// Turbo remote cache client.
//
// Provides exists/get/put operations against the Vercel turbo remote cache API.
// Handles both vercel.com (/api/v8/artifacts/) and custom self-hosted servers
// (/v8/artifacts/).
//
// put() accepts either a Buffer/Uint8Array or a string path to stream from disk
// (for large files that exceed Node's 2GB Buffer limit).
//
// Usage:
//   import * as cache from './turbo-cache.mjs'
//   await cache.exists(hexKey)          // -> boolean
//   await cache.get(hexKey)             // -> Buffer | null
//   await cache.put(hexKey, buffer)     // upload from memory
//   await cache.put(hexKey, '/path')    // stream upload from file

import fs from 'fs'
import { createHash } from 'crypto'
import { Readable } from 'stream'

const TURBO_API = process.env.TURBO_API || 'https://vercel.com'
const TURBO_TOKEN = process.env.TURBO_TOKEN
const TURBO_TEAM = process.env.TURBO_TEAM

const IS_VERCEL = new URL(TURBO_API).hostname === 'vercel.com'

// Vercel's cache API lives at /api/v8/artifacts/ and uses ?teamId=.
// Self-hosted turbo cache servers use /v8/artifacts/ and ?slug=.
export function artifactUrl(key) {
  if (IS_VERCEL) {
    const qs = TURBO_TEAM ? `?teamId=${TURBO_TEAM}` : ''
    return `https://vercel.com/api/v8/artifacts/${key}${qs}`
  }
  const qs = TURBO_TEAM ? `?slug=${TURBO_TEAM}` : ''
  return `${TURBO_API}/v8/artifacts/${key}${qs}`
}

function baseHeaders() {
  return {
    Authorization: `Bearer ${TURBO_TOKEN}`,
    'User-Agent': 'turbo 2 next.js-ci',
    'x-artifact-client-ci': 'GITHUB_ACTIONS',
  }
}

/** Check if an artifact exists. */
export async function exists(key) {
  const res = await fetch(artifactUrl(key), {
    method: 'HEAD',
    headers: baseHeaders(),
  })
  return res.status === 200
}

/** Download an artifact. Returns Buffer on hit, null on miss. */
export async function get(key) {
  const res = await fetch(artifactUrl(key), {
    method: 'GET',
    headers: baseHeaders(),
  })
  if (!res.ok) return null
  return Buffer.from(await res.arrayBuffer())
}

/**
 * Download an artifact as a Node.js Readable stream. Throws on failure.
 *
 * The returned stream has a `.stats` property with transfer metrics
 * (populated as data flows):
 *   { totalBytes, startTime, endTime, maxStallMs, stallWarned }
 *
 * A console warning is printed (once) if no data arrives for 5+ seconds.
 * The stream is destroyed if no data arrives within `stallTimeout` ms.
 */
export async function getStream(key, { stallTimeout = 30_000 } = {}) {
  const res = await fetch(artifactUrl(key), {
    method: 'GET',
    headers: baseHeaders(),
  })
  if (!res.ok) {
    throw new Error(`GET ${key} failed: ${res.status} ${res.statusText}`)
  }
  // Use a large buffer to avoid backpressure stalls — the default
  // highWaterMark for Readable.fromWeb() is only 16KB which throttles
  // throughput when piping large artifacts to shell commands.
  const stream = Readable.fromWeb(res.body, {
    highWaterMark: 16 * 1024 * 1024,
  })

  const stats = {
    totalBytes: 0,
    startTime: Date.now(),
    endTime: 0,
    maxStallMs: 0,
    stallWarned: false,
  }
  stream.stats = stats

  let lastDataTime = Date.now()

  // Stall detection: warn once at 5s, destroy at stallTimeout.
  let timer = setTimeout(() => {
    stream.destroy(new Error(`Download stalled: no data for ${stallTimeout}ms`))
  }, stallTimeout)

  const STALL_WARN_MS = 5_000
  let warnTimer = setTimeout(() => {
    if (!stats.stallWarned) {
      stats.stallWarned = true
      const elapsed = ((Date.now() - stats.startTime) / 1000).toFixed(1)
      const mb = (stats.totalBytes / 1024 / 1024).toFixed(1)
      console.log(
        `WARNING: download stall detected — ${mb} MB received in ${elapsed}s, no data for 5s+`
      )
    }
  }, STALL_WARN_MS)

  stream.on('data', (chunk) => {
    const now = Date.now()
    const gap = now - lastDataTime
    if (gap > stats.maxStallMs) stats.maxStallMs = gap
    lastDataTime = now
    stats.totalBytes += chunk.length

    clearTimeout(timer)
    timer = setTimeout(() => {
      stream.destroy(
        new Error(`Download stalled: no data for ${stallTimeout}ms`)
      )
    }, stallTimeout)

