using System.Threading.Channels;
using Xunit;
using YZWater.Core.Services;

namespace YZWater.Core.Tests.Services;

/// <summary>
/// 报警/审计写入队列"满了丢最旧"的可观测性回归。
/// 背景：两个服务都用 BoundedChannelFullMode.DropOldest，并且忽略 TryWrite 的返回值 ——
/// 队列塞满时记录被静默丢掉，界面和日志都不显示，事后看台账会以为"当时只发生过这些"。
/// 现在丢弃条数被计数、周期性写日志，并在报警页/审计页底部提示。
/// </summary>
public class QueueDropAccountingTests
{
    /// <summary>
    /// 这条测试盯的是整个改动的立足点：DropOldest 下 TryWrite 依然返回 true，
    /// 所以"写成功"不能当成"没丢数据"，唯一的丢弃入口是 itemDropped 回调。
    /// </summary>
    [Fact]
    public void DropOldest_KeepsTryWriteTrue_And_ReportsDroppedItem()
    {
        var dropped = new List<int>();
        var channel = Channel.CreateBounded<int>(
            new BoundedChannelOptions(2) { FullMode = BoundedChannelFullMode.DropOldest },
            item => dropped.Add(item));

        Assert.True(channel.Writer.TryWrite(1));
        Assert.True(channel.Writer.TryWrite(2));
        // 队列已满：这一次写仍然"成功"，但把最旧的 1 挤了出去
        Assert.True(channel.Writer.TryWrite(3));

        Assert.Equal(new[] { 1 }, dropped);
        Assert.Equal(new[] { 2, 3 }, ReadAll(channel));
    }

    /// <summary>
    /// 反向验证：只有 Wait 模式会在队满时让 TryWrite 返回 false，且不产生任何丢弃
    /// （实测 .NET 8：DropWrite/DropNewest/DropOldest 三种丢弃模式下 TryWrite 全部返回 true，
    /// 所以"写入成功"根本不能当成"没丢数据"）
    /// </summary>
    [Fact]
    public void WaitMode_ReportsFailureOnTryWrite_And_DropsNothing()
    {
        var dropped = new List<int>();
        var channel = Channel.CreateBounded<int>(
            new BoundedChannelOptions(2) { FullMode = BoundedChannelFullMode.Wait },
            item => dropped.Add(item));

        Assert.True(channel.Writer.TryWrite(1));
        Assert.True(channel.Writer.TryWrite(2));
        Assert.False(channel.Writer.TryWrite(3));

        Assert.Empty(dropped);
        Assert.Equal(new[] { 1, 2 }, ReadAll(channel));
    }

    /// <summary>正常写入不该被算成丢弃：计数只应在队列真的满过时才涨</summary>
    [Fact]
    public void NewAlarmService_StartsWithNoDroppedRecords()
    {
        var service = new AlarmService(PlcPollingService.Instance);
        try
        {
            service.RecordJournalAlarm("测试用流水报警", 1);
            Assert.Equal(0, service.DroppedRecordCount);
        }
        finally
        {
            service.Dispose();
        }
    }

    private static int[] ReadAll(Channel<int> channel)
    {
        var items = new List<int>();
        while (channel.Reader.TryRead(out var item)) items.Add(item);
        return items.ToArray();
    }
}