'use strict'
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/**
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* Expose compositor.
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*/
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module.exports = compose
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/**
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* Compose `middleware` returning
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* a fully valid middleware comprised
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* of all those which are passed.
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*
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* @param {Array} middleware
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* @return {Function}
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* @api public
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*/
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function compose (middleware) {
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if (!Array.isArray(middleware)) throw new TypeError('Middleware stack must be an array!')
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for (const fn of middleware) {
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if (typeof fn !== 'function') throw new TypeError('Middleware must be composed of functions!')
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}
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/**
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* @param {Object} context
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* @return {Promise}
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* @api public
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*/
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return function (context, next) {
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// last called middleware #
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let index = -1
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return dispatch(0)
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function dispatch (i) {
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if (i <= index) return Promise.reject(new Error('next() called multiple times'))
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index = i
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let fn = middleware[i]
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if (i === middleware.length) fn = next
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if (!fn) return Promise.resolve()
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try {
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return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
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} catch (err) {
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return Promise.reject(err)
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}
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}
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}
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}
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