ]

• Implement daily cron job checking /schedule for monitored stations
• Track zero_since timestamp; if 0 flights for N=3 consecutive days → status closed
• Update station_status table with zero_since, last_seen_flight
• When station closed, automatically substitute neighboring stations
• Write tests: TestStationClosureDetection, TestAutoClosureChronology
• Run tests - must pass before task 17

Task 17: Neighbor substitution in routing [ ]

• When station is closed, route automatically uses neighboring stations
• Update GET /v1/cities/{id}/stations to reflect closure status
• Write tests: TestRouteWithClosedStationSubstitution
• Run tests - must pass before task 18

Task 18: GeoJSON route visualization [ ]

• Implement route-to-GeoJSON conversion
• Real segments: solid lines, color by transport type
• Synthetic segments: dashed lines
• Transfer point markers with popup info (connection time, type)
• Write tests: TestRouteGeoJSON, TestGeoJSONVisualization
• Run tests - must pass before task 19

✅ Stage 3 Complete — Deep search + closure detection operational

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Этап 4 — Полировка (Polish)

Price consideration, flight change notifications, personalization

Implementation Steps

Task 19: Price as routing criterion [ ]

• Investigate price source data from Yandex.Schedules
• If price data available, add as 4th routing criterion
• If not available, add marker "цена не указана" in UI
• Write tests: TestPriceInRouting (if applicable)
• Run tests - must pass before task 20

Task 20: Flight change notifications [ ]

• Track already-built routes for status changes
• Implement re-search on significant changes (cancellation, major delay)
• Write tests: TestRouteReSearchOnChange
• Run tests - must pass before task 21

Task 21: Personalization [ ]

• Add user preferences (saved cities, history of searches)
• Store preferences in Redis or Postgres
• Write tests: TestUserPreferences
• Run tests - must pass before task 22

Task 22: Observability and metrics [ ]

• Add metrics: cache hit-rate per layer, API quota remaining, circuit breaker trips, average search time
• Add Prometheus metrics endpoints or logging structured
• Write tests: TestMetricsEndpoints
• Run tests - must pass before task 23

Task 23: Full test suite and linter [ ]

• Run entire test suite: go test ./...
• Fix all linter issues: go vet ./...
• Verify test coverage meets standard (80%+)
• Fix any remaining issues
• Final verification: all checkboxes marked [x], all tests passing

✅ Stage 4 Complete — Polish finished

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Post-Completion

Manual verification (if applicable)

• Manual UI/UX testing scenarios across all transport mode combinations
• Performance testing under load (simulate cold cache, warm cache scenarios)
• Security review considerations for admin endpoints

External system updates

• Consuming projects that may need updates after this library change
• Configuration changes in deployment systems (docker-compose, cron schedules)
• Third-party service integrations to verify (Yandex API access, Redis/PG connectivity)

Migration path from MVP to full

1. Stage 1 (MVP) → functional single-mode routing
2. Stage 2 → add planes/buses + MCT + manual neighbors
3. Stage 3 → lazy hub expansion + auto-closure + GeoJSON
4. Stage 4 → price, notifications, personalization, observability

Notes for ralphex:

• Auto-move completed plan to docs/plans/completed/ upon full task completion
• Each task MUST include tests as checklist items — they are not optional
• If tests cannot pass until a later task: write tests with TODO comment noting dependency, mark test checkbox as [x] write tests ... (fails until Task X), do NOT skip test writing
• Update plan file when scope changes during implementation