using Rmsys.Domain;
using Rmsys.Domain.Entities;

namespace Rmsys.Api.Auth;

/// <summary>
/// 会议状态守卫与状态流转规则。
///
/// 背景：此前只有「删除会议」检查了状态（已上会不许删），
/// 上传材料、改上会结果、写批注、改数据包设置全都没有判断，
/// 导致已归档的会议还能被追加材料、篡改表决结果，且审计里看不出是会后补的。
/// </summary>
public static class MeetingGuard
{
    /// <summary>允许修改内容的状态（结果登记后即冻结，归档后彻底冻结）</summary>
    private static readonly string[] Writable =
    {
        MeetingStatus.Draft, MeetingStatus.Reviewing,
        MeetingStatus.Delivered, MeetingStatus.Ongoing
    };

    /// <summary>返回 null 表示可写；否则返回拒绝原因</summary>
    public static string? CheckWritable(Meeting m)
    {
        if (Writable.Contains(m.Status)) return null;
        return m.Status switch
        {
            MeetingStatus.Registered =>
                "会议结果已登记，材料与表决不允许再修改（如需修改请先将状态撤回为「会议召开中」）",
            MeetingStatus.Archived =>
                "会议已归档，不允许修改（如需修改请先「撤回归档」）",
            _ => $"会议当前状态（{MeetingStatus.Label(m.Status)}）不允许修改"
        };
    }

    /// <summary>
    /// 状态流转表。只允许相邻推进/回退，不能从「已归档」直接跳回「筹备中」。
    /// 「撤回归档」是唯一合法的逆向出口。
    /// </summary>
    private static readonly Dictionary<string, string[]> Transitions = new()
    {
        [MeetingStatus.Draft] = new[] { MeetingStatus.Reviewing },
        [MeetingStatus.Reviewing] = new[] { MeetingStatus.Draft, MeetingStatus.Delivered },
        [MeetingStatus.Delivered] = new[] { MeetingStatus.Reviewing, MeetingStatus.Ongoing },
        [MeetingStatus.Ongoing] = new[] { MeetingStatus.Delivered, MeetingStatus.Registered },
        [MeetingStatus.Registered] = new[] { MeetingStatus.Ongoing, MeetingStatus.Archived },
        [MeetingStatus.Archived] = new[] { MeetingStatus.Registered }
    };

    public static bool CanTransition(string from, string to) =>
        !string.Equals(from, to, StringComparison.Ordinal)
        && Transitions.TryGetValue(from, out var allowed)
        && allowed.Contains(to);

    /// <summary>允许的目标状态（给前端下拉/提示用）</summary>
    public static string[] AllowedNext(string from) =>
        Transitions.TryGetValue(from, out var allowed) ? allowed : Array.Empty<string>();

    public static string TransitionDenied(string from, string to) =>
        $"不能从「{MeetingStatus.Label(from)}」直接变更为「{MeetingStatus.Label(to)}」" +
        $"（允许的下一步：{string.Join("、", AllowedNext(from).Select(MeetingStatus.Label))}）";
}