/**
 * A wrapper class of {@link TableFunction} for synchronously lookup rows matching the lookup keys
 * from external system.
 *
 * <p>The output type of this table function is fixed as {@link RowData}.
 */
@PublicEvolving
public abstract class LookupFunction extends TableFunction<RowData> {

    /**
     * Synchronously lookup rows matching the lookup keys.
     *
     * @param keyRow - A {@link RowData} that wraps keys to lookup.
     * @return A collections of all matching rows in the lookup table.
     */
    public abstract Collection<RowData> lookup(RowData keyRow) throws IOException;

    /** Invoke {@link #lookup} and handle exceptions. */
    public final void eval(Object... keys) {
        try {
            lookup(GenericRowData.of(keys)).forEach(this::collect);
        } catch (IOException e) {
            throw new RuntimeException("Failed to lookup values with given key", e);
        }
    }
}

/**
 * A wrapper class of {@link AsyncTableFunction} for asynchronously lookup rows matching the lookup
 * keys from external system.
 *
 * <p>The output type of this table function is fixed as {@link RowData}.
 */
@PublicEvolving
public abstract class AsyncLookupFunction extends AsyncTableFunction<RowData> {

    /**
     * Asynchronously lookup rows matching the lookup keys.
     *
     * @param keyRow - A {@link RowData} that wraps keys to lookup.
     * @return A collections of all matching rows in the lookup table.
     */
    public abstract CompletableFuture<Collection<RowData>> asyncLookup(RowData keyRow);

    /** Invokes {@link #asyncLookup} and chains futures. */
    public final void eval(CompletableFuture<Collection<RowData>> future, Object... keys) {
         asyncLookup(GenericRowData.of(keys))
                .whenCompleteAsync(
                        (result, exception) -> {
                            if (exception != null) {
                                future.completeExceptionally(exception);
                                return;
                            }
                            future.complete(result);
                        });
    }
}

/**
 * A semi-persistent mapping from keys to values for storing entries of lookup table.
 *
 * <p>The type of the caching key is a {@link RowData} with lookup key fields packed inside. The
 * type of value is a {@link Collection} of {@link RowData}, which are rows matching lookup key
 * fields.
 *
 * <p>Cache entries are manually added using {@link #put}, and are stored in the cache until either
 * evicted or manually invalidated.
 *
 * <p>Implementations of this interface are expected to be thread-safe, and can be safely accessed
 * by multiple concurrent threads.
 */
@PublicEvolving
public interface LookupCache {

    /**
     * Returns the value associated with key in this cache, or null if there is no cached value for
     * key.
     */
    @Nullable
    Collection<RowData> getIfPresent(RowData key);

    /**
     * Associates the specified value rows with the specified key row in the cache. If the cache
     * previously contained value associated with the key, the old value is replaced by the
     * specified value.
      *
     * @return the previous value rows associated with key, or null if there was no mapping for key.
     * @param key - key row with which the specified value is to be associated
     * @param value – value rows to be associated with the specified key
     */
    Collection<RowData> put(RowData key, Collection<RowData> value);

    /** Discards any cached value for the specified key. */
    void invalidate(RowData key);

    /** Returns the number of key-value mappings in the cache. */
    long size();
}

/** Factory for creating an instance of {@link LookupCache}. */
@PublicEvolving
public interface LookupCacheFactory extends Serializable {

    /**
     * Create a {@link LookupCache}.
     *
     * @param metricGroup - The lookup cache metric group in which the cache register predefined and
     *     custom metrics.
     */
    LookupCache createCache(LookupCacheMetricGroup metricGroup);
}

/** Factory for creating instance of {@link DefaultLookupCache}. */
@PublicEvolving
public class DefaultLookupCacheFactory implements LookupCacheFactory {
    private final Duration expireAfterAccessDuration;
    private final Duration expireAfterWriteDuration;
    private final Integer initialCapacity;
    private final Long maximumSize;

    public static DefaultLookupCacheFactory.Builder newBuilder() {
        return new Builder();
    }

    private DefaultLookupCacheFactory(
            Duration expireAfterAccessDuration,
            Duration expireAfterWriteDuration,
            Long maximumSize) {
        this.expireAfterAccessDuration = expireAfterAccessDuration;
        this.expireAfterWriteDuration = expireAfterWriteDuration;
        this.initialCapacity = initialCapacity;
        this.maximumSize = maximumSize;
    }

    @Override
    public LookupCache createCache(LookupCacheMetricGroup metricGroup) {
        // Create instance of DefaultLookupCache
    }

