namespace ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared;

/// <summary>
///     Caches a <c>DynamicComponent</c> parameter dictionary (R04 H2) and rebuilds it only when one of the
///     values it carries changed. The modals used to build a new dictionary, and new
///     <c>EventCallback</c>s, on every render. A plain build-once cache is wrong: it would pin the JSON
///     captured at first render and silently strand every later edit — so the cache is keyed on the
///     current values, and the callbacks it hands out are created once by the caller and reused.
///     <para>Note the limit: Blazor's change detection treats any <c>EventCallback</c> parameter as
///     possibly changed, so a hosted form still sees <c>SetParametersAsync</c> on each parent render. The
///     per-form <c>_lastParsed</c> guards remain load-bearing; this removes the per-render allocations and
///     gives the child a stable dictionary and callback identity.</para>
/// </summary>
public sealed class ParameterDictionaryCache
{
    private object?[]? _keyValues;
    private Dictionary<string, object>? _cached;

    /// <summary>Returns the cached dictionary when <paramref name="keyValues"/> equal the previous call's,
    /// otherwise builds, caches and returns a new one.</summary>
    /// <param name="keyValues">The values the dictionary carries (compared with <see cref="object.Equals(object, object)"/>).</param>
    /// <param name="build">Builds the dictionary from the current state.</param>
    /// <returns>The parameter dictionary.</returns>
    public Dictionary<string, object> Get(object?[] keyValues, Func<Dictionary<string, object>> build)
    {
        if (_cached is not null && _keyValues is not null && Same(_keyValues, keyValues)) return _cached;

        _cached = build();
        _keyValues = (object?[])keyValues.Clone();
        return _cached;
    }

    /// <summary>Drops the cached dictionary (e.g. on modal close) so the next <see cref="Get"/> rebuilds.</summary>
    public void Reset()
    {
        _cached = null;
        _keyValues = null;
    }

    private static bool Same(object?[] a, object?[] b)
    {
        if (a.Length != b.Length) return false;
        for (var i = 0; i < a.Length; i++)
        {
            if (!Equals(a[i], b[i])) return false;
        }

        return true;
    }
}