// Go reference: golang/nats-server/server/jetstream_versioning.go
// Versioning metadata management for JetStream streams and consumers.
// Manages the _nats.req.level, _nats.ver, _nats.level metadata keys.

using NATS.Server.JetStream.Models;

namespace NATS.Server.JetStream;

/// <summary>
/// JetStream API versioning constants and metadata management.
/// Go reference: server/jetstream_versioning.go
/// </summary>
public static class JsVersioning
{
    /// <summary>
    /// Current JetStream API level supported by this server.
    /// Go: JSApiLevel = 3 (jetstream_versioning.go:20)
    /// </summary>
    public const int JsApiLevel = 3;

    /// <summary>Server version string.</summary>
    public const string Version = "2.12.0";

    /// <summary>Metadata key for the minimum required API level to use this asset.</summary>
    public const string RequiredLevelKey = "_nats.req.level";

    /// <summary>Metadata key for the server version that last modified this asset.</summary>
    public const string ServerVersionKey = "_nats.ver";

    /// <summary>Metadata key for the server API level that last modified this asset.</summary>
    public const string ServerLevelKey = "_nats.level";

    /// <summary>
    /// Returns the required API level string from metadata, or empty if absent.
    /// Go: getRequiredApiLevel (jetstream_versioning.go:28)
    /// </summary>
    public static string GetRequiredApiLevel(Dictionary<string, string>? metadata)
    {
        if (metadata != null && metadata.TryGetValue(RequiredLevelKey, out var level) && level.Length > 0)
            return level;
        return string.Empty;
    }

    /// <summary>
    /// Returns whether the required API level is supported by this server.
    /// Go: supportsRequiredApiLevel (jetstream_versioning.go:36)
    /// </summary>
    public static bool SupportsRequiredApiLevel(Dictionary<string, string>? metadata)
    {
        var level = GetRequiredApiLevel(metadata);
        if (level.Length == 0)
            return true;
        if (!int.TryParse(level, out var li))
            return false;
        return li <= JsApiLevel;
    }

    /// <summary>
    /// Sets static (stored) versioning metadata on a stream config.
    /// Clears dynamic fields (server version/level) and sets the required API level.
    /// Go: setStaticStreamMetadata (jetstream_versioning.go:44)
    /// </summary>
    public static void SetStaticStreamMetadata(StreamConfig cfg)
    {
        if (cfg.Metadata == null)
            cfg.Metadata = [];
        else
            DeleteDynamicMetadata(cfg.Metadata);

        var requiredApiLevel = 0;
        void Requires(int level) { if (level > requiredApiLevel) requiredApiLevel = level; }

        // TTLs require API level 1 (added v2.11)
        if (cfg.AllowMsgTtl || cfg.SubjectDeleteMarkerTtlMs > 0)
            Requires(1);

        // Counter CRDTs require API level 2 (added v2.12)
        if (cfg.AllowMsgCounter)
            Requires(2);

        // Atomic batch publishing requires API level 2 (added v2.12)
        if (cfg.AllowAtomicPublish)
            Requires(2);

        // Message scheduling requires API level 2 (added v2.12)
        if (cfg.AllowMsgSchedules)
            Requires(2);

        // Async persist mode requires API level 2 (added v2.12)
        if (cfg.PersistMode == PersistMode.Async)
            Requires(2);

        cfg.Metadata[RequiredLevelKey] = requiredApiLevel.ToString();
    }

    /// <summary>
    /// Returns a copy of the stream config with dynamic metadata fields added.
    /// The original config is not modified.
    /// Go: setDynamicStreamMetadata (jetstream_versioning.go:88)
    /// </summary>
    public static StreamConfig SetDynamicStreamMetadata(StreamConfig cfg)
    {
        // Shallow copy the config
        var newCfg = ShallowCopyStream(cfg);
        newCfg.Metadata = [];
        if (cfg.Metadata != null)
        {
            foreach (var (k, v) in cfg.Metadata)
                newCfg.Metadata[k] = v;
        }
        newCfg.Metadata[ServerVersionKey] = Version;
        newCfg.Metadata[ServerLevelKey] = JsApiLevel.ToString();
        return newCfg;
    }

