@stdlib/string/base/format-interpolate/lib/format_double.js

String manipulation functions.

/**
* @license Apache-2.0
*
* Copyright (c) 2022 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 isNumber = require( './is_number.js' );

// NOTE: for the following, we explicitly avoid using stdlib packages in this particular package in order to avoid circular dependencies.
var abs = Math.abs; // eslint-disable-line stdlib/no-builtin-math
var lowercase = String.prototype.toLowerCase;
var uppercase = String.prototype.toUpperCase;
var replace = String.prototype.replace;


// VARIABLES //

var RE_EXP_POS_DIGITS = /e\+(\d)$/;
var RE_EXP_NEG_DIGITS = /e-(\d)$/;
var RE_ONLY_DIGITS = /^(\d+)$/;
var RE_DIGITS_BEFORE_EXP = /^(\d+)e/;
var RE_TRAILING_PERIOD_ZERO = /\.0$/;
var RE_PERIOD_ZERO_EXP = /\.0*e/;
var RE_ZERO_BEFORE_EXP = /(\..*[^0])0*e/;


// MAIN //

/**
* Formats a token object argument as a floating-point number.
*
* @private
* @param {Object} token - token object
* @throws {Error} must provide a valid floating-point number
* @returns {string} formatted token argument
*/
function formatDouble( token ) {
	var digits;
	var out;
	var f = parseFloat( token.arg );
	if ( !isFinite( f ) ) { // NOTE: We use the global `isFinite` function here instead of `@stdlib/math/base/assert/is-finite` in order to avoid circular dependencies.
		if ( !isNumber( token.arg ) ) {
			throw new Error( 'invalid floating-point number. Value: ' + out );
		}
		// Case: NaN, Infinity, or -Infinity
		f = token.arg;
	}
	switch ( token.specifier ) {
	case 'e':
	case 'E':
		out = f.toExponential( token.precision );
		break;
	case 'f':
	case 'F':
		out = f.toFixed( token.precision );
		break;
	case 'g':
	case 'G':
		if ( abs( f ) < 0.0001 ) {
			digits = token.precision;
			if ( digits > 0 ) {
				digits -= 1;
			}
			out = f.toExponential( digits );
		} else {
			out = f.toPrecision( token.precision );
		}
		if ( !token.alternate ) {
			out = replace.call( out, RE_ZERO_BEFORE_EXP, '$1e' );
			out = replace.call( out, RE_PERIOD_ZERO_EXP, 'e' );
			out = replace.call( out, RE_TRAILING_PERIOD_ZERO, '' );
		}
		break;
	default:
		throw new Error( 'invalid double notation. Value: ' + token.specifier );
	}
	out = replace.call( out, RE_EXP_POS_DIGITS, 'e+0$1' );
	out = replace.call( out, RE_EXP_NEG_DIGITS, 'e-0$1' );
	if ( token.alternate ) {
		out = replace.call( out, RE_ONLY_DIGITS, '$1.' );
		out = replace.call( out, RE_DIGITS_BEFORE_EXP, '$1.e' );
	}
	if ( f >= 0 && token.sign ) {
		out = token.sign + out;
	}
	out = ( token.specifier === uppercase.call( token.specifier ) ) ?
		uppercase.call( out ) :
		lowercase.call( out );
	return out;
}


// EXPORTS //

module.exports = formatDouble;