Airbnb Stays Marketplace, the whole design.

%% title: Search reads a copy; calendars, prices and money live elsewhere
flowchart TD
  G@{ icon: "sd:phone", label: "Guest app<br/>map rectangle · dates · guests" } ==> API@{ icon: "sd:api", label: "API gateway" }
  API ==> ROOT["Search root<br/>fan out · merge · re-rank · pins"]:::hot
  ROOT ==> LEAF["Search leaves<br/>geo cells · night bits · prices · ranker"]:::core
  EXT@{ icon: "sd:globe", label: "Other travel sites<br/>.ics feeds" } -.-> ICAL@{ icon: "sd:cron", label: "iCal poller<br/>by risk · refresh at Reserve" }
  ICAL --> CAL["Calendar service<br/>nights · blocks by source · rules"]:::service
  PR@{ icon: "tech:spark", label: "Smart Pricing<br/>Spark batch + fast path" } --> CAL
  CAL --> BUS@{ icon: "tech:kafka", label: "Kafka<br/>~10,000 listing updates / s" }
  BUS ==> LEAF
  API --> RES["Reservations<br/>unique listing + night"]:::service
  RES --> RISK@{ icon: "sd:shield", label: "Risk scoring<br/>allow · friction · block" }
  RES --> PAY["Payments<br/>pay-in · ledger · payouts"]:::core
  class G client
  class API edge
  class EXT external
  class BUS queue
  class ICAL,PR,RISK service

%% title: The ranking funnel, each stage an order of magnitude smaller
flowchart TD
  F["Free for the dates and party<br/>~20,000 homes in a big search"]:::service
  EBR["Retrieval · two towers, IVF clusters<br/>keep ~1,000"]:::core
  DNN["First-stage ranker<br/>booking probability"]:::core
  SET["Setwise re-ranker at the root<br/>the page as a whole"]:::hot
  PINS["Map pins<br/>full pins · mini-pins"]:::ok
  EMB@{ icon: "sd:ml", label: "Listing vectors<br/>rebuilt daily offline" }
  F ==> EBR ==> DNN ==> SET ==> PINS
  EMB -.-> EBR
  class EMB store

%% title: Rohan drags the map, then reserves Meera's home
sequenceDiagram
  autonumber
  participant R as Rohan's app
  participant S as Search root
  participant L as Leaves
  participant B as Reservations
  participant K as Risk scoring
  participant P as Payments
  R->>S: Map rectangle, 6–9 Nov, 5 guests
  S->>L: Fan out to every leaf
  L-->>S: Free all 3 nights, total price, ranked
  S-->>R: 18 cards, full pins and mini-pins
  R->>B: Reserve with the signed quote
  B->>K: Score this booking
  K-->>B: Low risk, no friction
  B->>B: Insert 3 nights, unique per listing-night
  B->>P: Charge ₹38,400, hold until check-in
  P-->>R: Confirmed

%% title: Refresh on intent: the Reserve button checks the other sites
sequenceDiagram
  autonumber
  participant R as Rohan's app
  participant B as Reservations
  participant Q as iCal poller
  participant O as Other site
  participant C as Calendar service
  R->>B: Reserve 6–9 Nov
  B->>Q: Feeds older than a few minutes?
  Q->>O: Conditional GET, about 1 s timeout
  alt 304 not modified
    O-->>Q: 304
    Q-->>B: Nothing new
    B->>C: Insert 3 nights
  else New file blocks 7 Nov
    O-->>Q: 200 with the new busy dates
    Q->>C: Apply snapshot for this source
    C-->>R: These dates are no longer available
  end
  Note over Q,O: no answer in time · book and flag the stay for the host

%% title: The money, from Rohan's charge to Meera's payout
sequenceDiagram
  autonumber
  participant P as Pay-in
  participant L as Ledger
  participant S as Payout scheduler
  participant O as Payout
  participant M as Meera's bank
  P->>L: Charge posted · held for host, unearned fee, tax
  Note over L: every posting sums to zero, append-only
  S->>S: Check-in Friday 6 Nov · next business day Monday
  S->>O: Pay stay, key payout per stay
  O->>L: Intent recorded before the call
  O->>M: Send rupees with the same key
  M-->>O: Accepted
  O->>L: Payable out, payouts in transit

%% title: Core entities
classDiagram
  class Listing {
    +listingId : int
    +geoCell : cell id
    +freeNights : 365 bits
    +nightlyPrice : 365 values
    +minNights : int
    +checkinDays : weekdays
  }
  class StayNight {
    +listingId : int
    +night : date · unique with listing
    +stayId : string
  }
  class CalendarBlock {
    +listingId : int
    +night : date
    +source : feed id or host
    +uid : iCal event id
  }
  class Quote {
    +listingId : int
    +nights : date range
    +total : money
    +expires : minutes
  }
  class Posting {
    +key : idempotency key
    +currency : string
    +entries : balanced, sum zero
  }
  class Payout {
    +key : payout per stay
    +host : hostId
    +status : INTENT / SENT / FAILED
  }
  Listing "1" --> "many" StayNight : booked nights
  Listing "1" --> "many" CalendarBlock : imported or manual
  Quote "1" --> "0..1" StayNight : becomes
  StayNight "many" --> "many" Posting : money events
  Posting "many" --> "1" Payout : paid by

%% title: A stay, from Reserve to payout
stateDiagram-v2
  [*] --> QUOTED: search returns a signed quote
  QUOTED --> VERIFYING: risk score in the middle
  QUOTED --> PAYMENT_PENDING: low risk
  VERIFYING --> PAYMENT_PENDING: friction cleared
  VERIFYING --> REJECTED: friction failed or blocked
  PAYMENT_PENDING --> CONFIRMED: charge or webhook succeeds
  CONFIRMED --> CHECKED_IN: check-in day · fee becomes revenue
  CHECKED_IN --> PAID_OUT: business day after check-in
  CONFIRMED --> CANCELLED: refund by reversing entries
  PAID_OUT --> [*]
  REJECTED --> [*]
  CANCELLED --> [*]
  class PAID_OUT ok
  class REJECTED bad
  class VERIFYING queue
  class PAYMENT_PENDING queue