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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2015 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.ma.arrays;

import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.lib.ExtensionFunctionCall;
import net.sf.saxon.lib.ExtensionFunctionDefinition;
import net.sf.saxon.lib.NamespaceConstant;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.om.StructuredQName;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.IntegerValue;
import net.sf.saxon.value.SequenceType;

import java.util.ArrayList;
import java.util.List;

/**
 * Implementation of the extension function array:subarray(array, xs:integer, xs:integer) => array
 */
public class ArraySubarray extends ExtensionFunctionDefinition {

    private final static StructuredQName name = new StructuredQName("array", NamespaceConstant.ARRAY_FUNCTIONS, "subarray");
    private final static SequenceType[] ARG_TYPES = new SequenceType[]{
            ArrayItem.SINGLE_ARRAY_TYPE, SequenceType.SINGLE_INTEGER, SequenceType.SINGLE_INTEGER};

    /**
     * Get the name of the function, as a QName.
     * This method must be implemented in all subclasses
     *
     * @return the function name
     */
    @Override
    public StructuredQName getFunctionQName() {
        return name;
    }

    /**
     * Get the minimum number of arguments required by the function
     *
     * @return the minimum number of arguments that must be supplied in a call to this function
     */

    public int getMinimumNumberOfArguments() {
        return 2;
    }

    /**
     * Get the maximum number of arguments allowed by the function.
     *
     * @return the maximum number of arguments that may be supplied in a call to this function
     */

    public int getMaximumNumberOfArguments() {
        return 3;
    }

    /**
     * Get the required types for the arguments of this function.
     * This method must be implemented in all subtypes.
     *
     * @return the required types of the arguments, as defined by the function signature. Normally
     * this should be an array of size {@link #getMaximumNumberOfArguments()}; however for functions
     * that allow a variable number of arguments, the array can be smaller than this, with the last
     * entry in the array providing the required type for all the remaining arguments.
     */
    @Override
    public SequenceType[] getArgumentTypes() {
        return ARG_TYPES;
    }

    /**
     * Get the type of the result of the function
     * This method must be implemented in all subtypes.
     *
     * @param suppliedArgumentTypes the static types of the supplied arguments to the function.
     *                              This is provided so that a more precise result type can be returned in the common
     *                              case where the type of the result depends on the types of the arguments.
     * @return the return type of the function, as defined by its function signature
     */
    @Override
    public SequenceType getResultType(SequenceType[] suppliedArgumentTypes) {
        return ArrayItem.SINGLE_ARRAY_TYPE;
    }

    /**
     * Ask whether the result actually returned by the function can be trusted,
     * or whether it should be checked against the declared type.
     *
     * @return true if the function implementation warrants that the value it returns will
     *         be an instance of the declared result type. The default value is false, in which case
     *         the result will be checked at run-time to ensure that it conforms to the declared type.
     *         If the value true is returned, but the function returns a value of the wrong type, the
     *         consequences are unpredictable.
     */

    public boolean trustResultType() {
        return true;
    }

    /**
     * Create a call on this function. This method is called by the compiler when it identifies
     * a function call that calls this function.
     *
     * @return an expression representing a call of this extension function
     */
    @Override
    public ExtensionFunctionCall makeCallExpression() {
        return new ExtensionFunctionCall() {
            public Sequence call(XPathContext context, Sequence[] arguments) throws XPathException {
                ArrayItem array = (ArrayItem) arguments[0].head();
                assert array != null;
                int start = (int) ((IntegerValue) arguments[1].head()).longValue();
                int length;
                if (arguments.length == 3) {
                    length = (int) ((IntegerValue) arguments[2].head()).longValue();
                }
                else {
                    length = array.size() - start + 1;
                }
                if (start < 1) {
                    throw new XPathException("Start position is less than one","FOAY0001");
                }
                if (start > array.size() + 1) {
                    throw new XPathException("Start position is out of bounds","FOAY0001");
                }
                if (length < 0) {
                    throw new XPathException("Specified length of subarray is less than zero","FOAY0002");
                }
                if (start + length > array.size() + 1) {
                    throw new XPathException("Specified length of subarray is too great for start position given","FOAY0001");
                }
                List list = new ArrayList(1);
                int i;
                for (i=0; i < length; i++) {
                    list.add(array.get(start - 1 + i));
                }
                return new SimpleArrayItem(list);
            }
        };
    }
}