// Copyright (C) 2002-2012 Nikolaus Gebhardt
// This file is part of the "Irrlicht Engine".
// For conditions of distribution and use, see copyright notice in irrlicht.h

#pragma once

#include "IAnimatedMesh.h"
#include "ISceneManager.h"
#include "CMeshBuffer.h"
#include "SSkinMeshBuffer.h"
#include "aabbox3d.h"
#include "irrMath.h"
#include "irrTypes.h"
#include "irr_ptr.h"
#include "matrix4.h"
#include "quaternion.h"
#include "vector3d.h"
#include "Transform.h"

#include <optional>
#include <string>
#include <variant>
#include <vector>

namespace scene
{

class AnimatedMeshSceneNode;
class IBoneSceneNode;
class ISceneManager;

class SkinnedMesh : public IAnimatedMesh
{
public:

	enum class SourceFormat {
		B3D,
		X,
		GLTF,
		OTHER,
	};

	//! constructor
	SkinnedMesh(SourceFormat src_format) :
		EndFrame(0.f), FramesPerSecond(25.f),
		HasAnimation(false), PreparedForSkinning(false),
		SrcFormat(src_format)
	{
		SkinningBuffers = &LocalBuffers;
	}

	//! destructor
	virtual ~SkinnedMesh();

	//! The source (file) format the mesh was loaded from.
	//! Important for legacy reasons pertaining to different mesh loader behavior.
	SourceFormat getSourceFormat() const { return SrcFormat; }

	//! If the duration is 0, it is a static (=non animated) mesh.
	f32 getMaxFrameNumber() const override;

	//! Turns the given array of local matrices into an array of global matrices
	//! by multiplying with respective parent matrices.
	void calculateGlobalMatrices(std::vector<core::matrix4> &matrices) const;

	//! Performs a software skin on this mesh based on the given joint matrices
	void skinMesh(const std::vector<core::matrix4> &animated_transforms);

	//! returns amount of mesh buffers.
	u32 getMeshBufferCount() const override;

	//! returns pointer to a mesh buffer
	IMeshBuffer *getMeshBuffer(u32 nr) const override;

	//! Returns pointer to a mesh buffer which fits a material
	/** \param material: material to search for
	\return Returns the pointer to the mesh buffer or
	NULL if there is no such mesh buffer. */
	IMeshBuffer *getMeshBuffer(const video::SMaterial &material) const override;

	u32 getTextureSlot(u32 meshbufNr) const override;

	//! Returns bounding box of the mesh *in static pose*.
	const core::aabbox3d<f32> &getBoundingBox() const override {
		// TODO ideally we shouldn't be forced to implement this
		return StaticPoseBox;
	}

	//! Set bounding box of the mesh *in static pose*.
	void setBoundingBox(const core::aabbox3df &box) override {
		StaticPoseBox = box;
	}

	//! set the hardware mapping hint, for driver
	void setHardwareMappingHint(E_HARDWARE_MAPPING newMappingHint, E_BUFFER_TYPE buffer = EBT_VERTEX_AND_INDEX) override;

	//! flags the meshbuffer as changed, reloads hardware buffers
	void setDirty(E_BUFFER_TYPE buffer = EBT_VERTEX_AND_INDEX) override;

	//! Returns the type of the animated mesh.
	E_ANIMATED_MESH_TYPE getMeshType() const override {
		return EAMT_SKINNED;
	}

	//! Gets joint count.
	u32 getJointCount() const;

	//! Gets the name of a joint.
	/** \param number: Zero based index of joint.
	\return Name of joint and null if an error happened. */
	const std::optional<std::string> &getJointName(u32 number) const;

	//! Gets a joint number from its name
	/** \param name: Name of the joint.
	\return Number of the joint or std::nullopt if not found. */
	std::optional<u32> getJointNumber(const std::string &name) const;

	//! converts the vertex type of all meshbuffers to tangents.
	/** E.g. used for bump mapping. */
	void convertMeshToTangents();

	//! Does the mesh have no animation
	bool isStatic() const {
		return !HasAnimation;
	}

	//! Back up static pose after local buffers have been modified directly
	void updateStaticPose();

	//! Moves the mesh into static position.
	void resetAnimation();

