import { app, net, shell, type WebContents } from 'electron'
import { createWriteStream, type WriteStream } from 'fs'
import { stat, unlink } from 'fs/promises'
import { join, normalize, dirname } from 'path'
import { createHash } from 'crypto'
import { getSettings } from './settings'
import {
  IpcChannels,
  type AppUpdateInfo,
  type AppUpdateDownload,
  type AppUpdateProgress
} from '@shared/ipc'

/**
 * Authorization header for the update host. Empty unless the user has set an
 * updateToken in Settings — needed when the release repo is private or the Gitea
 * instance requires sign-in for anonymous access (the default on this instance).
 *
 * The token must never reach an origin other than the host-pinned UPDATE_HOST.
 * Every request that carries it guards against that on its own terms: the REST
 * check refuses to follow redirects (`redirect: 'error'`), and the download paths
 * use `redirect: 'manual'` and re-validate each hop with isTrustedDownloadUrl. So
 * a redirect can't bounce the header to another host on any path.
 */
function authHeader(): Record<string, string> {
  const tok = getSettings().updateToken?.trim()
  return tok ? { Authorization: `token ${tok}` } : {}
}

// --- Update source -----------------------------------------------------------
// The Gitea repo whose Releases host the AeroFetch installers. The updater reads
// the repo's latest release over the public REST API and downloads the installer
// asset attached to it.
//
// IMPORTANT: this points at a repo whose releases must be ANONYMOUSLY readable —
// i.e. a public repo on a Gitea instance that permits anonymous API + downloads.
// AeroFetch never ships a token; on a sign-in-required instance the check simply
// reports that it couldn't reach the server. Change OWNER/REPO to retarget.
const UPDATE_HOST = 'https://gitea.netbird.zimspace.uk:5938'
const UPDATE_OWNER = 'debont80'
const UPDATE_REPO = 'AeroFetch'
const RELEASE_API = `${UPDATE_HOST}/api/v1/repos/${UPDATE_OWNER}/${UPDATE_REPO}/releases/latest`

// Security: only ever download or execute a file served by the trusted update
// host over HTTPS. downloadUrl comes from the release JSON, and Gitea 302-redirects
// release downloads to its attachment store — so this is re-checked on EVERY
// redirect hop (see downloadAppUpdate), which is what stops a tampered/MITM'd
// response from bouncing us off the trusted host.
export function isTrustedDownloadUrl(url: string): boolean {
  try {
    const u = new URL(url)
    return u.protocol === 'https:' && u.host === new URL(UPDATE_HOST).host
  } catch {
    return false
  }
}

/** Where downloaded installers are written (and the only dir we'll run one from). */
function updateDir(): string {
  return app.getPath('temp')
}

/**
 * Parse 'v1.2.3' / '1.2.3-rc.1' into the comparable numeric components of the
 * release CORE — the x.y.z before any '-prerelease' or '+build' suffix. Dropping
 * the suffix means a prerelease (e.g. 0.5.0-rc.1) never sorts ABOVE its final
 * release (0.5.0): at most it compares equal, so we won't offer a prerelease as
 * an "upgrade" over the same shipped version.
 */
function parseVersion(v: string): number[] {
  // split() always yields at least one element; `?? ''` only satisfies the type
  // checker (noUncheckedIndexedAccess) for the [0] access.
  const core = v.replace(/^v/i, '').split(/[-+]/)[0] ?? ''
  return core
    .split('.')
    .map((p) => parseInt(p, 10))
    .filter((n) => !Number.isNaN(n))
}

/** Component-wise numeric compare: -1 if a<b, 0 if equal, 1 if a>b. */
export function compareVersions(a: string, b: string): number {
  const pa = parseVersion(a)
  const pb = parseVersion(b)
  const len = Math.max(pa.length, pb.length)
  for (let i = 0; i < len; i++) {
    const x = pa[i] ?? 0
    const y = pb[i] ?? 0
    if (x !== y) return x < y ? -1 : 1
  }
  return 0
}

interface GiteaAsset {
  name: string
  browser_download_url: string
}
interface GiteaRelease {
  tag_name: string
  body?: string
  html_url?: string
  assets?: GiteaAsset[]
}

