using System.Text.Json;

namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;

/// <summary>
///     The Galaxy (<see cref="DriverTypeNames.Galaxy"/>) tag reference: the <c>attributeRef</c> a Galaxy raw tag's
///     <c>TagConfig</c> carries, <c>tag_name.AttributeName</c>, which the driver dials through MXAccess. One parser for the
///     driver (which dials it) and the address-space composer (which names the AVEVA event source it implies, Gitea #886),
///     so the two can never disagree about which tags carry one.
/// </summary>
public static class GalaxyAttributeRef
{
    /// <summary>The <c>TagConfig</c> key (camelCase; matched case-insensitively).</summary>
    public const string Key = "attributeRef";

    /// <summary>
    ///     Read the Galaxy dialled address from a tag's <c>TagConfig</c> JSON — the camelCase <c>attributeRef</c> key (the v3
    ///     rename of the pre-v3 PascalCase <c>FullName</c>). Case-insensitive on the property name for authoring tolerance;
    ///     returns null on an absent/blank/non-string value or an unparseable blob.
    /// </summary>
    /// <param name="tagConfigJson">The tag's <c>TagConfig</c> JSON.</param>
    /// <returns>The attributeRef, or null.</returns>
    public static string? TryRead(string? tagConfigJson)
    {
        if (string.IsNullOrWhiteSpace(tagConfigJson)) return null;
        try
        {
            using var doc = JsonDocument.Parse(tagConfigJson);
            if (doc.RootElement.ValueKind != JsonValueKind.Object) return null;
            foreach (var prop in doc.RootElement.EnumerateObject())
            {
                if (!prop.NameEquals(Key) && !string.Equals(prop.Name, Key, StringComparison.OrdinalIgnoreCase)) continue;
                if (prop.Value.ValueKind != JsonValueKind.String) return null;
                var v = prop.Value.GetString();
                return string.IsNullOrWhiteSpace(v) ? null : v;
            }
        }
        catch (JsonException)
        {
            // Malformed blob: no dialable address.
        }

        return null;
    }

    /// <summary>
    ///     The AVEVA alarm reference of a native-alarm tag, or null: the tag's <see cref="TryRead">attributeRef</see> when its
    ///     driver is the Galaxy driver, otherwise null (no other driver's alarms are stored by AVEVA under a Galaxy name).
    /// </summary>
    /// <param name="driverType">The owning driver's <c>DriverType</c>.</param>
    /// <param name="tagConfigJson">The tag's <c>TagConfig</c> JSON.</param>
    /// <returns>The Galaxy alarm reference (<c>tag_name.AlarmAttribute</c>), or null.</returns>
    public static string? AlarmReferenceOf(string? driverType, string? tagConfigJson) =>
        string.Equals(driverType, DriverTypeNames.Galaxy, StringComparison.Ordinal) ? TryRead(tagConfigJson) : null;

    /// <summary>
    ///     The Galaxy object (<c>tag_name</c>) a reference belongs to: the text before the first <c>.</c>, or the whole
    ///     reference when it has none. This is AVEVA's <c>Source_Object</c> for the object's events and its attributes'
    ///     alarms. Null for a blank reference or one that starts with a <c>.</c>.
    /// </summary>
    /// <param name="reference">A Galaxy reference, e.g. <c>Oven_007.TempHiAlarm</c>.</param>
    /// <returns>The object name, e.g. <c>Oven_007</c>.</returns>
    public static string? ObjectNameOf(string? reference)
    {
        if (string.IsNullOrWhiteSpace(reference)) return null;
        var trimmed = reference.Trim();
        var dot = trimmed.IndexOf('.');
        return dot switch
        {
            < 0 => trimmed,
            0 => null,
            _ => trimmed[..dot],
        };
    }
}