trip-plan/docs/API.md

Trip Plan — API Contract

All endpoints are JSON over REST, prefixed with /api. This document is the binding contract between backend and frontend. Do not deviate; extend only by agreement.

Conventions

• Dates: YYYY-MM-DD strings. Times: HH:MM 24h strings (optional fields).
• Auth: cookie session (cookie-session). All endpoints except account (create) / login require auth → otherwise 401 {"error":"unauthorized"}.
• Identity is Mullvad-style: an account is a random account token (the only credential — no username/password). Users additionally have a non-unique, editable display_name for humans.
• Trip access: user must be a member of the trip → otherwise 404 {"error":"not found"} (don't leak existence).
• Errors: 4xx/5xx with body {"error": "<human readable message>"}.
• IDs are integers.

Server layout

• src/server/app.js — builds and exports the Express app (export function createApp(dbPath) and export default a ready app is fine, but createApp must exist for tests).
• src/server/index.js — reads env (PORT default 3000, DATA_DIR default ./data, SESSION_SECRET default dev value with console warning), ensures DATA_DIR exists, starts listener, serves public/ statically.
• src/server/db.js — better-sqlite3 connection + schema creation (idempotent CREATE TABLE IF NOT EXISTS).
• src/server/routes/ — auth.js, trips.js, entries.js, geocode.js.
• src/server/util/distance.js — haversineKm(lat1, lng1, lat2, lng2) returns km (number).

Data model (SQLite)

users        (id INTEGER PK, token_hash TEXT UNIQUE NOT NULL,   -- sha256 hex of the account token
              display_name TEXT NOT NULL,                        -- auto-generated, editable, NOT unique
              created_at TEXT DEFAULT current_timestamp)
trips        (id INTEGER PK, name TEXT NOT NULL, start_date TEXT NOT NULL, end_date TEXT NOT NULL,
              owner_id INTEGER NOT NULL REFERENCES users(id),
              currency TEXT NOT NULL DEFAULT 'USD',   -- 3-letter code, display only (no FX)
              join_code TEXT UNIQUE NOT NULL,         -- share code for joining the trip
              created_at TEXT DEFAULT current_timestamp)
trip_members (trip_id INTEGER REFERENCES trips(id), user_id INTEGER REFERENCES users(id),
              role TEXT NOT NULL DEFAULT 'editor',  -- 'owner' | 'editor'
              PRIMARY KEY (trip_id, user_id))
entries      (id INTEGER PK, trip_id INTEGER NOT NULL REFERENCES trips(id),
              date TEXT NOT NULL, type TEXT NOT NULL,
              title TEXT NOT NULL, details TEXT DEFAULT '',
              start_time TEXT, end_time TEXT,
              location_name TEXT, lat REAL, lng REAL,
              sort_order INTEGER NOT NULL DEFAULT 0,
              price REAL,                             -- null = no cost tracked
              paid_by INTEGER REFERENCES users(id),   -- who paid (null = unassigned)
              split_mode TEXT NOT NULL DEFAULT 'equal', -- 'equal' | 'own' | 'payer'
              segments TEXT,                          -- JSON array, flight entries only (see below)
              created_at TEXT DEFAULT current_timestamp)
entry_participants (entry_id INTEGER REFERENCES entries(id), user_id INTEGER REFERENCES users(id),
              PRIMARY KEY (entry_id, user_id))
              -- no rows for an entry = "all trip members participate" (dynamic default)

Entry type ∈ flight | immigration | travel | hotel | activity | rental | note.

Rental car details

rental-type entries can carry structured rental data in entries.rental (TEXT, JSON — same storage pattern as flight segments). null/absent = plain entry.

"rental": {
  "brand": "Toyota", "model": "Yaris Cross", "car_type": "SUV",
  "booking_ref": "RC-889231", "included_km": 1500,
  "pickup":  { "date": "2026-08-01", "time": "09:00", "location_name": "CNX Airport",
               "lat": 18.77, "lng": 98.96 },
  "dropoff": { "date": "2026-08-07", "time": "18:00", "location_name": "Chiang Mai Old Town",
               "lat": 18.79, "lng": 98.98 }
}

Validation (POST/PATCH entries): only allowed when type === 'rental' (else 400); all fields optional; brand/model ≤60, car_type ≤40, booking_ref ≤60 chars; included_km null (= unlimited/unknown) or number ≥ 0; pickup/dropoff objects with date (YYYY-MM-DD, required within the object), optional time HH:MM, location_name ≤120, lat/lng both-or-neither in range. PATCH rental: null clears. Entry JSON always includes rental (parsed or null). The entry's own date should be the pickup date (frontend sets this); the entry's price/split fields carry the rental cost as usual.

Summary impact: summary.rentals counts rental entries; summary.includedKm = sum of non-null included_km across rentals, or null when no rental specifies one — the frontend pairs it with kmDriven ("≈ 520 km driven / 1,500 km included"). Rental pickup/dropoff locations do NOT feed the route (use the entry's normal location field for a map point if wanted).

