/**
 * POST /api/upload
 *
 * Multipart endpoint that accepts a single file plus the form's auth pair
 * (cid + cs) and the target Civi field reference. Verifies, validates,
 * stores in CiviCRM via Attachment.create, returns { id, file_name }.
 *
 * The form's file renderer calls this on file-pick (not at submit time)
 * so submit can stay a simple JSON POST. The returned { id, file_name }
 * is what gets put into RHF state and ultimately submitted as the field
 * value — the same shape /api/data uses for prefill, so the renderer's
 * FilePriorIndicator works unchanged for fresh uploads too.
 *
 * Request: multipart/form-data with parts:
 *   - file       the binary
 *   - cid        contact id (form auth)
 *   - cs         checksum    (form auth)
 *   - fieldRef   the Civi field reference, e.g. "Stage_1.Vision_Upload"
 *                or "Food_Co_op_Organizing.Certificate_of_Incorporation"
 *
 * Response: { id: number, file_name: string }  OR  { error: string }
 *
 * STUB MODE: if CiviCRM env vars are unset, returns a fake id + the
 * uploaded filename so frontend dev works without a live CRM.
 */

import { NextResponse } from "next/server";
import { civi, verifyChecksum } from "@/lib/civicrm";
import { allFields } from "@/config/form";
import { rateLimit, clientIp } from "@/lib/rate-limit";

// 5 MB hard cap. Sits under AWS Amplify Lambda's 6 MB sync invocation
// payload limit with headroom for multipart envelope overhead.
const MAX_BYTES = 5 * 1024 * 1024;

// Per the v1 spec: PDF, DOC/DOCX, XLS/XLSX, common image types.
const ALLOWED_MIME = new Set<string>([
  "application/pdf",
  "application/msword",
  "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
  "application/vnd.ms-excel",
  "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
  "image/jpeg",
  "image/png",
  "image/gif",
  "image/webp",
]);

// Magic-byte sniff for the most common forgeries. Don't trust client-
// reported MIME alone — a renamed .exe shouldn't slip past us on the
// strength of a "Content-Type: application/pdf" header.
function sniffMime(bytes: Uint8Array): string | null {
  if (bytes.length < 8) return null;
  const b = bytes;
  // %PDF
  if (b[0] === 0x25 && b[1] === 0x50 && b[2] === 0x44 && b[3] === 0x46) {
    return "application/pdf";
  }
  // PK (ZIP container — docx/xlsx)
  if (b[0] === 0x50 && b[1] === 0x4b && (b[2] === 0x03 || b[2] === 0x05 || b[2] === 0x07)) {
    return "application/zip"; // accept-with-allowlist handles docx/xlsx
  }
  // OLE compound (legacy doc/xls)
  if (
    b[0] === 0xd0 && b[1] === 0xcf && b[2] === 0x11 && b[3] === 0xe0 &&
    b[4] === 0xa1 && b[5] === 0xb1 && b[6] === 0x1a && b[7] === 0xe1
  ) {
    return "application/x-ole-storage";
  }
  // JPEG
  if (b[0] === 0xff && b[1] === 0xd8 && b[2] === 0xff) return "image/jpeg";
  // PNG
  if (b[0] === 0x89 && b[1] === 0x50 && b[2] === 0x4e && b[3] === 0x47) return "image/png";
  // GIF
  if (b[0] === 0x47 && b[1] === 0x49 && b[2] === 0x46 && b[3] === 0x38) return "image/gif";
  // WEBP — "RIFF????WEBP"
  if (b[0] === 0x52 && b[1] === 0x49 && b[2] === 0x46 && b[3] === 0x46 &&
      b[8] === 0x57 && b[9] === 0x45 && b[10] === 0x42 && b[11] === 0x50) {
    return "image/webp";
  }
  return null;
}

// Office formats (docx/xlsx) sniff as application/zip via PK header but
// are allowed at the client-reported MIME level. The mime check below
// keeps both axes honest: client mime must be in ALLOWED_MIME, AND the
// magic bytes must be plausible for that mime.
function mimePlausible(clientMime: string, sniffed: string | null): boolean {
  if (!sniffed) return false;
  if (sniffed === clientMime) return true;
  // docx/xlsx are zips under the hood — accept the alias.
  const zipAliased = new Set([
    "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
    "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
  ]);
  if (sniffed === "application/zip" && zipAliased.has(clientMime)) return true;
  // Legacy doc/xls share the OLE container.
  const oleAliased = new Set(["application/msword", "application/vnd.ms-excel"]);
  if (sniffed === "application/x-ole-storage" && oleAliased.has(clientMime)) return true;
  return false;
}

