using Fleet.Core;
using MoShiro.Protocol;

namespace MoShiro.Backend.Application;

/// <summary>
/// <c>moshiro.host</c>：Agent 每隔几秒上报的主机资源占用快照。最新值放在内存里并实时推给订阅者；每个节点每分钟存一个样本做历史。
/// 快照里没有 CPU 型号、主机名、网卡名和 IP（节点根本不采集它们）。
/// </summary>
public sealed class HostStatusService
{
    private static readonly TimeSpan s_stale = TimeSpan.FromSeconds(15);

    private readonly AgentRuntime _runtime;
    private readonly IHostStore _store;
    private readonly LiveHub _live;
    private readonly TimeProvider _time;
    private readonly Dictionary<NodeId, long> _lastSavedMinute = [];
    private readonly object _gate = new();

    public HostStatusService(AgentRuntime runtime, IHostStore store, LiveHub live, TimeProvider time)
    {
        _runtime = runtime;
        _store = store;
        _live = live;
        _time = time;
    }

    public async ValueTask OnHostAsync(NodeId agent, HostSnapshot snapshot, CancellationToken ct)
    {
        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        snapshot.AtUtcMs = now; // 以 Backend 收到的时间为准：节点的时钟不可信
        AgentRuntimeState state = _runtime.Get(agent);
        state.Host = snapshot;
        state.HostReceivedAtMs = now;
        _live.Publish(new HostSignal(agent, snapshot));

        long minute = now - (now % 60_000);
        bool save;
        lock (_gate)
        {
            save = !_lastSavedMinute.TryGetValue(agent, out long last) || last != minute;
            if (save)
            {
                _lastSavedMinute[agent] = minute;
            }
        }

        if (save)
        {
            await _store.SaveAsync(agent, minute, snapshot, ct);
        }
    }

    /// <summary>最新快照；超过 15 秒没有更新就是过期（Agent 离线或者没有开启上报）。</summary>
    public (HostSnapshot? Host, bool Stale) Latest(NodeId agent)
    {
        if (!_runtime.TryGet(agent, out AgentRuntimeState? state) || state.Host is null)
        {
            return (null, true);
        }

        return (state.Host, _time.GetUtcNow().ToUnixTimeMilliseconds() - state.HostReceivedAtMs > s_stale.TotalMilliseconds);
    }

    public ValueTask<IReadOnlyList<HostSample>> HistoryAsync(NodeId agent, long fromMs, long toMs, CancellationToken ct) => _store.ReadAsync(agent, fromMs, toMs, ct);
}