import json
import os
import threading
import time
import urllib.request

from flask import Flask, jsonify, render_template

app = Flask(__name__)

PROC = os.environ.get("SYSMON_PROC", "/host/proc")

# Server configuration: "name:url,name:url" where "local" means read from /proc
SYSMON_SERVERS = os.environ.get("SYSMON_SERVERS", "")
servers = []
if SYSMON_SERVERS:
    for entry in SYSMON_SERVERS.split(","):
        name, url = entry.strip().split(":", 1)
        servers.append({"name": name.strip(), "url": url.strip()})

# Shared state for per-core CPU usage
cpu_snapshot = {"cores": [], "overall": 0.0}
cpu_lock = threading.Lock()


def parse_proc_stat():
    """Parse /proc/stat and return per-cpu jiffies as list of (id, user+nice+system, total)."""
    cores = []
    overall = None
    with open(f"{PROC}/stat") as f:
        for line in f:
            if line.startswith("cpu"):
                parts = line.split()
                name = parts[0]
                vals = list(map(int, parts[1:]))
                idle = vals[3] + vals[4]
                total = sum(vals[:8])
                busy = total - idle
                if name == "cpu":
                    overall = (busy, total)
                else:
                    core_id = int(name[3:])
                    cores.append((core_id, busy, total))
    return cores, overall


def cpu_sampler():
    """Background thread: sample /proc/stat every 1s, compute deltas."""
    global cpu_snapshot
    prev_cores, prev_overall = parse_proc_stat()
    prev_map = {cid: (busy, total) for cid, busy, total in prev_cores}

    while True:
        time.sleep(1)
        cur_cores, cur_overall = parse_proc_stat()
        cur_map = {cid: (busy, total) for cid, busy, total in cur_cores}

        result = []
        for cid in sorted(cur_map.keys()):
            if cid in prev_map:
                db = cur_map[cid][0] - prev_map[cid][0]
                dt = cur_map[cid][1] - prev_map[cid][1]
                pct = (db / dt * 100) if dt > 0 else 0.0
            else:
                pct = 0.0
            result.append({"id": cid, "usage_percent": round(pct, 1)})

        overall_pct = 0.0
        if prev_overall and cur_overall:
            db = cur_overall[0] - prev_overall[0]
            dt = cur_overall[1] - prev_overall[1]
            overall_pct = (db / dt * 100) if dt > 0 else 0.0

        with cpu_lock:
            cpu_snapshot = {"cores": result, "overall": round(overall_pct, 1)}

        prev_map = cur_map
        prev_overall = cur_overall


def get_memory():
    """Parse /proc/meminfo, return dict with MB values."""
    info = {}
    with open(f"{PROC}/meminfo") as f:
        for line in f:
            parts = line.split()
            key = parts[0].rstrip(":")
            val_kb = int(parts[1])
            info[key] = val_kb

    total = info["MemTotal"]
    available = info["MemAvailable"]
    cached = info.get("Cached", 0) + info.get("Buffers", 0)
    used = total - available

    return {
        "total_mb": round(total / 1024),
        "used_mb": round(used / 1024),
        "available_mb": round(available / 1024),
        "cached_mb": round(cached / 1024),
        "percent": round(used / total * 100, 1),
    }


def get_load():
    """Parse /proc/loadavg."""
    with open(f"{PROC}/loadavg") as f:
        parts = f.read().split()
    return {
        "load1": float(parts[0]),
        "load5": float(parts[1]),
        "load15": float(parts[2]),
    }


def get_uptime():
    """Parse /proc/uptime, return human-readable string."""
    with open(f"{PROC}/uptime") as f:
        secs = float(f.read().split()[0])
    days = int(secs // 86400)
    hours = int((secs % 86400) // 3600)
    mins = int((secs % 3600) // 60)
    parts = []
    if days:
        parts.append(f"{days}d")
    if hours:
        parts.append(f"{hours}h")
    parts.append(f"{mins}m")
    return {"seconds": round(secs), "human": " ".join(parts)}


def get_local_stats():
    """Build stats dict from local /proc."""
    with cpu_lock:
        snap = cpu_snapshot.copy()
    return {
        "cores": snap["cores"],
        "overall_cpu": snap["overall"],
        "memory": get_memory(),
        "load": get_load(),
        "uptime": get_uptime(),
        "num_cores": len(snap["cores"]),
    }


def fetch_remote_stats(url, timeout=2):
    """Fetch /api/stats from a remote agent. Returns dict or None on failure."""
    try:
        req = urllib.request.Request(url.rstrip("/") + "/api/stats")
        with urllib.request.urlopen(req, timeout=timeout) as resp:
            return json.loads(resp.read().decode())
    except Exception:
        return None


@app.route("/")
def index():
    return render_template("index.html")


@app.route("/api/stats")
def stats():
    return jsonify(get_local_stats())


@app.route("/api/servers")
def all_servers():
    results = []
    for srv in servers:
        if srv["url"] == "local":
            data = get_local_stats()
            data["name"] = srv["name"]
            data["status"] = "online"
            results.append(data)
        else:
            data = fetch_remote_stats(srv["url"])
            if data:
                data["name"] = srv["name"]
                data["status"] = "online"
                data.setdefault("num_cores", len(data.get("cores", [])))
                results.append(data)
            else:
                results.append({"name": srv["name"], "status": "unreachable"})
    return jsonify(servers=results)


# Start background sampler
t = threading.Thread(target=cpu_sampler, daemon=True)
t.start()