import flat from 'flat'

import { DELIMITER } from './constants.js'
import { selectParams } from './select-params.js'
import { FlattenParams, GetOptions } from './flat.types.js'
import { propertyKeyRegex } from './property-key-regex.js'

const TEMP_HOLDING_KEY = 'TEMP_HOLDING_KEY'

/**
 * @load ./get.doc.md
 * @memberof module:flat
 * @param {FlattenParams}   params      flatten params from which property has to be taken
 * @param {string}          [propertyPath]  name of the property
 * @param {GetOptions}      options     options
 * @returns {any}                       when property key exists directly it returns what is inside,
 *                                      otherwise it tries to find any nested objects and returns
 *                                      them
 */
const get = (params: FlattenParams = {}, propertyPath?: string, options?: GetOptions): any => {
  if (!propertyPath) {
    return flat.unflatten(params)
  }

  // when object has this key - simply return it
  // we cannot rely on typeof params[propertyPath !== 'undefined' because params can actually be
  // undefined and in such case if would pass and function would return [undefined]
  if (Object.keys(params).find((key) => (key === propertyPath))) {
    return params[propertyPath]
  }

  const regex = propertyKeyRegex(propertyPath, options)
  const selectedParams = selectParams(params, propertyPath, options)

  const nestedProperties = Object.keys(selectedParams).reduce((memo, key, index) => {
    let newKey = key.replace(regex, `${TEMP_HOLDING_KEY}${DELIMITER}`)

    // when user wants to take allSiblings we have to fix the indexes so nested items from
    // different siblings don't overlap
    //
    // Example for key `nested.1.el`:
    //  'nested.0.el.0.value': 'val0.0',
    //  'nested.0.el.1.value': 'val0.1',
    //  'nested.1.el.0.value': 'val1',
    //  'nested.1.el.1.value': 'val2',
    //
    // has to be changed to:
    //  'TEMP_HOLDING_KEY.0.value': 'val0.0',
    //  'TEMP_HOLDING_KEY.1.value': 'val0.1',
    //  'TEMP_HOLDING_KEY.2.value': 'val1',
    //  'TEMP_HOLDING_KEY.3.value': 'val2',
    if (options?.includeAllSiblings) {
      newKey = newKey.replace(
        new RegExp(`${TEMP_HOLDING_KEY}\\${DELIMITER}(\\d*)`),
        `${TEMP_HOLDING_KEY}${DELIMITER}${index}`,
      )
    }

    memo[newKey] = selectedParams[key]

    return memo
  }, {} as FlattenParams)

  if (Object.keys(nestedProperties).length) {
    return (flat.unflatten(nestedProperties) as Record<string, unknown>)[TEMP_HOLDING_KEY]
  }
  return undefined
}

export { get }