/**
 * Server-side API proxy for the backend. ⭐ THE SYSTEMIC AUTH FIX ⭐
 *
 * Do NOT replace this with a static `rewrites()` proxy in next.config.mjs. A
 * static rewrite forwards requests as-is and CANNOT inject an Authorization
 * header — that was the root cause of the "no token reaches the backend" bug
 * (every browser fetch hit the backend unauthenticated → 401/500). This cost
 * ~9 days on CannaManage; the template ships the fix so it never recurs.
 *
 * This Route Handler runs on the server, reads the NextAuth session via
 * `auth()` (so the JWT never leaves the server), and forwards the request to
 * `${BACKEND_URL}/api/v1/<path>` with `Authorization: Bearer <accessToken>`.
 *
 * Method- and content-agnostic: query string preserved; raw request body
 * streamed unparsed (JSON + multipart uploads + binary all work); upstream
 * response body streamed back verbatim (byte-exact downloads).
 *
 * Adjust the upstream path prefix (`/api/v1/`) if your backend differs.
 */
import { NextResponse } from "next/server"

import type { NextRequest } from "next/server"

import { auth } from "@/lib/auth"

// Always run dynamically — this proxy depends on per-request auth + body.
export const dynamic = "force-dynamic"

const BACKEND_URL = process.env.BACKEND_URL || "http://localhost:8080"

// Hop-by-hop and host-specific headers that must not be forwarded upstream.
const STRIPPED_REQUEST_HEADERS = new Set([
  "host",
  "connection",
  "content-length",
  "transfer-encoding",
  "accept-encoding",
])

// Headers that must not be copied from the upstream response back to the client.
const STRIPPED_RESPONSE_HEADERS = new Set([
  "connection",
  "transfer-encoding",
  "content-encoding",
  "content-length",
])

async function proxy(req: NextRequest, path: string[]): Promise<NextResponse> {
  const session = await auth()
  const accessToken = session?.accessToken

  // Build the upstream URL: /api/backend/<path> → BACKEND_URL/api/v1/<path>
  const search = req.nextUrl.search // includes leading "?" or ""
  const upstreamUrl = `${BACKEND_URL}/api/v1/${path.join("/")}${search}`

  // Clone the incoming headers, stripping hop-by-hop/host ones, then inject auth.
  const headers = new Headers()
  req.headers.forEach((value, key) => {
    if (!STRIPPED_REQUEST_HEADERS.has(key.toLowerCase())) {
      headers.set(key, value)
    }
  })
  if (accessToken) {
    headers.set("Authorization", `Bearer ${accessToken}`)
  }

  const method = req.method.toUpperCase()
  const hasBody = method !== "GET" && method !== "HEAD"

  try {
    const upstream = await fetch(upstreamUrl, {
      method,
      headers,
      // Stream the raw body through unparsed (works for JSON + multipart + binary).
      body: hasBody ? req.body : undefined,
      // Required by undici/Node when sending a streaming request body.
      ...(hasBody ? { duplex: "half" } : {}),
      redirect: "manual",
      cache: "no-store",
    } as RequestInit)

    // Copy upstream response headers, dropping ones that break a re-emitted body.
    const responseHeaders = new Headers()
    upstream.headers.forEach((value, key) => {
      if (!STRIPPED_RESPONSE_HEADERS.has(key.toLowerCase())) {
        responseHeaders.set(key, value)
      }
    })

    // Stream the body straight back — byte-exact for downloads.
    return new NextResponse(upstream.body, {
      status: upstream.status,
      statusText: upstream.statusText,
      headers: responseHeaders,
    })
  } catch {
    return NextResponse.json(
      { code: "BACKEND_UNREACHABLE", message: "Unable to reach the API." },
      { status: 502 }
    )
  }
}

// Next.js 15: the second arg's `params` is a Promise.
type Ctx = { params: Promise<{ path: string[] }> }

export async function GET(req: NextRequest, ctx: Ctx) {
  return proxy(req, (await ctx.params).path)
}
export async function POST(req: NextRequest, ctx: Ctx) {
  return proxy(req, (await ctx.params).path)
}
export async function PUT(req: NextRequest, ctx: Ctx) {
  return proxy(req, (await ctx.params).path)
}
export async function PATCH(req: NextRequest, ctx: Ctx) {
  return proxy(req, (await ctx.params).path)
}
export async function DELETE(req: NextRequest, ctx: Ctx) {
  return proxy(req, (await ctx.params).path)
}