using System.Text.Json;
using Akka.Actor;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Flattening;
using ZB.MOM.WW.ScadaBridge.SiteRuntime.Scripts;

namespace ZB.MOM.WW.ScadaBridge.SiteRuntime.Deployment;

/// <summary>
/// Pure, thread-safe deploy-time gate: given a flattened-configuration JSON, it
/// compiles every script, every alarm on-trigger script, and every Expression
/// trigger just as <see cref="Actors.InstanceActor.CreateChildActors"/> does at
/// runtime — but WITHOUT touching any actor state. It returns the collected
/// compile errors so the Deployment Manager can reject a deployment whose scripts
/// do not compile on the site (design spec: site-side compile failure rejects the
/// deployment; no partial state is applied).
///
/// Because it holds no actor state and only calls <see cref="ScriptCompilationService"/>
/// (whose only state is a thread-safe compile cache), it is pure and thread-safe; the
/// Deployment Manager nevertheless invokes it <em>synchronously on the singleton's actor
/// thread</em> as a pure prefix step, preserving mailbox-FIFO deploy ordering (see
/// <see cref="Actors.DeploymentManagerActor.HandleDeploy"/>). Compiles of unchanged
/// script bodies are deduped by that cache, which is shared across the whole site because
/// the compilation service is a DI singleton.
/// </summary>
public sealed class DeployCompileValidator
{
    private readonly ScriptCompilationService _compilationService;

    /// <summary>Initializes a new instance of the <see cref="DeployCompileValidator"/>.</summary>
    /// <param name="compilationService">The same compilation service the Instance Actor uses at runtime.</param>
    public DeployCompileValidator(ScriptCompilationService compilationService)
        => _compilationService = compilationService;

    /// <summary>
    /// Prefix carried by every runtime-name error, so a caller can tell a name rejection
    /// (<see cref="IsActorNameError"/>) from a compile failure when wording its reply.
    /// </summary>
    private const string ActorNameErrorPrefix = "Invalid runtime name: ";

    /// <summary>True when <paramref name="error"/> came from the runtime-name check.</summary>
    /// <param name="error">One error returned by <see cref="Validate"/>.</param>
    /// <returns><see langword="true"/> for a runtime-name error.</returns>
    public static bool IsActorNameError(string error) =>
        error.StartsWith(ActorNameErrorPrefix, StringComparison.Ordinal);

    /// <summary>
    /// Validates every compilable artifact in the flattened configuration.
    /// Returns an empty list when the whole configuration compiles; otherwise
    /// one human-readable error per failing artifact. Malformed JSON is itself a
    /// single error (this also fronts the poison-config case for startup load).
    /// </summary>
    /// <param name="configJson">The flattened-configuration JSON to validate.</param>
    /// <param name="instanceName">
    /// The instance unique name the Deployment Manager will create the Instance Actor under.
    /// When supplied it is checked as an actor name along with every script/alarm/native-source
    /// child name (review 2026-10-21 01/SR-C1); <see langword="null"/> checks the child names only.
    /// </param>
    /// <returns>A list of compile-error messages; empty if the configuration is clean.</returns>
    public IReadOnlyList<string> Validate(string configJson, string? instanceName = null)
    {
        if (!TryParse(configJson, out var config, out var parseError))
            return [parseError!];

        return Validate(config!, instanceName);
    }

    /// <summary>
    /// Deserializes a flattened-configuration JSON exactly as <see cref="Validate(string, string?)"/>
    /// does, so a caller that needs the parsed object as well (the Deployment Manager, which hands
    /// it on to the Instance Actor — review 2026-10-21 01/SR-P5) parses once instead of once per
    /// consumer. The error text is the one <see cref="Validate(string, string?)"/> reports.
    /// </summary>
    /// <param name="configJson">The flattened-configuration JSON.</param>
    /// <param name="config">The parsed configuration, or <see langword="null"/> on failure.</param>
    /// <param name="error">The deserialization error, or <see langword="null"/> on success.</param>
    /// <returns><see langword="true"/> when the JSON produced a configuration.</returns>
    public static bool TryParse(string configJson, out FlattenedConfiguration? config, out string? error)
    {
        try
        {
            config = JsonSerializer.Deserialize<FlattenedConfiguration>(configJson);
        }
        catch (JsonException ex)
        {
            config = null;
            error = $"Configuration JSON failed to deserialize: {ex.Message}";
            return false;
        }

