import { createWriteStream } from 'node:fs'
import { Transform } from 'node:stream'
import { pipeline } from 'node:stream/promises'
import Busboy from 'busboy'

/**
 * 코드가 포함된 multipart 오류를 만든다.
 * @param {string} code - 오류 코드
 * @returns {Error & { code: string }} multipart 오류
 */
const createMultipartError = (code) => {
  const error = new Error(code)
  error.code = code
  return error
}

/**
 * busboy가 UTF-8 파일명 바이트를 Latin-1 문자열로 넘긴 경우를 복구한다.
 * 이미 유니코드 코드포인트로 해석된 파일명은 그대로 둔다.
 * @param {string|null|undefined} filename - multipart 파일명
 * @returns {string} NFC 정규화된 파일명
 */
export const decodeMultipartFilename = (filename) => {
  const value = String(filename || '')

  if (!value) {
    return ''
  }

  const hasNonLatin1 = [...value].some((char) => Number(char.codePointAt(0)) > 255)

  if (hasNonLatin1) {
    return value.normalize('NFC')
  }

  const repaired = Buffer.from(value, 'latin1').toString('utf8')

  if (!repaired.includes('\uFFFD')) {
    return repaired.normalize('NFC')
  }

  return value.normalize('NFC')
}

/**
 * multipart 파일 하나를 메모리에 올리지 않고 디스크로 저장한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {{ fieldName: string, filePath: string, maxBytes: number }} input - 저장 옵션
 * @returns {Promise<{ filename: string, mimeType: string, size: number }>} 저장 결과
 */
export const saveMultipartFileToDisk = async (event, input) => {
  return new Promise((resolve, reject) => {
    let parser = null

    try {
      parser = Busboy({
        headers: event.node.req.headers,
        limits: {
          files: 1,
          fields: 4,
          parts: 5,
          fileSize: input.maxBytes
        }
      })
    } catch {
      reject(createMultipartError('INVALID_MULTIPART_REQUEST'))
      return
    }

    let matched = false
    let truncated = false
    let filename = ''
    let mimeType = ''
    let size = 0
    /** @type {Promise<void>|null} */
    let fileWritePromise = null

    parser.on('file', (fieldName, fileStream, info) => {
      if (fieldName !== input.fieldName || matched) {
        fileStream.resume()
        return
      }

      matched = true
      filename = decodeMultipartFilename(info.filename)
      mimeType = String(info.mimeType || '')
      const output = createWriteStream(input.filePath, {
        flags: 'wx'
      })

      fileStream.on('data', (chunk) => {
        size += chunk.length
      })
      fileStream.on('limit', () => {
        truncated = true
      })
      fileWritePromise = pipeline(fileStream, output)
    })

    parser.on('filesLimit', () => {
      truncated = true
    })
    parser.on('error', async (error) => {
      if (fileWritePromise) {
        await fileWritePromise.catch(() => {})
      }
      reject(error)
    })
    parser.on('finish', async () => {
      try {
        if (fileWritePromise) {
          await fileWritePromise
        }

        if (!matched) {
          reject(createMultipartError('MULTIPART_FILE_NOT_FOUND'))
          return
        }

        if (truncated) {
          reject(createMultipartError('MULTIPART_FILE_TOO_LARGE'))
          return
        }

        resolve({
          filename,
          mimeType,
          size
        })
      } catch (error) {
        reject(error)
      }
    })

    event.node.req.on('aborted', () => {
      parser.destroy(createMultipartError('MULTIPART_REQUEST_ABORTED'))
    })
    event.node.req.pipe(parser)
  })
}

/**
 * multipart 파일 여러 개를 메모리에 올리지 않고 디스크로 저장한다.
 * @param {import('h3').H3Event} event - 요청 이벤트
 * @param {{
 *  fieldName: string,
 *  maxFiles: number,
 *  maxTotalBytes: number,
 *  createFileTarget: (file: { filename: string, mimeType: string }, index: number) => Promise<{ filePath: string, maxBytes: number, metadata?: Object }>
 * }} input - 저장 옵션
 * @returns {Promise<Array<{ filename: string, mimeType: string, size: number, filePath: string, metadata: Object }>>} 저장 결과
 */
export const saveMultipartFilesToDisk = async (event, input) => {
  return new Promise((resolve, reject) => {
    let parser = null

    try {
      parser = Busboy({
        headers: event.node.req.headers,
        limits: {
          files: input.maxFiles,
          fields: 4,
          parts: input.maxFiles + 4,
          fileSize: input.maxTotalBytes
        }
      })
    } catch {
      reject(createMultipartError('INVALID_MULTIPART_REQUEST'))
      return
    }

    let matchedFileCount = 0
    let totalSize = 0
    let limitError = null
    let taskError = null
    const savedFiles = []
    const fileTasks = []

    parser.on('file', (fieldName, fileStream, info) => {
      if (fieldName !== input.fieldName) {
        fileStream.resume()
        return
      }

      const fileIndex = matchedFileCount
      matchedFileCount += 1
      const filename = decodeMultipartFilename(info.filename)
      const mimeType = String(info.mimeType || '')

      const fileTask = (async () => {
        try {
          const target = await input.createFileTarget({ filename, mimeType }, fileIndex)
          let fileSize = 0

          const sizeLimiter = new Transform({
            transform(chunk, _encoding, callback) {
              fileSize += chunk.length
              totalSize += chunk.length

              if (!limitError && fileSize > target.maxBytes) {
                limitError = createMultipartError('MULTIPART_FILE_TOO_LARGE')
                limitError.maxBytes = target.maxBytes
                limitError.metadata = target.metadata || {}
              }
              if (!limitError && totalSize > input.maxTotalBytes) {
                limitError = createMultipartError('MULTIPART_TOTAL_SIZE_TOO_LARGE')
              }

              callback(null, limitError ? null : chunk)
            }
          })

          fileStream.on('limit', () => {
            limitError = limitError || createMultipartError('MULTIPART_TOTAL_SIZE_TOO_LARGE')
          })
          await pipeline(
            fileStream,
            sizeLimiter,
            createWriteStream(target.filePath, { flags: 'wx' })
          )

          savedFiles.push({
            filename,
            mimeType,
            size: fileSize,
            filePath: target.filePath,
            metadata: target.metadata || {},
            index: fileIndex
          })
        } catch (error) {
          taskError = taskError || error
          fileStream.resume()
        }
      })()

      fileTasks.push(fileTask)
    })

    parser.on('filesLimit', () => {
      limitError = limitError || createMultipartError('MULTIPART_TOO_MANY_FILES')
    })
    parser.on('partsLimit', () => {
      limitError = limitError || createMultipartError('MULTIPART_TOO_MANY_PARTS')
    })
    parser.on('error', async (error) => {
      await Promise.allSettled(fileTasks)
      reject(error)
    })
    parser.on('finish', async () => {
      await Promise.all(fileTasks)

      if (taskError) {
        reject(taskError)
        return
      }
      if (limitError) {
        reject(limitError)
        return
      }
      if (!matchedFileCount) {
        reject(createMultipartError('MULTIPART_FILE_NOT_FOUND'))
        return
      }

      resolve(savedFiles
        .sort((left, right) => left.index - right.index)
        .map(({ index: _index, ...file }) => file))
    })

    event.node.req.on('aborted', () => {
      parser.destroy(createMultipartError('MULTIPART_REQUEST_ABORTED'))
    })
    event.node.req.pipe(parser)
  })
}