const deepMap = (input, handler = v => v, path = ['$'], seen = new Set([input])) => {
  if (Array.isArray(input)) {
    const result = []
    for (let i = 0; i < input.length; i++) {
      const element = input[i]
      const elementPath = [...path, i]
      if (element instanceof Object) {
        if (!seen.has(element)) { // avoid getting stuck in circular reference
          seen.add(element)
          result.push(deepMap(handler(element, elementPath), handler, elementPath, seen))
        }
      } else {
        result.push(handler(element, elementPath))
      }
    }
    return result
  }

  if (input === null) {
    return null
  } else if (typeof input === 'object' || typeof input === 'function') {
    const result = {}

    if (input instanceof Error) {
      // `name` property is not included in `Object.getOwnPropertyNames(error)`
      result.errorType = input.name
    }

    for (const propertyName of Object.getOwnPropertyNames(input)) {
    // skip logging internal properties
      if (propertyName.startsWith('_')) {
        continue
      }

      try {
        const property = input[propertyName]
        const propertyPath = [...path, propertyName]
        if (property instanceof Object) {
          if (!seen.has(property)) { // avoid getting stuck in circular reference
            seen.add(property)
            result[propertyName] = deepMap(
              handler(property, propertyPath), handler, propertyPath, seen
            )
          }
        } else {
          result[propertyName] = handler(property, propertyPath)
        }
      } catch (err) {
      // a getter may throw an error
        result[propertyName] = `[error getting value: ${err.message}]`
      }
    }
    return result
  }

  return handler(input, path)
}

module.exports = { deepMap }