package polyglot.visit;

import polyglot.ast.Node;
import polyglot.util.*;
import java.util.*;

/**
 * A HaltingVisitor is used to prune the traversal of the AST at a
 * particular node.  Clients can call <code>bypass(Node n) </code> to 
 * have the visitor skip n and its children when recursing through the AST.
 */
public abstract class HaltingVisitor extends NodeVisitor implements Copy
{
    Node bypassParent;
    Collection bypass;

    public HaltingVisitor bypassChildren(Node n) {
        HaltingVisitor v = (HaltingVisitor) copy();
        v.bypassParent = n;
        return v;
    }

    public HaltingVisitor visitChildren() {
        HaltingVisitor v = (HaltingVisitor) copy();
        v.bypassParent = null;
        v.bypass = null;
        return v;
    }

    public HaltingVisitor bypass(Node n) {
        if (n == null) return this;

        HaltingVisitor v = (HaltingVisitor) copy();

        // FIXME: Using a collection is expensive, but is hopefully not
        // often used.
        if (this.bypass == null) {
            v.bypass = Collections.singleton(n);
        }
        else {
            v.bypass = new ArrayList(this.bypass.size()+1);
            v.bypass.addAll(bypass);
            v.bypass.add(n);
        }

        return v;
    }

    public HaltingVisitor bypass(Collection c) {
        if (c == null) return this;

        HaltingVisitor v = (HaltingVisitor) copy();

        // FIXME: Using a collection is expensive, but is hopefully not
        // often used.
        if (this.bypass == null) {
            v.bypass = new ArrayList(c);
        }
        else {
            v.bypass = new ArrayList(this.bypass.size()+c.size());
            v.bypass.addAll(bypass);
            v.bypass.addAll(c);
        }

        return v;
    }

    public final Node override(Node parent, Node n) {
        if (bypassParent != null && bypassParent == parent) {
            // System.out.println("bypassing " + n +
            //                    " (child of " + parent + ")");
            return n;
        }

        if (bypass != null) {
            for (Iterator i = bypass.iterator(); i.hasNext(); ) {
                if (i.next() == n) {
                    // System.out.println("bypassing " + n);
                    return n;
                }
            }
        }

        return null;
    }

    public Object copy() {
        try {
            HaltingVisitor v = (HaltingVisitor) super.clone();
            // v.bypassParent = null;
            // v.bypass = null;
            return v;
        }
        catch (CloneNotSupportedException e) {
            throw new InternalCompilerError("Java clone() weirdness.");
        }
    }
}