    /// <summary>
    /// Copies versioning fields from prevCfg into cfg (for stream update equality checks).
    /// Removes dynamic fields. If prevCfg has no metadata, removes the key from cfg.
    /// Go: copyStreamMetadata (jetstream_versioning.go:110)
    /// </summary>
    public static void CopyStreamMetadata(StreamConfig cfg, StreamConfig? prevCfg)
    {
        if (cfg.Metadata != null)
            DeleteDynamicMetadata(cfg.Metadata);
        SetOrDeleteInStreamMetadata(cfg, prevCfg, RequiredLevelKey);
    }

    /// <summary>
    /// Sets static (stored) versioning metadata on a consumer config.
    /// Go: setStaticConsumerMetadata (jetstream_versioning.go:136)
    /// </summary>
    public static void SetStaticConsumerMetadata(ConsumerConfig cfg)
    {
        if (cfg.Metadata == null)
            cfg.Metadata = [];
        else
            DeleteDynamicMetadata(cfg.Metadata);

        var requiredApiLevel = 0;
        void Requires(int level) { if (level > requiredApiLevel) requiredApiLevel = level; }

        // PauseUntil (non-zero) requires API level 1 (added v2.11)
        if (cfg.PauseUntil.HasValue && cfg.PauseUntil.Value != DateTime.MinValue && cfg.PauseUntil.Value != default)
            Requires(1);

        // Priority policy / groups / pinned TTL require API level 1
        if (cfg.PriorityPolicy != PriorityPolicy.None || cfg.PinnedTtlMs != 0 || cfg.PriorityGroups.Count > 0)
            Requires(1);

        cfg.Metadata[RequiredLevelKey] = requiredApiLevel.ToString();
    }

    /// <summary>
    /// Returns a copy of the consumer config with dynamic metadata fields added.
    /// Go: setDynamicConsumerMetadata (jetstream_versioning.go:164)
    /// </summary>
    public static ConsumerConfig SetDynamicConsumerMetadata(ConsumerConfig cfg)
    {
        var newCfg = ShallowCopyConsumer(cfg);
        newCfg.Metadata = [];
        if (cfg.Metadata != null)
        {
            foreach (var (k, v) in cfg.Metadata)
                newCfg.Metadata[k] = v;
        }
        newCfg.Metadata[ServerVersionKey] = Version;
        newCfg.Metadata[ServerLevelKey] = JsApiLevel.ToString();
        return newCfg;
    }

    /// <summary>
    /// Copies versioning fields from prevCfg into cfg (for consumer update equality checks).
    /// Removes dynamic fields.
    /// Go: copyConsumerMetadata (jetstream_versioning.go:198)
    /// </summary>
    public static void CopyConsumerMetadata(ConsumerConfig cfg, ConsumerConfig? prevCfg)
    {
        if (cfg.Metadata != null)
            DeleteDynamicMetadata(cfg.Metadata);
        SetOrDeleteInConsumerMetadata(cfg, prevCfg, RequiredLevelKey);
    }

    /// <summary>
    /// Removes dynamic metadata fields (server version and level) from a metadata dictionary.
    /// Go: deleteDynamicMetadata (jetstream_versioning.go:222)
    /// </summary>
    public static void DeleteDynamicMetadata(Dictionary<string, string> metadata)
    {
        metadata.Remove(ServerVersionKey);
        metadata.Remove(ServerLevelKey);
    }

