Response.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json.Serialization;

namespace JSONstat.Models;

/// <summary>
/// The parsed top-level JSON-stat response. Dispatches to the appropriate
/// class-specific object (<see cref="T:Dataset"/>, <see cref="T:Collection"/>, or
/// <see cref="T:Dimension"/>) and exposes the Toolkit-parity navigation entry
/// points (<c>Dataset</c>, <c>Item</c>).
/// </summary>
public sealed class Response
{
    /// <summary>The response class.</summary>
    [JsonIgnore]
    public ResponseClass Class { get; internal set; }

    /// <summary>JSON-stat version.</summary>
    [JsonIgnore]
    public string? Version { get; internal set; }

    /// <summary>Short descriptive text.</summary>
    [JsonIgnore]
    public string? Label { get; internal set; }

    /// <summary>The single dataset for a dataset response.</summary>
    internal Dataset? DatasetValue { get; set; }

    /// <summary>The collection for a collection response.</summary>
    internal Collection? CollectionValue { get; set; }

    /// <summary>The dimension for a dimension response.</summary>
    internal Dimension? DimensionValue { get; set; }

    /// <summary>The parsed collection (collection responses), or <c>null</c>.</summary>
    [JsonIgnore]
    public Collection? Collection => CollectionValue;

    /// <summary>The parsed dimension (dimension responses), or <c>null</c>.</summary>
    [JsonIgnore]
    public Dimension? Dimension => DimensionValue;

    /// <summary>All datasets reachable from this response.</summary>
    [JsonIgnore]
    public IReadOnlyList<Dataset> Datasets
    {
        get
        {
            if (Class == ResponseClass.Dataset && DatasetValue != null) return new[] { DatasetValue };
            if (Class == ResponseClass.Collection && CollectionValue != null) return CollectionValue.EmbeddedDatasets;
            return Array.Empty<Dataset>();
        }
    }

    /// <summary>Gets the first dataset, or <c>null</c>.</summary>
    public Dataset? Dataset() => DatasetValue;

    /// <summary>Gets the dataset at <paramref name="index"/>, or <c>null</c>.</summary>
    public Dataset? Dataset(int index)
    {
        var list = Datasets;
        return index >= 0 && index < list.Count ? list[index] : null;
    }

    /// <summary>Gets the dataset whose label matches <paramref name="id"/>, or <c>null</c>.</summary>
    public Dataset? Dataset(string id) =>
        Datasets.FirstOrDefault(d => string.Equals(d.Label, id, StringComparison.Ordinal));

    /// <summary>The collection items (collection responses).</summary>
    [JsonIgnore]
    public IReadOnlyList<LinkItem> Items => CollectionValue?.Items ?? Array.Empty<LinkItem>();

    /// <summary>Gets the collection item at <paramref name="index"/>, or <c>null</c>.</summary>
    public LinkItem? Item(int index) => CollectionValue?.Item(index);

    /// <summary>Gets the collection items of a given class.</summary>
    public IReadOnlyList<LinkItem> ItemsOf(ResponseClass filter) =>
        CollectionValue?.ItemsOf(filter) ?? Array.Empty<LinkItem>();
}