    /** Builder of {@link DefaultLookupCacheFactory}. */
    public static class Builder {
        private Duration expireAfterAccessDuration;
        private Duration expireAfterWriteDuration;
        private Integer initialCapacity;
        private Long maximumSize;

        public DefaultLookupCacheFactory.Builder expireAfterAccess(Duration duration) {
            expireAfterAccessDuration = duration;
            return this;
        }

        public DefaultLookupCacheFactory.Builder expireAfterWrite(Duration duration) {
            expireAfterWriteDuration = duration;
            return this;
        }

        public DefaultLookupCacheFactory.Builder maximumSize(long maximumSize) {
            this.maximumSize = maximumSize;
            return this;
        }

        public DefaultLookupCacheFactory build() {
            return new DefaultLookupCacheFactory(
                    expireAfterAccessDuration,
                    expireAfterWriteDuration,
                    maximumSize);
        }
    }
}

/**
 * Pre-defined metrics for {@code LookupCache}.
 *
 * <p>Please note that these methods should only be invoked once. Registering a metric with same
 * name for multiple times would lead to an undefined behavior.
 */
@PublicEvolving
public interface LookupCacheMetricGroup extends MetricGroup {
    /** The number of cache hits. */
    void hitCounter(Counter hitCounter);

    /** The number of cache misses. */
    void missCounter(Counter missCounter);

    /** The number of times to load data into cache from external system. */
    void loadCounter(Counter loadCounter);

    /** The number of load failures. */
    void numLoadFailuresCounter(Counter numLoadFailuresCounter);

    /** The time spent for the latest load operation. */
    void latestLoadTimeGauge(Gauge<Long> latestLoadTimeGauge);

    /** The number of records in cache. */
    void numCachedRecordsGauge(Gauge<Long> numCachedRecordsGauge);

    /** The number of bytes used by cache. */
    void numCachedBytesGauge(Gauge<Long> numCachedBytesGauge);
}

/**
 * Provider for creating {@link LookupFunction} and {@link LookupCacheFactory} if caching should be
 * enabled for the lookup table.
 */
@PublicEvolving
public interface LookupFunctionProvider extends LookupTableSource.LookupRuntimeProvider {
    
    /** Creates a builder of {@link LookupFunctionProvider}. */
    static Builder newBuilder() {
        return new Builder();
    }

    /** Creates an {@link LookupFunction} instance. */
    LookupFunction createLookupFunction();

    /**
     * Gets the {@link LookupCacheFactory} for creating lookup cache.
     *
     * <p>This factory will be used for creating an instance of cache during runtime execution for
     * optimizing the access to external lookup table.
     *
     * @return an {@link Optional} of {@link LookupCacheFactory}, or an empty {@link Optional} if
     *     caching shouldn't be applies to the lookup table.
     */
    Optional<LookupCacheFactory> getCacheFactory();

    /**
     * Whether the missing key (key fields without any matching value rows) should be stored in the
     * cache.
     *
     * <p>Please note that this option is required if {@link #getCacheFactory()} returns a non-empty
     * instance. If the cache factory is empty, the return value of this function will be ignored.
     *
     * @return true if a null or empty value should be stored in the cache.
     */
    Optional<Boolean> cacheMissingKey();

    /** Builder class for {@link LookupFunctionProvider}. */
    class Builder {

        private LookupFunction lookupFunction;
        private LookupCacheFactory cacheFactory;
        private Boolean enableCacheMissingKey;

        /** Sets lookup function. */
        public Builder withLookupFunction(LookupFunction lookupFunction) {
            this.lookupFunction = lookupFunction;
            return this;
        }

        /** Enables caching and sets the cache factory. */
        public Builder withCacheFactory(LookupCacheFactory cacheFactory) {
            this.cacheFactory = cacheFactory;
            return this;
        }

        /**
         * Enables storing missing key in the cache.
         *
         * <p>See {@link LookupFunctionProvider#cacheMissingKey()} for more details.
         */
        public Builder enableCacheMissingKey() {
            this.enableCacheMissingKey = true;
            return this;
        }

        public LookupFunctionProvider build() {
            // Build LookupFunctionProvider
        }
    }
}

@PublicEvolving
public interface AsyncLookupFunctionProvider extends LookupTableSource.LookupRuntimeProvider {

    /** Creates a builder of {@link LookupFunctionProvider}. */
    static Builder newBuilder() {
        return new Builder();
    }

    /** Creates an {@link AsyncLookupFunction} instance. */
    AsyncLookupFunction createAsyncLookupFunction();

