import crypto from 'node:crypto';
import fs from 'node:fs';
import path from 'node:path';
import { Readable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

import { NextResponse } from 'next/server';

import {
  maxRetentionSeconds,
  maxUploadBytes,
  shareDir,
  uploadTtlSeconds,
} from '@/src/lib/config.js';
import { get, logEvent, run, runCleanupIfNeeded } from '@/src/lib/db.js';
import { safeBaseName } from '@/src/lib/files.js';
import { sendUploadRequestCompletedMail } from '@/src/lib/mailer.js';
import { getRequestMeta } from '@/src/lib/security.js';

export const runtime = 'nodejs';
export const dynamic = 'force-dynamic';

function normalizeRequestId(value) {
  return String(value || '').trim().toUpperCase();
}

function isValidRequestId(value) {
  return /^[A-Z2-7]{6,24}$/.test(value);
}

function requestPageHref(requestId, params = {}) {
  const query = new URLSearchParams();
  for (const [key, value] of Object.entries(params)) {
    if (value) {
      query.set(key, String(value));
    }
  }

  const encodedId = encodeURIComponent(requestId);
  const serialized = query.toString();
  return serialized ? `/_request/${encodedId}?${serialized}` : `/_request/${encodedId}`;
}

function redirectToRequest(request, requestId, params = {}) {
  return NextResponse.redirect(new URL(requestPageHref(requestId, params), request.url), { status: 303 });
}

function toBase32(buffer) {
  const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';
  let bits = 0;
  let value = 0;
  let output = '';

  for (const byte of buffer) {
    value = (value << 8) | byte;
    bits += 8;

    while (bits >= 5) {
      output += alphabet[(value >>> (bits - 5)) & 31];
      bits -= 5;
    }
  }

  if (bits > 0) {
    output += alphabet[(value << (5 - bits)) & 31];
  }

  return output;
}

function createRandomId() {
  return toBase32(crypto.randomBytes(5));
}

function uploadedFileFromForm(formData, fieldName = 'file') {
  const candidate = formData.get(fieldName);
  if (!candidate || typeof candidate === 'string') {
    return null;
  }
  if (typeof candidate.arrayBuffer !== 'function') {
    return null;
  }
  return candidate;
}

async function writeUploadedFile(uploadedFile, targetPath) {
  try {
    if (typeof uploadedFile.stream === 'function') {
      await pipeline(Readable.fromWeb(uploadedFile.stream()), fs.createWriteStream(targetPath));
    } else {
      const buffer = Buffer.from(await uploadedFile.arrayBuffer());
      await fs.promises.writeFile(targetPath, buffer);
    }
  } catch (error) {
    await fs.promises.rm(targetPath, { force: true }).catch(() => undefined);
    throw error;
  }

  const declaredSize = Number(uploadedFile.size || 0);
  if (Number.isFinite(declaredSize) && declaredSize >= 0) {
    return declaredSize;
  }

  const stat = await fs.promises.stat(targetPath);
  return stat.size;
}

export async function POST(request, { params }) {
  await runCleanupIfNeeded();

  const resolvedParams = await params;
  const requestId = normalizeRequestId(resolvedParams.id);

  if (!isValidRequestId(requestId)) {
    return new NextResponse('Ungültige Anfrage-ID', { status: 400 });
  }

  let formData;
  try {
    formData = await request.formData();
  } catch {
    return redirectToRequest(request, requestId, { error: 'Ungültige Formulardaten.' });
  }

  const uploadRequest = await get(
    `SELECT id, owner, note, expires_at, completed_at
     FROM upload_requests
     WHERE id = ?`,
    [requestId]
  );

  if (!uploadRequest) {
    return redirectToRequest(request, requestId, { error: 'Anfrage nicht gefunden.' });
  }

  if (Number(uploadRequest.completed_at || 0) > 0) {
    return redirectToRequest(request, requestId, { success: 'Diese Anfrage wurde bereits erfüllt.' });
  }

  const now = Date.now();
  if (Number(uploadRequest.expires_at || 0) <= now) {
    return redirectToRequest(request, requestId, { error: 'Diese Anfrage ist bereits abgelaufen.' });
  }