	//! Creates an array of joints from this mesh as children of node
	std::vector<IBoneSceneNode *> addJoints(
			AnimatedMeshSceneNode *node, ISceneManager *smgr);

	template <class T>
	struct Channel {
		struct Frame {
			f32 time;
			T value;
		};
		std::vector<Frame> frames;
		bool interpolate = true;

		bool empty() const {
			return frames.empty();
		}

		f32 getEndFrame() const {
			return frames.empty() ? 0 : frames.back().time;
		}

		void pushBack(f32 time, const T &value) {
			frames.push_back({time, value});
		}

		void append(const Channel<T> &other) {
			frames.insert(frames.end(), other.frames.begin(), other.frames.end());
		}

		void cleanup() {
			if (frames.empty())
				return;

			std::vector<Frame> ordered;
			ordered.push_back(frames.front());
			// Drop out-of-order frames
			for (auto it = frames.begin() + 1; it != frames.end(); ++it) {
				if (it->time > ordered.back().time) {
					ordered.push_back(*it);
				}
			}
			frames.clear();
			// Drop redundant middle keys
			frames.push_back(ordered.front());
			for (u32 i = 1; i < ordered.size() - 1; ++i) {
				if (ordered[i - 1].value != ordered[i].value
						|| ordered[i + 1].value != ordered[i].value) {
					frames.push_back(ordered[i]);
				}
			}
			if (ordered.size() > 1)
				frames.push_back(ordered.back());
			frames.shrink_to_fit();
		}

		static core::quaternion interpolateValue(core::quaternion from, core::quaternion to, f32 time) {
			core::quaternion result;
			result.slerp(from, to, time);
			return result;
		}

		static core::vector3df interpolateValue(core::vector3df from, core::vector3df to, f32 time) {
			// Note: `from` and `to` are swapped here compared to quaternion slerp
			return to.getInterpolated(from, time);
		}

		std::optional<T> get(f32 time) const {
			if (frames.empty())
				return std::nullopt;

			const auto next = std::lower_bound(frames.begin(), frames.end(), time, [](const auto& frame, f32 time) {
				return frame.time < time;
			});
			if (next == frames.begin())
				return next->value;
			if (next == frames.end())
				return frames.back().value;

			const auto prev = next - 1;
			if (!interpolate)
				return prev->value;

			return interpolateValue(prev->value, next->value, (time - prev->time) / (next->time - prev->time));
		}
	};

	struct Keys {
		Channel<core::vector3df> position;
		Channel<core::quaternion> rotation;
		Channel<core::vector3df> scale;

		bool empty() const {
			return position.empty() && rotation.empty() && scale.empty();
		}

		void append(const Keys &other) {
			position.append(other.position);
			rotation.append(other.rotation);
			scale.append(other.scale);
		}

		f32 getEndFrame() const {
			return std::max({
				position.getEndFrame(),
				rotation.getEndFrame(),
				scale.getEndFrame()
			});
		}

		void updateTransform(f32 frame, core::Transform &transform) const
		{
			if (auto pos = position.get(frame))
				transform.translation = *pos;
			if (auto rot = rotation.get(frame))
				transform.rotation = *rot;
			if (auto scl = scale.get(frame))
				transform.scale = *scl;
		}

		void cleanup() {
			position.cleanup();
			rotation.cleanup();
			scale.cleanup();
		}
	};

	//! Joints
	struct SJoint
	{
		SJoint() {}

		//! The name of this joint
		std::optional<std::string> Name;

		//! Local transformation to be set by loaders. Mutated by animation.
		using VariantTransform = std::variant<core::Transform, core::matrix4>;
		VariantTransform transform{core::Transform{}};

		VariantTransform animate(f32 frame) const {
			if (keys.empty())
				return transform;

			if (std::holds_alternative<core::matrix4>(transform)) {
				// .x lets animations override matrix transforms entirely,
				// which is what we implement here.
				// .gltf does not allow animation of nodes using matrix transforms.
				// Note that a decomposition into a TRS transform need not exist!
				core::Transform trs;
				keys.updateTransform(frame, trs);
				return {trs};
			}

			auto trs = std::get<core::Transform>(transform);
			keys.updateTransform(frame, trs);
			return {trs};
		}


		//! List of attached meshes
		std::vector<u32> AttachedMeshes;
		// TODO ^ should turn this into optional meshbuffer parent field?

		// Animation keyframes for translation, rotation, scale
		Keys keys;

		//! Bounding box of all affected vertices, in local space
		core::aabbox3df LocalBoundingBox{{0, 0, 0}};

		//! Unnecessary for loaders, will be overwritten on finalize
		core::matrix4 GlobalMatrix; // loaders may still choose to set this (temporarily) to calculate absolute vertex data.

