/**
* @license Apache-2.0
*
* Copyright (c) 2021 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';

// MAIN //

/**
* Applies a unary callback to elements in a one-dimensional input ndarray and assigns results to elements in an equivalently shaped output ndarray.
*
* @private
* @param {Object} x - object containing input ndarray meta data
* @param {string} x.dtype - data type
* @param {Collection} x.data - data buffer
* @param {NonNegativeIntegerArray} x.shape - dimensions
* @param {IntegerArray} x.strides - stride lengths
* @param {NonNegativeInteger} x.offset - index offset
* @param {string} x.order - specifies whether `x` is row-major (C-style) or column-major (Fortran-style)
* @param {Object} y - object containing output ndarray meta data
* @param {string} y.dtype - data type
* @param {Collection} y.data - data buffer
* @param {NonNegativeIntegerArray} y.shape - dimensions
* @param {IntegerArray} y.strides - stride lengths
* @param {NonNegativeInteger} y.offset - index offset
* @param {string} y.order - specifies whether `y` is row-major (C-style) or column-major (Fortran-style)
* @param {Callback} fcn - unary callback
* @returns {void}
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* function scale( x ) {
*     return x * 10.0;
* }
*
* // Create data buffers:
* var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
* var ybuf = new Float64Array( 4 );
*
* // Define the shape of the input and output arrays:
* var shape = [ 4 ];
*
* // Define the array strides:
* var sx = [ 2 ];
* var sy = [ 1 ];
*
* // Define the index offsets:
* var ox = 1;
* var oy = 0;
*
* // Create the input and output ndarray-like objects:
* var x = {
*     'dtype': 'float64',
*     'data': xbuf,
*     'shape': shape,
*     'strides': sx,
*     'offset': ox,
*     'order': 'row-major'
* };
* var y = {
*     'dtype': 'float64',
*     'data': ybuf,
*     'shape': shape,
*     'strides': sy,
*     'offset': oy,
*     'order': 'row-major'
* };
*
* // Apply the unary function:
* unary1d( x, y, scale );
*
* console.log( y.data );
* // => <Float64Array>[ 20.0, 40.0, 60.0, 80.0 ]
*/
function unary1d( x, y, fcn ) {
	var xbuf;
	var ybuf;
	var dx0;
	var dy0;
	var S0;
	var ix;
	var iy;
	var i0;

	// Note on variable naming convention: S#, dx#, dy#, i# where # corresponds to the loop number, with `0` being the innermost loop...

	// Extract loop variables: dimensions and loop offset (pointer) increments...
	S0 = x.shape[ 0 ];
	dx0 = x.strides[ 0 ];
	dy0 = y.strides[ 0 ];

	// Set the pointers to the first indexed elements in the respective ndarrays...
	ix = x.offset;
	iy = y.offset;

	// Cache references to the input and output ndarray buffers...
	xbuf = x.data;
	ybuf = y.data;

	// Iterate over the ndarray dimensions...
	for ( i0 = 0; i0 < S0; i0++ ) {
		ybuf[ iy ] = fcn( xbuf[ ix ] );
		ix += dx0;
		iy += dy0;
	}
}


// EXPORTS //

module.exports = unary1d;