  const uploadedFile = uploadedFileFromForm(formData, 'file');
  if (!uploadedFile || Number(uploadedFile.size || 0) <= 0) {
    return redirectToRequest(request, requestId, { error: 'Keine Datei hochgeladen.' });
  }

  if (maxUploadBytes > 0 && Number(uploadedFile.size || 0) > maxUploadBytes) {
    return redirectToRequest(request, requestId, {
      error: `Datei überschreitet das Größenlimit (${maxUploadBytes} Bytes).`,
    });
  }

  const fulfilledBy = String(formData.get('fulfilledBy') || '').trim().slice(0, 200);
  const originalName = safeBaseName(uploadedFile.name, 'upload');

  let storedName = '';
  let storedPath = '';
  for (let attempts = 0; attempts < 12; attempts += 1) {
    const candidate = createRandomId();
    const candidatePath = path.join(shareDir, candidate);
    try {
      await fs.promises.access(candidatePath, fs.constants.F_OK);
    } catch {
      storedName = candidate;
      storedPath = candidatePath;
      break;
    }
  }

  if (!storedName || !storedPath) {
    return redirectToRequest(request, requestId, { error: 'Upload-ID konnte nicht erzeugt werden.' });
  }

  const uploadExpiry = Math.min(now + uploadTtlSeconds * 1000, now + maxRetentionSeconds * 1000);

  let uploadId = null;
  let sizeBytes = 0;
  try {
    sizeBytes = await writeUploadedFile(uploadedFile, storedPath);
    const insertResult = await run(
      `INSERT INTO uploads (owner, original_name, stored_name, stored_path, size_bytes, uploaded_at, expires_at)
       VALUES (?, ?, ?, ?, ?, ?, ?)`,
      [uploadRequest.owner, originalName, storedName, storedPath, sizeBytes, now, uploadExpiry]
    );
    uploadId = insertResult.lastID;
  } catch {
    return redirectToRequest(request, requestId, { error: 'Upload fehlgeschlagen.' });
  }

  const updateResult = await run(
    `UPDATE upload_requests
     SET completed_at = ?,
         upload_id = ?,
         uploaded_original_name = ?,
         uploaded_stored_name = ?,
         uploaded_stored_path = ?,
         uploaded_size_bytes = ?,
         fulfilled_by = ?
     WHERE id = ? AND completed_at IS NULL`,
    [now, uploadId, originalName, storedName, storedPath, sizeBytes, fulfilledBy || null, requestId]
  );

  if (!updateResult || updateResult.changes < 1) {
    await run('DELETE FROM uploads WHERE id = ?', [uploadId]).catch(() => undefined);
    await fs.promises.rm(storedPath, { force: true }).catch(() => undefined);
    return redirectToRequest(request, requestId, { success: 'Diese Anfrage wurde bereits erfüllt.' });
  }

  await logEvent(
    'request_fulfilled',
    uploadRequest.owner,
    { request_id: requestId, upload_id: uploadId, stored_name: storedName, fulfilled_by: fulfilledBy || null },
    await getRequestMeta()
  );

  const baseUrl = new URL(request.url).origin;
  const downloadUrl = `${baseUrl}/_share/${encodeURIComponent(storedName)}`;

  const mailResult = await sendUploadRequestCompletedMail({
    recipient: uploadRequest.owner,
    requestId,
    fileName: originalName,
    downloadUrl,
    requesterNote: uploadRequest.note || '',
    fulfilledBy,
  });

  if (mailResult.ok) {
    await run('UPDATE upload_requests SET notification_sent_at = ? WHERE id = ?', [Date.now(), requestId]);
    return redirectToRequest(request, requestId, { success: 'Datei erfolgreich hochgeladen. Vielen Dank!' });
  }

  await logEvent(
    'request_mail_failed',
    uploadRequest.owner,
    { request_id: requestId, reason: mailResult.reason || 'unknown' },
    await getRequestMeta()
  );

  return redirectToRequest(request, requestId, {
    success: 'Datei hochgeladen. Hinweis: E-Mail-Benachrichtigung konnte nicht gesendet werden.',
  });
}