"use strict";

const http = require("http");
const fs = require("fs");
const fsp = fs.promises;
const path = require("path");
const { URL } = require("url");

const { requireAdmin } = require("./auth");
const { SseHub } = require("./sse");
const { TaskRepository } = require("./data/repository");
const { pruneConversationContext } = require("./data/tree-pruner");

const HOST = process.env.HOST || "127.0.0.1";
const PORT = Number(process.env.PORT) || 3001;
const FRONTEND_DIR = path.join(__dirname, "..", "frontend");
const DATA_FILE = process.env.TASK_BOARD_DATA_FILE || path.join(__dirname, "..", "tasks.json");
const MAX_BODY_SIZE = 2 * 1024 * 1024;
const PUBLIC_RATE_LIMIT = Number.isFinite(Number(process.env.TASK_BOARD_PUBLIC_RATE_LIMIT))
  ? Math.max(20, Number(process.env.TASK_BOARD_PUBLIC_RATE_LIMIT))
  : 180;
const PUBLIC_RATE_WINDOW_MS = 60 * 1000;
const PUBLIC_ORIGIN_LIST = String(process.env.TASK_BOARD_PUBLIC_ORIGINS || "*")
  .split(",")
  .map((item) => item.trim())
  .filter(Boolean);

const MIME_TYPES = {
  ".html": "text/html; charset=utf-8",
  ".css": "text/css; charset=utf-8",
  ".js": "application/javascript; charset=utf-8",
  ".json": "application/json; charset=utf-8",
  ".svg": "image/svg+xml",
  ".png": "image/png",
  ".ico": "image/x-icon",
};

const repository = new TaskRepository({ filePath: DATA_FILE });
const sseHub = new SseHub();
const publicRateMap = new Map();

function nowIso() {
  return new Date().toISOString();
}

function sendJson(res, statusCode, payload, extraHeaders = {}) {
  res.writeHead(statusCode, {
    "Content-Type": "application/json; charset=utf-8",
    "Cache-Control": "no-store",
    ...extraHeaders,
  });
  res.end(JSON.stringify(payload));
}

function sendText(res, statusCode, text, extraHeaders = {}) {
  res.writeHead(statusCode, {
    "Content-Type": "text/plain; charset=utf-8",
    ...extraHeaders,
  });
  res.end(text);
}

function jsonError(res, statusCode, message) {
  sendJson(res, statusCode, { error: message });
}

function isOriginAllowed(origin) {
  if (!origin) return false;
  if (PUBLIC_ORIGIN_LIST.includes("*")) return true;
  return PUBLIC_ORIGIN_LIST.includes(origin);
}

function applyCors(req, res) {
  const origin = typeof req.headers.origin === "string" ? req.headers.origin : "";
  if (origin && isOriginAllowed(origin)) {
    res.setHeader("Access-Control-Allow-Origin", origin);
    res.setHeader("Vary", "Origin");
  } else if (!origin && PUBLIC_ORIGIN_LIST.includes("*")) {
    res.setHeader("Access-Control-Allow-Origin", "*");
  } else if (PUBLIC_ORIGIN_LIST.includes("*")) {
    res.setHeader("Access-Control-Allow-Origin", "*");
  }
  res.setHeader("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS");
  res.setHeader("Access-Control-Allow-Headers", "Content-Type,Authorization");
  res.setHeader("Access-Control-Expose-Headers", "Content-Type,Cache-Control");
}

function getClientIp(req) {
  const forwarded = req.headers["x-forwarded-for"];
  if (typeof forwarded === "string" && forwarded.trim()) {
    return forwarded.split(",")[0].trim();
  }
  return req.socket.remoteAddress || "unknown";
}

function checkPublicRateLimit(req, res) {
  const ip = getClientIp(req);
  const now = Date.now();
  const entry = publicRateMap.get(ip);
  if (!entry || now >= entry.resetAt) {
    publicRateMap.set(ip, {
      count: 1,
      resetAt: now + PUBLIC_RATE_WINDOW_MS,
    });
    return true;
  }

  entry.count += 1;
  if (entry.count <= PUBLIC_RATE_LIMIT) {
    return true;
  }

  const retrySec = Math.max(1, Math.ceil((entry.resetAt - now) / 1000));
  sendJson(
    res,
    429,
    {
      error: "Too Many Requests",
      retryAfterSec: retrySec,
    },
    { "Retry-After": String(retrySec) },
  );
  return false;
}

function parseBody(req) {
  return new Promise((resolve, reject) => {
    let body = "";
    let received = 0;

    req.on("data", (chunk) => {
      received += chunk.length;
      if (received > MAX_BODY_SIZE) {
        reject(new Error("Body too large"));
        req.destroy();
        return;
      }
      body += chunk.toString("utf8");
    });

    req.on("end", () => {
      if (!body.trim()) {
        resolve({});
        return;
      }
      try {
        const parsed = JSON.parse(body);
        resolve(parsed && typeof parsed === "object" ? parsed : {});
      } catch {
        reject(new Error("Invalid JSON"));
      }
    });
    req.on("error", reject);
  });
}