        if (config == null)
        {
            error = "Configuration JSON failed to deserialize: result was null.";
            return false;
        }

        error = null;
        return true;
    }

    /// <summary>
    /// Validates an already-parsed flattened configuration — the same checks as
    /// <see cref="Validate(string, string?)"/> without a second deserialization (01/SR-P5).
    /// </summary>
    /// <param name="config">The parsed flattened configuration.</param>
    /// <param name="instanceName">See <see cref="Validate(string, string?)"/>.</param>
    /// <returns>A list of error messages; empty if the configuration is clean.</returns>
    public IReadOnlyList<string> Validate(FlattenedConfiguration config, string? instanceName = null)
    {
        var errors = new List<string>();

        // Runtime names first: they are cheap, and a name Akka refuses would otherwise surface
        // as an InvalidActorNameException at Context.ActorOf instead of a readable rejection.
        AddActorNameErrors(errors, config, instanceName);

        // Scripts: full execution-path compile against ScriptGlobals.
        foreach (var script in config.Scripts)
        {
            var result = _compilationService.Compile(script.CanonicalName, script.Code);
            if (!result.IsSuccess)
                errors.Add($"Script '{script.CanonicalName}': {string.Join("; ", result.Errors)}");

            // Expression-triggered scripts also compile their trigger expression.
            AddTriggerExpressionError(errors, script.TriggerType, script.TriggerConfiguration,
                $"script-trigger-{script.CanonicalName}");
        }

        // Alarms: on-trigger script reference must resolve + compile, and any
        // Expression trigger must compile — mirrors InstanceActor.CreateChildActors.
        foreach (var alarm in config.Alarms)
        {
            if (!string.IsNullOrEmpty(alarm.OnTriggerScriptCanonicalName))
            {
                var triggerScriptDef = config.Scripts
                    .FirstOrDefault(s => s.CanonicalName == alarm.OnTriggerScriptCanonicalName);
                if (triggerScriptDef == null)
                {
                    errors.Add($"Alarm '{alarm.CanonicalName}': on-trigger script " +
                               $"'{alarm.OnTriggerScriptCanonicalName}' is not defined.");
                }
                else
                {
                    var result = _compilationService.Compile(
                        $"alarm-trigger-{alarm.CanonicalName}", triggerScriptDef.Code);
                    if (!result.IsSuccess)
                        errors.Add($"Alarm '{alarm.CanonicalName}' on-trigger script " +
                                   $"'{alarm.OnTriggerScriptCanonicalName}': {string.Join("; ", result.Errors)}");
                }
            }

            AddTriggerExpressionError(errors, alarm.TriggerType, alarm.TriggerConfiguration,
                $"alarm-trigger-expr-{alarm.CanonicalName}");
        }

        return errors;
    }

    /// <summary>
    /// Populates the shared compile cache for a whole startup batch (review 2026-10-21 01/SR-P3):
    /// every DISTINCT script body and trigger expression across <paramref name="configs"/> is
    /// compiled once, up to <paramref name="maxDegreeOfParallelism"/> at a time. Same compile units
    /// as <see cref="Validate(FlattenedConfiguration, string?)"/> — scripts and alarm on-trigger
    /// scripts against <c>ScriptGlobals</c>, Expression triggers against
    /// <c>TriggerExpressionGlobals</c> — but deduplicated first, because the cache is keyed on
    /// code: N instances of one template would otherwise race N identical cold compiles in
    /// parallel. Best-effort: verdicts are discarded and a throwing unit is skipped, since every
    /// Instance Actor's own compile remains the correctness backstop.
    /// </summary>
    /// <param name="configs">The batch's parsed configurations.</param>
    /// <param name="maxDegreeOfParallelism">Upper bound on concurrent Roslyn compiles.</param>
    public void WarmCompileCache(IReadOnlyList<FlattenedConfiguration> configs, int maxDegreeOfParallelism)
    {
        var units = new Dictionary<(bool IsTrigger, string Code), string>();
        foreach (var config in configs)
        {
            foreach (var script in config.Scripts)
            {
                units.TryAdd((false, script.Code), script.CanonicalName);
                AddTriggerUnit(units, script.TriggerType, script.TriggerConfiguration,
                    $"script-trigger-{script.CanonicalName}");
            }

