import { Platform } from 'react-native'

import type {
  XWebViewDownloadDecision,
  XWebViewDownloadProgress,
  XWebViewDownloadRequest,
  XWebViewDownloadResult,
} from '@xuqm/rn-common'

// Lazy import: react-native-blob-util calls getConstants() at module evaluation time,
// which crashes in RN 0.85 Bridgeless mode. Defer the require until actual download use.
// eslint-disable-next-line @typescript-eslint/no-require-imports
const getRNFetchBlob = () => (require('react-native-blob-util') as { default: typeof import('react-native-blob-util').default }).default

function parseContentDispositionFilename(header: string): string | null {
  const rfc5987 = header.match(/filename\*=(?:[^']*'[^']*')?([^;\s]+)/i)
  if (rfc5987?.[1]) {
    try {
      return decodeURIComponent(rfc5987[1].replace(/['"]/g, ''))
    } catch {}
  }

  const quoted = header.match(/filename="([^"]+)"/i)
  if (quoted?.[1]) return quoted[1].trim()

  const plain = header.match(/filename=([^;\s"]+)/i)
  if (plain?.[1]) return plain[1].trim()

  return null
}

function filenameFromUrl(url: string): string {
  try {
    const { pathname } = new URL(url)
    const parts = pathname.split('/').filter(Boolean)
    return parts[parts.length - 1] ? decodeURIComponent(parts[parts.length - 1]) : 'download'
  } catch {
    const path = url.split('?')[0]
    const parts = path.split('/').filter(Boolean)
    return parts[parts.length - 1] || 'download'
  }
}

export async function fetchDownloadInfo(
  url: string,
  hintFilename?: string,
): Promise<XWebViewDownloadRequest> {
  try {
    const res = await fetch(url, { method: 'HEAD' })
    const disposition = res.headers.get('content-disposition') ?? ''
    const mimeType = res.headers.get('content-type')?.split(';')[0].trim() || undefined
    const length = res.headers.get('content-length')
    const fileSize = length ? parseInt(length, 10) : undefined

    const suggestedFilename =
      (hintFilename && hintFilename.trim()) ||
      parseContentDispositionFilename(disposition) ||
      filenameFromUrl(url)

    return { url, suggestedFilename, mimeType, fileSize }
  } catch {
    return {
      url,
      suggestedFilename: (hintFilename && hintFilename.trim()) || filenameFromUrl(url),
    }
  }
}

async function resolveFilePath(
  dir: string,
  filename: string,
  conflict: 'rename' | 'overwrite',
): Promise<string> {
  const full = `${dir}/${filename}`
  if (conflict === 'overwrite') return full

  const exists = await getRNFetchBlob().fs.exists(full)
  if (!exists) return full

  const dot = filename.lastIndexOf('.')
  const base = dot >= 0 ? filename.slice(0, dot) : filename
  const ext = dot >= 0 ? filename.slice(dot) : ''

  let n = 1
  let candidate: string
  do {
    candidate = `${dir}/${base}(${n})${ext}`
    n++
  } while (await getRNFetchBlob().fs.exists(candidate))

  return candidate
}

export async function saveBase64File(
  base64: string,
  filename: string,
  savePath: string | undefined,
  conflict: 'rename' | 'overwrite',
): Promise<string> {
  const { dirs } = getRNFetchBlob().fs
  const dir =
    savePath ??
    (Platform.OS === 'android'
      ? (dirs.DownloadDir ?? dirs.DocumentDir)
      : dirs.DocumentDir)
  const filePath = await resolveFilePath(dir, filename, conflict)
  await getRNFetchBlob().fs.writeFile(filePath, base64, 'base64')
  return filePath
}

export type DownloadHandle = { cancel: () => void }

/**
 * 统一的下载请求处理函数。
 *
 * 封装 fetchDownloadInfo → onDownloadDecide → startDownload 的完整流程，
 * 供 XWebViewScreen / XWebViewView 及外部调用方使用。
 *
 * @returns DownloadHandle（可取消），若用户拒绝或无需下载则返回 null
 */
export async function handleDownloadRequest(
  url: string,
  hintFilename: string | undefined,
  options: {
    autoDownload?: boolean
    downloadConflict?: 'rename' | 'overwrite'
    savePath?: string
    onDownloadDecide?: (
      request: XWebViewDownloadRequest,
    ) => XWebViewDownloadDecision | Promise<XWebViewDownloadDecision>
    onDownloadStart?: (request: XWebViewDownloadRequest) => void
    onDownloadProgress?: (progress: XWebViewDownloadProgress) => void
    onDownloadComplete?: (result: XWebViewDownloadResult) => void
    onDownloadError?: (url: string, error: string) => void
  } = {},
): Promise<DownloadHandle | null> {
  const {
    autoDownload = true,
    downloadConflict = 'rename',
    savePath,
    onDownloadDecide,
    onDownloadStart,
    onDownloadProgress,
    onDownloadComplete,
    onDownloadError,
  } = options

  const info = await fetchDownloadInfo(url, hintFilename)
  let finalFilename = info.suggestedFilename
  let finalSavePath = savePath

  // 非自动下载模式：需要宿主决定是否允许
  if (!autoDownload) {
    if (!onDownloadDecide) return null
    const decision = await Promise.resolve(onDownloadDecide(info))
    if (!decision.allowed) return null
    if (decision.filename) finalFilename = decision.filename
    if (decision.savePath) finalSavePath = decision.savePath
  }

  onDownloadStart?.({ ...info, suggestedFilename: finalFilename })

  return startDownload(
    url,
    finalFilename,
    finalSavePath,
    downloadConflict,
    p => onDownloadProgress?.(p),
    r => onDownloadComplete?.(r),
    err => onDownloadError?.(url, err),
  )
}

export function startDownload(
  url: string,
  filename: string,
  savePath: string | undefined,
  conflict: 'rename' | 'overwrite',
  onProgress: (p: XWebViewDownloadProgress) => void,
  onComplete: (r: XWebViewDownloadResult) => void,
  onError: (error: string) => void,
): DownloadHandle {
  const { dirs } = getRNFetchBlob().fs
  const dir =
    savePath ??
    (Platform.OS === 'android'
      ? (dirs.DownloadDir ?? dirs.DocumentDir)
      : dirs.DocumentDir)

  let cancelled = false
  let cancelFn = () => {
    cancelled = true
  }

  resolveFilePath(dir, filename, conflict)
    .then(filePath => {
      if (cancelled) return

      const task = getRNFetchBlob().config({ path: filePath }).fetch('GET', url)
      cancelFn = () => task.cancel()

      task.progress({ interval: 300 }, (received: number, total: number) => {
        const recv = Number(received)
        const tot = Number(total)
        onProgress({
          url,
          filename,
          received: recv,
          total: tot,
          percentage: tot > 0 ? Math.round((recv / tot) * 100) : -1,
        })
      })

      task
        .then((res: { path: () => string }) => {
          onComplete({ url, filename, filePath: res.path(), fileSize: 0 })
        })
        .catch((err: Error) => {
          if (!String(err?.message ?? '').toLowerCase().includes('cancel')) {
            onError(err?.message ?? String(err))
          }
        })
    })
    .catch(err => onError(String(err)))

  return { cancel: () => cancelFn() }
}