HookData.java

package dev.openfeature.sdk;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Hook data provides a way for hooks to maintain state across their execution stages.
 * Each hook instance gets its own isolated data store that persists only for the duration
 * of a single flag evaluation.
 */
public interface HookData {

    /**
     * Sets a value for the given key.
     *
     * @param key the key to store the value under
     * @param value the value to store
     */
    void set(String key, Object value);

    /**
     * Gets the value for the given key.
     *
     * @param key the key to retrieve the value for
     * @return the value, or null if not found
     */
    Object get(String key);

    /**
     * Gets the value for the given key, cast to the specified type.
     *
     * @param <T> the type to cast to
     * @param key the key to retrieve the value for
     * @param type the class to cast to
     * @return the value cast to the specified type, or null if not found
     * @throws ClassCastException if the value cannot be cast to the specified type
     */
    <T> T get(String key, Class<T> type);

    /**
     * Default implementation using ConcurrentHashMap for thread safety.
     */
    static HookData create() {
        return new DefaultHookData();
    }

    /**
     * Default thread-safe implementation of HookData.
     */
    public class DefaultHookData implements HookData {
        private final Map<String, Object> data = Collections.synchronizedMap(new HashMap<>());

        @Override
        public void set(String key, Object value) {
            data.put(key, value);
        }

        @Override
        public Object get(String key) {
            return data.get(key);
        }

        @Override
        public <T> T get(String key, Class<T> type) {
            Object value = data.get(key);
            if (value == null) {
                return null;
            }
            if (!type.isInstance(value)) {
                throw new ClassCastException("Value for key '" + key + "' is not of type " + type.getName());
            }
            return type.cast(value);
        }
    }
}