/**
 * 进程监控指标采集（仅支持 Linux）
 * - CPU 占用率：两次采样 /proc/<pid>/stat 与 /proc/stat 差值计算，内部休眠约 1 秒
 * - 内存占用：/proc/<pid>/status 的 VmRSS，单位 MB
 * - 句柄数：/proc/<pid>/fd 目录条目数
 * - 端口 -> pid：端口解析逻辑见 ../linux/portpid.js（含 docker 端口发布）
 */
const fs = require("fs");
const portpid = require("../linux/portpid");
const os = require("os");

function isLinux() {
    return os.type() === "Linux";
}

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

function readPidTicks(pid) {
    const txt = fs.readFileSync(`/proc/${pid}/stat`, "utf8");
    // 字段 14=utime 15=stime，comm 可能含空格，按最后一个 ) 截断
    const rest = txt.slice(txt.lastIndexOf(")") + 1).trim().split(/\s+/);
    return Number(rest[11]) + Number(rest[12]);
}

function readCpuTotal() {
    const line = fs.readFileSync("/proc/stat", "utf8").split("\n")[0];
    // user nice system idle iowait irq softirq steal（guest 已计入 user）
    const parts = line.trim().split(/\s+/).slice(1, 9).map(Number);
    let total = 0;
    for (const v of parts) {
        total += Number.isFinite(v) ? v : 0;
    }
    return total;
}

function readMemMB(pid) {
    const status = fs.readFileSync(`/proc/${pid}/status`, "utf8");
    const m = status.match(/^VmRSS:\s+(\d+)\s+kB/m);
    if (!m) {
        return null;
    }
    return Math.round(Number(m[1]) / 1024 * 100) / 100;
}

function readHandleCount(pid) {
    return fs.readdirSync(`/proc/${pid}/fd`, { withFileTypes: true }).length;
}

/**
 * 采集单个进程的监控数据
 * @param {number} pid
 * @returns {Promise<{pid:number,cpu:number,mem:number,handle:number}|null>} 进程不存在/不可读返回 null
 */
async function collectPid(pid) {
    try {
        const beforePid = readPidTicks(pid);
        const beforeTotal = readCpuTotal();
        await sleep(1000);
        const afterPid = readPidTicks(pid);
        const afterTotal = readCpuTotal();

        const totalDelta = afterTotal - beforeTotal;
        const pidDelta = afterPid - beforePid;
        const cpu = totalDelta > 0 ? Math.round(pidDelta / totalDelta * 10000) / 100 : 0;

        const mem = readMemMB(pid);
        const handle = readHandleCount(pid);
        return { pid, cpu, mem, handle };
    } catch (e) {
        return null;
    }
}

module.exports = {
    isLinux,
    collectPid,
    findPortPid: portpid.findPortPid
};