using System;
using System.Numerics;
using AcDream.App.UI;

namespace AcDream.App.UI.Layout;

/// <summary>
/// Controller for the action bar's selected-object strip (ids 0x1000019E–0x100001A1).
/// Analogue of retail <c>gmToolbarUI::HandleSelectionChanged</c>
/// (<c>docs/research/named-retail/acclient_2013_pseudo_c.txt:198635</c>) +
/// <c>RecvNotice_UpdateObjectHealth</c> (<c>:196213</c>).
///
/// <para>
/// On selection change: clears the strip (name, overlay flash, health meter), then if a
/// guid is provided it sets the name, flashes the selection overlay briefly, and (for
/// health-bearing targets) sends a <c>QueryHealth (0x01BF)</c> request. The Health meter
/// becomes visible only when the server actually reports health for the selected guid —
/// either an <c>UpdateHealth (0x01C0)</c> arrives (retail
/// <c>RecvNotice_UpdateObjectHealth</c> → <c>SetVisible(1)</c>) or the value is already
/// cached. So a friendly NPC you have not assessed shows name-only (no bar), and a
/// monster's bar appears after damage / a successful assess — matching retail.
/// </para>
///
/// <para>
/// <strong>Retail element roles</strong> (PostInit, <c>:198119</c>): <c>m_pSelObjectField</c>
/// is the container <c>0x1000019E</c> whose <c>SetState(0x1000000b/0c)</c> drives a
/// 0.25s <c>Pause→Normal</c> flash that cascades to the overlay child's green frame.
/// acdream has no state-cascade / transition-animation system, so this controller drives
/// the overlay element <c>0x100001A0</c> directly and reverts it after the same
/// <see cref="FlashSeconds"/> to reproduce the brief flash. The name element
/// <c>0x1000019F</c> is bumped to the top of the strip's z-order so it draws OVER the
/// overlay frame and the health bar (retail draws the name over the bar — see the
/// "Drudge Slinker" reference shot).
/// </para>
///
/// <para>
/// <strong>Divergence — health-target gate approximation.</strong>
/// Retail sends <c>Event_QueryHealth</c> for <c>IsPlayer() || pet_owner || ObjectIsAttackable()</c>
/// (<c>:198754</c>). acdream uses <c>IsLiveCreatureTarget</c> (the <c>ItemType.Creature</c>
/// flag) to gate the QueryHealth send. Visibility itself is health-data-driven (above), so
/// the gate only affects whether we proactively query; recorded in the divergence register.
/// </para>
/// </summary>
public sealed class SelectedObjectController
{
    // ── Element ids (toolbar LayoutDesc 0x21000016) ─────────────────────────
    /// <summary>Selected-object container / field element id (retail m_pSelObjectField).</summary>
    public const uint ContainerId   = 0x1000019E;
    /// <summary>Selected-object name element id (retail m_pSelObjectName, UIElement_Text).</summary>
    public const uint NameId        = 0x1000019F;
    /// <summary>Selected-object overlay element id (states: ObjectSelected / StackedItemSelected).</summary>
    public const uint OverlayId     = 0x100001A0;
    /// <summary>Selected-object health meter element id (retail m_pSelObjectHealthMeter).</summary>
    public const uint HealthMeterId = 0x100001A1;

    /// <summary>Selection-overlay flash duration — retail's container ObjectSelected state is a
    /// Pause(0.25s)→Normal transition (toolbar dump, element 0x1000019E).</summary>
    private const double FlashSeconds = 0.25;

    /// <summary>Z-order for the name so it draws OVER the overlay frame + health bar.
    /// The strip's other children sit at ReadOrder 1–4; this floats the name to the top.</summary>
    private const int NameZOrderOnTop = 1_000_000;

    /// <summary>Z-order for the selection-flash overlay — above the health meter (so the green
    /// flash isn't hidden by the bar) but below the name (so the name stays readable).</summary>
    private const int OverlayZOrder = NameZOrderOnTop - 1;

    /// <summary>Height (px) of the black name band at the top of the 31px bar sprite. The name
    /// label is constrained to this band (top-aligned) so the health bar shows below it —
    /// retail "name on the black, bar below". The bar sprite's colored region starts ~y14.</summary>
    private const float NameBandHeight = 15f;

    // ── Found elements (any may be null for partial/test layouts) ───────────
    private readonly UiElement?     _name;
    private readonly UiDatElement?  _overlay;
    private readonly UiMeter?       _healthMeter;

