using Microsoft.Extensions.Logging;
using ZB.MOM.WW.OtOpcUa.Commons.Engines;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.Core.Scripting;
using ZB.MOM.WW.OtOpcUa.Core.VirtualTags;
using SerilogLogger = Serilog.ILogger;

namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;

/// <summary>
/// T0-4 — the Calculation driver's script evaluator. A calc tag is a raw tag whose value is
/// produced by a C# script over other tags' live values. This evaluator is a deliberate mirror of
/// the VirtualTag <c>RoslynVirtualTagEvaluator</c>: it compiles each unique source once via
/// <see cref="ScriptEvaluator{TContext, TResult}"/> (the Roslyn-backed sandbox), caches the
/// resulting evaluator keyed by source in a <see cref="CompiledScriptCache{TContext, TResult}"/>,
/// and runs steady-state evaluations as in-process method invocations against the dependency
/// dictionary — fast enough to run inline on the driver's dispatch. It reuses
/// <see cref="VirtualTagContext"/> verbatim so the Monaco editor, sandbox, and diagnostics pipeline
/// apply to calc scripts with no divergence.
///
/// <para>
///     <b>Single-tag mode.</b> A calc tag produces exactly one output value — its own — so cross-tag
///     <c>ctx.SetVirtualTag</c> writes are dropped (and logged at Debug). Fan-out between tags is owned
///     by the host's <c>DependencyMuxActor</c> (calc-of-calc chains re-enter the mux), never by the
///     eval engine, exactly as in the VirtualTag adapter.
/// </para>
/// <para>
///     <b>Error surfacing (for WP7).</b> This evaluator never throws for script faults: compile error,
///     sandbox violation, runtime throw, and timeout all return <see cref="VirtualTagEvalResult.Failure"/>
///     with a descriptive <c>Reason</c>. A successful run returns <see cref="VirtualTagEvalResult.Ok"/>
///     carrying the computed value (which may be null). WP7's <c>CalculationDriver</c> maps a
///     <c>Failure</c> to Bad quality + a <c>ScriptLogEntry</c> and an <c>Ok</c> to the published value.
/// </para>
/// <para>
///     <b>Cache management.</b> Implements <see cref="IScriptCacheOwner"/> so WP7 can drop compiled
///     scripts at each deploy generation whose source set changed — mirroring the VirtualTag adapter's
///     apply-boundary clear, which is what stops collectible <c>AssemblyLoadContext</c>s accreting across
///     script edits.
/// </para>
/// </summary>
public sealed class CalculationEvaluator : IScriptCacheOwner, IDisposable
{
    // Source-hash-keyed compile cache: Lazy single-compile (no double-compile race) and Clear()/Dispose()
    // that dispose each evaluator's collectible AssemblyLoadContext. ClearCompiledScripts() — driven by the
    // WP7 driver per deploy generation — is what stops ALCs accreting across script edits.
    private readonly CompiledScriptCache<VirtualTagContext, object?> _cache = new();
    private readonly ILogger<CalculationEvaluator> _logger;
    private readonly SerilogLogger _scriptRoot;
    private readonly TimeSpan _runTimeout;
    private bool _disposed;

    /// <summary>Initializes a new <see cref="CalculationEvaluator"/>.</summary>
    /// <param name="logger">Logger for host-side compilation/execution diagnostics.</param>
    /// <param name="scriptRoot">Root script logger; user <c>ctx.Logger.*</c> output flows through this to the Script-log page.</param>
    /// <param name="runTimeout">Wall-clock budget per script run; defaults to 2 seconds (parity with the VT evaluator).</param>
    public CalculationEvaluator(
        ILogger<CalculationEvaluator> logger,
        ScriptRootLogger scriptRoot,
        TimeSpan? runTimeout = null)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _scriptRoot = (scriptRoot ?? throw new ArgumentNullException(nameof(scriptRoot))).Logger;
        _runTimeout = runTimeout ?? TimeSpan.FromSeconds(2);
    }

    /// <summary>
    ///     Evaluate <paramref name="scriptSource"/> for the calc tag <paramref name="calcTagId"/> against
    ///     the snapshot in <paramref name="dependencies"/> (RawPath → last value). Never throws — script
    ///     faults are reported via <see cref="VirtualTagEvalResult.Failure"/>; a successful run returns
    ///     <see cref="VirtualTagEvalResult.Ok"/> carrying the single computed value.
    /// </summary>
    /// <param name="calcTagId">Identity of the calc tag (bound to the script log; in the live path equals the script id).</param>
    /// <param name="scriptSource">The C# script source producing the tag's value.</param>
    /// <param name="dependencies">Read-only snapshot of dependency values keyed by RawPath.</param>
    public VirtualTagEvalResult Evaluate(string calcTagId, string scriptSource, IReadOnlyDictionary<string, object?> dependencies)
    {
        if (_disposed) return VirtualTagEvalResult.Failure("evaluator disposed");
        if (string.IsNullOrWhiteSpace(scriptSource)) return VirtualTagEvalResult.Failure("empty expression");

