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 *  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
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 *    http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.cayenne.exp;

import java.io.PrintWriter;
import java.io.Reader;
import java.io.Serializable;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.apache.cayenne.exp.parser.ASTScalar;
import org.apache.cayenne.exp.parser.ExpressionParser;
import org.apache.cayenne.exp.parser.ParseException;
import org.apache.cayenne.util.ConversionUtil;
import org.apache.cayenne.util.Util;
import org.apache.cayenne.util.XMLEncoder;
import org.apache.cayenne.util.XMLSerializable;
import org.apache.commons.collections.Transformer;

/**
 * Superclass of Cayenne expressions that defines basic API for expressions use.
 */
public abstract class Expression implements Serializable, XMLSerializable {

    /**
     * A value that a Transformer might return to indicate that a node has to be pruned
     * from the expression during the transformation.
     * 
     * @since 1.2
     */
    public final static Object PRUNED_NODE = new Object();

    public static final int AND = 0;
    public static final int OR = 1;
    public static final int NOT = 2;
    public static final int EQUAL_TO = 3;
    public static final int NOT_EQUAL_TO = 4;
    public static final int LESS_THAN = 5;
    public static final int GREATER_THAN = 6;
    public static final int LESS_THAN_EQUAL_TO = 7;
    public static final int GREATER_THAN_EQUAL_TO = 8;
    public static final int BETWEEN = 9;
    public static final int IN = 10;
    public static final int LIKE = 11;
    public static final int LIKE_IGNORE_CASE = 12;
    public static final int ADD = 16;
    public static final int SUBTRACT = 17;
    public static final int MULTIPLY = 18;
    public static final int DIVIDE = 19;
    public static final int NEGATIVE = 20;
    public static final int TRUE = 21;
    public static final int FALSE = 22;

    /**
     * Expression describes a path relative to an ObjEntity. OBJ_PATH expression is
     * resolved relative to some root ObjEntity. Path expression components are separated
     * by "." (dot). Path can point to either one of these:
     * <ul>
     * <li><i>An attribute of root ObjEntity.</i> For entity Gallery OBJ_PATH expression
     * "galleryName" will point to ObjAttribute "galleryName"
     * <li><i>Another ObjEntity related to root ObjEntity via a chain of relationships.</i>
     * For entity Gallery OBJ_PATH expression "paintingArray.toArtist" will point to
     * ObjEntity "Artist"
     * <li><i>ObjAttribute of another ObjEntity related to root ObjEntity via a chain of
     * relationships.</i> For entity Gallery OBJ_PATH expression
     * "paintingArray.toArtist.artistName" will point to ObjAttribute "artistName"
     * </ul>
     */
    public static final int OBJ_PATH = 26;

    /**
     * Expression describes a path relative to a DbEntity. DB_PATH expression is resolved
     * relative to some root DbEntity. Path expression components are separated by "."
     * (dot). Path can point to either one of these:
     * <ul>
     * <li><i>An attribute of root DbEntity.</i> For entity GALLERY, DB_PATH expression
     * "GALLERY_NAME" will point to a DbAttribute "GALLERY_NAME". </li>
     * <li><i>Another DbEntity related to root DbEntity via a chain of relationships.</i>
     * For entity GALLERY DB_PATH expression "paintingArray.toArtist" will point to
     * DbEntity "ARTIST". </li>
     * <li><i>DbAttribute of another ObjEntity related to root DbEntity via a chain of
     * relationships.</i> For entity GALLERY DB_PATH expression
     * "paintingArray.toArtist.ARTIST_NAME" will point to DbAttribute "ARTIST_NAME". </li>
     * </ul>
     */
    public static final int DB_PATH = 27;

    /**
     * Interpreted as a comma-separated list of literals.
     */
    public static final int LIST = 28;

    public static final int NOT_BETWEEN = 35;
    public static final int NOT_IN = 36;
    public static final int NOT_LIKE = 37;
    public static final int NOT_LIKE_IGNORE_CASE = 38;

    protected int type;

