// Copyright 2017 The Dawn Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <array>
#include <cstring>
#include <random>
#include <vector>

#include "dawn/samples/SampleUtils.h"

#include "dawn/utils/ComboRenderPipelineDescriptor.h"
#include "dawn/utils/ScopedAutoreleasePool.h"
#include "dawn/utils/SystemUtils.h"
#include "dawn/utils/WGPUHelpers.h"

wgpu::Device device;
wgpu::Queue queue;
wgpu::SwapChain swapchain;
wgpu::TextureView depthStencilView;

wgpu::Buffer modelBuffer;
std::array<wgpu::Buffer, 2> particleBuffers;

wgpu::RenderPipeline renderPipeline;

wgpu::Buffer updateParams;
wgpu::ComputePipeline updatePipeline;
std::array<wgpu::BindGroup, 2> updateBGs;

size_t pingpong = 0;

static const uint32_t kNumParticles = 1000;

struct Particle {
    std::array<float, 2> pos;
    std::array<float, 2> vel;
};

struct SimParams {
    float deltaT;
    float rule1Distance;
    float rule2Distance;
    float rule3Distance;
    float rule1Scale;
    float rule2Scale;
    float rule3Scale;
    int particleCount;
};

void initBuffers() {
    std::array<std::array<float, 2>, 3> model = {{
        {-0.01, -0.02},
        {0.01, -0.02},
        {0.00, 0.02},
    }};
    modelBuffer =
        utils::CreateBufferFromData(device, &model, sizeof(model), wgpu::BufferUsage::Vertex);

    SimParams params = {0.04f, 0.1f, 0.025f, 0.025f, 0.02f, 0.05f, 0.005f, kNumParticles};
    updateParams =
        utils::CreateBufferFromData(device, &params, sizeof(params), wgpu::BufferUsage::Uniform);

    std::vector<Particle> initialParticles(kNumParticles);
    {
        std::mt19937 generator;
        std::uniform_real_distribution<float> dist(-1.0f, 1.0f);
        for (auto& p : initialParticles) {
            p.pos = {dist(generator), dist(generator)};
            p.vel = {dist(generator) * 0.1f, dist(generator) * 0.1f};
        }
    }

    for (size_t i = 0; i < 2; i++) {
        wgpu::BufferDescriptor descriptor;
        descriptor.size = sizeof(Particle) * kNumParticles;
        descriptor.usage =
            wgpu::BufferUsage::CopyDst | wgpu::BufferUsage::Vertex | wgpu::BufferUsage::Storage;
        particleBuffers[i] = device.CreateBuffer(&descriptor);

        queue.WriteBuffer(particleBuffers[i], 0,
                          reinterpret_cast<uint8_t*>(initialParticles.data()),
                          sizeof(Particle) * kNumParticles);
    }
}

void initRender() {
    wgpu::ShaderModule vsModule = utils::CreateShaderModule(device, R"(
        struct VertexIn {
            @location(0) a_particlePos : vec2<f32>;
            @location(1) a_particleVel : vec2<f32>;
            @location(2) a_pos : vec2<f32>;
        };

        @vertex
        fn main(input : VertexIn) -> @builtin(position) vec4<f32> {
            var angle : f32 = -atan2(input.a_particleVel.x, input.a_particleVel.y);
            var pos : vec2<f32> = vec2<f32>(
                (input.a_pos.x * cos(angle)) - (input.a_pos.y * sin(angle)),
                (input.a_pos.x * sin(angle)) + (input.a_pos.y * cos(angle)));
            return vec4<f32>(pos + input.a_particlePos, 0.0, 1.0);
        }
    )");

    wgpu::ShaderModule fsModule = utils::CreateShaderModule(device, R"(
        @fragment
        fn main() -> @location(0) vec4<f32> {
            return vec4<f32>(1.0, 1.0, 1.0, 1.0);
        }
    )");

    depthStencilView = CreateDefaultDepthStencilView(device);

    utils::ComboRenderPipelineDescriptor descriptor;