Flight segments

Flight entries can carry structured segments for multi-leg itineraries (e.g. CNX→BKK→DXB→FRA = 3 segments). Stored as JSON in entries.segments, returned parsed. null/absent = no segments (plain entry).

"segments": [
  { "flight_no": "TG103", "dep_time": "10:30", "arr_time": "11:45",
    "from": {"code": "CNX", "name": "Chiang Mai Intl", "lat": 18.77, "lng": 98.96},
    "to":   {"code": "BKK", "name": "Suvarnabhumi",    "lat": 13.68, "lng": 100.75} },
  { "flight_no": "EK385", "dep_time": "13:05", "arr_time": "17:10",
    "from": {"code": "BKK", "name": "Suvarnabhumi",    "lat": 13.68, "lng": 100.75},
    "to":   {"code": "DXB", "name": "Dubai Intl",      "lat": 25.25, "lng": 55.36} }
]

Validation (POST/PATCH entries): only allowed when type === 'flight' (else 400); array of 1–8 objects; each needs from and to with code (2–4 uppercase alphanumerics); name optional ≤80 chars; lat/lng both-or-neither, same ranges as entry lat/lng; flight_no optional ≤12 chars; dep_time/arr_time optional HH:MM. PATCH with segments: null clears them.

Route expansion: an entry whose segments have coordinates contributes airport stops to /route instead of its own lat/lng — from of the first segment, then to of every segment, in order (airports without coords are skipped; consecutive duplicate coords are collapsed). Stops derived this way have "kind": "airport" and include "code". So CNX-BKK-DXB-FRA yields 4 stops and 3 measured legs on the map.

Airports lookup

GET /api/airports?q=<query> → 200 {results: [{code, name, city, country, lat, lng}]} (max 8; requires auth).

Backed by a bundled dataset at src/server/data/airports.json generated from the public-domain OurAirports data (filter: has IATA code + scheduled service; keep code/name/municipality/iso_country/lat/lng). Matching: exact/prefix IATA code match first (case-insensitive), then name/city substring. This makes CNX → Chiang Mai Intl instant and offline.

Cost semantics

• Only entries with non-null price count toward costs.
• Effective participants of an entry = its entry_participants rows, or all current trip members if it has none.
• split_mode:
  • equal — price is the TOTAL; split equally among effective participants ("rental car 50/50"). paid_by is credited with having paid the total.
  • own — price is PER PERSON; each effective participant owes and pays their own ("everyone pays their own flight"). No debt created. Effective total = price × participant count.
  • payer — personal expense: paid_by owes and pays the whole price alone (requires paid_by; validation error otherwise).

Endpoints

Auth (Mullvad-style account tokens)

Method & path	Body	Response
POST /api/auth/account	{} (empty)	201 {user: {id, display_name}, token: "XXXX-XXXX-XXXX-XXXX"} — creates an account, logs it in. The raw token is returned ONLY here, never again.
POST /api/auth/login	{token}	200 {user}; 401 on unknown token
POST /api/auth/logout	—	204
GET /api/auth/me	—	200 {user: {id, display_name}} or 401
PATCH /api/auth/me	{display_name}	200 {user}; validates 1–40 chars after trim

Token rules:

• 16 chars from the unambiguous alphabet ABCDEFGHJKMNPQRSTUVWXYZ23456789 (no I/L/O/0/1), generated with crypto.randomBytes, displayed grouped XXXX-XXXX-XXXX-XXXX.
• Login normalizes input: strip dashes/spaces, uppercase, then compare sha256(token) against users.token_hash. Only the hash is stored.
• display_name is auto-generated at account creation as adjective-animal (e.g. brave-otter) from two small built-in word lists; not unique; user-editable via PATCH.

User JSON shape everywhere: {id, display_name}.

Trips

Method & path	Body	Response
GET /api/trips	—	200 {trips: [{id, name, start_date, end_date, owner_id, currency, role, member_count, entry_count}]} (trips where user is member, newest first)
POST /api/trips	{name, start_date, end_date, currency?}	201 {trip}; validates: name non-empty ≤120 chars, valid dates, end_date >= start_date, range ≤ 365 days, currency (if given) matches ^[A-Z]{3}$ (default USD). Creator becomes member with role owner.
GET /api/trips/:id	—	200 {trip: {id, name, start_date, end_date, owner_id, currency, join_code}, members: [{id, display_name, role}], entries: [entry…]} entries ordered by (date, sort_order, id)
PATCH /api/trips/:id	any of {name, start_date, end_date, currency}	200 {trip} (same validation; entries outside new range are kept)
DELETE /api/trips/:id	—	204 — owner only, else 403. Deletes members + entries too.
POST /api/trips/join	{code}	200 {trip} — joins the trip with that join_code as editor (idempotent: already a member → still 200 {trip}); 404 {"error":"not found"} on unknown code. Code normalized like tokens (strip dashes/spaces, uppercase).
POST /api/trips/:id/join-code	—	200 {trip} — regenerates join_code, owner only (403 otherwise)
DELETE /api/trips/:id/members/:userId	—	204 — owner only (owner cannot remove self)

join_code: 8 chars, same alphabet as account tokens, generated at trip creation, displayed grouped XXXX-XXXX. Members see it in trip JSON (it's how they invite others); it is NOT a credential — it only grants membership of that one trip.