    clearTimeout(warnTimer)
    warnTimer = setTimeout(() => {
      if (!stats.stallWarned) {
        stats.stallWarned = true
        const elapsed = ((Date.now() - stats.startTime) / 1000).toFixed(1)
        const mb = (stats.totalBytes / 1024 / 1024).toFixed(1)
        console.log(
          `WARNING: download stall detected — ${mb} MB received in ${elapsed}s, no data for 5s+`
        )
      }
    }, STALL_WARN_MS)
  })

  stream.on('end', () => {
    clearTimeout(timer)
    clearTimeout(warnTimer)
    stats.endTime = Date.now()
  })
  stream.on('error', () => {
    clearTimeout(timer)
    clearTimeout(warnTimer)
    stats.endTime = Date.now()
  })

  return stream
}

/** Format transfer stats as a human-readable string. */
export function formatStats(stats) {
  const duration = ((stats.endTime - stats.startTime) / 1000).toFixed(1)
  const mb = (stats.totalBytes / 1024 / 1024).toFixed(1)
  const speed = (
    stats.totalBytes /
    1024 /
    1024 /
    ((stats.endTime - stats.startTime) / 1000)
  ).toFixed(1)
  const stall =
    stats.maxStallMs > 1000
      ? `, max stall ${(stats.maxStallMs / 1000).toFixed(1)}s`
      : ''
  return `${mb} MB in ${duration}s (${speed} MB/s${stall})`
}

/**
 * Download an artifact to a file.
 * Returns { ok: true, stats } on hit, { ok: false } on miss/failure.
 * Uses streaming to handle files larger than 2GB.
 * Retries up to `retries` times on stall or network errors.
 */
export async function getToFile(key, destPath, { retries = 2 } = {}) {
  for (let attempt = 0; attempt <= retries; attempt++) {
    try {
      const stream = await getStream(key)
      await new Promise((resolve, reject) => {
        const ws = fs.createWriteStream(destPath)
        stream.pipe(ws)
        ws.on('finish', resolve)
        ws.on('error', reject)
        stream.on('error', reject)
      })
      return { ok: true, stats: stream.stats }
    } catch (e) {
      if (attempt < retries) {
        console.log(
          `Download attempt ${attempt + 1} failed: ${e.message} — retrying...`
        )
        continue
      }
      return { ok: false }
    }
  }
  return { ok: false }
}

/**
 * Upload an artifact.
 * @param {string} key - hex-only cache key
 * @param {Buffer|Uint8Array|string} data - Buffer/Uint8Array for in-memory,
 *   or a string file path to stream from disk (for large files).
 */
export async function put(key, data) {
  const isFile = typeof data === 'string'
  const size = isFile ? fs.statSync(data).size : data.length

  const headers = {
    ...baseHeaders(),
    'Content-Type': 'application/octet-stream',
    'Content-Length': String(size),
    'x-artifact-duration': '0',
  }

  let body
  if (isFile) {
    // Stream from file — avoids loading into memory
    body = Readable.toWeb(
      fs.createReadStream(data, { highWaterMark: 16 * 1024 * 1024 })
    )
  } else {
    body = data
  }

  const res = await fetch(artifactUrl(key), {
    method: 'PUT',
    headers,
    body,
    // Required for streaming request bodies in Node fetch
    duplex: isFile ? 'half' : undefined,
  })

  if (!res.ok) {
    const text = await res.text().catch(() => '')
    throw new Error(
      `PUT ${key} failed: ${res.status} ${res.statusText} ${text.slice(0, 200)}`
    )
  }
}

/**
 * Verify read+write access. Returns true if both work.
 */
export async function healthCheck() {
  const testKey = createHash('sha256')
    .update(`turbo-cache-health-${Date.now()}`)
    .digest('hex')

  console.error(`Turbo cache health check:`)
  console.error(`  API: ${IS_VERCEL ? 'vercel.com' : TURBO_API}`)
  console.error(`  Team: ${TURBO_TEAM || '(none)'}`)
  console.error(
    `  Token: ${TURBO_TOKEN ? TURBO_TOKEN.slice(0, 8) + '...' : '(not set)'}`
  )

  if (!TURBO_TOKEN) {
    console.error('  SKIP: no TURBO_TOKEN')
    return false
  }

  try {
    // READ
    const e = await exists(testKey)
    console.error(`  READ:   exists -> ${e}`)

    // WRITE
    const testData = Buffer.from('turbo-cache-write-test')
    await put(testKey, testData)
    console.error(`  WRITE:  put -> OK`)

    // VERIFY
    const readBack = await get(testKey)
    if (readBack && readBack.equals(testData)) {
      console.error(`  VERIFY: get -> OK (${readBack.length}B)`)
    } else {
      console.error(
        `  VERIFY: get -> mismatch (${readBack ? readBack.length : 0}B)`
      )
    }

    return true
  } catch (e) {
    console.error(`  FAIL: ${e.message}`)
    return false
  }
}