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var Promise = require('any-promise')
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var assert = require('assert')
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module.exports = thenify
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/**
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* Turn async functions into promises
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*
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* @param {Function} fn
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* @return {Function}
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* @api public
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*/
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function thenify(fn, options) {
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assert(typeof fn === 'function')
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return createWrapper(fn, options)
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}
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/**
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* Turn async functions into promises and backward compatible with callback
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*
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* @param {Function} fn
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* @return {Function}
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* @api public
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*/
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thenify.withCallback = function (fn, options) {
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assert(typeof fn === 'function')
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options = options || {}
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options.withCallback = true
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return createWrapper(fn, options)
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}
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function createCallback(resolve, reject, multiArgs) {
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// default to true
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if (multiArgs === undefined) multiArgs = true
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return function(err, value) {
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if (err) return reject(err)
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var length = arguments.length
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if (length <= 2 || !multiArgs) return resolve(value)
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if (Array.isArray(multiArgs)) {
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var values = {}
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for (var i = 1; i < length; i++) values[multiArgs[i - 1]] = arguments[i]
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return resolve(values)
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}
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var values = new Array(length - 1)
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for (var i = 1; i < length; ++i) values[i - 1] = arguments[i]
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resolve(values)
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}
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}
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function createWrapper(fn, options) {
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options = options || {}
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var name = fn.name;
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name = (name || '').replace(/\s|bound(?!$)/g, '')
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var newFn = function () {
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var self = this
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var len = arguments.length
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if (options.withCallback) {
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var lastType = typeof arguments[len - 1]
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if (lastType === 'function') return fn.apply(self, arguments)
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}
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var args = new Array(len + 1)
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for (var i = 0; i < len; ++i) args[i] = arguments[i]
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var lastIndex = i
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return new Promise(function (resolve, reject) {
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args[lastIndex] = createCallback(resolve, reject, options.multiArgs)
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fn.apply(self, args)
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})
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}
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Object.defineProperty(newFn, 'name', { value: name })
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return newFn
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}
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