Inventory and Order Fulfillment

1import java.util.*;
2/** Local warehouse inventory; physical shipping and durable transactions are external contracts. */
3public final class Solution {
4    private Solution() {}
5    public record Key(String warehouse,String sku){public Key{if(warehouse==null||warehouse.isBlank()||sku==null||sku.isBlank())throw new IllegalArgumentException("stock key");}}
6    public enum State { ACTIVE, COMPLETED, RELEASED, EXPIRED }
7    public record Reservation(String id,String order,Map<Key,Long> original,Map<Key,Long> remaining,Map<Key,Long> shipped,long expiresAt,int version,State state){public Reservation{original=Map.copyOf(original);remaining=Map.copyOf(remaining);shipped=Map.copyOf(shipped);}}
8    public record Stock(long onHand,long reserved,long version){}
9    public record Adjustment(Key key,long delta,String reason,long version){}
10    private record ReserveRequest(String order,Map<String,Long> demand,long ttl){public ReserveRequest{demand=Map.copyOf(demand);}}
11    private record ShipRequest(String reservation,Map<Key,Long> quantities){public ShipRequest{quantities=Map.copyOf(quantities);}}
12    private record Operation(Object fingerprint,String reservation){}
13    public static final class Inventory {
14        private final Map<Key,Long> onHand=new TreeMap<>(Comparator.comparing(Key::warehouse).thenComparing(Key::sku));
15        private final Map<Key,Long> held=new HashMap<>(),versions=new HashMap<>();
16        private final Map<String,Reservation> reservations=new LinkedHashMap<>();
17        private final Map<String,Operation> operations=new HashMap<>();
18        private final List<Adjustment> adjustments=new ArrayList<>();
19        private long sequence,time;
20        public Inventory(Map<Key,Long> initial){if(initial.isEmpty()||initial.values().stream().anyMatch(v->v==null||v<0))throw new IllegalArgumentException("initial stock");onHand.putAll(initial);initial.keySet().forEach(k->{held.put(k,0L);versions.put(k,0L);});}
21        private void key(Key k){if(!onHand.containsKey(k))throw new IllegalArgumentException("stock key");}
22        private static void id(String s){if(s==null||s.isBlank())throw new IllegalArgumentException("id");}
23        private void version(Key k){versions.put(k,Math.incrementExact(versions.get(k)));}
24        private void at(long now){if(now<time)throw new IllegalArgumentException("time");time=now;for(var r:new ArrayList<>(reservations.values()))if(r.state()==State.ACTIVE&&r.expiresAt()<=now)close(r,State.EXPIRED);}
25        private Reservation close(Reservation r,State state){r.remaining().forEach((k,q)->{held.put(k,held.get(k)-q);version(k);});var closed=new Reservation(r.id(),r.order(),r.original(),Map.of(),r.shipped(),r.expiresAt(),Math.incrementExact(r.version()),state);reservations.put(r.id(),closed);return closed;}
26        private Operation previous(String key,Object request){id(key);var op=operations.get(key);if(op!=null&&!op.fingerprint().equals(request))throw new IllegalArgumentException("key reused");return op;}
27        public synchronized Reservation reserve(String order,Map<String,Long> demand,long ttl,String operationKey,long now){
28            demand=Map.copyOf(demand);id(order);if(demand.isEmpty()||demand.keySet().stream().anyMatch(s->s==null||s.isBlank())||demand.values().stream().anyMatch(q->q==null||q<1)||ttl<1)throw new IllegalArgumentException("demand");
29            var request=new ReserveRequest(order,demand,ttl);var old=previous(operationKey,request);if(old!=null){at(now);return get(old.reservation());}long deadline=Math.addExact(now,ttl);at(now);
30            var allocation=new LinkedHashMap<Key,Long>();
31            for(var item:new TreeMap<>(demand).entrySet()){
32                long needed=item.getValue();for(var stock:onHand.entrySet())if(stock.getKey().sku().equals(item.getKey())){long take=Math.min(needed,stock.getValue()-held.get(stock.getKey()));if(take>0){allocation.put(stock.getKey(),take);needed-=take;}if(needed==0)break;}if(needed!=0)throw new IllegalStateException("insufficient stock");
33            }
34            var r=new Reservation("R"+(++sequence),order,allocation,allocation,Map.of(),deadline,0,State.ACTIVE);allocation.forEach((k,q)->{held.put(k,Math.addExact(held.get(k),q));version(k);});reservations.put(r.id(),r);operations.put(operationKey,new Operation(request,r.id()));return r;
35        }
36        public synchronized Reservation ship(String reservationId,Map<Key,Long> quantities,String operationKey,long now){
37            quantities=Map.copyOf(quantities);if(quantities.isEmpty()||quantities.values().stream().anyMatch(q->q==null||q<1))throw new IllegalArgumentException("shipment");var request=new ShipRequest(reservationId,quantities);var old=previous(operationKey,request);at(now);if(old!=null)return get(old.reservation());var r=get(reservationId);if(r.state()!=State.ACTIVE)throw new IllegalStateException("reservation not active");
38            for(var e:quantities.entrySet())if(e.getValue()>r.remaining().getOrDefault(e.getKey(),0L))throw new IllegalStateException("exceeds reservation");
39            var remaining=new HashMap<>(r.remaining());var shipped=new HashMap<>(r.shipped());
40            quantities.forEach((k,q)->{long left=remaining.get(k)-q;if(left==0)remaining.remove(k);else remaining.put(k,left);shipped.merge(k,q,Math::addExact);});
41            quantities.forEach((k,q)->{onHand.put(k,onHand.get(k)-q);held.put(k,held.get(k)-q);version(k);});
42            var next=new Reservation(r.id(),r.order(),r.original(),remaining,shipped,r.expiresAt(),Math.incrementExact(r.version()),remaining.isEmpty()?State.COMPLETED:State.ACTIVE);reservations.put(r.id(),next);operations.put(operationKey,new Operation(request,r.id()));return next;
43        }
44        public synchronized Reservation release(String id,long now){at(now);var r=get(id);if(r.state()!=State.ACTIVE)return r;return close(r,State.RELEASED);}
45        public synchronized Stock adjust(Key key,long delta,String reason,long expectedVersion,long now){key(key);id(reason);at(now);if(versions.get(key)!=expectedVersion)throw new IllegalStateException("stale stock version");long next=Math.addExact(onHand.get(key),delta);if(next<held.get(key))throw new IllegalStateException("adjustment violates reservations");onHand.put(key,next);version(key);adjustments.add(new Adjustment(key,delta,reason,versions.get(key)));return stock(key,now);}
46        public synchronized Reservation get(String id){var r=reservations.get(id);if(r==null)throw new IllegalArgumentException("reservation");return r;}
47        public synchronized Stock stock(Key key,long now){key(key);at(now);return new Stock(onHand.get(key),held.get(key),versions.get(key));}
48        public synchronized List<Adjustment> adjustments(){return List.copyOf(adjustments);}
49        public synchronized boolean invariantHolds(){var actual=new HashMap<Key,Long>();for(var r:reservations.values())if(r.state()==State.ACTIVE)r.remaining().forEach((k,q)->actual.merge(k,q,Math::addExact));return onHand.keySet().stream().allMatch(k->held.get(k)>=0&&held.get(k)<=onHand.get(k)&&held.get(k).equals(actual.getOrDefault(k,0L)));}
50    }
51}
52