/*
 * Copyright 2009-2016 the original author or authors.
 *
 * Licensed 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
 *
 *     http://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.codehaus.groovy.eclipse.dsl.pointcuts.impl;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;

import org.codehaus.groovy.ast.ClassNode;
import org.codehaus.groovy.ast.expr.ClassExpression;
import org.codehaus.groovy.eclipse.dsl.pointcuts.AbstractPointcut;
import org.codehaus.groovy.eclipse.dsl.pointcuts.GroovyDSLDContext;
import org.codehaus.groovy.eclipse.dsl.pointcuts.IPointcut;
import org.codehaus.groovy.eclipse.dsl.pointcuts.PointcutVerificationException;
import org.eclipse.core.resources.IStorage;

/**
 * An abstract pointcut that filters the value of {@link GroovyDSLDContext#getOuterPointcutBinding()}.
 *
 * You can think of the filter pointcut as taking a set of things from the outer pointcut, and
 * either sending it to the inner pointcut, which will do its own filter, or performing a filter
 * using its argument.
 *
 * @author andrew
 * @created Feb 11, 2011
 */
public abstract class FilteringPointcut<T> extends AbstractPointcut {

    private final Class<T> filterBy;

    public FilteringPointcut(IStorage containerIdentifier, String pointcutName, Class<T> filterBy) {
        super(containerIdentifier, pointcutName);
        this.filterBy = filterBy;
    }

    @Override
    public Collection<?> matches(GroovyDSLDContext pattern, Object toMatch) {
        Collection<T> explodedList = explodeObject(toMatch);
        if (explodedList != null && !explodedList.isEmpty()) {
            Object first = getFirstArgument();
            if (first instanceof IPointcut) {
                // pass the exploded list to the inner pointcut and match on each element of the list
                return matchOnPointcutArgument((IPointcut) first, pattern, explodedList);
            } else {
                Collection<?> filtered = filterResult(explodedList, pattern);
                if (filtered != null) {
                    return filtered;
                }
            }
        }
        return null;
    }

    protected Collection<?> filterResult(Collection<T> results, GroovyDSLDContext context) {
        Object o = getFirstArgument();
        String firstArg = asString(o);
        Collection<T> filtered = new ArrayList<T>(results.size());
        for (T obj : results) {
            T maybe = filterObject(obj, context, firstArg);
            if (maybe != null) {
                filtered.add(maybe);
            }
        }
        return reduce(filtered);
    }

    protected String asString(Object o) {
        if (o instanceof String) {
            return (String) o;
        } else if (o instanceof Class) {
            return ((Class<?>) o).getName();
        } else if (o instanceof ClassNode) {
            return ((ClassNode) o).getName();
        } else if (o instanceof ClassExpression) {
            return ((ClassExpression) o).getType().getName();
        }
        return null;
    }

    protected Collection<T> reduce(Collection<T> filtered) {
        if (filtered == null || filtered.size() == 0) {
            return null;
        } else {
            return filtered;
        }
    }

    /**
     * Filters an individual object based on some criteria in the concrete query
     */
    protected abstract T filterObject(T result, GroovyDSLDContext context, String firstArgAsString);

    /**
     * Converts element to a collection of the {@link #filterBy} type or returns null if no match.
     */
    @SuppressWarnings("unchecked")
    protected Collection<T> explodeObject(Object toMatch) {
        if (toMatch instanceof Collection) {
            Collection<T> objs = new ArrayList<T>();
            for (Object obj : (Collection<?>) toMatch) {
                if (filterBy.isInstance(obj)) {
                    objs.add((T) obj);
                }
            }
            if (!objs.isEmpty()) {
                return objs;
            }
        } else if (filterBy.isInstance(toMatch)) {
            return Collections.singletonList((T) toMatch);
        }
        return null;
    }

    /**
     * Expecting one argument that can either be a string or another pointcut
     */
    @Override
    public void verify() throws PointcutVerificationException {
        super.verify();

        String oneStringOrOnePointcutArg = oneStringOrOnePointcutOrOneClassArg();
        if (oneStringOrOnePointcutArg != null) {
            String hasNoArgs = hasNoArgs();
            if (hasNoArgs != null) {
                throw new PointcutVerificationException(
                    "This pointcut expects either no arguments or 1 String or 1 pointcut argument", this);
            }
        }
    }
}