using System.Text.Json;

namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;

/// <summary>
///     Minimal driver-side view of the deployment artifact emitted by
///     <c>ConfigComposer.SnapshotAndFlattenAsync</c>. The artifact JSON is the full snapshot —
///     for driver spawning we only need the <c>DriverInstances</c> array. Reading just the
///     subset keeps allocations cheap on every deploy.
/// </summary>
public sealed record DriverInstanceSpec(
    Guid DriverInstanceRowId,
    string DriverInstanceId,
    string Name,
    string DriverType,
    bool Enabled,
    string DriverConfig);

public static class DeploymentArtifact
{
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNameCaseInsensitive = true,
    };

    /// <summary>
    ///     Parse a deployment artifact blob into the list of driver-instance specs to spawn.
    ///     Empty / malformed blobs return an empty list — callers log + treat as "no drivers".
    /// </summary>
    public static IReadOnlyList<DriverInstanceSpec> ParseDriverInstances(ReadOnlySpan<byte> blob)
    {
        if (blob.IsEmpty) return Array.Empty<DriverInstanceSpec>();

        try
        {
            using var doc = JsonDocument.Parse(blob.ToArray());
            if (!doc.RootElement.TryGetProperty("DriverInstances", out var arr)
                || arr.ValueKind != JsonValueKind.Array)
            {
                return Array.Empty<DriverInstanceSpec>();
            }

            var result = new List<DriverInstanceSpec>(arr.GetArrayLength());
            foreach (var el in arr.EnumerateArray())
            {
                if (el.ValueKind != JsonValueKind.Object) continue;
                var spec = TryReadSpec(el);
                if (spec is not null) result.Add(spec);
            }
            return result;
        }
        catch (JsonException)
        {
            return Array.Empty<DriverInstanceSpec>();
        }
    }

    private static DriverInstanceSpec? TryReadSpec(JsonElement el)
    {
        var rowId = el.TryGetProperty("DriverInstanceRowId", out var rowEl)
            && rowEl.TryGetGuid(out var rid) ? rid : Guid.Empty;
        var id = el.TryGetProperty("DriverInstanceId", out var idEl) ? idEl.GetString() : null;
        var name = el.TryGetProperty("Name", out var nameEl) ? nameEl.GetString() : null;
        var type = el.TryGetProperty("DriverType", out var typeEl) ? typeEl.GetString() : null;
        var enabled = !el.TryGetProperty("Enabled", out var enEl) || enEl.GetBoolean();
        var config = el.TryGetProperty("DriverConfig", out var cfgEl) ? cfgEl.GetString() : null;

        if (string.IsNullOrWhiteSpace(id) || string.IsNullOrWhiteSpace(type)) return null;

        return new DriverInstanceSpec(
            DriverInstanceRowId: rowId,
            DriverInstanceId: id!,
            Name: name ?? id!,
            DriverType: type!,
            Enabled: enabled,
            DriverConfig: config ?? "{}");
    }
}