query.js

const encodeReserveRE = /[!'()*]/g
const encodeReserveReplacer = c => '%' + c.charCodeAt(0).toString(16)
const commaRE = /%2C/g

// fixed encodeURIComponent which is more conformant to RFC3986:
// - escapes [!'()*]
// - preserve commas
const encode = str => encodeURIComponent(str)
  .replace(encodeReserveRE, encodeReserveReplacer)
  .replace(commaRE, ',')

const decode = decodeURIComponent

export function parseQuery (query) {
  const res = {}

  query = query.trim().replace(/^(\?|#|&)/, '')

  if (!query) {
    return res
  }

  query.split('&').forEach(param => {
    const parts = param.replace(/\+/g, ' ').split('=')
    const key = decode(parts.shift())
    const val = parts.length > 0
      ? decode(parts.join('='))
      : null

    if (res[key] === undefined) {
      res[key] = val
    } else if (Array.isArray(res[key])) {
      res[key].push(val)
    } else {
      res[key] = [res[key], val]
    }
  })

  return res
}

export function stringifyQuery (obj, encodeStr = encode) {
  const res = obj ? Object.keys(obj).map(key => {
    const val = obj[key]

    if (val === undefined) {
      return ''
    }

    if (val === null) {
      return encodeStr(key)
    }

    if (Array.isArray(val)) {
      const result = []
      val.forEach(val2 => {
        if (val2 === undefined) {
          return
        }
        if (val2 === null) {
          result.push(encodeStr(key))
        } else {
          result.push(encodeStr(key) + '=' + encodeStr(val2))
        }
      })
      return result.join('&')
    }

    return encodeStr(key) + '=' + encodeStr(val)
  }).filter(x => x.length > 0).join('&') : null
  return res ? `?${res}` : ''
}

export function decodedQuery (query = {}) {
  const decodedQuery = {}
  Object.keys(query).forEach(name => {
    try {
      decodedQuery[name] = decode(query[name])
    } catch (e) {
      decodedQuery[name] = query[name]
    }
  })
  return decodedQuery
}