using System;
using System.Collections.Generic;
using AcDream.App.UI.Layout;

namespace AcDream.App.UI;

/// <summary>
/// Retail <c>UIElement_Panel</c> (dat class Type <c>8</c>) — the tab-strip host used by
/// the Options panel and, in principle, any panel that authors a tab table (dat property
/// <c>0x2E</c>, see <see cref="UiTabTableEntry"/>).
///
/// <para>
/// <b>Naming correction (OP2 rework):</b> the OP2 slice named this class/mechanism
/// <c>UIElement_TabControl</c>. No such class exists in the named-retail PDB — Type 8 is
/// registered as <c>UIElement_Panel::Create</c> (<c>UIElement::RegisterElementClass(8,
/// UIElement_Panel::Create) @0x0046C6B7</c>). Correct anchors:
/// <c>UIElement_Panel::SetupTabPageHash @0x0046C2E0</c> (tab-table read + default
/// selection), <c>::Update @0x0046BD00</c> (the one-visible-page switch + tab
/// Open/Closed state write), <c>::OpenTab @0x0046BE20</c> / <c>::InqTabFromPage
/// @0x0046BEB0</c> (the click entry points), <c>::ListenToElementMessage @0x0046BF90</c>.
/// </para>
///
/// <para>
/// <b>Shape correction (OP2 rework, `docs/research/2026-08-11-op2-review-blast.md` +
/// `docs/research/2026-08-11-op2-review-mechanism.md`):</b> OP2 mapped every dat Type-8
/// element unconditionally to this class and wired its tab table AT IMPORT TIME
/// (<c>OnChildrenAttached</c>). Four already-shipped panels (vendor `0x100000B8`,
/// character sheet root `0x10000227`, spellbook root `0x100002A8`, combat
/// `0x100000A2`) are Type 8 and authored a tab table, so they silently gained a SECOND,
/// import-time tab-switcher racing their own existing C# controllers
/// (<c>CharacterStatController</c>/<c>SpellbookWindowController</c>/
/// <c>VendorUiController</c> already own this exact switching for their panels; combat
/// has no re-binder at all — the table would have taken over outright). A fifth Type-8
/// element, vendor's media-bearing backdrop `0x1000008D`, has NO tab table at all and
/// simply lost its authored fill because the old bare-<see cref="UiElement"/> base drew
/// nothing and defaulted <see cref="UiElement.ClickThrough"/> to <c>false</c>.
/// </para>
///
/// <para>
/// This class now derives from <see cref="UiDatElement"/> and is DORMANT by default:
/// importing a Type-8 element only gets authored-media drawing, retail's
/// <c>ClickThrough = true</c> generic-decoration default, and <see cref="IUiDatStateful"/>
/// state propagation — identical to the pre-OP2 fallback for every element that doesn't
/// opt in. The tab-table switching mechanism (button ↔ page ↔ default, Open/Closed state)
/// only activates when a controller explicitly calls <see cref="ActivateTabBehavior"/> —
/// today, nobody does (OP2 ships the mechanism only; the Options panel controller,
/// Campaign OP slice OP3+, is the first caller). This is filed as an intentional
/// deviation from retail's unconditional per-instance activation — see the register row
/// added in this same commit.
/// </para>
///
/// <para>
/// The tab buttons and page-slot children are ORDINARY imported dat elements — this
/// widget does <b>not</b> set <see cref="UiElement.ConsumesDatChildren"/>, so
/// <c>LayoutImporter</c> builds them the normal recursive way (buttons build as
/// <see cref="UiText"/> with Open/Closed states — retail's tab buttons are Type 0xC
/// text elements, not Type-1 buttons; page slots build as generic containers whose
/// OWN children are the mounted page's content via <c>BaseLayoutId</c>/
/// <c>BaseElement</c> inheritance).
/// </para>
///
/// <para>
/// Retail anchors: <c>docs/research/2026-08-10-options-panel-structure.md</c> §1.3
/// (the tab table property <c>0x2E</c> struct shape), §10.1 (structural inventory —
/// tab buttons `0x1000020D..0x1000020F`/`0x1000050B`, page slots
/// `0x10000211..0x10000213`/`0x1000050C`, Gameplay the authored default). Verified
/// byte-for-byte against the regenerated <c>options_2100002B.json</c> fixture: four
/// entries, Gameplay (`0x1000020D`/`0x10000212`) is the sole <c>IsDefault</c> row.
/// </para>
///
/// <para>
/// Retail's <c>OnVisibilityChanged</c> auto-apply/auto-revert semantics (research doc
/// §3.6 — hiding a page reverts uncommitted edits, showing one applies + commits) are
/// OUT of this widget's scope: they belong to the <c>OptionPage</c>/
/// <c>PlayerOptionPage</c> model a page controller owns (Campaign OP slice OP3+).
/// This widget only switches which page slot is <see cref="UiElement.Visible"/>.
/// </para>
/// </summary>
public sealed class UiTabPanel : UiDatElement, IUiChildrenAttachedListener
{
    /// <summary>Retail element id this class was ported for: Type 8 = 8.</summary>
    public const uint RetailTypeId = 8u;

    private readonly IReadOnlyList<UiTabTableEntry> _tabs;
    private readonly List<UiTabTableEntry> _unresolved = new();
    private bool _behaviorActive;

    public UiTabPanel(
        ElementInfo info,
        Func<uint, (uint tex, int w, int h)> resolve,
        IReadOnlyList<UiTabTableEntry> tabs)
        : base(info, resolve)
    {
        _tabs = tabs;
    }

