MultiKeyMap

const MultiKeyMap = (() => {
  const symbols = {
    checkKeyLength: Symbol('checkKeyLength'),
    keyCount: Symbol('keyCount'),
    data: Symbol('data')
  }

  /**
   * @throws {NotEnoughKeys} When the list of keys given to a method is too short.
   * @throws {TooManyKeys} When the list of keys given to a method is too long.
   * @throws {KeyIsNotPresent} When no value was found in the get method.
   */
  class MultiKeyMap {
    /**
     * Constructs a new map with the given number of keys.
     * @param {number} n The number of keys.
     */
    constructor (n) {
      this[symbols.keyCount] = n
      this[symbols.data] = {}
    }

    [symbols.checkKeyLength] (n) {
      if (n < this[symbols.keyCount]) {
        throw Error(`Not enough keys. Expected ${this[symbols.keyCount]}, received ${n}.`)
      }

      if (n > this[symbols.keyCount]) {
        throw Error(`Too many keys. Expected ${this[symbols.keyCount]}, received ${n}.`)
      }
    }

    /**
     * Assigns the specified value to the given keys.
     * @param keys {string[]} An array of length n containing stringifiable items where n is the number of keys in the map.
     * @param value {*} The actual value.
     */
    set (keys, value) {
      keys = JSON.parse(JSON.stringify(keys))

      this[symbols.checkKeyLength](keys.length)

      let currentData = this[symbols.data]

      while (keys.length > 1) {
        const currentKey = keys.shift()

        if (!(currentKey in currentData)) {
          currentData[currentKey] = {}
        }

        currentData = currentData[currentKey]
      }

      const currentKey = keys.shift()
      currentData[currentKey] = value
    }

    /**
     * Checks whether the map contains any value assigned to the given keys.
     * @param keys {string[]} An array of length n containing stringifiable items where n is the number of keys in the map.
     *
     * @return {boolean} Whether an assigned value was found or not.
     */
    contains (keys) {
      keys = JSON.parse(JSON.stringify(keys))

      this[symbols.checkKeyLength](keys.length)

      let currentData = this[symbols.data]

      while (keys.length > 1) {
        const currentKey = keys.shift()

        if (!(currentKey in currentData)) {
          return false
        }

        currentData = currentData[currentKey]
      }

      const currentKey = keys.shift()
      return (currentKey in currentData)
    }

    /**
     * Gets the value stored behind the given keys.
     * @param keys {string[]} An array of length n containing stringifiable items where n is the number of keys in the map.
     *
     * @return {*} The requested value.
     */
    get (keys) {
      keys = JSON.parse(JSON.stringify(keys))

      const keyString = keys.join(' - ')

      this[symbols.checkKeyLength](keys.length)

      let currentData = this[symbols.data]

      while (keys.length > 1) {
        const currentKey = keys.shift()

        if (!(currentKey in currentData)) {
          throw Error(`Key is not present in map. (${keyString})`)
        }

        currentData = currentData[currentKey]
      }

      const currentKey = keys.shift()

      if (!(currentKey in currentData)) {
        throw Error(`Key is not present in map. (${keyString})`)
      }

      return currentData[currentKey]
    }

    /**
     * Returns a stringified JSON representation of the map.
     * @return {string} Stringified JSON representation of the map.
     */
    stringify () {
      return JSON.stringify(this[symbols.data], null, 2)
    }
  }

  return MultiKeyMap
})()