using Ananta.Server.Configuration;

namespace Ananta.Server.Handlers.Game;

/// <summary>
/// 服务端自建「红绿灯相位」表 —— 给 <see cref="GameRouter"/> 的车流提供「这条车道的尽头是不是
/// 一个路口、我是哪个进口道、现在放不放行」。
///
/// ★ 为什么不用客户端那套（详见 <c>PrivateServerConfig.TrafficSignalEnabled</c> 的注释）：
///   放行关系在客户端专属 blob 里，服务端够不着，只能自己算。
///
/// ★ 相位模型对齐官方 <c>MassIntersectionPeriodDetail</c>：
///   一个相位 = 一段时长（<c>PeriodTime</c>）+ 一组放行的车道（<c>VehicleLaneMetas</c>）。
///   官方由服务端只发 <c>CurrentPeriodIndex / NextPeriodIndex / RailPeriodIndex</c> 三个 byte，
///   我们这里直接把「相位号 → 放行腿」这件事在服务端查表完成，省掉一次 S2C。
///
/// 数据表（<c>_gen_junctions.py</c> 生成）：
///   <c>data/junctions.csv</c>      = id;cx;cz;groupCount;legCount;laneCount
///   <c>data/junction_lanes.csv</c> = laneHandle;junctionId;groupIndex
/// </summary>
internal static class JunctionSignals
{
    internal readonly struct StopLine
    {
        /// <summary>所属路口 id（仅用于日志/错峰）。</summary>
        internal readonly int JunctionId;

        /// <summary>本进口道所属的相位组序号。</summary>
        internal readonly byte GroupIndex;

        /// <summary>该路口一共有几个相位组（轮转周期长度）。</summary>
        internal readonly byte GroupCount;

        /// <summary>该路口的错峰偏移（毫秒），避免全城同时翻灯。</summary>
        internal readonly int OffsetMs;

        internal StopLine(int junctionId, byte groupIndex, byte groupCount, int offsetMs)
        {
            JunctionId = junctionId;
            GroupIndex = groupIndex;
            GroupCount = groupCount;
            OffsetMs = offsetMs;
        }
    }

    private sealed class Table
    {
        internal Dictionary<int, StopLine> ByLane = [];
        internal int Junctions;
        internal bool Ok;
    }

    private const string JunctionRelativePath = "Ananta.Server/Ananta.App/data/junctions.csv";
    private const string LaneRelativePath = "Ananta.Server/Ananta.App/data/junction_lanes.csv";

    private static readonly Lazy<Table> Cache = new(Load);

    internal static bool Available => Cache.Value.Ok;
    internal static int JunctionCount => Cache.Value.Junctions;
    internal static int LaneCount => Cache.Value.ByLane.Count;

    internal static bool TryGet(int laneHandle, out StopLine line)
        => Cache.Value.ByLane.TryGetValue(laneHandle, out line);

    /// <summary>
    /// 现在这条进口道是不是绿灯。
    /// 周期 = 组数 × (绿灯 + 全红清空)；组内前 <c>greenSec</c> 放行，其余为清空。
    /// </summary>
    internal static bool IsGreen(in StopLine line, long nowMs, float greenSec, float clearSec)
    {
        if (line.GroupCount <= 1)
            return true;                                  // 单组路口 = 不冲突，恒绿
        var greenMs = (long)(greenSec * 1000f);
        var slotMs = greenMs + (long)(clearSec * 1000f);
        if (slotMs <= 0)
            return true;

        var t = nowMs + line.OffsetMs;
        var slot = t / slotMs;
        var within = t % slotMs;
        var current = (int)(slot % line.GroupCount);
        return current == line.GroupIndex && within < greenMs;
    }

    /// <summary>距离下一次本组变绿还有多少毫秒（用于「别在红灯还剩 0.3 秒时刹停」的滞回）。</summary>
    internal static long MsToNextGreen(in StopLine line, long nowMs, float greenSec, float clearSec)
    {
        if (line.GroupCount <= 1)
            return 0;
        var greenMs = (long)(greenSec * 1000f);
        var slotMs = greenMs + (long)(clearSec * 1000f);
        if (slotMs <= 0)
            return 0;

        var t = nowMs + line.OffsetMs;
        var within = t % slotMs;
        var current = (int)((t / slotMs) % line.GroupCount);

        if (current == line.GroupIndex)
            return within < greenMs ? 0 : slotMs * line.GroupCount - within;   // 自己的清空段：等到下一轮
        // 本组在后面的某个 slot：算还要过几个 slot 才轮到
        var ahead = (line.GroupIndex - current + line.GroupCount) % line.GroupCount;
        return ahead * slotMs - within;
    }

    private static Table Load()
    {
        var table = new Table();
        var junctionPath = PrivateServerConfigStore.ResolveProjectPath(JunctionRelativePath);
        var lanePath = PrivateServerConfigStore.ResolveProjectPath(LaneRelativePath);
        if (!File.Exists(junctionPath) || !File.Exists(lanePath))
            return table;

        // id -> groupCount
        var groupCount = new Dictionary<int, int>();
        foreach (var raw in File.ReadLines(junctionPath))
        {
            if (raw.Length == 0)
                continue;
            var p = raw.Split(';');
            if (p.Length < 4 || !int.TryParse(p[0], out var id) || !int.TryParse(p[3], out var gc))
                continue;
            groupCount[id] = gc;
            table.Junctions++;
        }

        foreach (var raw in File.ReadLines(lanePath))
        {
            if (raw.Length == 0)
                continue;
            var p = raw.Split(';');
            if (p.Length < 3
                || !int.TryParse(p[0], out var lane)
                || !int.TryParse(p[1], out var jid)
                || !int.TryParse(p[2], out var gi))
                continue;
            if (!groupCount.TryGetValue(jid, out var gc) || gc <= 0)
                continue;
            // ⛑️ 错峰：按路口 id 打散到 0..29 秒，避免全城同拍翻灯（视觉上像故障）
            var offset = (jid * 137) % 30000;
            table.ByLane[lane] = new StopLine(jid, (byte)gi, (byte)Math.Min(gc, 255), offset);
        }

        table.Ok = table.ByLane.Count > 0;
        return table;
    }
}