/**
* @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 isPositiveInteger = require( '@stdlib/assert/is-positive-integer' ).isPrimitive;
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var PINF = require( '@stdlib/constants/float64/pinf' );
var NINF = require( '@stdlib/constants/float64/ninf' );
var Float64Array = require( '@stdlib/array/float64' );


// MAIN //

/**
* Returns an accumulator function which incrementally computes a moving range.
*
* @param {PositiveInteger} W - window size
* @throws {TypeError} must provide a positive integer
* @returns {Function} accumulator function
*
* @example
* var accumulator = incrmrange( 3 );
*
* var r = accumulator();
* // returns null
*
* r = accumulator( 2.0 );
* // returns 0.0
*
* r = accumulator( -5.0 );
* // returns 7.0
*
* r = accumulator( 3.0 );
* // returns 8.0
*
* r = accumulator( 5.0 );
* // returns 10.0
*
* r = accumulator();
* // returns 10.0
*/
function incrmrange( W ) {
	var buf;
	var min;
	var max;
	var N;
	var i;
	if ( !isPositiveInteger( W ) ) {
		throw new TypeError( 'invalid argument. Must provide a positive integer. Value: `' + W + '`.' );
	}
	buf = new Float64Array( W );
	min = PINF;
	max = NINF;
	i = -1;
	N = 0;

	return accumulator;

	/**
	* If provided a value, the accumulator function returns an updated range. If not provided a value, the accumulator function returns the current range.
	*
	* @private
	* @param {number} [x] - input value
	* @returns {(number|null)} range or null
	*/
	function accumulator( x ) {
		var v;
		var k;
		if ( arguments.length === 0 ) {
			if ( N === 0 ) {
				return null;
			}
			return max - min;
		}
		// Update the index for managing the circular buffer:
		i = (i+1) % W;

		if ( x === 0.0 ) {
			x = 0.0; // normalizes +-0
		}
		// Case: incoming value is NaN...
		if ( isnan( x ) ) {
			N = W; // explicitly set to avoid `N < W` branch
			min = x;
			max = x;
		}
		// Case: initial window...
		else if ( N < W ) {
			N += 1;
			if ( x < min ) {
				min = x;
			}
			if ( x > max ) {
				max = x;
			}
		}
		// Case: outgoing value is the current minimum or maximum and the new value is either greater than the minimum or less than the maximum, and, thus, we need to find a new accumulated values among the current buffer values...
		else if (
			( buf[ i ] === min && x > min ) ||
			( buf[ i ] === max && x < max ) ||
			isnan( buf[ i ] )
		) {
			min = x;
			max = x;
			for ( k = 0; k < W; k++ ) {
				if ( k !== i ) {
					v = buf[ k ];
					if ( isnan( v ) ) {
						min = v;
						max = v;
						break; // no need to continue searching
					}
					if ( v < min ) {
						min = v;
					}
					if ( v > max ) {
						max = v;
					}
				}
			}
		}
		// Case: incoming value is less than current minimum value...
		else if ( x < min ) {
			min = x;
		}
		// Case: incoming value is greater than current maximum value...
		else if ( x > max ) {
			max = x;
		}
		// Case: updating existing window; however, the minimum and maximum values do not change so nothing to do but update our buffer...
		buf[ i ] = x;

		return max - min;
	}
}


// EXPORTS //

module.exports = incrmrange;