package org.metricshub.jawk.ext;
   
   /*-
    * ╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲
    * Jawk
    * ჻჻჻჻჻჻
    * Copyright (C) 2006 - 2025 MetricsHub
    * ჻჻჻჻჻჻
    * This program is free software: you can redistribute it and/or modify
   * it under the terms of the GNU Lesser General Public License as
   * published by the Free Software Foundation, either version 3 of the
   * License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Lesser Public License for more details.
   *
   * You should have received a copy of the GNU General Lesser Public
   * License along with this program.  If not, see
   * <http://www.gnu.org/licenses/lgpl-3.0.html>.
   * ╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱
   */
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.Serializable;
  import java.lang.reflect.Array;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.lang.reflect.Parameter;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Objects;
  
  import org.metricshub.jawk.ext.annotations.JawkAssocArray;
  import org.metricshub.jawk.ext.annotations.JawkFunction;
  import org.metricshub.jawk.jrt.AssocArray;
  import org.metricshub.jawk.jrt.IllegalAwkArgumentException;
  
  /**
   * Metadata describing a single annotated extension function.
   */
  public final class ExtensionFunction implements Serializable {
  
  	private static final long serialVersionUID = 1L;
  
  	private final String keyword;
  	private final Class<? extends AbstractExtension> declaringType;
  	private final String methodName;
  	private final Class<?>[] parameterTypes;
  	private transient Method method;
  	private final boolean[] assocArrayParameters;
  	private final boolean varArgs;
  	private final int mandatoryParameterCount;
  	private final boolean varArgAssocArray;
  
  	ExtensionFunction(String keywordParam, Method methodParam) {
  		this.keyword = validateKeyword(keywordParam, methodParam);
  		this.declaringType = resolveDeclaringType(methodParam);
  		this.methodName = methodParam.getName();
  		this.parameterTypes = methodParam.getParameterTypes();
  		this.method = prepareMethod(methodParam);
  		this.varArgs = methodParam.isVarArgs();
  		this.assocArrayParameters = inspectParameters(methodParam, methodParam.getParameters());
  		this.mandatoryParameterCount = varArgs ? assocArrayParameters.length - 1 : assocArrayParameters.length;
  		this.varArgAssocArray = varArgs && assocArrayParameters[assocArrayParameters.length - 1];
  	}
  
  	private static String validateKeyword(String keyword, Method method) {
  		Objects.requireNonNull(method, "method");
  		if (keyword == null || keyword.trim().isEmpty()) {
  			throw new IllegalStateException(
  					"@" + JawkFunction.class.getSimpleName()
  							+ " on " + method + " must declare a non-empty name");
  		}
  		return keyword;
  	}
  
  	private static Class<? extends AbstractExtension> resolveDeclaringType(Method method) {
  		Class<?> declaringClass = method.getDeclaringClass();
  		if (!AbstractExtension.class.isAssignableFrom(declaringClass)) {
  			throw new IllegalStateException(
  					"@" + JawkFunction.class.getSimpleName()
  							+ " must be declared on a subclass of " + AbstractExtension.class.getName()
  							+ ": " + method);
  		}
  		@SuppressWarnings("unchecked")
  		Class<? extends AbstractExtension> type = (Class<? extends AbstractExtension>) declaringClass;
  		return type;
  	}
  
  	private static Method prepareMethod(Method method) {
  		if (java.lang.reflect.Modifier.isStatic(method.getModifiers())) {
  			throw new IllegalStateException(
  					"@" + JawkFunction.class.getSimpleName()
  							+ " does not support static methods: " + method.toGenericString());
  		}
  		method.setAccessible(true);
 		return method;
 	}
 
