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package oracle.toplink.essentials.internal.expressions;

import java.io.*;
import java.util.*;
import oracle.toplink.essentials.queryframework.*;
import oracle.toplink.essentials.expressions.*;
import oracle.toplink.essentials.internal.helper.*;
import oracle.toplink.essentials.internal.sessions.AbstractRecord;
import oracle.toplink.essentials.internal.sessions.AbstractSession;

/**
 * Used for wrapping constant values.
 */
public class ConstantExpression extends Expression {
    protected Object value;
    protected Expression localBase;

    public ConstantExpression() {
        super();
    }

    public ConstantExpression(Object newValue, Expression baseExpression) {
        super();
        value = newValue;
        localBase = baseExpression;
    }

    /**
     * INTERNAL:
     * Used for debug printing.
     */
    public String descriptionOfNodeType() {
        return "Constant";
    }

    /**
     * Return the expression builder which is the ultimate base of this expression, or
     * null if there isn't one (shouldn't happen if we start from a root)
     */
    public ExpressionBuilder getBuilder() {
        return getLocalBase().getBuilder();
    }

    protected Expression getLocalBase() {
        return localBase;
    }

    public Object getValue() {
        return value;
    }

    public boolean isConstantExpression() {
        return true;
    }

    /**
     * INTERNAL:
     */
    public boolean isValueExpression() {
        return true;
    }

    /**
     * INTERNAL:
     * Used for cloning.
     */
    protected void postCopyIn(Dictionary alreadyDone) {
        super.postCopyIn(alreadyDone);
        localBase = localBase.copiedVersionFrom(alreadyDone);
    }

    /**
     * INTERNAL:
     * Print SQL onto the stream, using the ExpressionPrinter for context
     */
    public void printSQL(ExpressionSQLPrinter printer) {
        Object value = getLocalBase().getFieldValue(getValue());
        if(value == null) {
            printer.printNull(this);
        } else {
            printer.printPrimitive(value);
        }
    }

    /**
     * INTERNAL:
     * Print SQL, this is called from functions, so must not be converted through the mapping.
     */
    public void printSQLWithoutConversion(ExpressionSQLPrinter printer) {
        printer.printPrimitive(getValue());
    }

    /**
     * INTERNAL:
     * Print java for project class generation
     */
    public void printJava(ExpressionJavaPrinter printer) {
        printer.printJava(getValue());
    }

    /**
     * INTERNAL:
     * This expression is built on a different base than the one we want. Rebuild it and
     * return the root of the new tree
     */
    public Expression rebuildOn(Expression newBase) {
        Expression result = (ConstantExpression)clone();
        result.setLocalBase(getLocalBase().rebuildOn(newBase));
        return result;
    }

    public void setLocalBase(Expression e) {
        localBase = e;
    }

    /**
     * INTERNAL:
     * Rebuild myself against the base, with the values of parameters supplied by the context
     * expression. This is used for transforming a standalone expression (e.g. the join criteria of a mapping)
     * into part of some larger expression. You normally would not call this directly, instead calling twist
     * See the comment there for more details"
     */
    public Expression twistedForBaseAndContext(Expression newBase, Expression context) {
        return (Expression)this.clone();
    }

    /**
     * INTERNAL:
     * Return the value for in memory comparison.
     * This is only valid for valueable expressions.
     */
    public Object valueFromObject(Object object, AbstractSession session, AbstractRecord translationRow, InMemoryQueryIndirectionPolicy valueHolderPolicy, boolean isObjectUnregistered) {
        return getLocalBase().getFieldValue(getValue());
    }

    /**
     * INTERNAL:
     * Used to print a debug form of the expression tree.
     */
    public void writeDescriptionOn(BufferedWriter writer) throws IOException {
        writer.write(String.valueOf(getValue()));
    }

    /**
     * INTERNAL:
     * Append the constant value into the printer
     */
    public void writeFields(ExpressionSQLPrinter printer, Vector newFields, SQLSelectStatement statement) {
        //print ", " before each selected field except the first one
        if (printer.isFirstElementPrinted()) {
            printer.printString(", ");
        } else {
            printer.setIsFirstElementPrinted(true);
        }

        // This field is a constant value, so any name can be used.
        newFields.addElement(new DatabaseField("*"));
        printSQL(printer);
    }
}