import { execFile } from "node:child_process";
import { hermesGatewayHealth } from "./schema.ts";

/** Keep subprocess deadlines slightly under typical sense timeout (30s). */
const EXEC_TIMEOUT_MS = 25_000;

/** HTTP probe stays below EXEC_TIMEOUT_MS and sense timeout (30s). */
const HTTP_TIMEOUT_MS = Math.min(23_000, EXEC_TIMEOUT_MS - 2000);

const HTTP_ERROR_MAX_LEN = 256;

function gatewayProbeUrl() {
  const u =
    process.env.HERMES_GATEWAY_HEALTH_URL ??
    process.env.NERVE_HERMES_GATEWAY_URL ??
    "";
  return String(u).trim();
}

function truncateHttpError(err) {
  const raw =
    err && typeof err === "object" && "code" in err && err.code
      ? String(err.code)
      : String(err?.message ?? err ?? "error");
  const s = raw.trim() || "error";
  return s.length > HTTP_ERROR_MAX_LEN ? s.slice(0, HTTP_ERROR_MAX_LEN) : s;
}

/**
 * GET the gateway URL; success = HTTP 200–399.
 * URL must be set via HERMES_GATEWAY_HEALTH_URL or NERVE_HERMES_GATEWAY_URL.
 */
async function probeGatewayHttp(url) {
  if (!url) {
    return {
      httpOk: 0,
      httpStatusCode: 0,
      httpLatencyMs: 0,
      httpError: "missing_url",
    };
  }
  const t0 = Date.now();
  try {
    const signal = AbortSignal.timeout(HTTP_TIMEOUT_MS);
    const res = await fetch(url, {
      method: "GET",
      signal,
      redirect: "follow",
    });
    const httpLatencyMs = Date.now() - t0;
    const code = res.status;
    const ok = code >= 200 && code < 400;
    return {
      httpOk: ok ? 1 : 0,
      httpStatusCode: code,
      httpLatencyMs,
      httpError: ok ? "" : truncateHttpError({ message: `HTTP ${code}` }),
    };
  } catch (err) {
    const httpLatencyMs = Date.now() - t0;
    return {
      httpOk: 0,
      httpStatusCode: 0,
      httpLatencyMs,
      httpError: truncateHttpError(err),
    };
  }
}

/**
 * When `ps` lacks `etimes` (wall-clock seconds since start), parse `etime`
 * ([[dd-]hh:]mm:ss) into seconds. See ps(1) `etime` field description.
 */
function etimeToSeconds(etime) {
  let s = String(etime).trim();
  if (!s) return 0;
  let days = 0;
  if (s.includes("-")) {
    const idx = s.indexOf("-");
    const d = Number.parseInt(s.slice(0, idx), 10);
    days = Number.isFinite(d) ? d : 0;
    s = s.slice(idx + 1);
  }
  const parts = s.split(":").map((x) => Number.parseInt(String(x).trim(), 10));
  if (parts.some((n) => !Number.isFinite(n))) return 0;
  if (parts.length === 3) {
    return Math.trunc(days * 86_400 + parts[0] * 3600 + parts[1] * 60 + parts[2]);
  }
  if (parts.length === 2) {
    return Math.trunc(days * 86_400 + parts[0] * 60 + parts[1]);
  }
  if (parts.length === 1) {
    return Math.trunc(days * 86_400 + parts[0]);
  }
  return 0;
}

function execFileUtf8(file, args, opts = {}) {
  return new Promise((resolve) => {
    execFile(
      file,
      args,
      {
        encoding: "utf8",
        maxBuffer: 8 * 1024 * 1024,
        timeout: EXEC_TIMEOUT_MS,
        ...opts,
      },
      (err, stdout, stderr) => {
        const exitCode =
          err && typeof err.status === "number" ? err.status : err ? -1 : 0;
        resolve({
          exitCode,
          errCode: err?.code,
          stdout: String(stdout ?? ""),
          stderr: String(stderr ?? ""),
        });
      },
    );
  });
}

function parseMainPidFromStatus(text) {
  const m = text.match(/Main PID:\s*(\d+)/i);
  return m ? Math.trunc(Number.parseInt(m[1], 10)) || 0 : 0;
}