    // =========================================================================
    // Private helpers
    // =========================================================================

    private static void SetOrDeleteInStreamMetadata(StreamConfig cfg, StreamConfig? prevCfg, string key)
    {
        if (prevCfg?.Metadata != null && prevCfg.Metadata.TryGetValue(key, out var value))
        {
            cfg.Metadata ??= [];
            cfg.Metadata[key] = value;
            return;
        }
        if (cfg.Metadata != null)
        {
            cfg.Metadata.Remove(key);
            if (cfg.Metadata.Count == 0)
                cfg.Metadata = null;
        }
    }

    private static void SetOrDeleteInConsumerMetadata(ConsumerConfig cfg, ConsumerConfig? prevCfg, string key)
    {
        if (prevCfg?.Metadata != null && prevCfg.Metadata.TryGetValue(key, out var value))
        {
            cfg.Metadata ??= [];
            cfg.Metadata[key] = value;
            return;
        }
        if (cfg.Metadata != null)
        {
            cfg.Metadata.Remove(key);
            if (cfg.Metadata.Count == 0)
                cfg.Metadata = null;
        }
    }

    /// <summary>Shallow copy of a StreamConfig for metadata mutation.</summary>
    private static StreamConfig ShallowCopyStream(StreamConfig src) => new()
    {
        Name = src.Name,
        Description = src.Description,
        Subjects = src.Subjects,
        MaxMsgs = src.MaxMsgs,
        MaxBytes = src.MaxBytes,
        MaxMsgsPer = src.MaxMsgsPer,
        MaxAgeMs = src.MaxAgeMs,
        MaxMsgSize = src.MaxMsgSize,
        MaxConsumers = src.MaxConsumers,
        DuplicateWindowMs = src.DuplicateWindowMs,
        Sealed = src.Sealed,
        DenyDelete = src.DenyDelete,
        DenyPurge = src.DenyPurge,
        AllowDirect = src.AllowDirect,
        AllowMsgTtl = src.AllowMsgTtl,
        FirstSeq = src.FirstSeq,
        Retention = src.Retention,
        Discard = src.Discard,
        Storage = src.Storage,
        Replicas = src.Replicas,
        Mirror = src.Mirror,
        Source = src.Source,
        Sources = src.Sources,
        SubjectTransformSource = src.SubjectTransformSource,
        SubjectTransformDest = src.SubjectTransformDest,
        RePublishSource = src.RePublishSource,
        RePublishDest = src.RePublishDest,
        RePublishHeadersOnly = src.RePublishHeadersOnly,
        SubjectDeleteMarkerTtlMs = src.SubjectDeleteMarkerTtlMs,
        AllowMsgSchedules = src.AllowMsgSchedules,
        AllowMsgCounter = src.AllowMsgCounter,
        AllowAtomicPublish = src.AllowAtomicPublish,
        PersistMode = src.PersistMode,
        Metadata = src.Metadata,
    };

    /// <summary>Shallow copy of a ConsumerConfig for metadata mutation.</summary>
    private static ConsumerConfig ShallowCopyConsumer(ConsumerConfig src) => new()
    {
        DurableName = src.DurableName,
        Ephemeral = src.Ephemeral,
        FilterSubject = src.FilterSubject,
        FilterSubjects = src.FilterSubjects,
        AckPolicy = src.AckPolicy,
        DeliverPolicy = src.DeliverPolicy,
        OptStartSeq = src.OptStartSeq,
        OptStartTimeUtc = src.OptStartTimeUtc,
        ReplayPolicy = src.ReplayPolicy,
        AckWaitMs = src.AckWaitMs,
        MaxDeliver = src.MaxDeliver,
        MaxAckPending = src.MaxAckPending,
        Push = src.Push,
        DeliverSubject = src.DeliverSubject,
        HeartbeatMs = src.HeartbeatMs,
        BackOffMs = src.BackOffMs,
        FlowControl = src.FlowControl,
        RateLimitBps = src.RateLimitBps,
        MaxWaiting = src.MaxWaiting,
        MaxRequestBatch = src.MaxRequestBatch,
        MaxRequestMaxBytes = src.MaxRequestMaxBytes,
        MaxRequestExpiresMs = src.MaxRequestExpiresMs,
        PauseUntil = src.PauseUntil,
        PriorityPolicy = src.PriorityPolicy,
        PriorityGroups = src.PriorityGroups,
        PinnedTtlMs = src.PinnedTtlMs,
        Metadata = src.Metadata,
    };
}