const display = (a, b, c, d, e, f, g, h) => [a, b, c, d, e, f, g, h]

/**
 * @description 函数柯里化（根据柯里化前的函数的参数数量决定柯里化后的函数需要执行多少次）
 * @description Function currying (based on the number of parameters of the function before currying, it determines how many times the curried function needs to be executed)
 * @param {Function} fn -柯里化的函数
 * @param {Function} fn - the function to be curried
 */

function curry(fn) {
  if (fn.length <= 1)
    return fn
  const generator = (...args) => {
    if (fn.length === args.length) {
      // 执行fn并且返回执行结果
      // Execute fn and return the result
      return fn(...args)
    }
    else {
      return (...args2) => {
        // 返回generator函数
        // Return the generator function
        return generator(...args, ...args2)
      }
    }
  }
  return generator
}

const curriedDisplay = curry(display)
console.log('curriedDisplay', curriedDisplay(1)(2)(3)(4)(5)(6)(7)(8))

// ES6简写
// ES6 shorthand
function curry2(fn) {
  if (fn.length <= 1)
    return fn
  const generator = (...args) => (args.length === fn.length ? fn(...args) : (...args2) => generator(...args, ...args2))
  return generator
}
const curriedDisplay2 = curry2(display)
console.log('curriedDisplay2', curriedDisplay2(1)(2)(3)(4)(5)(6)(7)(8))

/**
 * @description 函数柯里化（支持占位符版本）
 * @description Function currying (supports placeholder version)
 * @param {Function} fn -柯里化的函数
 * @param {Function} fn - the function to be curried
 * @param {string} [placeholder = "_"] -占位符
 * @param {string} [placeholder = "_"] - placeholder
 */

function curry3(fn, placeholder = '_') {
  curry3.placeholder = placeholder
  if (fn.length <= 1)
    return fn
  const argsList = []
  const generator = (...args) => {
    let currentPlaceholderIndex = -1 // 记录了非当前轮最近的一个占位符下标，防止当前轮元素覆盖了当前轮的占位符
    // Records the most recent placeholder index not from the current round to prevent the current round's element from overriding the current round's placeholder
    args.forEach((arg) => {
      const placeholderIndex = argsList.findIndex(item => item === curry3.placeholder)
      if (placeholderIndex < 0) { // 如果数组中没有占位符直接往数组末尾放入一个元素
        // If there is no placeholder in the array, directly add an element to the end of the array
        currentPlaceholderIndex = argsList.push(arg) - 1
        // 防止将元素填充到当前轮参数的占位符
        // Prevent filling the element into the placeholder of the current round parameters
        // (1,'_')('_',2) 数字2应该填充1后面的占位符，不能是2前面的占位符
        // (1,'_')('_',2) Number 2 should fill the placeholder after 1, not the one before 2
      }
      else if (placeholderIndex !== currentPlaceholderIndex) {
        argsList[placeholderIndex] = arg
      }
      else { // 当前元素是占位符的情况
        // In the case that the current element is a placeholder
        argsList.push(arg)
      }
    })
    const realArgsList = argsList.filter(arg => arg !== curry3.placeholder) // 过滤出不含占位符的数组
    // Filter out the array that does not contain placeholders
    if (realArgsList.length >= fn.length)
      return fn(...argsList)
    else
      return generator
  }

  return generator
}

const curriedDisplay3 = curry3(display)
console.log('curriedDisplay3', curriedDisplay3('_', 2)(1, '_', 4)(3, '_')('_', 5)(6)(7, 8))

/**
 * @example 函数组合 + 函数柯里化
 * @example Function composition + function currying
 */

const compose = function (...fns) {
  return function (initValue) {
    return fns.reduceRight((acc, cur) => {
      return cur(acc)
    }, initValue)
  }
}

const curriedJoin = curry3((separator, arr) => arr.join(separator))
const curriedMap = curry3((fn, arr) => arr.map(fn))
const curriedSplit = curry3((separator, str) => str.split(separator))

const composeFunc = compose(
  curriedJoin('1'),
  curriedMap(item => `${item}1`),
  curriedSplit(''),
)

console.log('compose + curry', composeFunc('helloworld'))

/**
 * @example  通过占位符将路径参数延迟到之后传入
 * @example  Delay path parameters via placeholders to be passed later
 */

if (!window) {
  const { readFile } = require('node:fs')
  const { join } = require('node:path')

  const callback = (err, data) => {
    err ? console.error(err) : console.log(data)
  }

  ['curry.js', 'curry.html'] // 将文件列表变成数组方便管理和维护
  // Turn the file list into an array for easier management and maintenance
    .map(file => join(__dirname, file)) // join 函数无法使用柯里化因为参数都是可选参数，length 为 0
  // The join function cannot be curried because all parameters are optional, length is 0
    .map(curry3(readFile)('_', 'utf-8', callback))
}
else {
  console.warn('请使用 nodejs 环境运行以下代码')
  console.warn('Please run the following code in a Node.js environment')
}