/**
 * Pull the SHA-256 hex out of a checksum file — a bare digest, `sha256sum`
 * output (`<hash>  file`), or PowerShell Get-FileHash (uppercase). Returns the
 * lowercase digest, or null if there's no standalone 64-char hex token (so a
 * longer run like a sha512 digest is ignored rather than sliced).
 *
 * When `fileName` is given (the installer asset's name), a multi-line / combined
 * checksum file is matched line-by-line and the hash on the line naming THIS
 * asset wins — so a `<asset>.sha256` that happens to list several files can't
 * verify the installer against the wrong line's hash (B3). Falls back to the
 * first standalone digest for bare single-hash files (no filename present).
 */
export function extractSha256(text: string, fileName?: string): string | null {
  const hashRe = /\b[a-f0-9]{64}\b/i
  if (fileName) {
    const base = fileName.toLowerCase()
    for (const line of text.split(/\r?\n/)) {
      const m = line.match(hashRe)
      if (!m) continue
      // The filename is the last whitespace-delimited token on a sha256sum /
      // Get-FileHash line (optionally with a '*' binary-mode marker). Match it
      // exactly — a loose substring would let 'App.exe' match a 'MyApp.exe' line.
      const last = (line.trim().split(/\s+/).pop() ?? '').replace(/^\*/, '')
      if (last.toLowerCase() === base) return m[0].toLowerCase()
    }
  }
  const m = text.match(hashRe)
  return m ? m[0].toLowerCase() : null
}

/** Pick the Windows installer asset — prefer the NSIS "Setup" .exe, else any .exe. */
function pickInstaller(assets: GiteaAsset[]): GiteaAsset | undefined {
  const exes = assets.filter((a) => /\.exe$/i.test(a.name))
  return exes.find((a) => /setup/i.test(a.name)) ?? exes[0]
}

/** Query the configured repo's latest release and compare it to the running app. */
export async function checkForAppUpdate(): Promise<AppUpdateInfo> {
  const currentVersion = app.getVersion()
  // Bound the check so a stalled/unreachable server can't hang the UI spinner
  // indefinitely — mirrors the timeouts on the yt-dlp calls.
  const controller = new AbortController()
  const timer = setTimeout(() => controller.abort(), 15_000)
  try {
    const res = await fetch(RELEASE_API, {
      headers: { Accept: 'application/json', ...authHeader() },
      // The API lives at an exact pinned URL and answers 200 directly. Refusing
      // redirects keeps an authenticated check from ever forwarding the token to
      // another origin; a stray redirect fails safe into the catch below.
      redirect: 'error',
      signal: controller.signal
    })
    if (!res.ok) {
      const auth = res.status === 401 || res.status === 403 || res.status === 404
      return {
        ok: false,
        available: false,
        currentVersion,
        error: auth
          ? 'Could not reach the update server (it may require sign-in for anonymous access).'
          : `Update check failed (HTTP ${res.status}).`
      }
    }
    const rel = (await res.json()) as GiteaRelease
    const latestVersion = (rel.tag_name ?? '').replace(/^v/i, '')
    const asset = pickInstaller(rel.assets ?? [])
    const available = latestVersion !== '' && compareVersions(latestVersion, currentVersion) > 0
    return {
      ok: true,
      available,
      currentVersion,
      latestVersion,
      notes: rel.body?.trim() || undefined,
      // Only ever hand the OS browser a release page on our own trusted host.
      htmlUrl: rel.html_url && isTrustedDownloadUrl(rel.html_url) ? rel.html_url : undefined,
      downloadUrl: asset?.browser_download_url,
      assetName: asset?.name
    }
  } catch (e) {
    const timedOut = e instanceof Error && e.name === 'AbortError'
    return {
      ok: false,
      available: false,
      currentVersion,
      error: timedOut
        ? 'Update check timed out — the server took too long to respond.'
        : e instanceof Error
          ? e.message
          : String(e)
    }
  } finally {
    clearTimeout(timer)
  }
}

/** How long the download may stall (no bytes received) before we give up. */
const DOWNLOAD_IDLE_TIMEOUT_MS = 60_000

// Integrity: every release MUST attach a checksum asset named `<installer>.sha256`
// (e.g. AeroFetch-Setup-0.5.0.exe.sha256) whose contents include the installer's
// lowercase SHA-256 hex — bare, or in `sha256sum`/`Get-FileHash` form. We refuse
// to run an installer we can't verify against it. Note this is INTEGRITY +
// defence-in-depth (corruption, truncation, tampering-after-publish, a redirect
// bounced to other storage), NOT protection against a fully compromised host —
// that host serves both files, so only Authenticode signing defends against it.
const REQUIRE_CHECKSUM: boolean = true