 	private boolean[] inspectParameters(Method methodParam, Parameter[] parameters) {
 		boolean[] assoc = new boolean[parameters.length];
 		for (int idx = 0; idx < parameters.length; idx++) {
 			Parameter parameter = parameters[idx];
 			if (parameter.isAnnotationPresent(JawkAssocArray.class)) {
 				Class<?> parameterType = parameter.getType();
 				if (parameter.isVarArgs()) {
 					parameterType = parameterType.getComponentType();
 				}
 				if (!AssocArray.class.isAssignableFrom(parameterType)) {
 					throw new IllegalStateException(
 							"Parameter " + idx + " of " + methodParam
 									+ " annotated with @" + JawkAssocArray.class.getSimpleName()
 									+ " must accept " + AssocArray.class.getName());
 				}
 				assoc[idx] = true;
 			}
 		}
 		return assoc;
 	}
 
 	private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
 		in.defaultReadObject();
 		try {
 			Method resolved = declaringType.getDeclaredMethod(methodName, parameterTypes);
 			this.method = prepareMethod(resolved);
 		} catch (NoSuchMethodException ex) {
 			throw new IllegalStateException(
 					"Unable to rehydrate extension method '" + methodName
 							+ "' on type " + declaringType.getName(),
 					ex);
 		}
 	}
 
 	/**
 	 * Returns the Awk keyword mapped to this extension function.
 	 *
 	 * @return the keyword exposed by the annotated method
 	 */
 	public String getKeyword() {
 		return keyword;
 	}
 
 	/**
 	 * Returns the extension type that declares the underlying Java method.
 	 *
 	 * @return declaring {@link AbstractExtension} subtype
 	 */
 	public Class<? extends AbstractExtension> getDeclaringType() {
 		return declaringType;
 	}
 
 	/**
 	 * Returns the fully-qualified class name of the declaring extension.
 	 *
 	 * @return extension class name
 	 */
 	public String getExtensionClassName() {
 		return declaringType.getName();
 	}
 
 	/**
 	 * Returns the minimum number of arguments required to invoke the function.
 	 *
 	 * @return required argument count before considering varargs
 	 */
 	public int getArity() {
 		return mandatoryParameterCount;
 	}
 
 	/**
 	 * Indicates whether the parameter at the supplied index must be an associative
 	 * array.
 	 *
 	 * @param index zero-based parameter index
 	 * @return {@code true} when the parameter must be an associative array
 	 * @throws IndexOutOfBoundsException when the index exceeds the parameter count
 	 */
 	public boolean expectsAssocArray(int index) {
 		if (index < 0 || index >= assocArrayParameters.length) {
 			throw new IndexOutOfBoundsException("Parameter index out of range: " + index);
 		}
 		return assocArrayParameters[index];
 	}
 
 	/**
 	 * Collects the indexes of arguments that must be associative arrays for a call
 	 * with the supplied argument count. Vararg positions are included when the
 	 * vararg parameter requires associative arrays.
 	 *
 	 * @param argCount number of arguments supplied by the caller
 	 * @return indexes of arguments that must be associative arrays
 	 */
 	public int[] collectAssocArrayIndexes(int argCount) {
 		verifyArgCount(argCount);
 		List<Integer> indexes = new ArrayList<Integer>();
 		int upperBound = Math.min(argCount, mandatoryParameterCount);
 		for (int idx = 0; idx < upperBound; idx++) {
 			if (assocArrayParameters[idx]) {
 				indexes.add(Integer.valueOf(idx));
 			}
 		}
 		if (varArgs && varArgAssocArray) {
 			for (int idx = mandatoryParameterCount; idx < argCount; idx++) {
 				indexes.add(Integer.valueOf(idx));
 			}
 		}
 		int[] result = new int[indexes.size()];
 		for (int idx = 0; idx < indexes.size(); idx++) {
 			result[idx] = indexes.get(idx).intValue();
 		}
 		return result;
 	}
 