    /**
     * Parses string, converting it to Expression. If string does not represent a
     * semantically correct expression, an ExpressionException is thrown.
     * 
     * @since 1.1
     */
    // TODO: cache expression strings, since this operation is pretty slow
    public static Expression fromString(String expressionString) {
        if (expressionString == null) {
            throw new NullPointerException("Null expression string.");
        }

        Reader reader = new StringReader(expressionString);
        try {
            return new ExpressionParser(reader).expression();
        }
        catch (ParseException ex) {
            throw new ExpressionException(ex.getMessage(), ex);
        }
        catch (Throwable th) {
            // another common error is TokenManagerError
            throw new ExpressionException(th.getMessage(), th);
        }
    }

    /**
     * Returns a map of path aliases for this expression. It returns a non-empty map only
     * if this is a path expression and the aliases are known at the expression creation
     * time. Otherwise an empty map is returned.
     * 
     * @since 3.0
     */
    public abstract Map<String, String> getPathAliases();

    /**
     * Returns String label for this expression. Used for debugging.
     */
    public String expName() {
        switch (type) {
            case AND:
                return "AND";
            case OR:
                return "OR";
            case NOT:
                return "NOT";
            case EQUAL_TO:
                return "=";
            case NOT_EQUAL_TO:
                return "<>";
            case LESS_THAN:
                return "<";
            case LESS_THAN_EQUAL_TO:
                return "<=";
            case GREATER_THAN:
                return ">";
            case GREATER_THAN_EQUAL_TO:
                return ">=";
            case BETWEEN:
                return "BETWEEN";
            case IN:
                return "IN";
            case LIKE:
                return "LIKE";
            case LIKE_IGNORE_CASE:
                return "LIKE_IGNORE_CASE";
            case OBJ_PATH:
                return "OBJ_PATH";
            case DB_PATH:
                return "DB_PATH";
            case LIST:
                return "LIST";
            case NOT_BETWEEN:
                return "NOT BETWEEN";
            case NOT_IN:
                return "NOT IN";
            case NOT_LIKE:
                return "NOT LIKE";
            case NOT_LIKE_IGNORE_CASE:
                return "NOT LIKE IGNORE CASE";
            default:
                return "other";
        }
    }

    @Override
    public boolean equals(Object object) {
        if (!(object instanceof Expression)) {
            return false;
        }

        Expression e = (Expression) object;

        if (e.getType() != getType() || e.getOperandCount() != getOperandCount()) {
            return false;
        }

        // compare operands
        int len = e.getOperandCount();
        for (int i = 0; i < len; i++) {
            if (!Util.nullSafeEquals(e.getOperand(i), getOperand(i))) {
                return false;
            }
        }

        return true;
    }

    /**
     * Returns a type of expression. Most common types are defined as public static fields
     * of this interface.
     */
    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    /**
     * A shortcut for <code>expWithParams(params, true)</code>.
     */
    public Expression expWithParameters(Map<String, ?> parameters) {
        return expWithParameters(parameters, true);
    }

    /**
     * Creates and returns a new Expression instance using this expression as a prototype.
     * All ExpressionParam operands are substituted with the values in the
     * <code>params</code> map.
     * <p>
     * <i>Null values in the <code>params</code> map should be explicitly created in the
     * map for the corresponding key. </i>
     * </p>
     * 
     * @param parameters a map of parameters, with each key being a string name of an
     *            expression parameter, and value being the value that should be used in
     *            the final expression.
     * @param pruneMissing If <code>true</code>, subexpressions that rely on missing
     *            parameters will be pruned from the resulting tree. If <code>false</code>,
     *            any missing values will generate an exception.
     * @return Expression resulting from the substitution of parameters with real values,
     *         or null if the whole expression was pruned, due to the missing parameters.
     */
    public Expression expWithParameters(
            final Map<String, ?> parameters,
            final boolean pruneMissing) {

