using Microsoft.Extensions.Logging;
using ZB.MOM.WW.ScadaBridge.SiteRuntime.Scripts;

namespace ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests.Scripts;

/// <summary>
/// Flow Debugger step logs (design 2026-09-09 D4/D5/D7): the <c>Log</c> global's two obligations —
/// ALWAYS forward to the node logger, emit a trace row ONLY when traced — plus the per-run line cap,
/// the per-message character cap, step attribution through <see cref="TraceStepScope"/>, and the
/// "never throws into the script" rule.
///
/// <para>Deliberately built without a <c>ScriptRuntimeContext</c>: the row emitter is a delegate
/// precisely so this surface is testable on its own.</para>
/// </summary>
public class ScriptLoggerTests
{
    /// <summary>One entry the logger under test forwarded to the node logger.</summary>
    private sealed record LogEntry(LogLevel Level, string Message, Exception? Exception);

    /// <summary>A minimal recording <see cref="ILogger"/> — clearer here than a mocking framework.</summary>
    private sealed class RecordingLogger(bool enabled = true) : ILogger
    {
        public List<LogEntry> Entries { get; } = [];

        public IDisposable? BeginScope<TState>(TState state) where TState : notnull => null;

        public bool IsEnabled(LogLevel logLevel) => enabled;

        public void Log<TState>(LogLevel level, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter) =>
            Entries.Add(new LogEntry(level, formatter(state, exception), exception));
    }

    /// <summary>One row the logger under test handed to its emitter.</summary>
    private sealed record Row(string Level, string Source, string Message, Exception? Exception, Guid? StepEventId);

    private static (ScriptLogger Logger, RecordingLogger Node, List<Row> Rows) MakeTraced(int maxLines = 200)
    {
        var node = new RecordingLogger();
        var rows = new List<Row>();
        var logger = new ScriptLogger(
            node,
            (level, source, message, exception, stepEventId) => rows.Add(new Row(level, source, message, exception, stepEventId)),
            maxLines,
            instance: "CvdReactor01",
            script: "OnHeartbeat",
            executionId: Guid.NewGuid());
        return (logger, node, rows);
    }

    [Fact]
    public void UntracedRun_ForwardsToTheNodeLogger_AndEmitsNoRow()
    {
        // D5: an untraced run is an ordinary logging surface — the author's messages are never lost,
        // but nothing is audited.
        var node = new RecordingLogger();
        var logger = new ScriptLogger(node, emit: null, maxLines: 200, "CvdReactor01", "OnHeartbeat", Guid.NewGuid());

        logger.Info("hello");
        logger.Warn("careful");

        Assert.Equal(2, node.Entries.Count);
        Assert.Equal(LogLevel.Information, node.Entries[0].Level);
        Assert.Contains("hello", node.Entries[0].Message);
        Assert.Equal(LogLevel.Warning, node.Entries[1].Level);
    }

    [Fact]
    public void TracedRun_EmitsOneScriptSourcedRowPerLine()
    {
        var (logger, node, rows) = MakeTraced();

        logger.Info("msg");

        Assert.Single(node.Entries);
        var row = Assert.Single(rows);
        Assert.Equal(("info", "script", "msg", (Exception?)null, (Guid?)null), (row.Level, row.Source, row.Message, row.Exception, row.StepEventId));
    }

    [Fact]
    public void EveryLevel_MapsToItsWireName()
    {
        var (logger, node, rows) = MakeTraced();

        logger.Debug("d");
        logger.Info("i");
        logger.Warn("w");
        logger.Error("e");

        Assert.Equal(["debug", "info", "warn", "error"], rows.Select(r => r.Level));
        Assert.Equal(
            [LogLevel.Debug, LogLevel.Information, LogLevel.Warning, LogLevel.Error],
            node.Entries.Select(e => e.Level));
    }

    [Fact]
    public void LineInsideAStepScope_IsAttributedToThatStep_AndTheScopeUnwinds()
    {
        // D6: the ambient scope is how a line written inside a helper body names its step node.
        var (logger, _, rows) = MakeTraced();
        var stepId = Guid.NewGuid();

        using (TraceStepScope.Enter(stepId))
        {
            Assert.Equal(stepId, TraceStepScope.Current);
            logger.Info("inside");
        }

        Assert.Null(TraceStepScope.Current);
        logger.Info("outside");

        Assert.Equal(stepId, rows[0].StepEventId);
        Assert.Null(rows[1].StepEventId);
    }

    [Fact]
    public void NestedStepScopes_Unwind_ToTheEnclosingStep()
    {
        // A helper calling another helper: the inner step owns its own lines, and the outer step
        // gets its attribution back the moment the inner scope closes.
        var (logger, _, rows) = MakeTraced();
        var outer = Guid.NewGuid();
        var inner = Guid.NewGuid();

        using (TraceStepScope.Enter(outer))
        {
            using (TraceStepScope.Enter(inner))
            {
                Assert.Equal(inner, TraceStepScope.Current);
                logger.Info("inner");
            }

            Assert.Equal(outer, TraceStepScope.Current);
            logger.Info("outer");
        }

        Assert.Null(TraceStepScope.Current);
        Assert.Equal(inner, rows[0].StepEventId);
        Assert.Equal(outer, rows[1].StepEventId);
    }

    [Fact]
    public void PastThePerRunCap_LinesAreDropped_AndFlushDroppedNamesTheCount_Once()
    {
        // D7: bounded per run; the closing row bypasses the cap because it is the only signal that
        // anything was lost — and it is idempotent so a double flush cannot duplicate it.
        var (logger, _, rows) = MakeTraced(maxLines: 3);

        for (var i = 0; i < 5; i++)
        {
            logger.Info($"line {i}");
        }