async function resolveStaticPath(urlPath) {
  const safePath = path.normalize(urlPath).replace(/^(\.\.[/\\])+/, "");
  if (safePath === "/" || safePath === ".") {
    return path.join(FRONTEND_DIR, "index.html");
  }
  const fullPath = path.join(FRONTEND_DIR, safePath);
  if (!fullPath.startsWith(FRONTEND_DIR)) return null;
  return fullPath;
}

function mapNodeToLegacyTask(node) {
  return {
    id: node.id,
    name: node.name,
    parentId: node.parentId,
    status: node.status,
    createdAt: node.timestamps.created,
    updatedAt: node.updatedAt,
    startTime: node.timestamps.started,
    endTime: node.timestamps.completed,
    plannedApproach: node.plannedApproach || "",
    bugDetails: node.bugDetails || "",
    notes: node.notes || node.content || "",
  };
}

async function handlePublicApi(req, res, pathname) {
  if (!checkPublicRateLimit(req, res)) return;

  if (req.method === "GET" && pathname === "/api/public/conversations") {
    const conversations = await repository.listConversations();
    sendJson(res, 200, conversations);
    return;
  }

  if (req.method === "GET" && pathname.startsWith("/api/public/tasks/")) {
    const conversationId = decodeURIComponent(pathname.replace("/api/public/tasks/", "").trim());
    if (!conversationId) {
      jsonError(res, 400, "conversationId 不能为空");
      return;
    }
    const graph = await repository.getConversationGraph(conversationId);
    sendJson(res, 200, graph);
    return;
  }

  if (req.method === "GET" && pathname.startsWith("/api/public/stream/")) {
    const conversationId = decodeURIComponent(pathname.replace("/api/public/stream/", "").trim()) || "*";
    sseHub.subscribe(conversationId, req, res);
    return;
  }

  if (req.method === "GET" && pathname.startsWith("/api/public/pruned/")) {
    const conversationId = decodeURIComponent(pathname.replace("/api/public/pruned/", "").trim());
    const reqUrl = new URL(req.url, `http://${req.headers.host || "localhost"}`);
    const focusNodeId = String(reqUrl.searchParams.get("focusNodeId") || "").trim();
    if (!conversationId || !focusNodeId) {
      jsonError(res, 400, "conversationId 和 focusNodeId 必填");
      return;
    }
    const graph = await repository.getConversationGraph(conversationId);
    const pruned = pruneConversationContext(graph, focusNodeId);
    sendJson(res, 200, pruned);
    return;
  }

  jsonError(res, 404, "Public API 路径不存在");
}

function resolveConversationIdForNode(node) {
  return node && node.conversationId ? node.conversationId : null;
}

async function handleAdminApi(req, res, pathname) {
  if (!requireAdmin(req, res)) return;

  if (req.method === "POST" && pathname === "/api/admin/nodes") {
    const body = await parseBody(req);
    const { result } = await repository.upsertNode(body);
    sseHub.publishConversation(resolveConversationIdForNode(result), {
      reason: "node_upsert",
      nodeId: result.id,
    });
    sendJson(res, 201, result);
    return;
  }

  if (req.method === "PUT" && pathname.startsWith("/api/admin/nodes/")) {
    const nodeId = decodeURIComponent(pathname.replace("/api/admin/nodes/", "").trim());
    if (!nodeId) {
      jsonError(res, 400, "节点 ID 无效");
      return;
    }
    const body = await parseBody(req);
    const { result } = await repository.upsertNode({ ...body, id: nodeId });
    sseHub.publishConversation(resolveConversationIdForNode(result), {
      reason: "node_update",
      nodeId: result.id,
    });
    sendJson(res, 200, result);
    return;
  }

  if (req.method === "DELETE" && pathname.startsWith("/api/admin/nodes/")) {
    const nodeId = decodeURIComponent(pathname.replace("/api/admin/nodes/", "").trim());
    if (!nodeId) {
      jsonError(res, 400, "节点 ID 无效");
      return;
    }
    const current = await repository.getNodeById(nodeId);
    const conversationId = resolveConversationIdForNode(current);
    const { result } = await repository.deleteNode(nodeId);
    sseHub.publishConversation(conversationId, {
      reason: "node_delete",
      nodeId,
      deletedCount: result.deletedCount,
    });
    sendJson(res, 200, result);
    return;
  }

  if (req.method === "POST" && pathname === "/api/admin/edges") {
    const body = await parseBody(req);
    const { result } = await repository.upsertEdge(body);
    const fromNode = await repository.getNodeById(result.from);
    const conversationId = resolveConversationIdForNode(fromNode);
    sseHub.publishConversation(conversationId, {
      reason: "edge_upsert",
      edgeId: result.id,
      from: result.from,
      to: result.to,
    });
    sendJson(res, 201, result);
    return;
  }