Entries

Method & path	Body	Response
POST /api/trips/:id/entries	{date, type, title, details?, start_time?, end_time?, location_name?, lat?, lng?, sort_order?, price?, paid_by?, split_mode?, participants?, segments?}	201 {entry}; validates type enum, date format, title non-empty ≤200 chars; lat/lng must both be present or both absent, lat ∈ [-90,90], lng ∈ [-180,180]; price null or number ≥ 0; paid_by null or a trip member's user id; split_mode ∈ equal|own|payer (payer requires paid_by); participants null/[] (= all members) or array of trip-member user ids; segments per "Flight segments" above
PATCH /api/entries/:id	any subset of the above	200 {entry} (member of the entry's trip required; participants replaces the whole set)
DELETE /api/entries/:id	—	204 (also deletes its entry_participants rows)

Entry JSON shape (always full row): {id, trip_id, date, type, title, details, start_time, end_time, location_name, lat, lng, sort_order, price, paid_by, split_mode, participants, segments} where participants is an array of user ids ([] = all members) and segments is the parsed array or null.

Route & summary (computed)

GET /api/trips/:id/route →

{
  "stops": [ {"entryId": 1, "date": "2026-08-01", "type": "flight",
              "title": "BKK → CNX", "location_name": "Chiang Mai", "lat": 18.79, "lng": 98.98} ],
  "legs":  [ {"fromEntryId": 1, "toEntryId": 4, "km": 587.3, "mode": "ground"} ],
  "totalKm": 587.3,
  "summary": {
    "days": 10, "nights": 9,
    "flights": 2, "flightSegments": 4, "hotels": 3, "travelLegs": 1, "activities": 4,
    "rentals": 1, "includedKm": 1500,
    "kmAir": 0, "kmDriven": 587.3,
    "locations": ["Bangkok", "Chiang Mai"]
  }
}

• stops = entries having lat/lng, ordered by (date, sort_order, id); flight entries with coordinate-bearing segments are expanded into airport stops instead (see "Flight segments" — kind: "airport", includes code).
• legs = consecutive stop pairs; skip zero-distance pairs (< 0.05 km) — still include the stop, just no leg.
• Every leg has mode: "air" when BOTH endpoints are kind:"airport" stops expanded from the SAME flight entry (i.e. actual flight segments); "ground" for everything else (hotel→airport transfers, city-to-city drives). summary.kmAir / summary.kmDriven are the per-mode sums (1 decimal). kmDriven is the rough rental-car figure: great-circle, so real road km will be somewhat higher.
• days = inclusive count from start_date to end_date; nights = days - 1 (0 for single-day trips).
• locations = unique location_name values in stop order.
• km rounded to 1 decimal.

Costs & splitting (computed)

GET /api/trips/:id/costs →

{
  "currency": "USD",
  "totalCost": 1450.0,
  "byType": { "flight": 800.0, "travel": 300.0, "hotel": 350.0 },
  "perUser": [
    { "userId": 1, "displayName": "brave-otter", "share": 725.0, "paid": 950.0, "net": 225.0 },
    { "userId": 2, "displayName": "calm-heron",  "share": 725.0, "paid": 500.0, "net": -225.0 }
  ],
  "settlements": [ { "fromUserId": 2, "toUserId": 1, "amount": 225.0 } ],
  "unassigned": 0.0
}

Computation (see Cost semantics above):

• share = what the user's part of the trip costs; paid = what they actually paid; net = paid - share (positive → others owe them).
• equal with paid_by null: the cost still counts into shares and byType, but nobody is credited as payer — accumulate that amount into unassigned (frontend shows a hint to assign payers).
• own: adds price to each participant's share AND paid (self-paid, no debt).
• settlements: minimal-transfer greedy — repeatedly match the largest debtor with the largest creditor until all nets are settled; amounts rounded to 2 decimals, drop transfers < 0.01.
• totalCost = sum of effective totals of all priced entries; byType groups the same by entry type.
• All money values rounded to 2 decimals in the response.

Geocoding proxy

GET /api/geocode?q=<query> → 200 {results: [{name, lat, lng}]} (max 5).

Proxies https://nominatim.openstreetmap.org/search?format=jsonv2&limit=5&accept-language=en&q=… server-side with header User-Agent: trip-plan-app/0.1 (self-hosted) (accept-language=en so results come back in Latin script, not the local language). Map Nominatim's display_name→name, parse lat/lon to numbers. On upstream failure return 502 {"error":"geocoding unavailable"}. Cache identical queries in-memory for 10 minutes.

Frontend contract notes

• SPA served from public/; all non-/api GETs fall back to public/index.html is NOT required — a single index.html with hash-based routing (#/login, #/trips, #/trip/:id) is the expected design, so no server-side fallback is needed.
• Leaflet 1.9.x via unpkg CDN in index.html.
• Session cookie is httpOnly; frontend detects auth state via GET /api/auth/me on load.