    // ── Captured delegates ───────────────────────────────────────────────────
    private readonly Func<uint, bool>    _isHealthTarget;
    private readonly Func<uint, string?> _resolveName;
    private readonly Func<uint, float>   _healthPercent;
    private readonly Func<uint, bool>    _hasHealth;
    private readonly Func<uint, uint>    _stackSize;
    private readonly Action<uint>        _sendQueryHealth;

    // ── Live state (read by closures on the per-frame draw path) ────────────
    private uint?   _current;
    private string? _currentName;
    private double  _flashRemaining;   // > 0 while the selection overlay is flashing

    /// <summary>White label color for the name line.</summary>
    private static readonly Vector4 NameColor = new(1f, 1f, 1f, 1f);

    private SelectedObjectController(
        ImportedLayout layout,
        Action<Action<uint?>>        subscribeSelectionChanged,
        Action<Action<uint, float>>  subscribeHealthChanged,
        Func<uint, bool>    isHealthTarget,
        Func<uint, string?> name,
        Func<uint, float>   healthPercent,
        Func<uint, bool>    hasHealth,
        Func<uint, uint>    stackSize,
        Action<uint>        sendQueryHealth,
        UiDatFont?          datFont)
    {
        _isHealthTarget  = isHealthTarget;
        _resolveName     = name;
        _healthPercent   = healthPercent;
        _hasHealth       = hasHealth;
        _stackSize       = stackSize;
        _sendQueryHealth = sendQueryHealth;

        // Find elements — silently skip absent ones (partial/test layouts).
        _name        = layout.FindElement(NameId);
        _overlay     = layout.FindElement(OverlayId)     as UiDatElement;
        _healthMeter = layout.FindElement(HealthMeterId) as UiMeter;

        // The selection-flash overlay must draw OVER the health meter (which spans the whole
        // strip) — otherwise the meter hides the green flash whenever a bar is visible (i.e.
        // for players/monsters). Float it just below the name so the name stays readable.
        if (_overlay is not null) _overlay.ZOrder = OverlayZOrder;

        // This controller owns the health meter's initial-hidden state.
        if (_healthMeter is not null)
        {
            _healthMeter.Visible = false;
            // Fill polls live: _current holds the currently-selected guid (or null).
            _healthMeter.Fill = () => _current is uint g ? _healthPercent(g) : (float?)0f;
        }

        // Attach a centered UiText child to the name element for the object name display.
        // Mirrors VitalsController.BindMeter's number attach. The name is floated to the
        // top of the strip's z-order so it draws OVER the overlay frame and the health bar
        // (retail renders the object name over the bar).
        //
        // The bar sprite (0x0600193E/F, 146x31) carries a ~14px BLACK name band across its
        // TOP with the colored bar in the lower portion (confirmed from the dat). Retail
        // draws the object name in that black band with the health bar BELOW it — so the
        // label is TOP-aligned by constraining its height to the band, not centered over the
        // whole 31px strip (which overlapped the bar's middle).
        if (_name is not null)
        {
            _name.ZOrder = NameZOrderOnTop;
            var label = new UiText
            {
                Left = 0f, Top = 0f, Width = _name.Width, Height = NameBandHeight,
                Anchors = AnchorEdges.Left | AnchorEdges.Top | AnchorEdges.Right,
                Centered            = true,
                DatFont             = datFont,
                ClickThrough        = true,
                AcceptsFocus        = false,
                IsEditControl       = false,
                CapturesPointerDrag = false,
                LinesProvider = () =>
                {
                    var n = _currentName;
                    return string.IsNullOrEmpty(n)
                        ? Array.Empty<UiText.Line>()
                        : new[] { new UiText.Line(n, NameColor) };
                },
            };
            _name.AddChild(label);
        }

        // Register the handlers LAST so the initial state is fully set up first.
        subscribeSelectionChanged(OnSelectionChanged);
        subscribeHealthChanged(OnHealthChanged);
    }

