using Godot;

namespace Theriapolis.GodotHost.Scenes;

/// <summary>
/// Character creation wizard shell. Mirrors <c>src/app.jsx</c> per
/// GODOT_PORTING_GUIDE.md §4: header + stepper + page (step + aside) +
/// nav bar. Owns the <see cref="CharacterDraft"/> resource and dispatches
/// each step's content into the StepHost.
///
/// Default theme only at this layer — per guide §12 (build order),
/// the parchment Theme lands as a final pass once structural correctness
/// is verified. Until then, font/colour issues are clearly font/colour
/// issues, not layout issues.
/// </summary>
public partial class Wizard : Control
{
    [Signal] public delegate void BackToTitleEventHandler();

    private static readonly string[] StepKeys =
        { "clade", "species", "class", "subclass", "background", "stats", "skills", "review" };
    private static readonly string[] StepNames =
        { "Clade", "Species", "Calling", "Subclass", "History", "Abilities", "Skills", "Sign" };

    public UI.CharacterDraft Character { get; private set; } = null!;

    private UI.Widgets.CodexStepper _stepper = null!;
    private Control _stepHost = null!;
    private Label _folioLabel = null!;
    private Label _validation = null!;
    private Label _navProgress = null!;
    private Button _backBtn = null!;
    private Button _nextBtn = null!;

    // Scroll preservation: snapshot scroll position when the draft changes
    // (which fires before the active step's Refresh tears down + rebuilds
    // child nodes), then restore on the next _Process frame so the user
    // doesn't get punted to the top of the page when selecting a card.
    private ScrollContainer? _scroll;
    private int _savedScroll = -1;
    private bool _scrollPending;

    private int _step;
    private Steps.IStep? _activeStep;
    private static readonly System.Type?[] StepTypes =
    {
        typeof(Steps.StepClade),       // 0 Clade
        typeof(Steps.StepSpecies),     // 1 Species
        typeof(Steps.StepClass),       // 2 Calling
        typeof(Steps.StepSubclass),    // 3 Subclass
        typeof(Steps.StepBackground),  // 4 History
        typeof(Steps.StepStats),       // 5 Abilities
        typeof(Steps.StepSkills),      // 6 Skills
        null,                           // 7 Sign      — M6.6
    };

    public override void _Ready()
    {
        Character = new UI.CharacterDraft();

        _stepper     = GetNode<UI.Widgets.CodexStepper>("%Stepper");
        _stepHost    = GetNode<Control>("%StepHost");
        _folioLabel  = GetNode<Label>("%FolioLabel");
        _validation  = GetNode<Label>("%ValidationLabel");
        _navProgress = GetNode<Label>("%NavProgress");
        _backBtn     = GetNode<Button>("%BackButton");
        _nextBtn     = GetNode<Button>("%NextButton");
        _scroll      = GetNode<ScrollContainer>("%Scroll");

        var aside = GetNode<Aside>("%Aside");
        aside.SetDraft(Character);

        _stepper.StepClicked += OnStepperClicked;
        _backBtn.Pressed     += OnBackPressed;
        _nextBtn.Pressed     += OnNextPressed;
        Character.Changed    += UpdateChrome;

        SwitchToStep(0);
    }

    // ──────────────────────────────────────────────────────────────────────
    // Step lifecycle

    private void SwitchToStep(int index)
    {
        if (index < 0 || index >= StepKeys.Length) return;
        _step = index;

        foreach (var c in _stepHost.GetChildren()) c.QueueFree();
        _activeStep = null;

        var t = StepTypes[index];
        if (t is null)
        {
            _stepHost.AddChild(new Label
            {
                Text = $"{StepNames[index]} step — coming soon.",
            });
        }
        else
        {
            var instance = (Steps.IStep)System.Activator.CreateInstance(t)!;
            _activeStep = instance;
            instance.Bind(Character);
            _stepHost.AddChild((Control)instance);
        }