        // create transformer for named parameters
        Transformer transformer = new Transformer() {

            public Object transform(Object object) {
                if (!(object instanceof ExpressionParameter)) {
                    return object;
                }

                String name = ((ExpressionParameter) object).getName();
                if (!parameters.containsKey(name)) {
                    if (pruneMissing) {
                        return PRUNED_NODE;
                    }
                    else {
                        throw new ExpressionException("Missing required parameter: $"
                                + name);
                    }
                }
                else {
                    Object value = parameters.get(name);

                    // wrap lists (for now); also support null parameters
                    // TODO: andrus 8/14/2007 - shouldn't we also wrap non-null object
                    // values in ASTScalars?
                    return (value != null)
                            ? ExpressionFactory.wrapPathOperand(value)
                            : new ASTScalar(null);
                }
            }
        };

        return transform(transformer);
    }

    /**
     * Creates a new expression that joins this object with another expression, using
     * specified join type. It is very useful for incrementally building chained
     * expressions, like long AND or OR statements.
     */
    public Expression joinExp(int type, Expression exp) {
        Expression join = ExpressionFactory.expressionOfType(type);
        join.setOperand(0, this);
        join.setOperand(1, exp);
        join.flattenTree();
        return join;
    }

    /**
     * Chains this expression with another expression using "and".
     */
    public Expression andExp(Expression exp) {
        return joinExp(Expression.AND, exp);
    }

    /**
     * Chains this expression with another expression using "or".
     */
    public Expression orExp(Expression exp) {
        return joinExp(Expression.OR, exp);
    }

    /**
     * Returns a logical NOT of current expression.
     * 
     * @since 1.0.6
     */
    public abstract Expression notExp();

    /**
     * Returns a count of operands of this expression. In real life there are unary (count ==
     * 1), binary (count == 2) and ternary (count == 3) expressions.
     */
    public abstract int getOperandCount();

    /**
     * Returns a value of operand at <code>index</code>. Operand indexing starts at 0.
     */
    public abstract Object getOperand(int index);

    /**
     * Sets a value of operand at <code>index</code>. Operand indexing starts at 0.
     */
    public abstract void setOperand(int index, Object value);

    /**
     * Calculates expression value with object as a context for path expressions.
     * 
     * @since 1.1
     */
    public abstract Object evaluate(Object o);

    /**
     * Calculates expression boolean value with object as a context for path expressions.
     * 
     * @since 1.1
     */
    public boolean match(Object o) {
        return ConversionUtil.toBoolean(evaluate(o));
    }

    /**
     * Returns a list of objects that match the expression.
     */
    public <T> List<T> filterObjects(List<T> objects) {
        if (objects == null || objects.size() == 0) {
            return Collections.EMPTY_LIST;
        }

        return (List<T>) filter(objects, new LinkedList<T>());
    }

    /**
     * Adds objects matching this expression from the source collection to the target
     * collection.
     * 
     * @since 1.1
     */
    public <T> Collection<?> filter(Collection<T> source, Collection<T> target) {
        for (T o : source) {
            if (match(o)) {
                target.add(o);
            }
        }

        return target;
    }

    /**
     * Clones this expression.
     * 
     * @since 1.1
     */
    public Expression deepCopy() {
        return transform(null);
    }

    /**
     * Creates a copy of this expression node, without copying children.
     * 
     * @since 1.1
     */
    public abstract Expression shallowCopy();

    /**
     * Returns true if this node should be pruned from expression tree in the event a
     * child is removed.
     * 
     * @since 1.1
     */
    protected abstract boolean pruneNodeForPrunedChild(Object prunedChild);

    /**
     * Restructures expression to make sure that there are no children of the same type as
     * this expression.
     * 
     * @since 1.1
     */
    protected abstract void flattenTree();