    /**
     * Gets the {@link LookupCacheFactory} for creating lookup cache.
     *
     * <p>This factory will be used for creating an instance of cache during runtime execution for
     * optimizing the access to external lookup table.
     *
     * @return an {@link Optional} of {@link LookupCacheFactory}, or an empty {@link Optional} if
     *     caching shouldn't be applies to the lookup table.
     */
    Optional<LookupCacheFactory> getCacheFactory();

    /**
     * Whether the missing key (key fields without any matching value rows) should be stored in the
     * cache.
     *
     * <p>Please note that this option is required if {@link #getCacheFactory()} returns a non-empty
     * instance. If the cache factory is empty, the return value of this function will be ignored.
     *
     * @return true if a null or empty value should be stored in the cache.
     */
    Optional<Boolean> cacheMissingKey();
    
    /** Builder class for {@link AsyncLookupFunctionProvider}. */
    class Builder {

        private AsyncLookupFunction asyncLookupFunction;
        private LookupCacheFactory cacheFactory;
        private Boolean enableCacheMissingKey;

        /** Sets lookup function. */
        public Builder withAsyncLookupFunction(AsyncLookupFunction asyncLookupFunction) {
            this.asyncLookupFunction = asyncLookupFunction;
            return this;
        }

        /** Enables caching and sets the cache factory. */
        public Builder withCacheFactory(LookupCacheFactory cacheFactory) {
            this.cacheFactory = cacheFactory;
            return this;
        }

        /**
         * Enables storing missing key in the cache.
         *
         * <p>See {@link AsyncLookupFunctionProvider#cacheMissingKey()} for more details.
         */
        public Builder enableCacheMissingKey() {
            this.enableCacheMissingKey = true;
            return this;
        }

        public AsyncLookupFunctionProvider build() {
            // Build AsyncLookupFunctionProvider
        }
    }
}

/**
 * Runtime provider for fully loading and periodically reloading all entries of the lookup table and
 * storing the table locally for lookup.
 *
 * <p>Implementations should provide a {@link ScanTableSource.ScanRuntimeProvider} in order to reuse
 * the ability of scanning for loading all entries from the lookup table.
 */
@PublicEvolving
public interface FullCachingLookupProvider extends LookupTableSource.LookupRuntimeProvider {      
	/**
     * Creates {@link FullCachingLookupProvider} with provided scan runtime provider and reload
     * time.
     */
    static FullCachingLookupProvider of(
            ScanTableSource.ScanRuntimeProvider scanRuntimeProvider, ReloadTime reloadTime) {
        return new FullCachingLookupProvider() {
            @Override
            public ScanTableSource.ScanRuntimeProvider getScanRuntimeProvider() {
                return scanRuntimeProvider;
            }

            @Override
            public ReloadTime getReloadTime() {
                return reloadTime;
            }
        };
    }      


	/**
     * Gets the {@link org.apache.flink.table.connector.source.ScanTableSource.ScanRuntimeProvider}
     * for executing the periodically reload.
     */
    ScanTableSource.ScanRuntimeProvider getScanRuntimeProvider();  
	/** Gets the time when to reload cache. See {@link ReloadTime}. */
    ReloadTime getReloadTime();

    /** Defines at what time the cache should be reloaded. */
    interface ReloadTime extends Serializable {
        /** Gets the interval between two reload operations. */
        Duration getReloadInterval();

        /** Gets the start time of the reload operation in UTC. */
        LocalTime getReloadStartTime();

        /** Creates reload time with periodic intervals. */
        static ReloadTime withInterval(Duration reloadInterval) {
            return new ReloadTime() {
                @Override
                public Duration getReloadInterval() {
                    return reloadInterval;
                }

                @Override
                public LocalTime getReloadStartTime() {
                    return LocalTime.now(ZoneOffset.UTC);
                }
            };
        }

        /**
         * Creates reload time with periodic intervals after initial delay up to {@code
         * reloadStartTime}.
         */
        static ReloadTime withIntervalAfterDelay(
                Duration reloadInterval, LocalTime reloadStartTime) {
            return new ReloadTime() {
                @Override
                public Duration getReloadInterval() {
                    return reloadInterval;
                }

                @Override
                public LocalTime getReloadStartTime() {
                    return reloadStartTime;
                }
            };
        }

        /** Creates reload time daily at specified {@code reloadStartTime}. */
        static ReloadTime dailyAtSpecifiedTime(LocalTime reloadStartTime) {
            return new ReloadTime() {
                @Override
                public Duration getReloadInterval() {
                    return Duration.ofDays(1);
                }

                @Override
                public LocalTime getReloadStartTime() {
                    return reloadStartTime;
                }
            };
        }
    }
 }