  if (req.method === "DELETE" && pathname === "/api/admin/edges") {
    const reqUrl = new URL(req.url, `http://${req.headers.host || "localhost"}`);
    const from = String(reqUrl.searchParams.get("from") || "").trim();
    const to = String(reqUrl.searchParams.get("to") || "").trim();
    const type = String(reqUrl.searchParams.get("type") || "").trim() || null;
    if (!from || !to) {
      jsonError(res, 400, "from 和 to 必填");
      return;
    }
    const { result } = await repository.deleteEdge({ from, to, type });
    const fromNode = await repository.getNodeById(from);
    const conversationId = resolveConversationIdForNode(fromNode);
    sseHub.publishConversation(conversationId, {
      reason: "edge_delete",
      from,
      to,
      type,
      deletedCount: result.deletedCount,
    });
    sendJson(res, 200, result);
    return;
  }

  if (req.method === "GET" && pathname.startsWith("/api/admin/nodes/")) {
    const nodeId = decodeURIComponent(pathname.replace("/api/admin/nodes/", "").trim());
    if (!nodeId) {
      jsonError(res, 400, "节点 ID 无效");
      return;
    }
    const node = await repository.getNodeById(nodeId);
    if (!node) {
      jsonError(res, 404, "节点不存在");
      return;
    }
    sendJson(res, 200, node);
    return;
  }

  jsonError(res, 404, "Admin API 路径不存在");
}

async function handleCompatApi(req, res, pathname) {
  // Read-only compatibility endpoint for old scripts.
  if (req.method === "GET" && pathname === "/api/tasks") {
    const conversations = await repository.listConversations();
    const allTasks = [];
    for (const conv of conversations) {
      const graph = await repository.getConversationGraph(conv.conversationId);
      allTasks.push(...graph.nodes.map(mapNodeToLegacyTask));
    }
    sendJson(res, 200, allTasks);
    return;
  }

  if (pathname.startsWith("/api/tasks")) {
    jsonError(res, 410, "Legacy write API 已废弃，请改用 /api/admin/*");
    return;
  }
}

async function serveStatic(req, res, pathname) {
  const staticPath = await resolveStaticPath(pathname);
  if (!staticPath) {
    sendText(res, 403, "Forbidden");
    return;
  }

  let filePath = staticPath;
  try {
    let stat = await fsp.stat(filePath);
    if (stat.isDirectory()) {
      filePath = path.join(filePath, "index.html");
      stat = await fsp.stat(filePath);
    }

    const ext = path.extname(filePath).toLowerCase();
    const type = MIME_TYPES[ext] || "application/octet-stream";
    const stream = fs.createReadStream(filePath);

    res.writeHead(200, {
      "Content-Type": type,
      "Cache-Control": ext === ".html" ? "no-cache" : "public, max-age=60",
      "Content-Length": stat.size,
    });
    stream.pipe(res);
  } catch {
    try {
      const fallback = await fsp.readFile(path.join(FRONTEND_DIR, "index.html"), "utf8");
      res.writeHead(200, { "Content-Type": "text/html; charset=utf-8" });
      res.end(fallback);
    } catch {
      sendText(res, 404, "Not Found");
    }
  }
}

function isPublicApi(pathname) {
  return pathname.startsWith("/api/public/");
}

function isAdminApi(pathname) {
  return pathname.startsWith("/api/admin/");
}

function isCompatApi(pathname) {
  return pathname.startsWith("/api/tasks");
}

const server = http.createServer(async (req, res) => {
  try {
    applyCors(req, res);
    if (req.method === "OPTIONS") {
      res.writeHead(204);
      res.end();
      return;
    }

    const reqUrl = new URL(req.url, `http://${req.headers.host || "localhost"}`);
    const pathname = reqUrl.pathname;

    if (pathname === "/health") {
      sendJson(res, 200, { ok: true, now: nowIso() });
      return;
    }

    if (isPublicApi(pathname)) {
      await handlePublicApi(req, res, pathname);
      return;
    }

    if (isAdminApi(pathname)) {
      await handleAdminApi(req, res, pathname);
      return;
    }

    if (isCompatApi(pathname)) {
      await handleCompatApi(req, res, pathname);
      return;
    }

    if (req.method !== "GET" && req.method !== "HEAD") {
      sendText(res, 405, "Method Not Allowed");
      return;
    }

    await serveStatic(req, res, pathname);
  } catch (error) {
    const message = error instanceof Error ? error.message : String(error);
    sendJson(res, 500, { error: "服务器内部错误", detail: message });
  }
});

async function start() {
  await repository.ensureFile();
  server.listen(PORT, HOST, () => {
    console.log(`[task-board-v2] listening on http://${HOST}:${PORT}`);
    console.log(`[task-board-v2] data file: ${DATA_FILE}`);
    console.log(`[task-board-v2] public origins: ${PUBLIC_ORIGIN_LIST.join(",") || "*"}`);
  });
}

if (require.main === module) {
  void start();
}

module.exports = {
  start,
  server,
};