function parseActiveLineFromStatus(text) {
  for (const line of text.split("\n")) {
    if (/^\s*Active:/i.test(line)) {
      const m = line.match(/Active:\s*(\S+)\s*\(([^)]*)\)/i);
      if (m) {
        return {
          active: m[1].toLowerCase() === "active",
          subRunning: m[2].toLowerCase().includes("running"),
        };
      }
    }
  }
  return { active: false, subRunning: false };
}

function parseSystemctlShow(text) {
  let mainPid = 0;
  let active = false;
  let subRunning = false;
  for (const line of text.split("\n")) {
    const t = line.trim();
    if (t.startsWith("MainPID=")) {
      mainPid = Math.trunc(Number.parseInt(t.slice("MainPID=".length), 10)) || 0;
    } else if (t.startsWith("ActiveState=")) {
      active = t.slice("ActiveState=".length).trim().toLowerCase() === "active";
    } else if (t.startsWith("SubState=")) {
      subRunning = t.slice("SubState=".length).trim().toLowerCase() === "running";
    }
  }
  return { mainPid, active, subRunning };
}

async function readSystemdState() {
  const status = await execFileUtf8("systemctl", [
    "--user",
    "--no-pager",
    "status",
    "hermes-gateway",
  ]);
  const combined = `${status.stdout}\n${status.stderr}`.trim();
  let mainPid = parseMainPidFromStatus(combined);
  let { active, subRunning } = parseActiveLineFromStatus(combined);

  const needShow =
    mainPid <= 0 || !active || !subRunning;

  if (needShow) {
    const show = await execFileUtf8("systemctl", [
      "--user",
      "--no-pager",
      "show",
      "hermes-gateway",
      "-p",
      "MainPID",
      "-p",
      "ActiveState",
      "-p",
      "SubState",
    ]);
    const showText = `${show.stdout}\n${show.stderr}`;
    const s = parseSystemctlShow(showText);
    if (mainPid <= 0 && s.mainPid > 0) mainPid = s.mainPid;
    if (!active) active = s.active;
    if (!subRunning) subRunning = s.subRunning;
  }

  return { mainPid, systemdActiveRunning: active && subRunning };
}

async function processExists(mainPid) {
  if (mainPid <= 0) return false;
  const r = await execFileUtf8("ps", ["-p", String(mainPid), "-o", "pid="]);
  if (r.errCode === "ENOENT") return false;
  return r.stdout.trim().length > 0;
}

async function readPsMetrics(mainPid) {
  if (mainPid <= 0) {
    return { rssBytes: 0, cpuPercent: 0, uptimeSec: 0 };
  }
  let r = await execFileUtf8("ps", [
    "-p",
    String(mainPid),
    "-o",
    "rss=,%cpu=,etimes=",
  ]);
  let line = r.stdout.trim().replace(/\s+/g, " ");
  if (r.errCode === "ENOENT" || !line) {
    return { rssBytes: 0, cpuPercent: 0, uptimeSec: 0 };
  }
  let parts = line.split(" ").filter(Boolean);
  if (parts.length < 3) {
    r = await execFileUtf8("ps", [
      "-p",
      String(mainPid),
      "-o",
      "rss=,%cpu=,etime=",
    ]);
    line = r.stdout.trim().replace(/\s+/g, " ");
    parts = line.split(" ").filter(Boolean);
    if (parts.length < 3) {
      return { rssBytes: 0, cpuPercent: 0, uptimeSec: 0 };
    }
    const rssKiB = Number(parts[0]);
    const cpu = Number(parts[1]);
    const uptimeSec = etimeToSeconds(parts.slice(2).join(" "));
    const rssBytes = Number.isFinite(rssKiB)
      ? Math.trunc(rssKiB * 1024)
      : 0;
    const cpuPercent = Number.isFinite(cpu)
      ? Math.round(cpu * 100) / 100
      : 0;
    return { rssBytes, cpuPercent, uptimeSec };
  }
  const rssKiB = Number(parts[0]);
  const cpu = Number(parts[1]);
  const etimes = Number(parts[2]);
  const rssBytes = Number.isFinite(rssKiB) ? Math.trunc(rssKiB * 1024) : 0;
  const cpuPercent = Number.isFinite(cpu) ? Math.round(cpu * 100) / 100 : 0;
  const uptimeSec = Number.isFinite(etimes)
    ? Math.trunc(etimes)
    : 0;
  return { rssBytes, cpuPercent, uptimeSec };
}