 	/**
 	 * Invokes the underlying Java method on the supplied target instance.
 	 *
 	 * @param target extension instance to receive the call
 	 * @param args arguments evaluated by the interpreter
 	 * @return result of the Java invocation
 	 * @throws IllegalAwkArgumentException when the arguments violate the metadata
 	 * @throws IllegalStateException when reflection cannot invoke the method
 	 */
 	public Object invoke(AbstractExtension target, Object[] args) {
 		Objects.requireNonNull(target, "target");
 		if (!declaringType.isInstance(target)) {
 			throw new IllegalArgumentException(
 					"Extension instance " + target.getClass().getName()
 							+ " is not compatible with " + declaringType.getName());
 		}
 		int argCount = args == null ? 0 : args.length;
 		verifyArgCount(argCount);
 		enforceAssocArrayParameters(args);
 		Object[] invocationArgs = prepareArguments(args);
 		try {
 			return method.invoke(target, invocationArgs);
 		} catch (IllegalAccessException ex) {
 			throw new IllegalStateException(
 					"Unable to access extension function method for keyword '" + keyword + "'",
 					ex);
 		} catch (InvocationTargetException ex) {
 			Throwable cause = ex.getCause();
 			if (cause instanceof RuntimeException) {
 				throw (RuntimeException) cause;
 			}
 			if (cause instanceof Error) {
 				throw (Error) cause;
 			}
 			throw new IllegalStateException(
 					"Invocation of extension function '" + keyword + "' failed",
 					cause);
 		}
 	}
 
 	private Object[] prepareArguments(Object[] args) {
 		int argCount = args == null ? 0 : args.length;
 		if (argCount == 0) {
 			return varArgs ?
 					new Object[]
 					{ Array.newInstance(parameterTypes[parameterTypes.length - 1].getComponentType(), 0) } : new Object[0];
 		}
 		if (!varArgs) {
 			Object[] invocationArgs = new Object[argCount];
 			System.arraycopy(args, 0, invocationArgs, 0, argCount);
 			return invocationArgs;
 		}
 		Object[] invocationArgs = new Object[mandatoryParameterCount + 1];
 		for (int idx = 0; idx < mandatoryParameterCount; idx++) {
 			invocationArgs[idx] = args[idx];
 		}
 		int varArgCount = argCount - mandatoryParameterCount;
 		Class<?> componentType = parameterTypes[parameterTypes.length - 1].getComponentType();
 		Object varArgArray = Array.newInstance(componentType, varArgCount);
 		for (int idx = 0; idx < varArgCount; idx++) {
 			Array.set(varArgArray, idx, args[mandatoryParameterCount + idx]);
 		}
 		invocationArgs[mandatoryParameterCount] = varArgArray;
 		return invocationArgs;
 	}
 
 	/**
 	 * Verifies that the provided argument count satisfies the arity constraints
 	 * encoded in the metadata.
 	 *
 	 * @param argCount number of arguments the caller supplied
 	 * @throws IllegalAwkArgumentException when the count violates the signature
 	 */
 	public void verifyArgCount(int argCount) {
 		if (!varArgs) {
 			if (argCount != mandatoryParameterCount) {
 				throw new IllegalAwkArgumentException(
 						"Extension function '" + keyword + "' expects " + mandatoryParameterCount
 								+ " argument(s), not " + argCount);
 			}
 			return;
 		}
 		if (argCount < mandatoryParameterCount) {
 			throw new IllegalAwkArgumentException(
 					"Extension function '" + keyword + "' expects " + getArity()
 							+ " argument(s), not " + argCount);
 		}
 	}
 
 	private void enforceAssocArrayParameters(Object[] args) {
 		if (args == null) {
 			return;
 		}
 		int argCount = args.length;
 		int upperBound = Math.min(argCount, mandatoryParameterCount);
 		for (int idx = 0; idx < upperBound; idx++) {
 			if (!assocArrayParameters[idx]) {
 				continue;
 			}
 			Object argument = args[idx];
 			if (!(argument instanceof AssocArray)) {
 				throw new IllegalAwkArgumentException(
 						"Argument " + idx + " passed to extension function '" + keyword
 								+ "' must be an associative array");
 			}
 		}
 		if (varArgs && varArgAssocArray) {
 			for (int idx = mandatoryParameterCount; idx < argCount; idx++) {
 				Object argument = args[idx];
 				if (!(argument instanceof AssocArray)) {
 					throw new IllegalAwkArgumentException(
 							"Argument " + idx + " passed to extension function '" + keyword
 									+ "' must be an associative array");
 				}
 			}
 		}
 	}
 }