/* Copyright (C) 2026 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "precompiled.h"

#include "ParticleEmitter.h"

#include "graphics/LOSTexture.h"
#include "graphics/LightEnv.h"
#include "graphics/ParticleEmitterType.h"
#include "graphics/ParticleManager.h"
#include "graphics/RenderableObject.h"
#include "graphics/TextureManager.h"
#include "lib/allocators/STLAllocators.h"
#include "lib/debug.h"
#include "lib/types.h"
#include "maths/Matrix3D.h"
#include "ps/memory/LinearAllocator.h"
#include "ps/CStrIntern.h"
#include "ps/CStrInternStatic.h"
#include "renderer/Renderer.h"
#include "renderer/Scene.h"
#include "renderer/SceneRenderer.h"
#include "renderer/backend/Format.h"
#include "renderer/backend/IBuffer.h"
#include "renderer/backend/IDeviceCommandContext.h"
#include "renderer/backend/IShaderProgram.h"

#include <array>
#include <cmath>
#include <cstdint>

namespace
{

struct ParticleYoungestInFrontCompare
{
	bool operator()(const SParticle& lhs, const SParticle& rhs) const
	{
		return lhs.age > rhs.age;
	}
};

struct ParticleOldestInFrontCompare
{
	bool operator()(const SParticle& lhs, const SParticle& rhs) const
	{
		return lhs.age < rhs.age;
	}
};

struct ParticleClosestInFrontCompare
{
	bool operator()(const SParticle& lhs, const SParticle& rhs) const
	{
		return cameraForward.Dot(lhs.pos) > cameraForward.Dot(rhs.pos);
	}

	CVector3D cameraForward;
};

} // anonymous namespace

CParticleEmitter::CParticleEmitter(const CParticleEmitterTypePtr& type) :
	m_Type(type), m_Active(true), m_NextParticleIdx(0), m_EmissionRoundingError(0.f),
	m_LastUpdateTime(type->m_Manager.GetCurrentTime()),
	m_IndexArray(Renderer::Backend::IBuffer::Usage::TRANSFER_DST),
	m_VertexArray(Renderer::Backend::IBuffer::Type::VERTEX,
		Renderer::Backend::IBuffer::Usage::DYNAMIC | Renderer::Backend::IBuffer::Usage::TRANSFER_DST),
	m_LastFrameNumber(-1)
{
	// If we should start with particles fully emitted, pretend that we
	// were created in the past so the first update will produce lots of
	// particles.
	// TODO: instead of this, maybe it would make more sense to do a full
	// lifetime-length update of all emitters when the game first starts
	// (so that e.g. buildings constructed later on won't have fully-started
	// emitters, but those at the start will)?
	if (m_Type->m_StartFull)
		m_LastUpdateTime -= m_Type->m_MaxLifetime;

	m_Particles.reserve(m_Type->m_MaxParticles);

	m_AttributePos.format = Renderer::Backend::Format::R32G32B32_SFLOAT;
	m_VertexArray.AddAttribute(&m_AttributePos);

	m_AttributeAxis.format = Renderer::Backend::Format::R32G32_SFLOAT;
	m_VertexArray.AddAttribute(&m_AttributeAxis);

	m_AttributeUV.format = Renderer::Backend::Format::R32G32_SFLOAT;
	m_VertexArray.AddAttribute(&m_AttributeUV);

	m_AttributeColor.format = Renderer::Backend::Format::R8G8B8A8_UNORM;
	m_VertexArray.AddAttribute(&m_AttributeColor);

	m_AttributeAxisX.format = Renderer::Backend::Format::R32G32B32_SFLOAT;
	m_VertexArray.AddAttribute(&m_AttributeAxisX);

	m_AttributeAxisY.format = Renderer::Backend::Format::R32G32B32_SFLOAT;
	m_VertexArray.AddAttribute(&m_AttributeAxisY);

	m_VertexArray.SetNumberOfVertices(m_Type->m_MaxParticles * 4);
	m_VertexArray.Layout();

