import fs from 'fs'
import LRUCache from 'lru-cache'
import path from 'path'
import { promisify } from 'util'
import { PrerenderManifest } from '../../build'
import { PRERENDER_MANIFEST } from '../lib/constants'
import { normalizePagePath } from './normalize-page-path'

const mkdir = promisify(fs.mkdir)
const readFile = promisify(fs.readFile)
const writeFile = promisify(fs.writeFile)

function toRoute(pathname: string): string {
  return pathname.replace(/\/$/, '').replace(/\/index$/, '') || '/'
}

type SprCacheValue = {
  html: string
  pageData: any
  isStale?: boolean
  curRevalidate?: number | false
  // milliseconds to revalidate after
  revalidateAfter: number | false
}

let cache: LRUCache<string, SprCacheValue>
let prerenderManifest: PrerenderManifest
let sprOptions: {
  flushToDisk?: boolean
  pagesDir?: string
  distDir?: string
  dev?: boolean
} = {}

const getSeedPath = (pathname: string, ext: string): string => {
  return path.join(sprOptions.pagesDir!, `${pathname}.${ext}`)
}

export const calculateRevalidate = (pathname: string): number | false => {
  pathname = toRoute(pathname)

  // in development we don't have a prerender-manifest
  // and default to always revalidating to allow easier debugging
  const curTime = new Date().getTime()
  if (sprOptions.dev) return curTime - 1000

  const { initialRevalidateSeconds } = prerenderManifest.routes[pathname] || {
    initialRevalidateSeconds: 1,
  }
  const revalidateAfter =
    typeof initialRevalidateSeconds === 'number'
      ? initialRevalidateSeconds * 1000 + curTime
      : initialRevalidateSeconds

  return revalidateAfter
}

// initialize the SPR cache
export function initializeSprCache({
  max,
  dev,
  distDir,
  pagesDir,
  flushToDisk,
}: {
  dev: boolean
  max?: number
  distDir: string
  pagesDir: string
  flushToDisk?: boolean
}) {
  sprOptions = {
    dev,
    distDir,
    pagesDir,
    flushToDisk:
      !dev && (typeof flushToDisk !== 'undefined' ? flushToDisk : true),
  }

  if (dev) {
    prerenderManifest = {
      version: -1 as any, // letting us know this doesn't conform to spec
      routes: {},
      dynamicRoutes: {},
      preview: null as any, // `preview` is special case read in next-dev-server
    }
  } else {
    prerenderManifest = JSON.parse(
      fs.readFileSync(path.join(distDir, PRERENDER_MANIFEST), 'utf8')
    )
  }

  cache = new LRUCache({
    // default to 50MB limit
    max: max || 50 * 1024 * 1024,
    length(val) {
      // rough estimate of size of cache value
      return val.html.length + JSON.stringify(val.pageData).length
    },
  })
}

export async function getFallback(page: string): Promise<string> {
  page = normalizePagePath(page)
  return readFile(getSeedPath(page, 'html'), 'utf8')
}

// get data from SPR cache if available
export async function getSprCache(
  pathname: string
): Promise<SprCacheValue | undefined> {
  if (sprOptions.dev) return
  pathname = normalizePagePath(pathname)

  let data: SprCacheValue | undefined = cache.get(pathname)

  // let's check the disk for seed data
  if (!data) {
    try {
      const html = await readFile(getSeedPath(pathname, 'html'), 'utf8')
      const pageData = JSON.parse(
        await readFile(getSeedPath(pathname, 'json'), 'utf8')
      )

      data = {
        html,
        pageData,
        revalidateAfter: calculateRevalidate(pathname),
      }
      cache.set(pathname, data)
    } catch (_) {
      // unable to get data from disk
    }
  }

  if (
    data &&
    data.revalidateAfter !== false &&
    data.revalidateAfter < new Date().getTime()
  ) {
    data.isStale = true
  }
  const manifestEntry = prerenderManifest.routes[pathname]

  if (data && manifestEntry) {
    data.curRevalidate = manifestEntry.initialRevalidateSeconds
  }
  return data
}

// populate the SPR cache with new data
export async function setSprCache(
  pathname: string,
  data: {
    html: string
    pageData: any
  },
  revalidateSeconds?: number | false
) {
  if (sprOptions.dev) return
  if (typeof revalidateSeconds !== 'undefined') {
    // TODO: Update this to not mutate the manifest from the
    // build.
    prerenderManifest.routes[pathname] = {
      dataRoute: path.posix.join(
        '/_next/data',
        `${normalizePagePath(pathname)}.json`
      ),
      srcRoute: null, // FIXME: provide actual source route, however, when dynamically appending it doesn't really matter
      initialRevalidateSeconds: revalidateSeconds,
    }
  }

  pathname = normalizePagePath(pathname)
  cache.set(pathname, {
    ...data,
    revalidateAfter: calculateRevalidate(pathname),
  })

  // TODO: This option needs to cease to exist unless it stops mutating the
  // `next build` output's manifest.
  if (sprOptions.flushToDisk) {
    try {
      const seedPath = getSeedPath(pathname, 'html')
      await mkdir(path.dirname(seedPath), { recursive: true })
      await writeFile(seedPath, data.html, 'utf8')
      await writeFile(
        getSeedPath(pathname, 'json'),
        JSON.stringify(data.pageData),
        'utf8'
      )
    } catch (error) {
      // failed to flush to disk
      console.warn('Failed to update prerender files for', pathname, error)
    }
  }
}