    /**
     * Traverses itself and child expressions, notifying visitor via callback methods as
     * it goes. This is an Expression-specific implementation of the "Visitor" design
     * pattern.
     * 
     * @since 1.1
     */
    public void traverse(TraversalHandler visitor) {
        if (visitor == null) {
            throw new NullPointerException("Null Visitor.");
        }

        traverse(null, visitor);
    }

    /**
     * Traverses itself and child expressions, notifying visitor via callback methods as
     * it goes.
     * 
     * @since 1.1
     */
    protected void traverse(Expression parentExp, TraversalHandler visitor) {

        visitor.startNode(this, parentExp);

        // recursively traverse each child
        int count = getOperandCount();
        for (int i = 0; i < count; i++) {
            Object child = getOperand(i);

            if (child instanceof Expression) {
                Expression childExp = (Expression) child;
                childExp.traverse(this, visitor);
            }
            else {
                visitor.objectNode(child, this);
            }

            visitor.finishedChild(this, i, i < count - 1);
        }

        visitor.endNode(this, parentExp);
    }

    /**
     * Creates a transformed copy of this expression, applying transformation provided by
     * Transformer to all its nodes. Null transformer will result in an identical deep
     * copy of this expression.
     * <p>
     * To force a node and its children to be pruned from the copy, Transformer should
     * return Expression.PRUNED_NODE. Otherwise an expectation is that if a node is an
     * Expression it must be transformed to null or another Expression. Any other object
     * type would result in a ExpressionException.
     * 
     * @since 1.1
     */
    public Expression transform(Transformer transformer) {
        Object transformed = transformExpression(transformer);

        if (transformed == PRUNED_NODE || transformed == null) {
            return null;
        }
        else if (transformed instanceof Expression) {
            return (Expression) transformed;
        }

        throw new ExpressionException("Invalid transformed expression: " + transformed);
    }

    /**
     * A recursive method called from "transform" to do the actual transformation.
     * 
     * @return null, Expression.PRUNED_NODE or transformed expression.
     * @since 1.2
     */
    protected Object transformExpression(Transformer transformer) {
        Expression copy = shallowCopy();
        int count = getOperandCount();
        for (int i = 0, j = 0; i < count; i++) {
            Object operand = getOperand(i);
            Object transformedChild;

            if (operand instanceof Expression) {
                transformedChild = ((Expression) operand)
                        .transformExpression(transformer);
            }
            else if (transformer != null) {
                transformedChild = transformer.transform(operand);
            }
            else {
                transformedChild = operand;
            }

            // prune null children only if there is a transformer and it indicated so
            boolean prune = transformer != null && transformedChild == PRUNED_NODE;

            if (!prune) {
                copy.setOperand(j, transformedChild);
                j++;
            }

            if (prune && pruneNodeForPrunedChild(operand)) {
                // bail out early...
                return PRUNED_NODE;
            }
        }

        // all the children are processed, only now transform this copy
        return (transformer != null) ? (Expression) transformer.transform(copy) : copy;
    }

    /**
     * Encodes itself, wrapping the string into XML CDATA section.
     * 
     * @since 1.1
     */
    public void encodeAsXML(XMLEncoder encoder) {
        encoder.print("<![CDATA[");
        encodeAsString(encoder.getPrintWriter());
        encoder.print("]]>");
    }

    /**
     * Stores a String representation of Expression using a provided PrintWriter.
     * 
     * @since 1.1
     */
    public abstract void encodeAsString(PrintWriter pw);

    /**
     * Stores a String representation of Expression as EJBQL using a provided PrintWriter.
     * DB path expressions produce non-standard EJBQL path expressions.
     * 
     * @since 3.0
     */
    public abstract void encodeAsEJBQL(PrintWriter pw, String rootId);

    @Override
    public String toString() {
        StringWriter buffer = new StringWriter();
        PrintWriter pw = new PrintWriter(buffer);
        encodeAsString(pw);
        pw.close();
        buffer.flush();
        return buffer.toString();
    }

    public String toEJBQL(String rootId) {
        StringWriter buffer = new StringWriter();
        PrintWriter pw = new PrintWriter(buffer);
        encodeAsEJBQL(pw, rootId);
        pw.close();
        buffer.flush();
        return buffer.toString();
    }
}
