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

namespace AcDream.App.Tests.UI.Layout;

/// <summary>
/// Loads the committed vitals ElementInfo fixture and builds the widget tree —
/// no dats required. The fixture was generated from layout <c>0x2100006C</c>
/// via 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 fixturePath = Path.Combine(AppContext.BaseDirectory, "UI", "Layout", "fixtures", "vitals_2100006C.json");
        if (!File.Exists(fixturePath))
            throw new FileNotFoundException($"Vitals fixture not found at: {fixturePath}");

        var bytes = File.ReadAllBytes(fixturePath);
        // 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..];
        var root = JsonSerializer.Deserialize<AcDream.App.UI.Layout.ElementInfo>(span, _opts)
            ?? throw new InvalidOperationException($"fixture deserialized to null: {fixturePath}");

        return LayoutImporter.Build(root, _ => (0u, 0, 0), null);
    }
}