org.snapscript.core.type.extend.ExtensionRegistry Maven / Gradle / Ivy

package org.snapscript.core.type.extend;

import static org.snapscript.core.function.Origin.DEFAULT;

import java.util.Collections;
import java.util.List;

import org.snapscript.common.Cache;
import org.snapscript.common.CopyOnWriteCache;
import org.snapscript.common.LazyBuilder;
import org.snapscript.common.LazyCache;
import org.snapscript.core.error.InternalException;
import org.snapscript.core.function.Function;
import org.snapscript.core.module.Module;
import org.snapscript.core.type.Type;
import org.snapscript.core.type.TypeLoader;

public class ExtensionRegistry {

   private final Cache> cache;
   private final ExtensionBuilder builder;
   
   public ExtensionRegistry(TypeLoader loader){
      this.builder = new ExtensionBuilder(loader);
      this.cache = new LazyCache>(builder);
   }
   
   public void register(Class type, Class extension) {
      builder.register(type, extension);
   }
   
   public List extract(Class type) {
      return cache.fetch(type); // cached
   }
   
   private static class ExtensionBuilder implements LazyBuilder> {      

      private final Cache extensions;
      private final FunctionExtractor extractor;
      private final TypeLoader loader;
      
      public ExtensionBuilder(TypeLoader loader){
         this.extractor = new FunctionExtractor(loader, DEFAULT);
         this.extensions = new CopyOnWriteCache();
         this.loader = loader;
      }
      
      public void register(Class type, Class extension) {
         extensions.cache(type, extension);
      }
      
      @Override
      public List create(Class type) {
         Class extension = extensions.fetch(type);
         
         if(extension != null) {
            try {
               Object instance = extension.newInstance();
               Type match = loader.loadType(type);
               Module module = match.getModule();
               
               return extractor.extract(module, type, instance);
            } catch(Exception e) {
               throw new InternalException("Could not extend " + type, e);
            }
         }
         return Collections.emptyList();
      }
   }
}