using System.Text.Json;

namespace ZB.MOM.WW.OtOpcUa.Configuration.Validation;

/// <summary>
///     The one place that decides whether a persisted config blob carries a literal Sql
///     <c>connectionString</c> (Gitea #498 / #499).
/// </summary>
/// <remarks>
///     <para>
///         A <c>Sql</c> driver names its credentials indirectly — <c>connectionStringRef</c> resolves from
///         the environment / secret store at Initialize — so nothing persisted should ever contain a
///         database password. The typed <c>SqlDriverConfigDto</c> already drops a <c>connectionString</c>
///         key on <b>read</b>, but discarding a secret on read is not the same as refusing to store it:
///         config blobs are schemaless JSON columns authored through raw-JSON textareas, so the key can
///         be written even though the runtime ignores it.
///     </para>
///     <para>
///         There are <b>three</b> surfaces a Sql driver's config is persisted on, and they need different
///         enforcement points:
///         <list type="bullet">
///             <item><c>DriverInstance.DriverConfig</c> and <c>Device.DeviceConfig</c> — both in the
///             deployed artifact, both visible to <c>DraftSnapshot</c>, both gated by
///             <c>DraftValidator</c>.</item>
///             <item><c>ClusterNode.DriverConfigOverridesJson</c> — the per-node override map. It is
///             <b>not</b> in <c>DraftSnapshot</c>, and deliberately does not go there: adding a
///             <c>ClusterNode</c> collection would widen the snapshot (and every builder of one) for a
///             single rule about a value that is not part of the artifact at all. More to the point, a
///             deploy gate is the wrong instrument here — the artifact never carries node overrides, so
///             blocking a deploy would not stop the credential being stored. It is already in the
///             database by then. This surface is therefore gated at the <b>save</b>, which is the only
///             point where "refuse to store it" is literally true.</item>
///         </list>
///     </para>
///     <para>
///         <b>Deliberately narrow.</b> This checks the <c>Sql</c> driver's <c>connectionString</c> key
///         only — not a general "credential-shaped key" sweep over every driver type. A broader rule
///         would start refusing configs that are legitimate today for drivers that never made this
///         guarantee, turning defence-in-depth into a regression. Widen it per driver, as each driver
///         gains an indirect-credential contract of its own.
///     </para>
/// </remarks>
public static class SqlCredentialGuard
{
    /// <summary>The config key a Sql driver must never persist. Matched case-insensitively.</summary>
    public const string ForbiddenKey = "connectionString";

    /// <summary>
    ///     Whether <paramref name="configJson"/> is a JSON object carrying <see cref="ForbiddenKey"/> at
    ///     its top level.
    /// </summary>
    /// <remarks>
    ///     Matched <b>case-insensitively</b>: <c>System.Text.Json</c> binds <c>ConnectionString</c> to a
    ///     <c>connectionString</c> property by default, so a case variant is the same key, not a
    ///     different one. Only the top level is scanned — the DTO is flat, so a nested occurrence cannot
    ///     bind and is not the credential-shaped mistake this exists to catch.
    /// </remarks>
    /// <param name="configJson">The config blob to inspect.</param>
    /// <returns><see langword="true"/> when the key is present at the top level.</returns>
    public static bool CarriesLiteralConnectionString(string? configJson)
    {
        if (string.IsNullOrWhiteSpace(configJson)) return false;
        try
        {
            using var doc = JsonDocument.Parse(configJson);
            return doc.RootElement.ValueKind == JsonValueKind.Object
                   && HasTopLevelKey(doc.RootElement, ForbiddenKey);
        }
        catch (JsonException)
        {
            // A malformed blob simply has no keys. Shaping the config JSON is another rule's job, and
            // throwing here would turn a formatting mistake into a credential-guard failure.
            return false;
        }
    }

    /// <summary>
    ///     The <c>DriverInstanceId</c>s in a <c>ClusterNode.DriverConfigOverridesJson</c> map whose
    ///     override object carries a literal connection string, restricted to instances that are actually
    ///     Sql drivers.
    /// </summary>
    /// <remarks>
    ///     The override map is shaped <c>{ "&lt;DriverInstanceId&gt;": { …driver config keys… } }</c> and is
    ///     merged onto the cluster-level <c>DriverConfig</c>, so a credential pasted into one lands in
    ///     exactly the place <see cref="CarriesLiteralConnectionString"/> already refuses on the driver
    ///     itself.
    /// </remarks>
    /// <param name="overridesJson">The node's override map. Null / blank / malformed yields no
    /// violations.</param>
    /// <param name="sqlDriverInstanceIds">The ids of driver instances whose <c>DriverType</c> is
    /// <c>Sql</c>. Keys outside this set are ignored — a non-Sql driver never made the indirect-credential
    /// guarantee, so flagging it would be a regression, not defence in depth.</param>
    /// <returns>The offending driver-instance ids, in document order; empty when there are none.</returns>
    public static IReadOnlyList<string> FindNodeOverrideViolations(
        string? overridesJson, IReadOnlyCollection<string> sqlDriverInstanceIds)
    {
        if (string.IsNullOrWhiteSpace(overridesJson) || sqlDriverInstanceIds.Count == 0)
        {
            return [];
        }

        var sqlIds = sqlDriverInstanceIds as IReadOnlySet<string>
                     ?? sqlDriverInstanceIds.ToHashSet(StringComparer.Ordinal);

        try
        {
            using var doc = JsonDocument.Parse(overridesJson);
            if (doc.RootElement.ValueKind != JsonValueKind.Object) return [];

            List<string>? offenders = null;
            foreach (var entry in doc.RootElement.EnumerateObject())
            {
                if (!sqlIds.Contains(entry.Name)) continue;
                if (entry.Value.ValueKind != JsonValueKind.Object) continue;
                if (!HasTopLevelKey(entry.Value, ForbiddenKey)) continue;

                (offenders ??= []).Add(entry.Name);
            }

            return (IReadOnlyList<string>?)offenders ?? [];
        }
        catch (JsonException)
        {
            return [];
        }
    }

    /// <summary>Whether <paramref name="obj"/> carries <paramref name="key"/> at its top level,
    /// case-insensitively.</summary>
    private static bool HasTopLevelKey(JsonElement obj, string key)
    {
        foreach (var property in obj.EnumerateObject())
        {
            if (string.Equals(property.Name, key, StringComparison.OrdinalIgnoreCase)) return true;
        }

        return false;
    }
}