InMemoryTable

InMemoryTable.java

// package

import java.time.LocalDateTime;
import java.util.*;
import java.util.function.Function;
import java.util.function.Supplier;

public class InMemoryTable<K, V> {
    private final Map<K, List<Record<K, V>>> map = new HashMap<>();
    private final Supplier<LocalDateTime> localDateTimeSupplier;

    private long id = 1;

    public InMemoryTable(Supplier<LocalDateTime> localDateTimeSupplier) {
        this.localDateTimeSupplier = localDateTimeSupplier;
    }

    public InMemoryTable() {
        this.localDateTimeSupplier = LocalDateTime::now;
    }

    private long createId() {
        return id++;
    }

    public List<Record<K, V>> find(K key) {
        if(!map.containsKey(key)) {
            return new ArrayList<>();
        }
        return map.get(key);
    }

    public Optional<Record<K, V>> findById(String id) {
        return map.values()
                .stream()
                .map(l -> l.stream().filter(v -> v.getId().equals(id)).findFirst())
                .filter(Optional::isPresent)
                .map(Optional::get)
                .findFirst();
    }

    public Optional<Record<K, V>> findLast(K key) {
        List<Record<K, V>> l = find(key);
        return l.isEmpty() ? Optional.empty() : Optional.of(l.get(l.size() - 1));
    }

    public String insert(Function<Long, String> idFactory, RecordContainer<K, V> recordContainer) {
        if(!map.containsKey(recordContainer.getKey())) {
            map.put(recordContainer.getKey(), new ArrayList<>());
        }
        String id = idFactory.apply(createId());
        map.get(recordContainer.getKey()).add(new Record<K, V>(recordContainer, id, localDateTimeSupplier.get()));
        return id;
    }

    public String insert(RecordContainer<K, V> recordContainer) {
        return insert((v) -> "" + v, recordContainer);
    }


    public static class RecordContainer<K, V> {
        private final K key;
        private final V value;

        public RecordContainer(K key, V value) {
            this.key = key;
            this.value = value;
        }

        public K getKey() {
            return key;
        }

        public V getValue() {
            return value;
        }
    }
    public static class Record<K, V> extends RecordContainer<K, V> {
        private final String id;
        private final LocalDateTime eventDateTime;


        public Record(K key, V value, String id, LocalDateTime eventDateTime) {
            super(key, value);
            this.id = id;
            this.eventDateTime = eventDateTime;
        }

        public Record(RecordContainer<K, V> recordContainer, String id, LocalDateTime eventDateTime) {
            super(recordContainer.getKey(), recordContainer.getValue());
            this.id = id;
            this.eventDateTime = eventDateTime;
        }

        public String getId() {
            return id;
        }

        public LocalDateTime getEventDateTime() {
            return eventDateTime;
        }
    }
}