// Path-traversal scrub + length cap. Civi will store its own normalized
// name internally; this is purely defensive.
function sanitizeFilename(name: string): string {
  const base = name.split(/[\\/]/).pop() ?? name;
  // Drop control chars and anything that's not letters/digits/dot/dash/underscore/space.
  const cleaned = base.replace(/[^\w.\- ]/g, "_").trim();
  return cleaned.slice(0, 200) || "upload";
}

function isStubMode(): boolean {
  return !(
    process.env.CIVI_BASE_URL &&
    process.env.CIVI_API_KEY &&
    process.env.CIVI_SITE_KEY
  );
}

const FILE_FIELD_REFS = new Set(
  allFields
    .filter((f) => f.type === "file" && (f.civiField || f.civiContactField))
    .map((f) => f.civiField ?? f.civiContactField!),
);

export async function POST(req: Request) {
  // Generous-but-not-unlimited: 5 uploads per minute per IP. Captures
  // accidental retry loops without throttling legitimate use (a form
  // with 4 file fields fills in well under a minute).
  const ip = clientIp(req);
  const rl = rateLimit(`upload:${ip}`, { capacity: 5, windowMs: 60_000 });
  if (!rl.allowed) {
    return NextResponse.json(
      { error: "Too many uploads. Please wait a moment and try again." },
      { status: 429, headers: { "Retry-After": String(Math.ceil(rl.resetMs / 1000)) } },
    );
  }

  // Parse multipart. Next 16 supports Request.formData() natively.
  let form: FormData;
  try {
    form = await req.formData();
  } catch {
    return NextResponse.json({ error: "Expected multipart/form-data." }, { status: 400 });
  }

  const cid = (form.get("cid") as string | null) ?? "";
  const cs = (form.get("cs") as string | null) ?? "";
  const fieldRef = (form.get("fieldRef") as string | null) ?? "";
  const fileEntry = form.get("file");

  if (!cid || !cs) {
    return NextResponse.json({ error: "Missing cid or cs." }, { status: 400 });
  }
  if (!fieldRef || !FILE_FIELD_REFS.has(fieldRef)) {
    // Refusing unknown fieldRefs blocks the obvious abuse vector: a
    // client posting an upload pointed at an arbitrary Civi field.
    return NextResponse.json({ error: "Unknown or non-file field reference." }, { status: 400 });
  }
  if (!(fileEntry instanceof File)) {
    return NextResponse.json({ error: "Missing file part." }, { status: 400 });
  }
  if (fileEntry.size === 0) {
    return NextResponse.json({ error: "Empty file." }, { status: 400 });
  }
  if (fileEntry.size > MAX_BYTES) {
    return NextResponse.json(
      { error: `File too large. Maximum is ${MAX_BYTES / (1024 * 1024)} MB.` },
      { status: 413 },
    );
  }
  const clientMime = fileEntry.type || "application/octet-stream";
  if (!ALLOWED_MIME.has(clientMime)) {
    return NextResponse.json(
      { error: `File type ${clientMime} is not allowed.` },
      { status: 415 },
    );
  }

  const bytes = new Uint8Array(await fileEntry.arrayBuffer());
  const sniffed = sniffMime(bytes);
  if (!mimePlausible(clientMime, sniffed)) {
    return NextResponse.json(
      { error: "File contents don't match the declared type." },
      { status: 415 },
    );
  }

  const safeName = sanitizeFilename(fileEntry.name);

  if (isStubMode()) {
    console.warn(
      "[upload:STUB] would Attachment.create",
      JSON.stringify({ name: safeName, mime: clientMime, bytes: fileEntry.size, fieldRef }),
    );
    return NextResponse.json({ id: -1, file_name: safeName, stub: true });
  }

  // Auth: verify the form's checksum before doing anything Civi-side.
  const ok = await verifyChecksum(cid, cs);
  if (!ok) {
    return NextResponse.json(
      { error: "Link is invalid or has expired." },
      { status: 401 },
    );
  }

  // APIv4 File.create with inline base64 content. Spike (June 2026) on
  // this Civi instance confirmed:
  //   - APIv4 Attachment is NOT exposed
  //   - APIv4 File + EntityFile ARE exposed
  //   - File.create with file_name + mime_type + content (base64) returns
  //     a usable file id
  //   - Custom file fields store the file id directly in the custom
  //     column, so EntityFile linkage is not needed for our use case
  //   - Round-trip via Contact.update + Contact.get .file_name join works
  //
  // We do not create EntityFile rows here. Civi's custom-field renderer
  // joins through the custom column to civicrm_file directly, and the
  // form-side prefill/read code in /api/data uses the same join.
  //
  // The returned id is what the frontend stores in RHF state and
  // ultimately sends as the field value on /api/submit. /api/submit then
  // writes that id to the activity custom field (for stage-N file fields)
  // or to the org contact custom field (for Food_Co_op_Organizing.*).
  //
  // Orphan files: if the user uploads and then abandons the form, the
  // File row persists with no entity referencing it. Cleanup is handled
  // by a CiviCRM scheduled job (configured separately by the Civi admin)
  // that deletes File rows with no inbound references older than ~24h.
  let fileId: number;
  try {
    const res = await civi<{ id: number }>("File", "create", {
      values: {
        file_name: safeName,
        mime_type: clientMime,
        content: Buffer.from(bytes).toString("base64"),
      },
    });
    const id = res.values?.[0]?.id;
    if (!id) throw new Error("File.create returned no id");
    fileId = Number(id);
  } catch (err) {
    const msg = err instanceof Error ? err.message : String(err);
    console.error("[upload] File.create failed:", msg);
    return NextResponse.json(
      { error: "Could not save the upload. Please try again." },
      { status: 502 },
    );
  }

  return NextResponse.json({ id: fileId, file_name: safeName });
}