        UpdateChrome();
    }

    private void OnStepperClicked(int index)
    {
        if (index <= _step) { SwitchToStep(index); return; }
        // Forward jump requires every step in [0..index-1] satisfied — not
        // just the current step. Otherwise picking a clade would let you
        // skip straight to Abilities without picking species/calling/etc.
        for (int i = 0; i < index; i++)
            if (UI.WizardValidation.Validate(i, Character) is not null) return;
        SwitchToStep(index);
    }

    private void OnBackPressed()
    {
        if (_step == 0) { EmitSignal(SignalName.BackToTitle); return; }
        SwitchToStep(_step - 1);
    }

    private void OnNextPressed()
    {
        if (_step < StepKeys.Length - 1) SwitchToStep(_step + 1);
    }

    // ──────────────────────────────────────────────────────────────────────
    // Chrome (header, stepper, nav-bar) refresh

    private void UpdateChrome()
    {
        // Snapshot scroll BEFORE the active step's Refresh handler fires
        // (it's the next subscriber in the Changed chain). The scroll
        // position then survives the rebuild via _Process below.
        if (_scroll is not null)
        {
            _savedScroll = _scroll.ScrollVertical;
            if (_savedScroll > 0) _scrollPending = true;
        }

        _folioLabel.Text = $"Folio {Roman(_step + 1)} of VIII — {StepNames[_step]}";

        // Validate via the static helper so stepper-state propagation and
        // the active-step banner share one source of truth.
        string? err = UI.WizardValidation.Validate(_step, Character);
        bool valid = err is null;
        _validation.Text = err ?? (_step == StepKeys.Length - 1 ? "Ready to sign" : "Folio complete");
        _nextBtn.Disabled = !valid;
        _nextBtn.Visible = _step < StepKeys.Length - 1;
        _backBtn.Text = _step == 0 ? "← Title" : "← Back";
        _navProgress.Text = $"{_step + 1} / {StepKeys.Length}";

        RebuildStepperStates();
    }

    private void RebuildStepperStates()
    {
        // Mirrors app.jsx's lock semantics exactly: a step is Locked iff
        // some EARLIER step's validator fails. Use FirstIncomplete to find
        // the boundary, then state each step accordingly. This is what
        // makes "pick a clade and skip straight to Abilities" impossible —
        // any step after FirstIncomplete is Locked.
        int firstIncomplete = UI.WizardValidation.FirstIncomplete(Character, StepNames.Length);
        var states = new UI.Widgets.CodexStepper.StepState[StepNames.Length];

        for (int i = 0; i < StepNames.Length; i++)
        {
            if (i == _step)
            {
                states[i] = UI.Widgets.CodexStepper.StepState.Active;
            }
            else if (i < _step)
            {
                // Already-visited step. Complete if it still validates,
                // Locked if the user has since invalidated it (e.g. cleared
                // a field). Locked variants past _step also show.
                states[i] = UI.WizardValidation.Validate(i, Character) is null
                    ? UI.Widgets.CodexStepper.StepState.Complete
                    : UI.Widgets.CodexStepper.StepState.Locked;
            }
            else
            {
                // Future step. Locked iff some earlier step is incomplete.
                bool locked = firstIncomplete != -1 && firstIncomplete < i;
                states[i] = locked
                    ? UI.Widgets.CodexStepper.StepState.Locked
                    : UI.Widgets.CodexStepper.StepState.Pending;
            }
        }
        _stepper.SetSteps(StepNames, states);
    }

    public override void _Process(double delta)
    {
        if (_scrollPending && _scroll is not null && IsInstanceValid(_scroll))
        {
            _scroll.ScrollVertical = _savedScroll;
        }
        _scrollPending = false;
    }

    private static string Roman(int n) => n switch
    {
        1 => "I",  2 => "II", 3 => "III", 4 => "IV",
        5 => "V",  6 => "VI", 7 => "VII", 8 => "VIII",
        _ => n.ToString(),
    };
}