/**
 * GET a small text resource from the trusted host, re-validating the host on
 * every redirect hop (same discipline as the installer download) and capping the
 * body so a hostile/huge response can't exhaust memory. Used for the .sha256 file.
 */
function fetchTrustedText(
  url: string,
  maxBytes = 64 * 1024,
  timeoutMs = 15_000
): Promise<{ ok: true; text: string } | { ok: false; status?: number; error: string }> {
  return new Promise((resolve) => {
    let settled = false
    const done = (
      r: { ok: true; text: string } | { ok: false; status?: number; error: string }
    ): void => {
      if (settled) return
      settled = true
      clearTimeout(timer)
      if (!r.ok) request.abort()
      resolve(r)
    }
    const request = net.request({ url, redirect: 'manual' })
    for (const [k, v] of Object.entries(authHeader())) request.setHeader(k, v)
    const timer = setTimeout(() => done({ ok: false, error: 'timed out' }), timeoutMs)
    request.on('redirect', (_s, _m, redirectUrl) => {
      if (!isTrustedDownloadUrl(redirectUrl)) {
        done({ ok: false, error: 'redirect to an untrusted location' })
        return
      }
      request.followRedirect()
    })
    request.on('response', (response) => {
      const status = response.statusCode
      if (status < 200 || status >= 300) {
        done({ ok: false, status, error: `HTTP ${status}` })
        return
      }
      const chunks: Buffer[] = []
      let size = 0
      response.on('data', (c: Buffer) => {
        size += c.length
        if (size > maxBytes) done({ ok: false, error: 'checksum file too large' })
        else chunks.push(c)
      })
      response.on('end', () => done({ ok: true, text: Buffer.concat(chunks).toString('utf8') }))
      response.on('aborted', () => done({ ok: false, error: 'interrupted' }))
      response.on('error', (e: Error) => done({ ok: false, error: e.message }))
    })
    request.on('error', (e: Error) => done({ ok: false, error: e.message }))
    request.end()
  })
}

/** Stream the installer to a temp file, pushing progress events to the renderer. */
export async function downloadAppUpdate(url: string, wc: WebContents): Promise<AppUpdateDownload> {
  if (!isTrustedDownloadUrl(url)) {
    return { ok: false, error: 'Refused to download from an untrusted location.' }
  }

  // Derive a safe .exe filename from the URL; fall back to a fixed name.
  const urlName = decodeURIComponent(new URL(url).pathname.split('/').pop() || '')
  const safeName = /^[\w.\- ]+\.exe$/i.test(urlName) ? urlName : 'AeroFetch-Setup.exe'
  const filePath = join(updateDir(), safeName)

  // Resolve the published checksum up front (tiny, fails fast) so we never pull a
  // ~300 MB installer we'd then refuse to run. The .sha256 sits next to the asset,
  // so its URL is the installer URL + '.sha256' — still on the host-pinned origin.
  const checksumUrl = (() => {
    const u = new URL(url)
    u.pathname += '.sha256'
    return u.toString()
  })()
  const sum = await fetchTrustedText(checksumUrl)
  let expectedSha: string | null = null
  if (sum.ok) {
    expectedSha = extractSha256(sum.text, safeName)
    if (!expectedSha) return { ok: false, error: "The update's checksum file is malformed." }
  } else if (sum.status === 404) {
    if (REQUIRE_CHECKSUM) {
      return {
        ok: false,
        error: `This release has no checksum (${safeName}.sha256) attached — refusing to install an unverified update.`
      }
    }
  } else {
    return { ok: false, error: `Couldn't fetch the update's checksum — ${sum.error}.` }
  }

  return new Promise<AppUpdateDownload>((resolve) => {
    let settled = false
    let fileStream: WriteStream | null = null
    let idle: NodeJS.Timeout | null = null

    // Single teardown point. On failure it also aborts the request, so a write
    // error (disk full, etc.) can't leave Electron pulling bytes into a dead
    // stream. abort() is idempotent, so the call sites below don't repeat it.
    const finish = (result: AppUpdateDownload): void => {
      if (settled) return
      settled = true
      if (idle) clearTimeout(idle)
      if (!result.ok) {
        request.abort()
        // Close the handle before unlinking (Windows won't delete an open file)
        // and never leave a partial/aborted installer lying around in temp.
        if (fileStream && !fileStream.destroyed) fileStream.destroy()
        unlink(filePath).catch(() => {})
      }
      resolve(result)
    }

