/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.bcel.verifier.structurals;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import org.apache.bcel.generic.CodeExceptionGen;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.MethodGen;

/**
 * This class allows easy access to ExceptionHandler objects.
 */
public class ExceptionHandlers {

    /**
     * Empty array.
     */
    private static final ExceptionHandler[] EMPTY_ARRAY = {};

    /**
     * The ExceptionHandler instances. Key: InstructionHandle objects, Values: HashSet<ExceptionHandler> instances.
     */
    private final Map<InstructionHandle, Set<ExceptionHandler>> exceptionHandlers;

    /**
     * Constructs a new ExceptionHandlers instance.
     *
     * @param mg the method generator.
     */
    public ExceptionHandlers(final MethodGen mg) {
        exceptionHandlers = new HashMap<>();
        final CodeExceptionGen[] cegs = mg.getExceptionHandlers();
        for (final CodeExceptionGen ceg : cegs) {
            final ExceptionHandler eh = new ExceptionHandler(ceg.getCatchType(), ceg.getHandlerPC());
            for (InstructionHandle ih = ceg.getStartPC(); ih != ceg.getEndPC().getNext(); ih = ih.getNext()) {
                exceptionHandlers.computeIfAbsent(ih, k -> new HashSet<>()).add(eh);
            }
        }
    }

    /**
     * Returns all the ExceptionHandler instances representing exception handlers that protect the instruction ih.
     *
     * @param ih the instruction handle.
     * @return array of exception handlers.
     */
    public ExceptionHandler[] getExceptionHandlers(final InstructionHandle ih) {
        final Set<ExceptionHandler> hsSet = exceptionHandlers.get(ih);
        if (hsSet == null) {
            return EMPTY_ARRAY;
        }
        return hsSet.toArray(ExceptionHandler.EMPTY_ARRAY);
    }

}
