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/*
 * Copyright (c) 1997, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package com.sun.faces.util.copier;

import static com.sun.faces.util.ReflectionUtils.instance;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import javax.faces.context.FacesContext;

public class CopierUtils {
    
    private static final String ERROR_COPIER_NAME = "The copier name should be a Java valid simple/qualified name.";
    private static final String COPIER_PREFIX = "com.sun.faces.util.copier.";
    
    private final static Set keywords;

    static {
        Set s = new HashSet();
        String[] kws = {
            "abstract", "continue", "for", "new", "switch",
            "assert", "default", "if", "package", "synchronized",
            "boolean", "do", "goto", "private", "this",
            "break", "double", "implements", "protected", "throw",
            "byte", "else", "import", "public", "throws",
            "case", "enum", "instanceof", "return", "transient",
            "catch", "extends", "int", "short", "try",
            "char", "final", "interface", "static", "void",
            "class", "finally", "long", "strictfp", "volatile",
            "const", "float", "native", "super", "while",
            // literals
            "null", "true", "false"
        };
        for (String kw : kws) {
            s.add(kw);
        }
        keywords = Collections.unmodifiableSet(s);
    }    
    
    public static Copier getCopier(FacesContext context, String copierType) {
        Copier copier = null;

        if (!isEmpty(copierType)) {

            // TODO: or should validate only against {"MultiStrategyCopier", "SerializationCopier",
            // "NewInstanceCopier", "CopyCtorCopier", "CloneCopier"} strings / enum
            
            if (isCopierTypeSimpleName(copierType)) {                
                copierType = COPIER_PREFIX.concat(copierType);
            } else if (!isName(copierType)) {
                throw new IllegalArgumentException(ERROR_COPIER_NAME);
            }

            Object expressionResult = evaluateExpressionGet(context, copierType);

            if (expressionResult instanceof Copier) {
                copier = (Copier) expressionResult;
            } else if (expressionResult instanceof String) {
                copier = instance((String) expressionResult);
            }
        }

        if (copier == null) {
            copier = new MultiStrategyCopier();
        }
        
        return copier;
    }

    @SuppressWarnings("unchecked")
    private static  T evaluateExpressionGet(FacesContext context, String expression) {
        if (expression == null) {
            return null;
        }

        return (T) context.getApplication().evaluateExpressionGet(context, expression, Object.class);
    }

    private static boolean isCopierTypeSimpleName(String copierType) {
        return (isIdentifier(copierType) && !(isKeyword(copierType)));
    }

    // maybe the following four methods should be moved in com.sun.faces.util   
    private static boolean isEmpty(String string) {
        return string == null || string.isEmpty();
    }

    private static boolean isName(CharSequence name) {
        String id = name.toString();

        for (String s : id.split("\\.", -1)) {
            if (!isIdentifier(s) || isKeyword(s)) {
                return false;
            }
        }
        return true;
    }

    private static boolean isIdentifier(CharSequence name) {
        String id = name.toString();

        if (id.length() == 0) {
            return false;
        }
        int cp = id.codePointAt(0);
        if (!Character.isJavaIdentifierStart(cp)) {
            return false;
        }
        for (int i = Character.charCount(cp);
                i < id.length();
                i += Character.charCount(cp)) {
            cp = id.codePointAt(i);
            if (!Character.isJavaIdentifierPart(cp)) {
                return false;
            }
        }
        return true;
    }

    private static boolean isKeyword(CharSequence s) {
        String keywordOrLiteral = s.toString();
        return keywords.contains(keywordOrLiteral);
    }

}