    /// <summary>The authored tab table this control was built from, in authored array order.</summary>
    public IReadOnlyList<UiTabTableEntry> Tabs => _tabs;

    /// <summary>Dat element id of the currently active page slot. 0 before the first
    /// switch (either <see cref="ActivateTabBehavior"/>'s default-entry switch, or a
    /// direct <see cref="SwitchTo"/> call).</summary>
    public uint ActivePageElementId { get; private set; }

    /// <summary>
    /// Fires at the end of every <see cref="SwitchTo"/> call that actually
    /// changes the active page — including the FIRST switch, from
    /// <see cref="ActivateTabBehavior"/>'s default-entry activation (old = 0).
    /// A page-model owner (Campaign OP slice OP3's <c>OptionsPanelController</c>)
    /// subscribes here to drive retail's per-page
    /// <c>OnVisibilityChanged(false)</c>/<c>OnVisibilityChanged(true)</c> pair
    /// (research doc §3.6) on the leaving/entering page — this widget only
    /// owns which page slot is <see cref="UiElement.Visible"/>, not the
    /// page-model semantics layered on top of that switch.
    /// </summary>
    public event Action<uint, uint>? ActivePageChanged;

    /// <summary>
    /// True once <see cref="ActivateTabBehavior"/> has run. Dormant instances (every
    /// pre-existing Type-8 host today) never flip this.
    /// </summary>
    public bool BehaviorActive => _behaviorActive;

    /// <summary>
    /// Tab-table entries whose button, page, or both did not resolve against this
    /// element's built subtree the last time <see cref="ActivateTabBehavior"/> ran — a
    /// silently-empty tab table and one that entirely fails to resolve are otherwise
    /// indistinguishable (round-2 review SHOULD-FIX 3), so this is loud instead of a
    /// mere no-op. Each miss is also logged via <see cref="Console.WriteLine"/>.
    /// </summary>
    public IReadOnlyList<UiTabTableEntry> UnresolvedEntries => _unresolved;

    /// <summary>
    /// Dormant by design (see class doc) — importing a Type-8 element performs no
    /// wiring. <see cref="ActivateTabBehavior"/> is the explicit, controller-driven
    /// opt-in that does the equivalent work once the subtree exists AND a controller
    /// actually wants this element to own tab switching.
    /// </summary>
    void IUiChildrenAttachedListener.OnChildrenAttached()
    {
    }

    /// <summary>
    /// Opts this instance into retail's tab-table switching mechanism: binds every tab
    /// button's click to switch to its paired page (<c>UIElement_Panel::OpenTab</c>),
    /// then activates the authored default entry — the entry with
    /// <see cref="UiTabTableEntry.IsDefault"/> true. Idempotent; a second call is a
    /// no-op. Retail resolves both the button and the page via
    /// <c>GetChildRecursive</c> (a descendant search, not direct-children-only), which
    /// this ports so cross-layout mounts (a tab page's content built from a different
    /// LayoutDesc, e.g. Configure Keyboard) still resolve.
    /// </summary>
    public void ActivateTabBehavior()
    {
        if (_behaviorActive) return;
        _behaviorActive = true;

        _unresolved.Clear();
        UiTabTableEntry? defaultEntry = null;
        foreach (UiTabTableEntry entry in _tabs)
        {
            UiElement? button = FindDescendant(this, entry.ButtonElementId);
            UiElement? page = FindDescendant(this, entry.PageElementId);
            if (button is null || page is null)
            {
                _unresolved.Add(entry);
                Console.WriteLine(
                    $"[D.2b] UiTabPanel 0x{Info.Id:X8}: tab entry button=0x{entry.ButtonElementId:X8} "
                    + $"page=0x{entry.PageElementId:X8} did not resolve against the built subtree "
                    + $"(button {(button is null ? "MISSING" : "ok")}, page {(page is null ? "MISSING" : "ok")}).");
            }

            uint pageId = entry.PageElementId;
            RetailTabBinding.SetClick(button, () => SwitchTo(pageId));

            if (entry.IsDefault)
                defaultEntry = entry;
        }

        // Retail UIElement_Panel::Update(0, 0) — the guard when neither
        // m_OpenPageToken nor m_OpenTabToken has been seeded — performs no switch at
        // all. No entry authoring 0x32==true means retail never activates a page here;
        // do not fabricate a fallback to the first entry (the OP2 REJECT-review
        // SHOULD-FIX 2 finding).
        if (defaultEntry is { } def)
            SwitchTo(def.PageElementId);
    }

    /// <summary>
    /// Activates the page slot named <paramref name="pageElementId"/>: shows it, hides
    /// every other authored page slot, and sets each tab button's Open/Closed state to
    /// match (<see cref="RetailTabBinding.SetOpen"/>). No-op if the page is already
    /// active. Safe to call directly (e.g. from a test or a controller that wants
    /// programmatic navigation) without going through <see cref="ActivateTabBehavior"/>
    /// first, though the authored click bindings only exist after activation.
    /// </summary>
    public void SwitchTo(uint pageElementId)
    {
        if (ActivePageElementId == pageElementId) return;
        uint previousPageElementId = ActivePageElementId;

        foreach (UiTabTableEntry entry in _tabs)
        {
            bool active = entry.PageElementId == pageElementId;
            UiElement? page = FindDescendant(this, entry.PageElementId);
            if (page is not null) page.Visible = active;

            UiElement? button = FindDescendant(this, entry.ButtonElementId);
            RetailTabBinding.SetOpen(button, active);
        }

        ActivePageElementId = pageElementId;
        ActivePageChanged?.Invoke(previousPageElementId, pageElementId);
    }
}