	m_IndexArray.SetNumberOfVertices(m_Type->m_MaxParticles * 6);
	m_IndexArray.Layout();
	VertexArrayIterator<u16> index = m_IndexArray.GetIterator();
	for (u16 i = 0; i < m_Type->m_MaxParticles; ++i)
	{
		*index++ = i*4 + 0;
		*index++ = i*4 + 1;
		*index++ = i*4 + 2;
		*index++ = i*4 + 2;
		*index++ = i*4 + 3;
		*index++ = i*4 + 0;
	}
	m_IndexArray.Upload();
	m_IndexArray.FreeBackingStore();

	const uint32_t stride = m_VertexArray.GetStride();
	const std::array<Renderer::Backend::SVertexAttributeFormat, 6> attributes{{
		{Renderer::Backend::VertexAttributeStream::POSITION,
			m_AttributePos.format, m_AttributePos.offset, stride,
			Renderer::Backend::VertexAttributeRate::PER_VERTEX, 0},
		{Renderer::Backend::VertexAttributeStream::COLOR,
			m_AttributeColor.format, m_AttributeColor.offset, stride,
			Renderer::Backend::VertexAttributeRate::PER_VERTEX, 0},
		{Renderer::Backend::VertexAttributeStream::UV0,
			m_AttributeUV.format, m_AttributeUV.offset, stride,
			Renderer::Backend::VertexAttributeRate::PER_VERTEX, 0},
		{Renderer::Backend::VertexAttributeStream::UV1,
			m_AttributeAxis.format, m_AttributeAxis.offset, stride,
			Renderer::Backend::VertexAttributeRate::PER_VERTEX, 0},
		{Renderer::Backend::VertexAttributeStream::UV2,
			m_AttributeAxisX.format, m_AttributeAxisX.offset, stride,
			Renderer::Backend::VertexAttributeRate::PER_VERTEX, 0},
		{Renderer::Backend::VertexAttributeStream::UV3,
			m_AttributeAxisY.format, m_AttributeAxisY.offset, stride,
			Renderer::Backend::VertexAttributeRate::PER_VERTEX, 0},
	}};
	m_VertexInputLayout = g_Renderer.GetVertexInputLayout(attributes);
}

void CParticleEmitter::UpdateArrayData(int frameNumber)
{
	if (m_LastFrameNumber == frameNumber)
		return;

	PS::Memory::ScopedLinearAllocator scopedLinearAllocator{g_Renderer.GetLinearAllocator()};

	using ParticlesVector = std::vector<SParticle, ProxyAllocator<SParticle, PS::Memory::ScopedLinearAllocator>>;
	ParticlesVector sortedParticles((ParticlesVector::allocator_type(scopedLinearAllocator)));

	m_LastFrameNumber = frameNumber;

	// Update m_Particles
	m_Type->UpdateEmitter(*this, m_Type->m_Manager.GetCurrentTime() - m_LastUpdateTime);
	m_LastUpdateTime = m_Type->m_Manager.GetCurrentTime();

	// Regenerate the vertex array data:

	VertexArrayIterator<CVector3D> attrPos = m_AttributePos.GetIterator<CVector3D>();
	VertexArrayIterator<float[2]> attrAxis = m_AttributeAxis.GetIterator<float[2]>();
	VertexArrayIterator<float[2]> attrUV = m_AttributeUV.GetIterator<float[2]>();
	VertexArrayIterator<SColor4ub> attrColor = m_AttributeColor.GetIterator<SColor4ub>();
	VertexArrayIterator<CVector3D> attrAxisX = m_AttributeAxisX.GetIterator<CVector3D>();
	VertexArrayIterator<CVector3D> attrAxisY = m_AttributeAxisY.GetIterator<CVector3D>();

	ENSURE(m_Particles.size() <= m_Type->m_MaxParticles);