    // net.request (not fetch) so we can re-validate the host on EVERY redirect
    // hop: Gitea 302s a release download to its attachment store, and undici's
    // fetch hides the Location header under redirect:'manual', so it can't gate
    // hops. 'manual' here means a hop only proceeds if we call followRedirect().
    const request = net.request({ url, redirect: 'manual' })
    for (const [k, v] of Object.entries(authHeader())) request.setHeader(k, v)

    const armIdle = (): void => {
      if (idle) clearTimeout(idle)
      idle = setTimeout(() => {
        finish({ ok: false, error: 'Download stalled — please try again.' })
      }, DOWNLOAD_IDLE_TIMEOUT_MS)
    }

    request.on('redirect', (_status, _method, redirectUrl) => {
      if (!isTrustedDownloadUrl(redirectUrl)) {
        finish({ ok: false, error: 'Refused to follow a redirect to an untrusted location.' })
        return
      }
      request.followRedirect()
    })

    request.on('response', (response) => {
      const status = response.statusCode
      if (status < 200 || status >= 300) {
        finish({ ok: false, error: `Download failed (HTTP ${status}).` })
        return
      }

      const lenHeader = response.headers['content-length']
      const total = Number(Array.isArray(lenHeader) ? lenHeader[0] : lenHeader) || undefined

      const stream = createWriteStream(filePath)
      fileStream = stream
      // Hash the bytes as they stream by, so verification needs no second pass.
      const hash = createHash('sha256')
      // Electron's IncomingMessage is event-based (no .pipe). pause()/resume()
      // exist at runtime but aren't in its type, so feature-detect them to apply
      // backpressure — without it a ~300 MB installer can buffer in memory.
      const flow = response as unknown as { pause?(): void; resume?(): void }
      let received = 0
      armIdle()

      response.on('data', (chunk: Buffer) => {
        armIdle()
        received += chunk.length
        hash.update(chunk)
        if (!stream.write(chunk) && flow.pause && flow.resume) {
          flow.pause()
          stream.once('drain', () => flow.resume?.())
        }
        if (!wc.isDestroyed()) {
          const progress: AppUpdateProgress = {
            received,
            total,
            fraction: total ? received / total : undefined
          }
          wc.send(IpcChannels.appUpdateProgress, progress)
        }
      })

      response.on('end', () => {
        // Body fully received — "stalled" is no longer meaningful past this point.
        if (idle) clearTimeout(idle)
        stream.end(() => {
          // A truncated download (connection dropped mid-stream) must never be run.
          if (total !== undefined && received !== total) {
            finish({ ok: false, error: 'The download was incomplete — please try again.' })
            return
          }
          // Verify the bytes we wrote match the release's published SHA-256.
          if (expectedSha && hash.digest('hex') !== expectedSha) {
            finish({
              ok: false,
              error:
                'The downloaded update failed its checksum check — it may be corrupt or tampered with. Nothing was installed.'
            })
            return
          }
          finish({ ok: true, filePath })
        })
      })

      // A mid-stream abort emits neither 'end' nor always 'error'; catch it so the
      // promise can't hang.
      response.on('aborted', () => finish({ ok: false, error: 'The download was interrupted.' }))
      response.on('error', (e: Error) => finish({ ok: false, error: e.message }))
      stream.on('error', (e: Error) => finish({ ok: false, error: e.message }))
    })

    request.on('error', (e: Error) => finish({ ok: false, error: e.message }))
    request.end()
  })
}

/** Launch a freshly-downloaded installer, then quit so it can replace the app. */
export async function runAppUpdate(filePath: string): Promise<{ ok: boolean; error?: string }> {
  try {
    // Defence in depth: only run a .exe that sits DIRECTLY in our own temp dir,
    // never an arbitrary path handed over IPC. Compare the parent directory by
    // equality — startsWith() is defeated by a sibling like `<temp>_evil\x.exe`.
    const expectedDir = normalize(updateDir()).toLowerCase()
    const target = normalize(filePath)
    if (dirname(target).toLowerCase() !== expectedDir || !/\.exe$/i.test(target)) {
      return { ok: false, error: 'Refused to run an unexpected file.' }
    }
    await stat(target) // throws if the file is missing
    // Hand the installer to the OS via ShellExecute, which (unlike a raw
    // CreateProcess/spawn) honors the NSIS elevation manifest — needed if the
    // build ever flips to perMachine. openPath resolves once the launch is
    // initiated, so the installer process already exists when we quit.
    const err = await shell.openPath(target)
    if (err) return { ok: false, error: err }
    // Quit on the next tick so this IPC response reaches the renderer first; the
    // launched installer is independent of our process and survives the quit.
    setImmediate(() => app.quit())
    return { ok: true }
  } catch (e) {
    return { ok: false, error: e instanceof Error ? e.message : String(e) }
  }
}