mathjs/src/utils/optimizeCallback.js

import typed from 'typed-function'
import { get, arraySize } from './array.js'
import { typeOf as _typeOf } from './is.js'

/**
 * Simplifies a callback function by reducing its complexity and potentially improving its performance.
 *
 * @param {Function} callback The original callback function to simplify.
 * @param {Array|Matrix} array The array that will be used with the callback function.
 * @param {string} name The name of the function that is using the callback.
 * @param {boolean} [isUnary=false] If true, the callback function is unary and will be optimized as such.
 * @returns {Function} Returns a simplified version of the callback function.
 */
export function optimizeCallback (callback, array, name, isUnary = false) {
  if (typed.isTypedFunction(callback)) {
    let numberOfArguments
    if (isUnary) {
      numberOfArguments = 1
    } else {
      const firstIndex = (array.isMatrix ? array.size() : arraySize(array)).map(() => 0)
      const firstValue = array.isMatrix ? array.get(firstIndex) : get(array, firstIndex)
      numberOfArguments = _findNumberOfArgumentsTyped(callback, firstValue, firstIndex, array)
    }
    let fastCallback
    if (array.isMatrix && (array.dataType !== 'mixed' && array.dataType !== undefined)) {
      const singleSignature = _findSingleSignatureWithArity(callback, numberOfArguments)
      fastCallback = (singleSignature !== undefined) ? singleSignature : callback
    } else {
      fastCallback = callback
    }
    if (numberOfArguments >= 1 && numberOfArguments <= 3) {
      return {
        isUnary: numberOfArguments === 1,
        fn: (...args) => _tryFunctionWithArgs(fastCallback, args.slice(0, numberOfArguments), name, callback.name)
      }
    }
    return { isUnary: false, fn: (...args) => _tryFunctionWithArgs(fastCallback, args, name, callback.name) }
  }
  if (isUnary === undefined) {
    return { isUnary: _findIfCallbackIsUnary(callback), fn: callback }
  } else {
    return { isUnary, fn: callback }
  }
}

function _findSingleSignatureWithArity (callback, arity) {
  const matchingFunctions = []
  Object.entries(callback.signatures).forEach(([signature, func]) => {
    if (signature.split(',').length === arity) {
      matchingFunctions.push(func)
    }
  })
  if (matchingFunctions.length === 1) {
    return matchingFunctions[0]
  }
}

/**
 * Determines if a given callback function is unary (i.e., takes exactly one argument).
 *
 * This function checks the following conditions to determine if the callback is unary:
 * 1. The callback function should have exactly one parameter.
 * 2. The callback function should not use the `arguments` object.
 * 3. The callback function should not use rest parameters (`...`).
 * If in doubt, this function shall return `false` to be safe
 *
 * @param {Function} callback - The callback function to be checked.
 * @returns {boolean} - Returns `true` if the callback is unary, otherwise `false`.
 */
function _findIfCallbackIsUnary (callback) {
  if (callback.length !== 1) return false

  const callbackStr = callback.toString()
  // Check if the callback function uses `arguments`
  if (/arguments/.test(callbackStr)) return false

  // Extract the parameters of the callback function
  const paramsStr = callbackStr.match(/\(.*?\)/)
  // Check if the callback function uses rest parameters
  if (/\.\.\./.test(paramsStr)) return false
  return true
}

function _findNumberOfArgumentsTyped (callback, value, index, array) {
  const testArgs = [value, index, array]
  for (let i = 3; i > 0; i--) {
    const args = testArgs.slice(0, i)
    if (typed.resolve(callback, args) !== null) {
      return i
    }
  }
}

/**
   * @param {function} func The selected function taken from one of the signatures of the callback function
   * @param {Array} args List with arguments to apply to the selected signature
   * @param {string} mappingFnName the name of the function that is using the callback
   * @param {string} callbackName the name of the callback function
   * @returns {*} Returns the return value of the invoked signature
   * @throws {TypeError} Throws an error when no matching signature was found
   */
function _tryFunctionWithArgs (func, args, mappingFnName, callbackName) {
  try {
    return func(...args)
  } catch (err) {
    _createCallbackError(err, args, mappingFnName, callbackName)
  }
}

/**
 * Creates and throws a detailed TypeError when a callback function fails.
 *
 * @param {Error} err The original error thrown by the callback function.
 * @param {Array} args The arguments that were passed to the callback function.
 * @param {string} mappingFnName The name of the function that is using the callback.
 * @param {string} callbackName The name of the callback function.
 * @throws {TypeError} Throws a detailed TypeError with enriched error message.
 */
function _createCallbackError (err, args, mappingFnName, callbackName) {
  // Enrich the error message so the user understands that it took place inside the callback function
  if (err instanceof TypeError && err.data?.category === 'wrongType') {
    const argsDesc = []
    argsDesc.push(`value: ${_typeOf(args[0])}`)
    if (args.length >= 2) { argsDesc.push(`index: ${_typeOf(args[1])}`) }
    if (args.length >= 3) { argsDesc.push(`array: ${_typeOf(args[2])}`) }

    throw new TypeError(`Function ${mappingFnName} cannot apply callback arguments ` +
      `${callbackName}(${argsDesc.join(', ')}) at index ${JSON.stringify(args[1])}`)
  } else {
    throw new TypeError(`Function ${mappingFnName} cannot apply callback arguments ` +
      `to function ${callbackName}: ${err.message}`)
  }
}