        Assert.Equal(3, rows.Count);
        Assert.Equal(["line 0", "line 1", "line 2"], rows.Select(r => r.Message));

        logger.FlushDropped();

        Assert.Equal(4, rows.Count);
        var closing = rows[^1];
        Assert.Equal("warn", closing.Level);
        Assert.Equal("runtime", closing.Source);
        // M3: worded identically to the central InboundScriptLogger closing row.
        Assert.Contains("2 further log line(s) were not captured", closing.Message);
        Assert.Contains("ScadaBridge:SiteRuntime:MaxLogLinesPerRun = 3", closing.Message);
        Assert.Null(closing.StepEventId);

        logger.FlushDropped();

        Assert.Equal(4, rows.Count);
    }

    [Fact]
    public void FlushDropped_EmitsNothing_WhenNoLineWasDropped()
    {
        var (logger, _, rows) = MakeTraced(maxLines: 3);

        logger.Info("only one");
        logger.FlushDropped();

        Assert.Single(rows);
    }

    [Fact]
    public void MessagesLongerThanTheCap_AreClippedWithAnEllipsis()
    {
        var (logger, _, rows) = MakeTraced();

        logger.Info(new string('x', 2_500));

        var message = Assert.Single(rows).Message;
        Assert.Equal(ScriptLogger.MaxMessageChars + 1, message.Length);
        Assert.EndsWith("…", message);
    }

    [Fact]
    public void AMessageExactlyAtTheCap_PassesThroughUnclipped()
    {
        var (logger, _, rows) = MakeTraced();
        var exact = new string('x', ScriptLogger.MaxMessageChars);

        logger.Info(exact);

        Assert.Equal(exact, Assert.Single(rows).Message);
    }

    [Fact]
    public void ASurrogatePairStraddlingTheCap_IsDroppedWhole()
    {
        // Cutting between the halves would leave a lone surrogate, which breaks JSON serialization
        // of the audit row further down the pipe.
        var (logger, _, rows) = MakeTraced();
        var straddling = new string('x', ScriptLogger.MaxMessageChars - 1) + "🚀" + new string('y', 10);

        logger.Info(straddling);

        var message = Assert.Single(rows).Message;
        Assert.Equal(ScriptLogger.MaxMessageChars, message.Length);
        Assert.EndsWith("…", message);
        Assert.DoesNotContain(message, static c => char.IsSurrogate(c));
    }

    [Fact]
    public void AThrowingEmitter_NeverReachesTheScript_AndTheNodeLoggerStillGotTheLine()
    {
        // The whole feature is a debug observer: a broken observer must not fail a production run.
        var node = new RecordingLogger();
        var logger = new ScriptLogger(
            node,
            (_, _, _, _, _) => throw new InvalidOperationException("collector is broken"),
            maxLines: 200,
            "CvdReactor01",
            "OnHeartbeat",
            Guid.NewGuid());

        logger.Info("still logged");

        Assert.Single(node.Entries);
        Assert.Contains("still logged", node.Entries[0].Message);
    }

    [Fact]
    public void AThrowingNodeLogger_NeverReachesTheScript_AndTheRowIsStillEmitted()
    {
        var rows = new List<Row>();
        var logger = new ScriptLogger(
            new ThrowingLogger(),
            (level, source, message, exception, stepEventId) => rows.Add(new Row(level, source, message, exception, stepEventId)),
            maxLines: 200,
            "CvdReactor01",
            "OnHeartbeat",
            Guid.NewGuid());

        logger.Warn("sink is down");

        Assert.Single(rows);
    }

    /// <summary>A node logger whose sink fails, standing in for a wedged Serilog sink.</summary>
    private sealed class ThrowingLogger : ILogger
    {
        public IDisposable? BeginScope<TState>(TState state) where TState : notnull => null;

        public bool IsEnabled(LogLevel logLevel) => true;

        public void Log<TState>(LogLevel level, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter) =>
            throw new InvalidOperationException("sink is down");
    }

    [Fact]
    public void AnAttachedException_ReachesBothTheNodeLoggerAndTheRow()
    {
        var (logger, node, rows) = MakeTraced();
        var boom = new InvalidOperationException("boom");

        logger.Error("x", boom);

        Assert.Same(boom, node.Entries[0].Exception);
        Assert.Same(boom, Assert.Single(rows).Exception);
    }

    [Fact]
    public void RuntimeLines_AreRowOnly_AndCarryTheRuntimeSource()
    {
        // The capturing logger has already written the entry to the node logger; re-logging it here
        // would double it (and loop straight back through the decorator).
        var (logger, node, rows) = MakeTraced();

        logger.Runtime("warn", "tag write timed out", null);

        Assert.Empty(node.Entries);
        var row = Assert.Single(rows);
        Assert.Equal("warn", row.Level);
        Assert.Equal("runtime", row.Source);
    }

    [Fact]
    public void RuntimeLines_ShareThePerRunCapWithScriptLines()
    {
        var (logger, _, rows) = MakeTraced(maxLines: 2);

        logger.Info("script line");
        logger.Runtime("info", "runtime line", null);
        logger.Runtime("info", "dropped", null);

        Assert.Equal(2, rows.Count);
        logger.FlushDropped();
        Assert.Contains("1 further log line(s) were not captured", rows[^1].Message);
    }

    [Fact]
    public void MaxLinesMustBePositive()
    {
        Assert.Throws<ArgumentOutOfRangeException>(() =>
            new ScriptLogger(new RecordingLogger(), emit: null, maxLines: 0, "i", "s", null));
    }

    [Fact]
    public void TheNodeLoggerIsRequired()
    {
        Assert.Throws<ArgumentNullException>(() => new ScriptLogger(null!, emit: null, maxLines: 1, "i", "s", null));
    }
}