        // Passthrough fast-path: the mirror shape `return ctx.GetTag("X").Value;` needs no Roslyn.
        // Semantics are byte-identical to the compiled mirror: a present dependency returns its value
        // (Ok), an absent one makes GetTag yield a Bad snapshot whose .Value is null, so the script
        // returns null — Ok(null) here too. Near-misses fall through to the compiled path.
        if (PassthroughScript.TryMatch(scriptSource, out var passthroughRef))
        {
            return dependencies.TryGetValue(passthroughRef, out var ptValue)
                ? VirtualTagEvalResult.Ok(ptValue)
                : VirtualTagEvalResult.Ok(null);
        }

        var readCache = BuildReadCache(dependencies);
        // Per-evaluation script logger: bind both ScriptId and CalcTagId (via the VirtualTagId slot, which
        // the Script-log page attributes on) from the calc-tag id so each line is attributable.
        var scriptLog = _scriptRoot
            .ForContext(ScriptLoggerFactory.ScriptIdProperty, calcTagId)
            .ForContext(ScriptLoggerFactory.VirtualTagIdProperty, calcTagId);
        var context = new VirtualTagContext(
            readCache,
            // Single-tag mode: a calc tag has exactly one output (its own), so cross-tag writes are dropped.
            setVirtualTag: (path, _) =>
                _logger.LogDebug("Calculation {Id}: cross-tag write to {Path} dropped (single-tag evaluator)",
                    calcTagId, path),
            logger: scriptLog);

        // Fetch + run inside a bounded loop so an ObjectDisposedException caused by a concurrent
        // ClearCompiledScripts (which disposed the evaluator between GetOrCompile and the run's
        // disposed guard) re-fetches and retries exactly once. The loop runs at most twice.
        for (var attempt = 0; ; attempt++)
        {
            ScriptEvaluator<VirtualTagContext, object?> evaluator;
            try
            {
                evaluator = _cache.GetOrCompile(scriptSource);
            }
            catch (CompilationErrorException ex)
            {
                _logger.LogWarning(ex, "Calculation {Id}: Roslyn compile failed", calcTagId);
                return VirtualTagEvalResult.Failure($"compile error: {ex.Message}");
            }
            catch (ScriptSandboxViolationException ex)
            {
                _logger.LogWarning(ex, "Calculation {Id}: sandbox violation", calcTagId);
                return VirtualTagEvalResult.Failure($"sandbox violation: {ex.Message}");
            }
            catch (ObjectDisposedException)
            {
                // Fetch-time disposal is a shutdown signal (the cache is tearing down), not the
                // apply-boundary race — never retry.
                return VirtualTagEvalResult.Failure("evaluator disposed");
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Calculation {Id}: compile threw", calcTagId);
                return VirtualTagEvalResult.Failure($"compile failure: {ex.Message}");
            }

            try
            {
                // Route through TimedScriptEvaluator (Task.Run + WaitAsync): a raw CancellationToken can't
                // interrupt a CPU-bound/infinite-loop Roslyn script, so the timed wrapper is what bounds a
                // runaway script to the wall-clock budget instead of wedging the driver's dispatch.
                var timed = new TimedScriptEvaluator<VirtualTagContext, object?>(evaluator, _runTimeout);
                var raw = timed.RunAsync(context).GetAwaiter().GetResult();
                return VirtualTagEvalResult.Ok(raw);
            }
            catch (ScriptTimeoutException)
            {
                return VirtualTagEvalResult.Failure($"script timed out after {_runTimeout.TotalSeconds:F1}s");
            }
            catch (ObjectDisposedException) when (!_disposed && attempt == 0)
            {
                // A concurrent ClearCompiledScripts disposed the evaluator between our GetOrCompile and the
                // run's disposed-guard. Re-fetch (recompiling the same source into the CURRENT generation)
                // and retry once. A second disposal mid-retry falls through to the failure path below.
                continue;
            }
            catch (ObjectDisposedException)
            {
                return VirtualTagEvalResult.Failure("evaluator disposed during evaluation");
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Calculation {Id}: script execution threw", calcTagId);
                return VirtualTagEvalResult.Failure($"script threw: {ex.Message}");
            }
        }
    }

    /// <inheritdoc />
    public void ClearCompiledScripts() => _cache.Clear();

    private static IReadOnlyDictionary<string, DataValueSnapshot> BuildReadCache(
        IReadOnlyDictionary<string, object?> deps)
    {
        // VirtualTagContext.GetTag returns a DataValueSnapshot — wrap each raw dep value as Good-quality
        // so the script's `(int)ctx.GetTag("a").Value` pattern works. Null values stay null.
        var nowUtc = DateTime.UtcNow;
        var cache = new Dictionary<string, DataValueSnapshot>(StringComparer.Ordinal);
        foreach (var kv in deps)
        {
            cache[kv.Key] = new DataValueSnapshot(kv.Value, StatusCode: 0u, SourceTimestampUtc: nowUtc, ServerTimestampUtc: nowUtc);
        }
        return cache;
    }

    /// <summary>Disposes the evaluator, draining + disposing every cached compile's collectible ALC.</summary>
    public void Dispose()
    {
        if (_disposed) return;
        _disposed = true;
        _cache.Dispose();
    }
}
