import { createHash, randomUUID } from "node:crypto";
import { constants as fsConstants, createReadStream, createWriteStream } from "node:fs";
import { chmod, mkdir, open, readFile, readdir, rename, rm, stat, unlink } from "node:fs/promises";
import path from "node:path";
import { Transform } from "node:stream";
import { pipeline } from "node:stream/promises";
import type { MultipartFile } from "@fastify/multipart";
import type Database from "better-sqlite3";
import { XMLParser, XMLValidator } from "fast-xml-parser";
import { PDFDocument } from "pdf-lib";
import sharp from "sharp";
import yauzl from "yauzl";
import type { AttachmentKind } from "../shared/contracts.js";
import type { AppConfig } from "./config.js";
import { AppError } from "./errors.js";

export type StagedFile = {
  id: string;
  originalName: string;
  stagingPath: string;
  sizeBytes: number;
  sha256: string;
  mimeType: string;
  extension: string;
  kind: AttachmentKind;
};

const imageTypes = new Map([
  ["jpeg", { mimeType: "image/jpeg", extension: "jpg" }],
  ["png", { mimeType: "image/png", extension: "png" }],
  ["webp", { mimeType: "image/webp", extension: "webp" }],
]);

export function sanitizeOriginalName(value: string): string {
  const normalized = path.basename(value.normalize("NFKC").replaceAll("\\", "/")).replace(/[\u0000-\u001f\u007f]/g, "").trim();
  return (normalized || "未命名文件").slice(0, 200);
}

function detectBasic(buffer: Buffer): "jpeg" | "png" | "webp" | "pdf" | "ofd" | "xml" | null {
  if (buffer.length >= 4 && buffer[0] === 0xff && buffer[1] === 0xd8 && buffer[2] === 0xff) return "jpeg";
  if (buffer.subarray(0, 8).equals(Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]))) return "png";
  if (buffer.subarray(0, 4).toString("ascii") === "RIFF" && buffer.subarray(8, 12).toString("ascii") === "WEBP") return "webp";
  if (buffer.subarray(0, 5).toString("ascii") === "%PDF-") return "pdf";
  if (buffer[0] === 0x50 && buffer[1] === 0x4b) return "ofd";
  const prefix = buffer.subarray(0, 256).toString("utf8").trimStart();
  if (prefix.startsWith("<?xml") || prefix.startsWith("<")) return "xml";
  return null;
}

async function validateOfd(buffer: Buffer): Promise<void> {
  await new Promise<void>((resolve, reject) => {
    yauzl.fromBuffer(buffer, { lazyEntries: true, validateEntrySizes: true }, (error, zip) => {
      if (error || !zip) return reject(error ?? new Error("无法读取 OFD"));
      let entries = 0;
      let total = 0;
      let hasRoot = false;
      let settled = false;
      const fail = (reason: Error) => {
        if (settled) return;
        settled = true;
        zip.close();
        reject(reason);
      };
      zip.on("entry", (entry) => {
        entries += 1;
        total += entry.uncompressedSize;
        const name = entry.fileName.replaceAll("\\", "/");
        if (name === "OFD.xml") hasRoot = true;
        if (entries > 2000 || total > 200 * 1024 * 1024 || name.startsWith("/") || name.split("/").includes("..")) {
          fail(new Error("OFD 结构超出安全限制"));
          return;
        }
        zip.readEntry();
      });
      zip.on("end", () => {
        if (settled) return;
        settled = true;
        hasRoot ? resolve() : reject(new Error("缺少 OFD.xml"));
      });
      zip.on("error", fail);
      zip.readEntry();
    });
  });
}

