const DEFAULT_FILE_NAME = 'data'
const DEFAULT_MIME_TYPE = 'application/octet-stream'

const encoder = new TextEncoder()
const decoder = new TextDecoder()

const normalizeSuffix = (suffix) => {
  const value = String(suffix || '').trim()
  if (!value) throw new Error('INVALID_SUFFIX')
  return value.startsWith('.') ? value : `.${value}`
}

const sanitizeFileNamePart = (value) => {
  const cleaned = String(value || '')
    .replace(/[\\/:*?"<>|]/g, '_')
    .replace(/\s+/g, ' ')
    .trim()

  return cleaned || DEFAULT_FILE_NAME
}

const formatTimestamp = (date = new Date()) => {
  const year = date.getFullYear()
  const month = String(date.getMonth() + 1).padStart(2, '0')
  const day = String(date.getDate()).padStart(2, '0')
  const hour = String(date.getHours()).padStart(2, '0')
  const minute = String(date.getMinutes()).padStart(2, '0')
  const second = String(date.getSeconds()).padStart(2, '0')

  return `${year}${month}${day}-${hour}${minute}${second}`
}

const encodeData = (data) => {
  const json = JSON.stringify(data)
  return encoder.encode(json)
}

const decodeData = (bytes) => {
  const text = decoder.decode(bytes)
  return JSON.parse(text)
}

const downloadBlob = (blob, fileName) => {
  const url = URL.createObjectURL(blob)
  const link = document.createElement('a')

  link.href = url
  link.download = fileName
  document.body.appendChild(link)
  link.click()
  document.body.removeChild(link)
  URL.revokeObjectURL(url)
}

const pickFile = (accept) => {
  return new Promise((resolve, reject) => {
    const input = document.createElement('input')
    input.type = 'file'
    input.accept = accept
    input.style.display = 'none'

    const cleanup = () => {
      input.removeEventListener('change', handleChange)
      input.remove()
    }

    const handleChange = () => {
      const file = input.files?.[0] || null
      cleanup()

      if (!file) {
        reject(new Error('FILE_NOT_SELECTED'))
        return
      }

      resolve(file)
    }

    input.addEventListener('change', handleChange, { once: true })
    document.body.appendChild(input)
    input.click()
  })
}

export const exportData = async (data, suffix, options = {}) => {
  const normalizedSuffix = normalizeSuffix(suffix)
  const bytes = encodeData(data)
  const blob = new Blob([bytes], {
    type: options.mimeType || DEFAULT_MIME_TYPE
  })
  const baseName = sanitizeFileNamePart(options.fileName)
  const fileName = `${baseName}-${formatTimestamp()}${normalizedSuffix}`
  const shouldDownload = options.download !== false

  if (shouldDownload) {
    downloadBlob(blob, fileName)
  }

  return {
    blob,
    fileName,
    bytes
  }
}

export const importData = async (suffix) => {
  const normalizedSuffix = normalizeSuffix(suffix)
  const file = await pickFile(normalizedSuffix)
  const fileName = String(file.name || '')

  if (!fileName.toLowerCase().endsWith(normalizedSuffix.toLowerCase())) {
    throw new Error('INVALID_FILE_SUFFIX')
  }

  const bytes = new Uint8Array(await file.arrayBuffer())
  return decodeData(bytes)
}