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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2023 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.expr.instruct;

import net.sf.saxon.expr.Expression;
import net.sf.saxon.expr.Operand;
import net.sf.saxon.expr.TailCallLoop;
import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.expr.elab.*;
import net.sf.saxon.expr.parser.ExpressionTool;
import net.sf.saxon.expr.parser.RebindingMap;
import net.sf.saxon.om.StandardNames;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.EmptyIterator;

import java.util.Collections;

/**
 * A compiled xsl:break instruction. The effect of executing this instruction is to register with the
 * dynamic context that a tail call on a pseudo-function break() has been made; the enclosing xsl:iterate
 * loop detects this tail call request and uses it as a signal to terminate execution of the loop.
 */
public class BreakInstr extends Instruction implements TailCallLoop.TailCallInfo {

    /**
     * Create the instruction
     */
    public BreakInstr() {
    }

    @Override
    public Iterable operands() {
        return Collections.emptyList();
    }

    /*@NotNull*/
    @Override
    public Expression copy(RebindingMap rebindings) {
        BreakInstr b2 = new BreakInstr();
        ExpressionTool.copyLocationInfo(this, b2);
        return b2;
    }


    @Override
    public boolean mayCreateNewNodes() {
        // this is a fiction, but it prevents the instruction being moved to a global variable,
        // which would be pointless and possibly harmful
        return true;
    }

    /**
     * Ask whether the expression can be lifted out of a loop, assuming it has no dependencies
     * on the controlling variable/focus of the loop
     * @param forStreaming true if we are optimizing for streamed evaluation
     * @return for a {@code BreakInstr}, always false
     */

    @Override
    public boolean isLiftable(boolean forStreaming) {
        return false;
    }

    /**
     * Get the namecode of the instruction for use in diagnostics
     *
     * @return a code identifying the instruction: typically but not always
     * the fingerprint of a name in the XSLT namespace
     */
    @Override
    public int getInstructionNameCode() {
        return StandardNames.XSL_BREAK;
    }

    public void markContext(XPathContext context) {
        context.getMajorContext().requestTailCall(this, null);
    }

    @Override
    public String getExpressionName() {
        return "xsl:break";
    }

    @Override
    public void export(ExpressionPresenter out) throws XPathException {
        out.startElement("break", this);
        out.endElement();
    }

    @Override
    public Elaborator getElaborator() {
        return new BreakElaborator();
    }

    public static class BreakElaborator extends PushElaborator {
        @Override
        public PushEvaluator elaborateForPush() {
            BreakInstr expr = (BreakInstr)getExpression();
            return (output, context) -> {
                expr.markContext(context);
                return null;
            };
        }

        public ItemEvaluator elaborateForItem() {
            BreakInstr expr = (BreakInstr) getExpression();
            return (context) -> {
                expr.markContext(context);
                return null;
            };
        }

        public PullEvaluator elaborateForPull() {
            BreakInstr expr = (BreakInstr) getExpression();
            return (context) -> {
                expr.markContext(context);
                return EmptyIterator.getInstance();
            };
        }
    }

}