async function validateContent(buffer: Buffer, kind: AttachmentKind): Promise<{ mimeType: string; extension: string }> {
  const detected = detectBasic(buffer);
  if (!detected) throw new AppError(415, "UNSUPPORTED_MEDIA_TYPE", "无法识别文件格式");
  if (imageTypes.has(detected)) {
    const metadata = await sharp(buffer, { failOn: "error", limitInputPixels: 40_000_000 }).metadata();
    if (!metadata.width || !metadata.height || !metadata.format || !imageTypes.has(metadata.format)) {
      throw new AppError(415, "INVALID_IMAGE", "图片内容无效");
    }
    return imageTypes.get(metadata.format)!;
  }
  if (kind === "payment_proof") {
    throw new AppError(415, "PAYMENT_PROOF_MUST_BE_IMAGE", "付款凭证仅支持 JPEG、PNG 或 WebP 图片");
  }
  if (detected === "pdf") {
    // Inspect the binary token stream case-insensitively. PDF names are
    // case-sensitive in theory, but rejecting common active-content aliases
    // avoids browser/plugin execution surprises across viewers.
    const pdfTokens = buffer.toString("latin1");
    const suspicious = /\/(?:JavaScript|JS|Launch|EmbeddedFile|OpenAction|AA)\b/i.test(pdfTokens);
    if (suspicious) throw new AppError(415, "UNSAFE_PDF", "PDF 包含不受支持的活动内容");
    const document = await PDFDocument.load(buffer, { ignoreEncryption: false, throwOnInvalidObject: true });
    if (document.getPageCount() < 1 || document.getPageCount() > 2000) throw new Error("PDF 页数无效");
    return { mimeType: "application/pdf", extension: "pdf" };
  }
  if (detected === "ofd") {
    await validateOfd(buffer);
    return { mimeType: "application/ofd", extension: "ofd" };
  }
  const xml = buffer.toString("utf8");
  if (/<!DOCTYPE|<!ENTITY/i.test(xml)) throw new AppError(415, "UNSAFE_XML", "XML 不允许 DTD 或实体声明");
  if (XMLValidator.validate(xml) !== true) throw new AppError(415, "INVALID_XML", "XML 内容无效");
  new XMLParser({ processEntities: false, ignoreAttributes: false }).parse(xml);
  return { mimeType: "application/xml", extension: "xml" };
}

export async function stageMultipartFile(config: AppConfig, part: MultipartFile, kind: AttachmentKind): Promise<StagedFile> {
  const id = randomUUID();
  const stagingPath = path.join(config.stagingDir, `${id}.part`);
  let sizeBytes = 0;
  const hash = createHash("sha256");
  const meter = new Transform({
    transform(chunk: Buffer, _encoding, callback) {
      sizeBytes += chunk.length;
      if (sizeBytes > config.maxFileBytes) return callback(new AppError(413, "FILE_TOO_LARGE", "单个文件超过大小限制"));
      hash.update(chunk);
      callback(null, chunk);
    },
  });
  try {
    await pipeline(part.file, meter, createWriteStream(stagingPath, { flags: "wx", mode: 0o600 }));
    if (part.file.truncated || sizeBytes === 0) throw new AppError(413, "FILE_TOO_LARGE", "文件为空或超过大小限制");
    const buffer = await readFile(stagingPath);
    const type = await validateContent(buffer, kind);
    return {
      id,
      originalName: sanitizeOriginalName(part.filename),
      stagingPath,
      sizeBytes,
      sha256: hash.digest("hex"),
      mimeType: type.mimeType,
      extension: type.extension,
      kind,
    };
  } catch (error) {
    await rm(stagingPath, { force: true });
    if (error instanceof AppError) throw error;
    throw new AppError(415, "INVALID_FILE", "文件内容校验失败");
  }
}

export async function promoteStagedFile(config: AppConfig, file: StagedFile): Promise<string> {
  const relative = path.join(file.id.slice(0, 2), `${file.id}.${file.extension}`);
  const destination = safeStoragePath(config.filesDir, relative);
  await mkdir(path.dirname(destination), { recursive: true, mode: 0o700 });
  await chmod(path.dirname(destination), 0o700);
  await rename(file.stagingPath, destination);
  const directory = await open(path.dirname(destination), "r");
  await directory.sync();
  await directory.close();
  return relative;
}

