import type {Upload} from './Upload.js'

const ASCII_SPACE = ' '.codePointAt(0)
const ASCII_COMMA = ','.codePointAt(0)
const BASE64_REGEX = /^[\d+/A-Za-z]*={0,2}$/

export function validateKey(key: string) {
  if (key.length === 0) {
    return false
  }

  for (let i = 0; i < key.length; ++i) {
    const charCodePoint = key.codePointAt(i) as number
    if (
      charCodePoint > 127 ||
      charCodePoint === ASCII_SPACE ||
      charCodePoint === ASCII_COMMA
    ) {
      return false
    }
  }

  return true
}

export function validateValue(value: string) {
  if (value.length % 4 !== 0) {
    return false
  }

  return BASE64_REGEX.test(value)
}

export function parse(str?: string) {
  const meta: Record<string, string | null> = {}

  if (!str || str.trim().length === 0) {
    throw new Error('Metadata string is not valid')
  }

  for (const pair of str.split(',')) {
    const tokens = pair.split(' ')
    const [key, value] = tokens
    if (
      ((tokens.length === 1 && validateKey(key)) ||
        (tokens.length === 2 && validateKey(key) && validateValue(value))) &&
      !(key in meta)
    ) {
      const decodedValue = value ? Buffer.from(value, 'base64').toString('utf8') : null
      meta[key] = decodedValue
    } else {
      throw new Error('Metadata string is not valid')
    }
  }

  return meta
}

export function stringify(metadata: NonNullable<Upload['metadata']>): string {
  return Object.entries(metadata)
    .map(([key, value]) => {
      if (value === null) {
        return key
      }

      const encodedValue = Buffer.from(value, 'utf8').toString('base64')
      return `${key} ${encodedValue}`
    })
    .join(',')
}