import { mkdirSync, writeFileSync } from 'node:fs'
import { dirname, join } from 'node:path'
import type { Context } from 'hono'

/**
 * Forward unmatched requests to a real upstream (PROXY_TARGET).
 * With record=true, persist the upstream JSON response as a mock file so the
 * next run serves it locally — record-once, replay-forever.
 */
export async function proxyPass(
  c: Context,
  opts: { target: string; record: boolean; routesDir: string },
): Promise<Response> {
  const reqUrl = new URL(c.req.url)
  const upstream = new URL(reqUrl.pathname + reqUrl.search, opts.target)

  const init: RequestInit = {
    method: c.req.method,
    headers: stripHopHeaders(c.req.raw.headers),
  }
  if (!['GET', 'HEAD'].includes(c.req.method)) init.body = await c.req.raw.arrayBuffer()

  const res = await fetch(upstream, init)
  const buf = await res.arrayBuffer()

  if (opts.record && res.ok && (res.headers.get('content-type') ?? '').includes('json')) {
    try {
      recordMock(opts.routesDir, reqUrl.pathname, c.req.method, JSON.parse(Buffer.from(buf).toString('utf8')))
    } catch {
      /* non-json body — skip recording */
    }
  }

  const headers = new Headers(res.headers)
  headers.set('X-Mock-Proxy', upstream.href)
  if (opts.record) headers.set('X-Mock-Recorded', 'true')
  return new Response(buf, { status: res.status, headers })
}

function recordMock(routesDir: string, pathname: string, method: string, body: unknown) {
  const segs = pathname.split('/').filter(Boolean)
  const base = segs.length ? segs.join('/') : 'index'
  const suffix = method.toLowerCase() === 'get' ? '' : `.${method.toLowerCase()}`
  const file = join(routesDir, `${base}${suffix}.json`)
  mkdirSync(dirname(file), { recursive: true })
  writeFileSync(file, JSON.stringify(body, null, 2) + '\n')
  console.log(`⤓ recorded ${method} ${pathname} -> ${file}`)
}

function stripHopHeaders(h: Headers): Headers {
  const out = new Headers(h)
  for (const k of ['host', 'connection', 'content-length', 'accept-encoding']) out.delete(k)
  return out
}