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* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var setReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
var isFunction = require( '@stdlib/assert/is-function' );
var isCollection = require( '@stdlib/assert/is-collection' );
var isNonNegativeInteger = require( '@stdlib/assert/is-nonnegative-integer' ).isPrimitive;
var isInteger = require( '@stdlib/assert/is-integer' ).isPrimitive;
var isAccessorArray = require( '@stdlib/array/base/assert/is-accessor-array' );
var iteratorSymbol = require( '@stdlib/symbol/iterator' );
var accessorGetter = require( '@stdlib/array/base/accessor-getter' );
var getter = require( '@stdlib/array/base/getter' );
var dtype = require( '@stdlib/array/dtype' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* Returns an iterator which iterates over elements in an array-like object according to specified stride parameters.
*
* @param {NonNegativeInteger} N - number of values to iterate
* @param {Collection} src - input value
* @param {integer} stride - stride length
* @param {NonNegativeInteger} offset - starting index
* @param {Function} [mapFcn] - function to invoke for each iterated value
* @param {*} [thisArg] - execution context
* @throws {TypeError} first argument must be a nonnegative integer
* @throws {TypeError} second argument must be an array-like object
* @throws {TypeError} third argument must be an integer
* @throws {TypeError} fourth argument must be a nonnegative integer
* @throws {TypeError} fifth argument must be a function
* @returns {Iterator} iterator
*
* @example
* var values = [ 1, 2, 3, 4, 5, 6, 7, 8 ];
*
* var N = 4;
* var stride = -2;
* var offset = 6;
*
* var iter = stridedarray2iterator( N, values, stride, offset );
*
* var v = iter.next().value;
* // returns 7
*
* v = iter.next().value;
* // returns 5
*
* v = iter.next().value;
* // returns 3
*
* // ...
*/
function stridedarray2iterator( N, src, stride, offset ) {
var thisArg;
var iter;
var FLG;
var fcn;
var idx;
var get;
var dt;
var i;
if ( !isNonNegativeInteger( N ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a nonnegative integer. Value: `%s`.', N ) );
}
if ( !isCollection( src ) ) {
throw new TypeError( format( 'invalid argument. Second argument must be an array-like object. Value: `%s`.', src ) );
}
if ( !isInteger( stride ) ) {
throw new TypeError( format( 'invalid argument. Third argument must be an integer. Value: `%s`.', stride ) );
}
if ( !isNonNegativeInteger( offset ) ) {
throw new TypeError( format( 'invalid argument. Fourth argument must be a nonnegative integer. Value: `%s`.', offset ) );
}
if ( arguments.length > 4 ) {
fcn = arguments[ 4 ];
if ( !isFunction( fcn ) ) {
throw new TypeError( format( 'invalid argument. Fifth argument must be a function. Value: `%s`.', fcn ) );
}
thisArg = arguments[ 5 ];
}
idx = offset;
i = -1;
// Create an iterator protocol-compliant object:
iter = {};
if ( fcn ) {
setReadOnly( iter, 'next', next1 );
} else {
setReadOnly( iter, 'next', next2 );
}
setReadOnly( iter, 'return', end );
// If an environment supports `Symbol.iterator`, make the iterator iterable:
if ( iteratorSymbol ) {
setReadOnly( iter, iteratorSymbol, factory );
}
// Resolve an accessor for retrieving array elements (e.g., to accommodate `Complex64Array`, etc):
dt = dtype( src );
if ( isAccessorArray( src ) ) {
get = accessorGetter( dt );
} else {
get = getter( dt );
}
return iter;
/**
* Returns an iterator protocol-compliant object containing the next iterated value.
*
* @private
* @returns {Object} iterator protocol-compliant object
*/
function next1() {
var v;
i += 1;
if ( FLG || i >= N ) {
return {
'done': true
};
}
v = fcn.call( thisArg, get( src, idx ), idx, i, src );
idx += stride;
return {
'value': v,
'done': false
};
}
/**
* Returns an iterator protocol-compliant object containing the next iterated value.
*
* @private
* @returns {Object} iterator protocol-compliant object
*/
function next2() {
var v;
i += 1;
if ( FLG || i >= N ) {
return {
'done': true
};
}
v = get( src, idx );
idx += stride;
return {
'value': v,
'done': false
};
}
/**
* Finishes an iterator.
*
* @private
* @param {*} [value] - value to return
* @returns {Object} iterator protocol-compliant object
*/
function end( value ) {
FLG = true;
if ( arguments.length ) {
return {
'value': value,
'done': true
};
}
return {
'done': true
};
}
/**
* Returns a new iterator.
*
* @private
* @returns {Iterator} iterator
*/
function factory() {
if ( fcn ) {
return stridedarray2iterator( N, src, stride, offset, fcn, thisArg ); // eslint-disable-line max-len
}
return stridedarray2iterator( N, src, stride, offset );
}
}
// EXPORTS //
module.exports = stridedarray2iterator;
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