using AcDream.App.UI;
using AcDream.App.UI.Layout;
using DatReaderWriter;

namespace AcDream.App.Studio;

/// <summary>Which kind of source the studio is currently previewing.</summary>
public enum LayoutSourceKind { DatLayout, Markup }

/// <summary>
/// Wraps the two ways the UI Studio can load a panel to preview:
/// a LayoutDesc dat id, or a KSML markup file path (Task 6 — unsupported now).
///
/// <para>Call <see cref="Load"/> with the current <see cref="StudioOptions"/> to
/// import the layout and get the root <see cref="UiElement"/>. The result is also
/// cached in <see cref="CurrentLayout"/> so <see cref="Reload"/> can re-run the same
/// source without re-reading the options.</para>
/// </summary>
public sealed class LayoutSource
{
    private readonly DatCollection _dats;
    private readonly Func<uint, (uint, int, int)> _resolve;
    private readonly UiDatFont? _datFont;
    private readonly Func<uint, UiDatFont?>? _fontResolve;

    public LayoutSourceKind Kind         { get; private set; }
    public uint?            LayoutId     { get; private set; }
    public string?          MarkupPath   { get; private set; }
    public string?          LastError    { get; private set; }
    public ImportedLayout?  CurrentLayout { get; private set; }

    /// <summary>
    /// Create a LayoutSource.
    /// </summary>
    /// <param name="fontResolve">Optional per-element font resolver: FontDid →
    /// <see cref="UiDatFont"/> (null when the font isn't in the dats). When supplied,
    /// elements with a non-zero FontDid receive their own dat font at build time
    /// instead of the shared <paramref name="datFont"/> global. Controllers that
    /// explicitly set <see cref="UiText.DatFont"/> after
    /// <see cref="ImportedLayout.FindElement"/> still override the build-time value.
    /// Pass null (default) for the original single-font behavior — the live
    /// <see cref="GameWindow"/> path passes null so it is provably unchanged.</param>
    public LayoutSource(
        DatCollection dats,
        Func<uint, (uint, int, int)> resolve,
        UiDatFont? datFont,
        Func<uint, UiDatFont?>? fontResolve = null)
    {
        _dats        = dats    ?? throw new ArgumentNullException(nameof(dats));
        _resolve     = resolve ?? throw new ArgumentNullException(nameof(resolve));
        _datFont     = datFont;
        _fontResolve = fontResolve;
    }

    /// <summary>
    /// Load the layout described by <paramref name="opts"/>. For a dat layout
    /// (<see cref="StudioOptions.LayoutId"/> is non-null) calls
    /// <see cref="LayoutImporter.Import"/>. For a markup path sets
    /// <see cref="LastError"/> and returns null (Task 6, not yet implemented).
    ///
    /// Returns the root <see cref="UiElement"/> on success, or null on failure
    /// (check <see cref="LastError"/>).
    /// </summary>
    public UiElement? Load(StudioOptions opts)
    {
        LastError    = null;
        CurrentLayout = null;

        if (opts.MarkupPath is not null)
        {
            Kind       = LayoutSourceKind.Markup;
            MarkupPath = opts.MarkupPath;
            LastError  = "markup unsupported (Task 6)";
            return null;
        }

        if (opts.LayoutId is null)
        {
            LastError = "ui-studio: no layout id or markup path specified.";
            return null;
        }

        Kind     = LayoutSourceKind.DatLayout;
        LayoutId = opts.LayoutId;
        return LoadDat(opts.LayoutId.Value);
    }

    /// <summary>Re-run the most-recently-configured source without re-reading options.</summary>
    public UiElement? Reload()
    {
        LastError     = null;
        CurrentLayout = null;

        if (Kind == LayoutSourceKind.Markup)
        {
            LastError = "markup unsupported (Task 6)";
            return null;
        }

        if (LayoutId is null)
        {
            LastError = "ui-studio: no layout id to reload.";
            return null;
        }

        return LoadDat(LayoutId.Value);
    }

    // ── Private ──────────────────────────────────────────────────────────────────

    private UiElement? LoadDat(uint layoutId)
    {
        var imported = LayoutImporter.Import(_dats, layoutId, _resolve, _datFont, _fontResolve);
        if (imported is null)
        {
            LastError = $"ui-studio: LayoutDesc 0x{layoutId:X8} not found in dats.";
            return null;
        }

        CurrentLayout = imported;
        return imported.Root;
    }
}