#nullable enable annotations

using System;
using System.Linq;
using HumanoidRetargeter.Maths;
using SkeletonModel = HumanoidRetargeter.Skeleton.Skeleton;

namespace HumanoidRetargeter.Target;

/// <summary>Reuses the shipped animation setup, never the shipped character's mesh or materials.</summary>
public static class CitizenAnimationSetup
{
    internal const string ConstraintFolder = "HumanoidRetargeter_CitizenConstraints";
    // Physics, body groups, LODs and materials belong to the custom mesh, not its armature.
    private static readonly string[] Categories =
    {
        "AnimationList", "AnimConstraintList", "BoneMarkupList", "AttachmentList",
        "IKData", "PoseParamList", "WeightListList", "GameDataList"
    };

    /// <summary>Both skeletons must be compiled, in engine space. Names alone are not sufficient.</summary>
    public static string? CompatibilityError(SkeletonModel custom, SkeletonModel reference)
        => CheckSkeleton(custom, reference, checkBind: true);

    /// <summary>Complete fitted armatures can be retargeted, but cannot directly reuse stock channels.</summary>
    public static string? HierarchyError(SkeletonModel custom, SkeletonModel reference)
        => CheckSkeleton(custom, reference, checkBind: false);

    private static string? CheckSkeleton(SkeletonModel custom, SkeletonModel reference, bool checkBind)
    {
        foreach (var bone in reference.Bones)
        {
            var index = custom.IndexOf(bone.Name);
            // Facial joints are optional on custom meshes. If present, they must still match.
            if (index < 0 && (bone.Name.StartsWith("face_", StringComparison.Ordinal)
                || bone.Name.StartsWith("eye_", StringComparison.Ordinal)
                || bone.Name.StartsWith("ear_", StringComparison.Ordinal)))
                continue;
            if (index < 0)
                return $"Missing bone '{bone.Name}'.";
            var actual = custom[index];
            var parent = actual.ParentIndex < 0 ? null : custom[actual.ParentIndex].Name;
            var expectedParent = bone.ParentIndex < 0 ? null : reference[bone.ParentIndex].Name;
            if (parent != expectedParent)
                return $"Bone '{bone.Name}' has a different parent.";
            var distance = System.Numerics.Vector3.Distance(actual.RestLocal.Pos, bone.RestLocal.Pos);
            var angle = MathQ.AngleBetween(actual.RestLocal.Rot, bone.RestLocal.Rot);
            // Small FBX/compiler rounding differences are acceptable, altered proportions are not.
            if (!float.IsFinite(distance) || !float.IsFinite(angle))
                return $"Bone '{bone.Name}' has an invalid bind transform.";
            if (checkBind && (distance > 0.05f || angle > 0.035f))
                return $"Bone '{bone.Name}' has a different bind pose or scale; stock animations require retargeting.";
        }
        return null;
    }

    /// <summary>Attaches the complete stock setup to a standalone custom model. Conflicts fail closed.</summary>
    public static string Apply(string customVmdl, string shippedVmdl, bool preserveFittedSettings = false)
    {
        var document = Kv3.Parse(customVmdl);
        var root = (KvObject)((KvObject)document.Root)["rootNode"];
        var shipped = (KvObject)((KvObject)Kv3.Parse(shippedVmdl).Root)["rootNode"];
        var graph = shipped.GetString("anim_graph_name");
        if (string.IsNullOrEmpty(graph))
            throw new InvalidOperationException("The shipped model has no animation graph.");
        if (!string.IsNullOrEmpty(root.GetString("base_model_name")))
            throw new InvalidOperationException("Use a standalone custom model, not an animation-only Base Model.");
        var existingGraph = root.GetString("anim_graph_name");
        if (!string.IsNullOrEmpty(existingGraph) && existingGraph != graph)
            throw new InvalidOperationException("The custom model already uses a different animation graph.");
        var children = (KvArray)root["children"];
        var shippedChildren = (KvArray)shipped["children"];
        ValidateSourceScale(customVmdl);
        foreach (var category in Categories)
        {
            var source = shippedChildren.Items.OfType<KvObject>().SingleOrDefault(n => n.GetString("_class") == category);
            if (source is null) continue;
            var existing = children.Items.OfType<KvObject>().SingleOrDefault(n => n.GetString("_class") == category);
            // The rigger already fitted these offsets/constraints to the custom mesh.
            // Only animation sources are replaced, and existing clips still fail closed.
            if (preserveFittedSettings && category != "AnimationList" && existing is not null
                && existing.GetOrNull("children") is KvArray fitted && fitted.Items.Count > 0)
            {
                if (category == "AnimConstraintList" && !fitted.Items.OfType<KvObject>().Any(n => n.GetString("name") == ConstraintFolder))
                {
                    var wrapped = new KvArray();
                    wrapped.Items.Add(new KvObject { ["_class"] = new KvString("Folder"),
                        ["name"] = new KvString(ConstraintFolder), ["children"] = fitted });
                    existing["children"] = wrapped;
                }
                continue;
            }
            var matchesStock = existing is not null && KvValue.DeepEquals(existing, source);
            if (category == "AnimConstraintList" && source.GetOrNull("children") is KvArray stockConstraints
                && stockConstraints.Items.OfType<KvObject>().Any(n => n.GetString("name") == "CopyPinky"))
            {
                var constraints = new KvArray();
                constraints.Items.Add(new KvObject
                {
                    ["_class"] = new KvString("Folder"),
                    ["name"] = new KvString(ConstraintFolder),
                    ["children"] = source["children"],
                });
                source["children"] = constraints;
            }
            if (existing is not null)
            {
                if (KvValue.DeepEquals(existing, source)) continue;
                if (!matchesStock && existing.GetOrNull("children") is KvArray entries && entries.Items.Count > 0)
                    throw new InvalidOperationException($"The custom model already has {category} settings. Use its source mesh to create a new Citizen-ready model.");
                children.Items.Remove(existing);
            }
            // Includes Human's inline CopyPinky constraints as well as all animation prefabs.
            children.Items.Add(source);
        }
        root["anim_graph_name"] = new KvString(graph);
        return Kv3.Serialize(document);
    }

    /// <summary>Stock Citizen animation sources use centimeters, even when the compiled rig uses inches.</summary>
    public static void ValidateSourceScale(string vmdl)
    {
        var root = (KvObject)((KvObject)Kv3.Parse(vmdl).Root)["rootNode"];
        if (!string.IsNullOrEmpty(root.GetString("base_model_name")))
            throw new InvalidOperationException("Use a standalone model, not an animation-only Base Model.");
        var children = (KvArray)root["children"];
        var modifiers = children.Items.OfType<KvObject>().SingleOrDefault(n => n.GetString("_class") == "ModelModifierList");
        var scale = 1.0;
        if (modifiers?.GetOrNull("children") is KvArray items)
        foreach (var modifier in items.Items.OfType<KvObject>())
        {
            if (ModelGrounding.IsGrounding(modifier)) { _ = ModelGrounding.Offset(vmdl); continue; }
            if (modifier.GetString("_class") != "ModelModifier_ScaleAndMirror"
                || modifier.Keys.Any(k => modifier[k] is KvBool b && b.Value))
                throw new InvalidOperationException("Unsupported or mirrored model modifier; stock animations require retargeting.");
            scale *= modifier["scale"] is KvDouble d ? d.Value : ((KvLong)modifier["scale"]).Value;
        }
        if (!double.IsFinite(scale) || Math.Abs(scale - 0.3937) > 0.000001)
            throw new InvalidOperationException("The custom VMDL must use the Citizen source scale. Import its source mesh instead.");
    }
}