export function safeStoragePath(root: string, relative: string): string {
  if (path.isAbsolute(relative)) throw new AppError(500, "INVALID_STORAGE_PATH", "附件路径无效");
  const resolvedRoot = path.resolve(root);
  const resolved = path.resolve(root, relative);
  if (!resolved.startsWith(`${resolvedRoot}${path.sep}`)) throw new AppError(500, "INVALID_STORAGE_PATH", "附件路径无效");
  return resolved;
}

export async function discardStaged(files: StagedFile[]): Promise<void> {
  await Promise.all(files.map((file) => rm(file.stagingPath, { force: true })));
}

export async function processFileDeletions(sqlite: Database.Database, config: AppConfig): Promise<void> {
  const rows = sqlite.prepare(`
    SELECT id, storage_path AS storagePath FROM file_deletions
    WHERE status IN ('pending','failed') AND attempts < 10 ORDER BY created_at LIMIT 100
  `).all() as Array<{ id: string; storagePath: string }>;
  for (const row of rows) {
    try {
      await unlink(safeStoragePath(config.filesDir, row.storagePath)).catch((error: NodeJS.ErrnoException) => {
        if (error.code !== "ENOENT") throw error;
      });
      sqlite.prepare("UPDATE file_deletions SET status='complete', attempts=attempts+1, last_error=NULL, completed_at=? WHERE id=?").run(Date.now(), row.id);
    } catch (error) {
      sqlite.prepare("UPDATE file_deletions SET status='failed', attempts=attempts+1, last_error=? WHERE id=?").run(String(error).slice(0, 500), row.id);
    }
  }
}

export async function cleanupStaging(config: AppConfig): Promise<void> {
  const cutoff = Date.now() - 24 * 60 * 60 * 1000;
  for (const entry of await readdir(config.stagingDir, { withFileTypes: true })) {
    const target = path.join(config.stagingDir, entry.name);
    const info = await stat(target).catch(() => null);
    if (info && info.mtimeMs < cutoff) await rm(target, { recursive: true, force: true });
  }
}

export async function cleanupOrphanedFiles(sqlite: Database.Database, config: AppConfig): Promise<void> {
  const referenced = new Set((sqlite.prepare("SELECT storage_path AS storagePath FROM attachments").all() as Array<{ storagePath: string }>).map((row) => row.storagePath));
  const cutoff = Date.now() - 24 * 60 * 60 * 1000;
  const walk = async (directory: string, prefix: string): Promise<void> => {
    for (const entry of await readdir(directory, { withFileTypes: true })) {
      const relative = path.join(prefix, entry.name);
      const target = path.join(directory, entry.name);
      if (entry.isDirectory()) {
        await walk(target, relative);
        continue;
      }
      if (!entry.isFile() && !entry.isSymbolicLink()) continue;
      const info = await stat(target).catch(() => null);
      if (info && info.mtimeMs < cutoff && !referenced.has(relative)) await rm(target, { force: true });
    }
  };
  await walk(config.filesDir, "");
}

export async function fileReadStream(config: AppConfig, storagePath: string) {
  return safeReadStream(config.filesDir, storagePath);
}

/** Open a private file by descriptor and keep the no-follow guarantee through
 * the subsequent read. Used for both attachment and export downloads. */
export async function safeReadStream(root: string, relativePath: string) {
  const handle = await open(safeStoragePath(root, relativePath), fsConstants.O_RDONLY | (fsConstants.O_NOFOLLOW ?? 0));
  try {
    const info = await handle.stat();
    if (!info.isFile()) throw new AppError(410, "ATTACHMENT_MISSING", "附件文件已不可用");
    return handle.createReadStream({ autoClose: true });
  } catch (error) {
    await handle.close().catch(() => undefined);
    throw error;
  }
}

export async function readStorageFile(config: AppConfig, storagePath: string): Promise<Buffer> {
  const handle = await open(safeStoragePath(config.filesDir, storagePath), fsConstants.O_RDONLY | (fsConstants.O_NOFOLLOW ?? 0));
  try {
    const info = await handle.stat();
    if (!info.isFile()) throw new AppError(410, "ATTACHMENT_MISSING", "附件文件已不可用");
    return await handle.readFile();
  } finally {
    await handle.close();
  }
}