using System;
using System.Globalization;
using System.Numerics;
using System.Reflection;
using System.Xml.Linq;

namespace AcDream.App.UI;

/// <summary>
/// Parses our KSML-style panel markup (mirrors retail's ElementDesc fields)
/// into a live <see cref="UiElement"/> subtree. <c>{Binding}</c> attribute
/// values resolve against a supplied object by property name (reflection).
/// This is the format the future LayoutDesc importer will emit. See D.2b spec §7.
/// </summary>
public static class MarkupDocument
{
    /// <param name="xml">Raw XML markup for a single panel.</param>
    /// <param name="binding">Object whose public properties are bound to <c>{PropName}</c> attributes.</param>
    /// <param name="resolve">Surface id → (GL handle, width, height) for chrome sprites.</param>
    /// <param name="style">Optional controls.ini stylesheet for the title color.</param>
    public static UiNineSlicePanel Build(
        string xml, object binding, Func<uint, (uint, int, int)> resolve,
        ControlsIni? style = null)
    {
        var root = XDocument.Parse(xml).Root ?? throw new FormatException("empty markup");
        if (root.Name.LocalName != "panel")
            throw new FormatException($"root must be <panel>, got <{root.Name.LocalName}>");

        var panel = new UiNineSlicePanel(resolve)
        {
            Left   = F(root, "x"),
            Top    = F(root, "y"),
            Width  = F(root, "w"),
            Height = F(root, "h"),
        };

        // Optional per-window resize-axis lock: resize="x" | "y" | "both" | "none".
        string? resize = (string?)root.Attribute("resize");
        if (resize is not null)
        {
            panel.ResizeX = resize is "x" or "both";
            panel.ResizeY = resize is "y" or "both";
        }

        string? title = (string?)root.Attribute("title");
        if (!string.IsNullOrEmpty(title))
        {
            Vector4 tc = style is not null && style.TryColor("title", "color", out var c) ? c : Vector4.One;
            panel.AddChild(new UiLabel { Text = title, Left = 8, Top = 4, TextColor = tc });
        }

        foreach (var el in root.Elements())
        {
            switch (el.Name.LocalName)
            {
                case "meter":
                    var cur = BindUint((string?)el.Attribute("cur"), binding);
                    var max = BindUint((string?)el.Attribute("max"), binding);
                    panel.AddChild(new UiMeter
                    {
                        Left          = F(el, "x"),
                        Top           = F(el, "y"),
                        Width         = F(el, "w"),
                        Height        = F(el, "h"),
                        BarColor      = Color((string?)el.Attribute("color")),
                        Fill          = BindFloat((string?)el.Attribute("fill"), binding),
                        Label         = () => (cur(), max()) is (uint c, uint m) ? $"{c}/{m}" : null,
                        Anchors       = Anchor((string?)el.Attribute("anchor")),
                        SpriteResolve = resolve,
                        BackLeft      = Hex((string?)el.Attribute("backleft")),
                        BackTile      = Hex((string?)el.Attribute("backtile")),
                        BackRight     = Hex((string?)el.Attribute("backright")),
                        FrontLeft     = Hex((string?)el.Attribute("frontleft")),
                        FrontTile     = Hex((string?)el.Attribute("fronttile")),
                        FrontRight    = Hex((string?)el.Attribute("frontright")),
                    });
                    break;

                case "label":
                    // Text may be a literal or a {Binding}. Bound labels re-read
                    // their property every frame through the Func, so a plugin
                    // updates its status line by assigning a property rather
                    // than by touching UI objects from its own thread.
                    var label = new UiLabel
                    {
                        Left = F(el, "x"),
                        Top = F(el, "y"),
                        TextSource = BindString((string?)el.Attribute("text"), binding),
                    };
                    if (el.Attribute("color") is not null)
                        label.TextColor = Color((string?)el.Attribute("color"));
                    panel.AddChild(label);
                    break;

                case "button":
                    // onclick binds to an Action property on the binding
                    // object. Resolved once at build time: a button whose
                    // handler silently failed to bind is a bug worth failing
                    // loudly for, and MarkupDocument.Build is already inside
                    // the host's try/catch that reports panel load failures.
                    string? clickName = (string?)el.Attribute("onclick");
                    Action? onClick = BindAction(clickName, binding);
                    if (clickName is not null && onClick is null)
                    {
                        throw new FormatException(
                            $"<button onclick=\"{clickName}\"> did not resolve to an "
                            + $"Action property on {binding.GetType().Name}");
                    }
                    // UiSimpleButton, not the dat-sprite UiButton: a plugin
                    // panel has no LayoutDesc behind it and no StateDesc
                    // sprites to name, so the plain rect-and-text button is the
                    // one that can actually render from markup alone.
                    var button = new UiSimpleButton
                    {
                        Left = F(el, "x"),
                        Top = F(el, "y"),
                        Width = F(el, "w"),
                        Height = F(el, "h"),
                        Text = (string?)el.Attribute("text") ?? string.Empty,
                    };
                    if (el.Attribute("color") is not null)
                        button.TextColor = Color((string?)el.Attribute("color"));
                    if (onClick is not null)
                        button.Click += onClick;
                    panel.AddChild(button);
                    break;
            }
        }
        return panel;
    }