		// The .x and .gltf formats pre-calculate this
		std::optional<core::matrix4> GlobalInversedMatrix;

		void setParent(SJoint *parent) {
			ParentJointID = parent ? parent->JointID : std::optional<u16>{};
		}

		u16 JointID; // TODO refactor away: pointers -> IDs (problem: .x loader abuses SJoint)
		std::optional<u16> ParentJointID;
	};

	//! Animates joints based on frame input
	std::vector<SJoint::VariantTransform> animateMesh(f32 frame);

	//! Calculates a bounding box given an animation in the form of global joint transforms.
	core::aabbox3df calculateBoundingBox(
			const std::vector<core::matrix4> &global_transforms);

	void recalculateBaseBoundingBoxes();

	const std::vector<SJoint *> &getAllJoints() const {
		return AllJoints;
	}

protected:
	bool checkForAnimation() const;

	void prepareForSkinning();

	void calculateStaticBoundingBox();
	void calculateJointBoundingBoxes();
	void calculateBufferBoundingBoxes();

	void calculateTangents(core::vector3df &normal,
			core::vector3df &tangent, core::vector3df &binormal,
			const core::vector3df &vt1, const core::vector3df &vt2, const core::vector3df &vt3,
			const core::vector2df &tc1, const core::vector2df &tc2, const core::vector2df &tc3);

	friend class SkinnedMeshBuilder;

	std::vector<SSkinMeshBuffer *> *SkinningBuffers; // Meshbuffer to skin, default is to skin localBuffers

	std::vector<SSkinMeshBuffer *> LocalBuffers;

	//! Mapping from meshbuffer number to bindable texture slot
	std::vector<u32> TextureSlots;

	//! Joints, topologically sorted (parents come before their children).
	std::vector<SJoint *> AllJoints;

	//! Bounding box of just the static parts of the mesh
	core::aabbox3df StaticPartsBox{{0, 0, 0}};

	//! Bounding box of the mesh in static pose
	core::aabbox3df StaticPoseBox{{0, 0, 0}};

	f32 EndFrame;
	f32 FramesPerSecond;

	bool HasAnimation;
	bool PreparedForSkinning;

	SourceFormat SrcFormat;
};

// Interface for mesh loaders
class SkinnedMeshBuilder {
	using SJoint = SkinnedMesh::SJoint;

public:

	// HACK the .x and .b3d loader do not separate the "loader" class from an "extractor" class
	// used and destroyed in a specific loading process (contrast with the .gltf mesh loader).
	// This means we need an empty skinned mesh builder.
	SkinnedMeshBuilder() {}

	SkinnedMeshBuilder(SkinnedMesh::SourceFormat src_format)
		: mesh(new SkinnedMesh(src_format))
	{}

	//! loaders should call this after populating the mesh
	SkinnedMesh *finalize() &&;

	//! alternative method for adding joints
	std::vector<SJoint *> &getJoints() { return mesh->AllJoints; }

	//! Adds a new meshbuffer to the mesh, access it as last one
	SSkinMeshBuffer *addMeshBuffer();

	//! Adds a new meshbuffer to the mesh, returns ID
	u32 addMeshBuffer(SSkinMeshBuffer *meshbuf);

	u32 getMeshBufferCount() { return mesh->getMeshBufferCount(); }

	void setTextureSlot(u32 meshbufNr, u32 textureSlot)
	{
		mesh->TextureSlots.at(meshbufNr) = textureSlot;
	}

	//! Adds a new joint to the mesh, access it as last one
	SJoint *addJoint(SJoint *parent = nullptr);

	std::optional<u32> getJointNumber(const std::string &name) const
	{
		return mesh->getJointNumber(name);
	}

	void addPositionKey(SJoint *joint, f32 frame, core::vector3df pos);
	void addRotationKey(SJoint *joint, f32 frame, core::quaternion rotation);
	void addScaleKey(SJoint *joint, f32 frame, core::vector3df scale);

	//! Adds a new weight to the mesh
	void addWeight(SJoint *joint, u16 buf, u32 vert_id, f32 strength);

private:

	void topoSortJoints();

	//! The mesh that is being built
	irr_ptr<SkinnedMesh> mesh;

	struct Weight {
		u16 joint_id;
		u16 buffer_id;
		u32 vertex_id;
		f32 strength;
	};

	//! Weights to be added once all mesh buffers have been loaded
	std::vector<Weight> weights;

};

} // end namespace scene