using System.Text.Json.Nodes;
using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;

namespace ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors;

/// <summary>Typed working model for a TwinCAT ADS tag's TagConfig JSON (the driver-specific addressing/encoding
/// fields; name/writable live on the Tag entity). Preserves unrecognised JSON keys across a load→save.</summary>
public sealed class TwinCATTagConfigModel
{
    /// <summary>Which device (<c>TwinCATDeviceOptions.HostAddress</c>) this tag lives on. Optional.</summary>
    public string DeviceHostAddress { get; set; } = "";

    /// <summary>Full TwinCAT symbolic name, e.g. <c>MAIN.bStart</c>, <c>GVL.Counter</c>. Required.</summary>
    public string SymbolPath { get; set; } = "";

    /// <summary>TwinCAT / IEC 61131-3 atomic data type.</summary>
    public TwinCATDataType DataType { get; set; } = TwinCATDataType.DInt;

    /// <summary>Optional writable flag (R2-11); <c>null</c> ⇒ omitted (driver default true), explicit
    /// <c>false</c> ⇒ read-only. Preserved across load→save.</summary>
    public bool? Writable { get; set; }

    private JsonObject _bag = new();

    /// <summary>Loads a model from a TagConfig JSON string, defaulting any absent field and retaining
    /// every original key (so fields this editor doesn't expose survive a load→save).</summary>
    /// <param name="json">The TagConfig JSON string to parse, or null/empty for a fresh model.</param>
    /// <returns>A populated <see cref="TwinCATTagConfigModel"/>.</returns>
    public static TwinCATTagConfigModel FromJson(string? json)
    {
        var o = TagConfigJson.ParseOrNew(json);
        return new TwinCATTagConfigModel
        {
            DeviceHostAddress = TagConfigJson.GetString(o, "deviceHostAddress") ?? "",
            SymbolPath = TagConfigJson.GetString(o, "symbolPath") ?? "",
            DataType = TagConfigJson.GetEnum(o, "dataType", TwinCATDataType.DInt),
            Writable = TagConfigJson.GetBoolNullable(o, "writable"),
            _bag = o,
        };
    }

    /// <summary>Serialises this model back to a TagConfig JSON string, writing the exposed fields
    /// (enum as its name string; the optional host address omitted when blank) over the preserved key bag.</summary>
    /// <returns>The serialised TagConfig JSON string.</returns>
    public string ToJson()
    {
        TagConfigJson.Set(_bag, "deviceHostAddress", string.IsNullOrWhiteSpace(DeviceHostAddress) ? null : DeviceHostAddress.Trim());
        TagConfigJson.Set(_bag, "symbolPath", SymbolPath.Trim());
        TagConfigJson.Set(_bag, "dataType", DataType);
        TagConfigJson.Set(_bag, "writable", Writable);
        return TagConfigJson.Serialize(_bag);
    }

    /// <summary>Validation hook; returns an error message or null when the model is valid.</summary>
    /// <returns>An error message describing the validation failure, or null when the model is valid.</returns>
    public string? Validate()
        => string.IsNullOrWhiteSpace(SymbolPath) ? "Symbol path is required." : null;
}