    /// <summary>
    /// Create and bind a <see cref="SelectedObjectController"/> to <paramref name="layout"/>.
    /// Port of retail <c>gmToolbarUI::HandleSelectionChanged</c> + <c>RecvNotice_UpdateObjectHealth</c>.
    /// </summary>
    /// <param name="layout">Imported toolbar layout (LayoutDesc 0x21000016).</param>
    /// <param name="subscribeSelectionChanged">Called once with <see cref="OnSelectionChanged"/>
    /// (typical host: <c>h =&gt; SelectionChanged += h</c>).</param>
    /// <param name="subscribeHealthChanged">Called once with <see cref="OnHealthChanged"/>
    /// (typical host: <c>h =&gt; Combat.HealthChanged += h</c>) — drives meter visibility.</param>
    /// <param name="isHealthTarget">Returns true for guids that may show a health meter
    /// (proxy for retail's <c>IsPlayer() || pet_owner || ObjectIsAttackable()</c>).</param>
    /// <param name="name">Returns the display name for a given guid (or null if unknown).</param>
    /// <param name="healthPercent">Returns the health fill fraction [0..1] for a given guid.</param>
    /// <param name="hasHealth">Returns true if real health has been received for a guid
    /// (so a re-selected, already-known target shows its bar immediately).</param>
    /// <param name="stackSize">Returns the stack size for a guid (0 or 1 = non-stacked).</param>
    /// <param name="sendQueryHealth">Sends retail <c>QueryHealth (0x01BF)</c>; may be a no-op offline.</param>
    /// <param name="datFont">Dat font for the name label; null = debug bitmap font fallback.</param>
    public static SelectedObjectController Bind(
        ImportedLayout layout,
        Action<Action<uint?>>        subscribeSelectionChanged,
        Action<Action<uint, float>>  subscribeHealthChanged,
        Func<uint, bool>    isHealthTarget,
        Func<uint, string?> name,
        Func<uint, float>   healthPercent,
        Func<uint, bool>    hasHealth,
        Func<uint, uint>    stackSize,
        Action<uint>        sendQueryHealth,
        UiDatFont?          datFont)
        => new SelectedObjectController(
            layout, subscribeSelectionChanged, subscribeHealthChanged,
            isHealthTarget, name, healthPercent, hasHealth, stackSize, sendQueryHealth, datFont);

    /// <summary>
    /// Port of <c>gmToolbarUI::HandleSelectionChanged</c> (<c>:198635</c>):
    /// clear-then-populate the selected-object strip on any selection change.
    /// </summary>
    public void OnSelectionChanged(uint? guid)
    {
        // ── 1. Clear first (retail: SetText("") + m_pSelObjectField->SetState(0)
        //       + SetVisible(0) on the meters). ──────────────────────────────────────
        if (_healthMeter is not null) _healthMeter.Visible = false;
        _currentName    = null;
        _current        = guid;

        if (guid is null)
        {
            // Deselect: clear the overlay flash immediately too.
            SetOverlayState("");
            _flashRemaining = 0;
            return;
        }

        uint g = guid.Value;

        // ── 2. Name (displayed via the UiText child's LinesProvider reading _currentName). ──
        _currentName = _resolveName(g);

        // ── 3. Selection overlay: brief flash (retail container ObjectSelected
        //       = Pause(0.25s)→Normal). "StackedItemSelected" for stacks. ──────────────
        SetOverlayState(_stackSize(g) > 1u ? "StackedItemSelected" : "ObjectSelected");
        _flashRemaining = FlashSeconds;

        // ── 4. Health: query, and show the meter only if real health is already known.
        //       Otherwise the meter appears when OnHealthChanged fires for this guid
        //       (retail RecvNotice_UpdateObjectHealth :196213). ──────────────────────────
        if (_isHealthTarget(g))
        {
            _sendQueryHealth(g);
            if (_hasHealth(g) && _healthMeter is not null)
                _healthMeter.Visible = true;
        }
    }

    /// <summary>
    /// Port of <c>gmToolbarUI::RecvNotice_UpdateObjectHealth</c> (<c>:196213</c>): when the
    /// server reports health for the currently-selected guid, make the Health meter visible.
    /// The fill value is read live by the meter's <see cref="UiMeter.Fill"/> provider.
    /// </summary>
    public void OnHealthChanged(uint guid, float percent)
    {
        if (_current is uint c && c == guid && _isHealthTarget(guid) && _healthMeter is not null)
            _healthMeter.Visible = true;
    }

    /// <summary>Per-frame tick: reverts the selection overlay after the brief flash window.</summary>
    public void Tick(double deltaSeconds)
    {
        if (_flashRemaining <= 0) return;
        _flashRemaining -= deltaSeconds;
        if (_flashRemaining <= 0)
            SetOverlayState("");   // flash done → overlay back to blank
    }

    private void SetOverlayState(string state)
    {
        if (_overlay is not null) _overlay.ActiveState = state;
    }
}