magic.js

import { isObj, isArr, isDef } from './is.js'

const results = {
  obj: 'Object.create(null)',
  arr: 'Array(max)',
}

const accumulators = {
  obj: 'collection[keys[++i]]',
  arr: 'collection[++key]',
}

const iterator = {
  obj: '++i < max',
  arr: '++key < max',
}

const preparations = {
  obj: 'key = keys[i]',
  arr: '',
}

const declarations = {
  obj: [
    'var keys = Object.keys(collection)',
    'var max = keys.length',
    'var i = -1, key\n',
  ].join(';'),
  arr: [
    'var max = collection.length',
    'var key = -1',
  ].join(';')
}

export default (type, op, opts) => {
  if (isObj(op)) {
    opts = op
    if (opts.acc) {
      op = 'accumulator'
    } else if (op.result) {
      op = 'result'
    }
  } else if (!opts) {
    opts = {}
  }

  const args = isArr(opts.args) ? opts.args : [ 'fn', 'collection' ]
  let declaration = declarations[type]
  let extraArgs = ''
  let returnValue = isDef(opts.nok) ? opts.nok : 'collection'
  let prep = preparations[type]
  let post = opts.post || ''
  let pre = opts.pre || ''

  switch (op) {
    case 'accumulator': {
      args.push('acc')
      extraArgs += 'acc, '
      declaration += `;acc || (acc = ${opts.acc || accumulators[type]})`
      pre || (pre = 'acc = ')
      returnValue = 'acc'
      break
    }
    case 'result': {
      declaration += `;var result = ${opts.result || results[type]}`
      pre || (pre = 'result[key] = ')
      returnValue = 'result'
      break
    }
    default: {
      const test = isDef(opts.test) ? opts.test : false
      if (Boolean(test)) {
        pre || (pre = test ? 'if (' : 'if (!')
        post || (post = `) return ${isDef(opts.ok) ? opts.ok : returnValue}`)
        break
      }
      pre || (pre = 'if (')
      post || (post = `=== ${test}) return ${isDef(opts.ok)
        ? opts.ok
        : returnValue}`)
      break
    }
  }

  return Function(args, [
    `${declaration};`,
    `while (${iterator[type]}) {`,
    `  ${preparations[type]}`,
    `  ${pre}fn(${extraArgs}collection[key], key, collection)${post}`,
    `} return ${returnValue}`,
  ].join('\n'))
}