function parseActiveSessionsFromHermesStats(text) {
  const src = String(text);
  const patterns = [
    /^\s*Active\s+sessions?:\s*(\d+)/gim,
    /^\s*active\s+sessions?:\s*(\d+)/gim,
    /^\s*Total\s+sessions?:\s*(\d+)/gim,
  ];
  for (const re of patterns) {
    re.lastIndex = 0;
    const m = re.exec(src);
    if (m) {
      const n = Math.trunc(Number.parseInt(m[1], 10));
      return Number.isFinite(n) ? n : 0;
    }
  }
  return 0;
}

async function readActiveSessions() {
  try {
    const r = await execFileUtf8("hermes", ["sessions", "stats"]);
    if (r.errCode === "ENOENT") return 0;
    return parseActiveSessionsFromHermesStats(`${r.stdout}\n${r.stderr}`);
  } catch {
    return 0;
  }
}

async function countDirectChildren(mainPid) {
  if (mainPid <= 0) return 0;
  try {
    const r = await execFileUtf8("ps", [
      "--no-headers",
      "-o",
      "pid",
      "--ppid",
      String(mainPid),
    ]);
    if (r.errCode === "ENOENT") return 0;
    const lines = r.stdout
      .split("\n")
      .map((l) => l.trim())
      .filter(Boolean);
    return lines.length;
  } catch {
    return 0;
  }
}

export async function compute(db, _peers) {
  const ts = Date.now();

  let mainPid = 0;
  let systemdActiveRunning = false;

  try {
    const st = await readSystemdState();
    mainPid = st.mainPid;
    systemdActiveRunning = st.systemdActiveRunning;
  } catch {
    mainPid = 0;
    systemdActiveRunning = false;
  }

  let psOk = false;
  try {
    psOk = await processExists(mainPid);
  } catch {
    psOk = false;
  }

  let rssBytes = 0;
  let cpuPercent = 0;
  let uptimeSec = 0;
  if (psOk) {
    try {
      const m = await readPsMetrics(mainPid);
      rssBytes = m.rssBytes;
      cpuPercent = m.cpuPercent;
      uptimeSec = m.uptimeSec;
    } catch {
      rssBytes = 0;
      cpuPercent = 0;
      uptimeSec = 0;
    }
  }

  const alive =
    systemdActiveRunning && mainPid > 0 && psOk ? 1 : 0;

  let activeSessions = 0;
  try {
    activeSessions = await readActiveSessions();
  } catch {
    activeSessions = 0;
  }

  let childProcessCount = 0;
  if (alive && mainPid > 0) {
    try {
      childProcessCount = await countDirectChildren(mainPid);
    } catch {
      childProcessCount = 0;
    }
  }

  let httpOk = 0;
  let httpStatusCode = 0;
  let httpLatencyMs = 0;
  let httpError = "";
  try {
    const h = await probeGatewayHttp(gatewayProbeUrl());
    httpOk = h.httpOk;
    httpStatusCode = h.httpStatusCode;
    httpLatencyMs = h.httpLatencyMs;
    httpError = h.httpError;
  } catch {
    httpOk = 0;
    httpStatusCode = 0;
    httpLatencyMs = 0;
    httpError = "probe_failed";
  }

  const storedMainPid = mainPid > 0 ? mainPid : 0;

  const row = {
    ts,
    alive,
    mainPid: storedMainPid,
    rssBytes: alive ? rssBytes : 0,
    cpuPercent: alive ? cpuPercent : 0,
    uptimeSec: alive ? uptimeSec : 0,
    activeSessions,
    childProcessCount: alive ? childProcessCount : 0,
    httpOk,
    httpStatusCode,
    httpLatencyMs,
    httpError,
  };

  await db.insert(hermesGatewayHealth).values(row);

  return {
    ts: row.ts,
    alive: row.alive,
    mainPid: row.mainPid,
    rssBytes: row.rssBytes,
    cpuPercent: row.cpuPercent,
    uptimeSec: row.uptimeSec,
    activeSessions: row.activeSessions,
    childProcessCount: row.childProcessCount,
    httpOk: row.httpOk,
    httpStatusCode: row.httpStatusCode,
    httpLatencyMs: row.httpLatencyMs,
    httpError: row.httpError,
  };
}