    /// <summary>
    /// Resolves <c>{PropName}</c> to a live string reader, or returns the
    /// literal text unchanged. The indirection matters: binding to a
    /// <see cref="Func{T}"/> rather than copying the value once is what makes a
    /// plugin's status text update as its state changes.
    /// </summary>
    private static Func<string?> BindString(string? attribute, object binding)
    {
        if (attribute is null)
            return static () => null;
        if (!IsBinding(attribute))
            return () => attribute;

        string name = attribute[1..^1];
        PropertyInfo? property = binding.GetType().GetProperty(name);
        if (property is null)
            return () => attribute;
        return () => property.GetValue(binding)?.ToString();
    }

    /// <summary>Resolves <c>{PropName}</c> to an <see cref="Action"/> property.</summary>
    private static Action? BindAction(string? attribute, object binding)
    {
        if (attribute is null || !IsBinding(attribute))
            return null;

        string name = attribute[1..^1];
        PropertyInfo? property = binding.GetType().GetProperty(name);
        if (property is null || !typeof(Action).IsAssignableFrom(property.PropertyType))
            return null;

        // Read through on each click rather than capturing the delegate now, so
        // a binding object may swap its handler (or null it out while busy)
        // without rebuilding the panel.
        return () => (property.GetValue(binding) as Action)?.Invoke();
    }

    private static bool IsBinding(string value) =>
        value.Length > 2 && value[0] == '{' && value[^1] == '}';

    private static float F(XElement e, string attr)
        => float.TryParse((string?)e.Attribute(attr), NumberStyles.Float,
            CultureInfo.InvariantCulture, out var v) ? v : 0f;

    /// <summary>
    /// Parses <c>#AARRGGBB</c> → RGBA <see cref="Vector4"/> (alpha first, matching
    /// controls.ini convention). Falls back to opaque white on bad input.
    /// </summary>
    private static Vector4 Color(string? hex)
    {
        if (hex is { Length: 9 } && hex[0] == '#'
            && uint.TryParse(hex.AsSpan(1), NumberStyles.HexNumber,
                             CultureInfo.InvariantCulture, out uint argb))
            return new Vector4(
                ((argb >> 16) & 0xFF) / 255f,
                ((argb >> 8)  & 0xFF) / 255f,
                (argb         & 0xFF) / 255f,
                ((argb >> 24) & 0xFF) / 255f);
        return Vector4.One;
    }

    private static Func<float?> BindFloat(string? expr, object binding)
    {
        var pi = Prop(expr, binding);
        if (pi is null) return () => 0f;
        return () => pi.GetValue(binding) switch
        {
            float f  => f,
            null     => (float?)null,
            var v    => Convert.ToSingle(v, CultureInfo.InvariantCulture),
        };
    }

    private static Func<uint?> BindUint(string? expr, object binding)
    {
        var pi = Prop(expr, binding);
        if (pi is null) return () => null;
        return () => pi.GetValue(binding) switch
        {
            uint u => u,
            null   => (uint?)null,
            var v  => Convert.ToUInt32(v, CultureInfo.InvariantCulture),
        };
    }

    private static PropertyInfo? Prop(string? expr, object binding)
    {
        if (expr is null || expr.Length < 3 || expr[0] != '{' || expr[^1] != '}') return null;
        return binding.GetType().GetProperty(expr[1..^1]);
    }

    private static uint Hex(string? s)
    {
        if (string.IsNullOrWhiteSpace(s)) return 0;
        var t = s.Trim();
        if (t.StartsWith("0x", System.StringComparison.OrdinalIgnoreCase)) t = t[2..];
        return uint.TryParse(t, System.Globalization.NumberStyles.HexNumber,
            System.Globalization.CultureInfo.InvariantCulture, out var v) ? v : 0u;
    }

    private static AnchorEdges Anchor(string? csv)
    {
        if (string.IsNullOrWhiteSpace(csv)) return AnchorEdges.Left | AnchorEdges.Top;
        var a = AnchorEdges.None;
        foreach (var part in csv.Split(',', System.StringSplitOptions.TrimEntries | System.StringSplitOptions.RemoveEmptyEntries))
            a |= part.ToLowerInvariant() switch
            {
                "left"   => AnchorEdges.Left,
                "top"    => AnchorEdges.Top,
                "right"  => AnchorEdges.Right,
                "bottom" => AnchorEdges.Bottom,
                _        => AnchorEdges.None,
            };
        return a == AnchorEdges.None ? AnchorEdges.Left | AnchorEdges.Top : a;
    }
}