import { createServer } from "node:http";
import { arch, cpus, hostname, platform, release } from "node:os";

import {
  telegrafBatchToHostTelemetry,
} from "../../packages/infrastructure-telemetry-contract/src/index.mjs";

const MAX_BODY_BYTES = 512 * 1024;

export function createHostTelemetryCollector(options = {}) {
  const config = normalizeConfig(options);
  let accepted = 0;
  let rejected = 0;
  let lastObservedAt = null;
  let lastAcceptedAt = null;
  let lastErrorCode = null;
  let pending = false;

  const server = createServer(async (request, response) => {
    response.setHeader("Content-Type", "application/json; charset=utf-8");
    response.setHeader("Cache-Control", "no-store");
    response.setHeader("X-Content-Type-Options", "nosniff");
    if (request.method !== "POST" || request.url !== "/internal/v1/host-telemetry") {
      response.statusCode = 404;
      response.end(JSON.stringify({ ok: false, error: "not_found" }));
      return;
    }
    if (pending) {
      rejected += 1;
      response.statusCode = 429;
      response.end(JSON.stringify({ ok: false, error: "host_telemetry_busy" }));
      return;
    }
    pending = true;
    try {
      const body = await readJsonBody(request, MAX_BODY_BYTES);
      const processors = cpus();
      const snapshot = telegrafBatchToHostTelemetry(body, {
        hostKey: config.hostKey,
        hostname: hostname(),
        architecture: arch(),
        platform: platform(),
        kernelRelease: release(),
        cpuModel: processors[0]?.model ?? null,
        logicalProcessors: processors.length || null,
        agentVersion: config.agentVersion,
      });
      lastObservedAt = snapshot.observedAt;
      await config.submit(snapshot);
      accepted += 1;
      lastAcceptedAt = new Date().toISOString();
      lastErrorCode = null;
      response.statusCode = 202;
      response.end(JSON.stringify({ ok: true, accepted: true }));
    } catch (error) {
      rejected += 1;
      lastErrorCode = safeErrorCode(error);
      response.statusCode = lastErrorCode.includes("too_large") ? 413 : 503;
      response.end(JSON.stringify({ ok: false, error: lastErrorCode }));
    } finally {
      pending = false;
    }
  });

  return Object.freeze({
    async start() {
      await listen(server, config.port, config.host);
      return server.address();
    },
    async stop() {
      await closeServer(server);
    },
    status() {
      return Object.freeze({
        listening: server.listening,
        host: config.host,
        port: config.port,
        profile: "linux-host-telegraf-v1",
        accepted,
        rejected,
        pending,
        lastObservedAt,
        lastAcceptedAt,
        lastErrorCode,
      });
    },
  });
}

function normalizeConfig(options) {
  if (typeof options.submit !== "function") {
    throw new TypeError("host_telemetry_submit_required");
  }
  return Object.freeze({
    submit: options.submit,
    hostKey: normalizeRef(options.hostKey, "host_telemetry_host_key_invalid"),
    agentVersion: String(options.agentVersion ?? "1.38.4"),
    host: normalizeLoopbackHost(options.host ?? "127.0.0.1"),
    port: normalizePort(options.port ?? 18223),
  });
}

async function readJsonBody(request, maximumBytes) {
  const chunks = [];
  let total = 0;
  for await (const chunk of request) {
    total += chunk.length;
    if (total > maximumBytes) throw new Error("host_telemetry_body_too_large");
    chunks.push(chunk);
  }
  if (total < 2) throw new Error("host_telemetry_body_invalid");
  try {
    return JSON.parse(Buffer.concat(chunks).toString("utf8"));
  } catch {
    throw new Error("host_telemetry_body_invalid");
  }
}

function normalizeRef(value, errorCode) {
  if (typeof value !== "string" || !/^[a-z][a-z0-9-]{1,62}$/.test(value)) {
    throw new TypeError(errorCode);
  }
  return value;
}

function normalizeLoopbackHost(value) {
  if (!["127.0.0.1", "::1"].includes(value)) {
    throw new TypeError("host_telemetry_host_invalid");
  }
  return value;
}

function normalizePort(value) {
  const normalized = Number(value);
  if (!Number.isSafeInteger(normalized) || normalized < 0 || normalized > 65_535) {
    throw new TypeError("host_telemetry_port_invalid");
  }
  return normalized;
}

function safeErrorCode(error) {
  const value = String(error?.message || "host_telemetry_internal_error");
  return /^[a-z0-9_.:-]{3,160}$/.test(value)
    ? value
    : "host_telemetry_internal_error";
}

function listen(server, port, host) {
  return new Promise((resolve, reject) => {
    server.once("error", reject);
    server.listen(port, host, () => {
      server.off("error", reject);
      resolve();
    });
  });
}

function closeServer(server) {
  if (!server.listening) return Promise.resolve();
  return new Promise((resolve) => server.close(() => resolve()));
}