	CBoundingBoxAligned bounds;

	if (m_Type->m_SortMode != CParticleEmitterType::SortMode::UNSPECIFIED)
	{
		sortedParticles.insert(sortedParticles.end(), m_Particles.begin(), m_Particles.end());

		switch (m_Type->m_SortMode)
		{
		case CParticleEmitterType::SortMode::YOUNGEST_IN_FRONT:
			std::sort(sortedParticles.begin(), sortedParticles.end(), ParticleYoungestInFrontCompare{});
			break;
		case CParticleEmitterType::SortMode::OLDEST_IN_FRONT:
			std::sort(sortedParticles.begin(), sortedParticles.end(), ParticleOldestInFrontCompare{});
			break;
		case CParticleEmitterType::SortMode::CLOSEST_IN_FRONT:
			std::sort(sortedParticles.begin(), sortedParticles.end(), ParticleClosestInFrontCompare{
				g_Renderer.GetSceneRenderer().GetViewCamera().GetOrientation().GetIn()});
			break;
		default:
			break;
		}
	}

	const std::span<SParticle> particles{
		m_Type->m_SortMode == CParticleEmitterType::SortMode::UNSPECIFIED ?
			std::span<SParticle>{m_Particles} : std::span<SParticle>{sortedParticles}};
	for (const SParticle& particle : particles)
	{
		// TODO: for more efficient rendering, maybe we should replace this with
		// a degenerate quad if alpha is 0

		bounds += particle.pos;

		*attrPos++ = particle.pos;
		*attrPos++ = particle.pos;
		*attrPos++ = particle.pos;
		*attrPos++ = particle.pos;

		// Compute corner offsets, split into sin/cos components so the vertex
		// shader can multiply by the camera-right (or left?) and camera-up vectors
		// to get rotating billboards:

		float s = sin(particle.angle) * particle.size * 0.5f;
		float c = cos(particle.angle) * particle.size * 0.5f;

		(*attrAxis)[0] = c;
		(*attrAxis)[1] = s;
		++attrAxis;
		(*attrAxis)[0] = s;
		(*attrAxis)[1] = -c;
		++attrAxis;
		(*attrAxis)[0] = -c;
		(*attrAxis)[1] = -s;
		++attrAxis;
		(*attrAxis)[0] = -s;
		(*attrAxis)[1] = c;
		++attrAxis;

		(*attrUV)[0] = 1;
		(*attrUV)[1] = 0;
		++attrUV;
		(*attrUV)[0] = 0;
		(*attrUV)[1] = 0;
		++attrUV;
		(*attrUV)[0] = 0;
		(*attrUV)[1] = 1;
		++attrUV;
		(*attrUV)[0] = 1;
		(*attrUV)[1] = 1;
		++attrUV;

		SColor4ub color{particle.color};

		// Special case: If the blending depends on the source color, not the source alpha,
		// then pre-multiply by the alpha. (This is kind of a hack.)
		if (m_Type->m_BlendMode == CParticleEmitterType::BlendMode::OVERLAY ||
			m_Type->m_BlendMode == CParticleEmitterType::BlendMode::MULTIPLY)
		{
			color.R = (color.R * color.A) / 255;
			color.G = (color.G * color.A) / 255;
			color.B = (color.B * color.A) / 255;
		}

		*attrColor++ = color;
		*attrColor++ = color;
		*attrColor++ = color;
		*attrColor++ = color;

		*attrAxisX++ = particle.axisX;
		*attrAxisX++ = particle.axisX;
		*attrAxisX++ = particle.axisX;
		*attrAxisX++ = particle.axisX;

		*attrAxisY++ = particle.axisY;
		*attrAxisY++ = particle.axisY;
		*attrAxisY++ = particle.axisY;
		*attrAxisY++ = particle.axisY;
	}

	m_ParticleBounds = bounds;

	m_VertexArray.Upload();
}

void CParticleEmitter::PrepareForRendering()
{
	m_VertexArray.PrepareForRendering();
}

void CParticleEmitter::UploadData(
	Renderer::Backend::IDeviceCommandContext* deviceCommandContext)
{
	m_VertexArray.UploadIfNeeded(deviceCommandContext);
}

void CParticleEmitter::Bind(
	Renderer::Backend::IDeviceCommandContext* deviceCommandContext,
	Renderer::Backend::IShaderProgram* shader)
{
	m_Type->m_Texture->UploadBackendTextureIfNeeded(deviceCommandContext);

