using System.IO;
using System.Text.Json;
using AcDream.App.UI.Layout;

namespace AcDream.App.Tests.UI.Layout;

/// <summary>
/// Loads the committed layout ElementInfo fixtures and builds widget trees —
/// no dats required. Fixtures were generated from the real portal.dat and
/// serialized with <see cref="System.Text.Json"/>.
/// </summary>
public static class FixtureLoader
{
    private static readonly JsonSerializerOptions _opts = new()
    {
        IncludeFields = true,
    };

    /// <summary>
    /// Deserializes the committed <c>vitals_2100006C.json</c> fixture (copied to
    /// the test output directory via the csproj <c>CopyToOutputDirectory</c> item)
    /// into an <see cref="ElementInfo"/> tree, then builds and returns the
    /// <see cref="ImportedLayout"/> using a null-returning sprite resolver and no
    /// dat font — sufficient for conformance checks on tree structure and slice ids.
    /// </summary>
    public static ImportedLayout LoadVitals()
    {
        var root = LoadVitalsInfos();
        return LayoutImporter.Build(root, _ => (0u, 0, 0), null);
    }

    /// <summary>
    /// Deserializes the committed <c>vitals_2100006C.json</c> fixture into a raw
    /// <see cref="ElementInfo"/> tree WITHOUT calling <see cref="LayoutImporter.Build"/>.
    /// Use this when the test needs to inspect the resolved <see cref="ElementInfo"/>
    /// tree directly (e.g. inheritance-resolution checks) without exercising the
    /// widget factory.
    /// </summary>
    public static AcDream.App.UI.Layout.ElementInfo LoadVitalsInfos()
        => LoadInfos("vitals_2100006C.json");

    /// <summary>
    /// Deserializes the committed <c>chat_21000006.json</c> fixture into a raw
    /// <see cref="ElementInfo"/> tree and builds the <see cref="ImportedLayout"/>
    /// using a null-returning sprite resolver and no dat font — sufficient for
    /// conformance checks on tree structure and resolved types.
    /// </summary>
    public static ImportedLayout LoadChat()
        => LayoutImporter.Build(LoadChatInfos(), _ => (0u, 0, 0), null);

    /// <summary>
    /// Deserializes the committed <c>chat_21000006.json</c> fixture into a raw
    /// <see cref="ElementInfo"/> tree WITHOUT calling <see cref="LayoutImporter.Build"/>.
    /// Use this when the test needs to inspect the resolved <see cref="ElementInfo"/>
    /// tree directly (e.g. resolved Type values per element id).
    /// </summary>
    public static AcDream.App.UI.Layout.ElementInfo LoadChatInfos()
        => LoadInfos("chat_21000006.json");

    // ── Shared loader ────────────────────────────────────────────────────────

    private static AcDream.App.UI.Layout.ElementInfo LoadInfos(string fileName)
    {
        var path = Path.Combine(AppContext.BaseDirectory, "UI", "Layout", "fixtures", fileName);
        if (!File.Exists(path)) throw new FileNotFoundException($"fixture not found at: {path}");
        var bytes = File.ReadAllBytes(path);
        // Strip UTF-8 BOM (EF BB BF) if present so JsonSerializer.Deserialize<T>(ReadOnlySpan<byte>)
        // does not reject the first byte.
        ReadOnlySpan<byte> span = bytes;
        if (span.Length >= 3 && span[0] == 0xEF && span[1] == 0xBB && span[2] == 0xBF)
            span = span[3..];
        return JsonSerializer.Deserialize<AcDream.App.UI.Layout.ElementInfo>(span, _opts)
            ?? throw new InvalidOperationException($"fixture deserialized to null: {path}");
    }
}