            // Alarm on-trigger scripts compile the referenced SCRIPT's body against ScriptGlobals,
            // i.e. the same cache key as that script — already a unit above.
            foreach (var alarm in config.Alarms)
                AddTriggerUnit(units, alarm.TriggerType, alarm.TriggerConfiguration,
                    $"alarm-trigger-expr-{alarm.CanonicalName}");
        }

        Parallel.ForEach(
            units,
            new ParallelOptions { MaxDegreeOfParallelism = Math.Max(1, maxDegreeOfParallelism) },
            unit =>
            {
                try
                {
                    if (unit.Key.IsTrigger)
                        _compilationService.CompileTriggerExpression(unit.Value, unit.Key.Code);
                    else
                        _compilationService.Compile(unit.Value, unit.Key.Code);
                }
                catch
                {
                    // Best-effort warm — the Instance Actor's PreStart compiles it the hard way.
                }
            });
    }

    private static void AddTriggerUnit(
        Dictionary<(bool IsTrigger, string Code), string> units,
        string? triggerType, string? triggerConfigJson, string compileName)
    {
        if (!string.Equals(triggerType, "Expression", StringComparison.OrdinalIgnoreCase))
            return;

        var expression = TriggerExpressionGlobals.ExtractExpression(triggerConfigJson);
        if (expression != null)
            units.TryAdd((true, expression), compileName);
    }

    /// <summary>
    /// Review 2026-10-21 01/SR-C1: every name that becomes an Akka actor name on the site — the
    /// Instance Actor itself (<c>DeploymentManagerActor.CreateInstanceActor</c>) and its
    /// <c>script-</c>/<c>alarm-</c>/<c>native-alarm-</c> children
    /// (<c>InstanceActor.CreateChildActors</c>) — must be a legal path element. An instance named
    /// <c>"Furnace #3"</c> used to make <c>Context.ActorOf</c> throw on the Deployment Manager
    /// singleton's own thread, restarting it and every Instance Actor on the site.
    ///
    /// <para>
    /// Decided with Akka's own <see cref="ActorPath.IsValidPathElement"/>, not the Commons mirror
    /// <c>ActorNameRules</c>: the mirror is currently STRICTER (it refuses <c>"</c>, <c>(</c> and
    /// <c>)</c>, which Akka accepts), so gating on it would reject deployments that work today.
    /// </para>
    /// </summary>
    private static void AddActorNameErrors(
        List<string> errors, FlattenedConfiguration config, string? instanceName)
    {
        if (instanceName != null)
            AddActorNameError(errors, "Instance", instanceName, instanceName);

        foreach (var script in config.Scripts)
            AddActorNameError(errors, "Script", script.CanonicalName, $"script-{script.CanonicalName}");

        foreach (var alarm in config.Alarms)
            AddActorNameError(errors, "Alarm", alarm.CanonicalName, $"alarm-{alarm.CanonicalName}");

        foreach (var source in config.NativeAlarmSources)
            AddActorNameError(errors, "Native alarm source", source.CanonicalName,
                $"native-alarm-{source.CanonicalName}");
    }

    private static void AddActorNameError(
        List<string> errors, string kind, string? name, string actorName)
    {
        if (ActorPath.IsValidPathElement(actorName))
            return;

        errors.Add($"{ActorNameErrorPrefix}{kind} name '{name}' cannot be used as a runtime actor " +
                   "name — use ASCII letters, digits and -_.*$+:@&=,!~';() only (no spaces, '#', " +
                   "'/', '[', ']', '%' or non-ASCII letters), and do not start it with '$'.");
    }

    /// <summary>
    /// Compiles the boolean trigger expression for an Expression-triggered script
    /// or alarm and records any failure. No-op for non-Expression triggers or a
    /// blank/malformed expression config — mirroring
    /// <c>InstanceActor.CompileTriggerExpression</c>, where those cases yield an
    /// inert trigger rather than a deployment error.
    /// </summary>
    private void AddTriggerExpressionError(
        List<string> errors, string? triggerType, string? triggerConfigJson, string compileName)
    {
        if (!string.Equals(triggerType, "Expression", StringComparison.OrdinalIgnoreCase))
            return;

        var expression = TriggerExpressionGlobals.ExtractExpression(triggerConfigJson);
        if (expression == null)
            return;

        var result = _compilationService.CompileTriggerExpression(compileName, expression);
        if (!result.IsSuccess)
            errors.Add($"Trigger expression '{compileName}': {string.Join("; ", result.Errors)}");
    }
}