	CLOSTexture& los = g_Renderer.GetSceneRenderer().GetScene().GetLOSTexture();
	deviceCommandContext->SetTexture(
		shader->GetBindingSlot(str_losTex), los.GetTextureSmooth());
	deviceCommandContext->SetUniform(
		shader->GetBindingSlot(str_losTransform),
		los.GetTextureMatrix()[0], los.GetTextureMatrix()[12]);

	g_Renderer.GetSceneRenderer().GetLightEnv().Bind(deviceCommandContext, shader);

	deviceCommandContext->SetTexture(
		shader->GetBindingSlot(str_baseTex), m_Type->m_Texture->GetBackendTexture());
}

void CParticleEmitter::RenderArray(
	Renderer::Backend::IDeviceCommandContext* deviceCommandContext)
{
	if (m_Particles.empty())
		return;

	const uint32_t stride = m_VertexArray.GetStride();
	const uint32_t firstVertexOffset = m_VertexArray.GetOffset() * stride;

	deviceCommandContext->SetVertexInputLayout(m_VertexInputLayout);

	deviceCommandContext->SetVertexBuffer(
		0, m_VertexArray.GetBuffer(), firstVertexOffset);
	deviceCommandContext->SetIndexBuffer(m_IndexArray.GetBuffer());

	deviceCommandContext->DrawIndexed(m_IndexArray.GetOffset(), m_Particles.size() * 6, 0);

	g_Renderer.GetStats().m_DrawCalls++;
	g_Renderer.GetStats().m_Particles += m_Particles.size();
}

void CParticleEmitter::Unattach(const CParticleEmitterPtr& self)
{
	m_Active = false;
	m_Type->m_Manager.AddUnattachedEmitter(self);
}

void CParticleEmitter::AddParticle(const SParticle& particle)
{
	if (m_NextParticleIdx >= m_Particles.size())
		m_Particles.push_back(particle);
	else
		m_Particles[m_NextParticleIdx] = particle;

	m_NextParticleIdx = (m_NextParticleIdx + 1) % m_Type->m_MaxParticles;
}

void CParticleEmitter::SetEntityVariable(const std::string& name, float value)
{
	m_EntityVariables[name] = value;
}

CModelParticleEmitter::CModelParticleEmitter(const CParticleEmitterTypePtr& type) :
	m_Type(type)
{
	m_Emitter = CParticleEmitterPtr(new CParticleEmitter(m_Type));
}

CModelParticleEmitter::~CModelParticleEmitter()
{
	m_Emitter->Unattach(m_Emitter);
}

void CModelParticleEmitter::SetEntityVariable(const std::string& name, float value)
{
	m_Emitter->SetEntityVariable(name, value);
}

std::unique_ptr<CModelAbstract> CModelParticleEmitter::Clone() const
{
	return std::make_unique<CModelParticleEmitter>(m_Type);
}

void CModelParticleEmitter::CalcBounds()
{
	// TODO: we ought to compute sensible bounds here, probably based on the
	// current computed particle positions plus the emitter type's largest
	// potential bounding box at the current position

	m_WorldBounds = m_Type->CalculateBounds(m_Emitter->GetPosition(), m_Emitter->GetParticleBounds());
}

void CModelParticleEmitter::ValidatePosition()
{
	// TODO: do we need to do anything here?

	// This is a convenient (though possibly not particularly appropriate) place
	// to invalidate bounds so they'll be recomputed from the recent particle data
	InvalidateBounds();
}

void CModelParticleEmitter::InvalidatePosition()
{
}

void CModelParticleEmitter::SetTransform(const CMatrix3D& transform)
{
	if (m_Transform == transform)
		return;

	m_Emitter->SetPosition(transform.GetTranslation());
	m_Emitter->SetRotation(transform.GetRotation());

	// call base class to set transform on this object
	CRenderableObject::SetTransform(transform);
}