    descriptor.vertex.module = vsModule;
    descriptor.vertex.bufferCount = 2;
    descriptor.cBuffers[0].arrayStride = sizeof(Particle);
    descriptor.cBuffers[0].stepMode = wgpu::VertexStepMode::Instance;
    descriptor.cBuffers[0].attributeCount = 2;
    descriptor.cAttributes[0].offset = offsetof(Particle, pos);
    descriptor.cAttributes[0].format = wgpu::VertexFormat::Float32x2;
    descriptor.cAttributes[1].shaderLocation = 1;
    descriptor.cAttributes[1].offset = offsetof(Particle, vel);
    descriptor.cAttributes[1].format = wgpu::VertexFormat::Float32x2;
    descriptor.cBuffers[1].arrayStride = 2 * sizeof(float);
    descriptor.cBuffers[1].attributeCount = 1;
    descriptor.cBuffers[1].attributes = &descriptor.cAttributes[2];
    descriptor.cAttributes[2].shaderLocation = 2;
    descriptor.cAttributes[2].format = wgpu::VertexFormat::Float32x2;

    descriptor.cFragment.module = fsModule;
    descriptor.EnableDepthStencil(wgpu::TextureFormat::Depth24PlusStencil8);
    descriptor.cTargets[0].format = GetPreferredSwapChainTextureFormat();

    renderPipeline = device.CreateRenderPipeline(&descriptor);
}

void initSim() {
    wgpu::ShaderModule module = utils::CreateShaderModule(device, R"(
        struct Particle {
            pos : vec2<f32>;
            vel : vec2<f32>;
        };
        struct SimParams {
            deltaT : f32;
            rule1Distance : f32;
            rule2Distance : f32;
            rule3Distance : f32;
            rule1Scale : f32;
            rule2Scale : f32;
            rule3Scale : f32;
            particleCount : u32;
        };
        struct Particles {
            particles : array<Particle>;
        };
        @binding(0) @group(0) var<uniform> params : SimParams;
        @binding(1) @group(0) var<storage, read_write> particlesA : Particles;
        @binding(2) @group(0) var<storage, read_write> particlesB : Particles;

        // https://github.com/austinEng/Project6-Vulkan-Flocking/blob/master/data/shaders/computeparticles/particle.comp
        @compute @workgroup_size(1)
        fn main(@builtin(global_invocation_id) GlobalInvocationID : vec3<u32>) {
            var index : u32 = GlobalInvocationID.x;
            if (index >= params.particleCount) {
                return;
            }
            var vPos : vec2<f32> = particlesA.particles[index].pos;
            var vVel : vec2<f32> = particlesA.particles[index].vel;
            var cMass : vec2<f32> = vec2<f32>(0.0, 0.0);
            var cVel : vec2<f32> = vec2<f32>(0.0, 0.0);
            var colVel : vec2<f32> = vec2<f32>(0.0, 0.0);
            var cMassCount : u32 = 0u;
            var cVelCount : u32 = 0u;
            var pos : vec2<f32>;
            var vel : vec2<f32>;

            for (var i : u32 = 0u; i < params.particleCount; i = i + 1u) {
                if (i == index) {
                    continue;
                }

                pos = particlesA.particles[i].pos.xy;
                vel = particlesA.particles[i].vel.xy;
                if (distance(pos, vPos) < params.rule1Distance) {
                    cMass = cMass + pos;
                    cMassCount = cMassCount + 1u;
                }
                if (distance(pos, vPos) < params.rule2Distance) {
                    colVel = colVel - (pos - vPos);
                }
                if (distance(pos, vPos) < params.rule3Distance) {
                    cVel = cVel + vel;
                    cVelCount = cVelCount + 1u;
                }
            }

            if (cMassCount > 0u) {
                cMass = (cMass / vec2<f32>(f32(cMassCount), f32(cMassCount))) - vPos;
            }

            if (cVelCount > 0u) {
                cVel = cVel / vec2<f32>(f32(cVelCount), f32(cVelCount));
            }
            vVel = vVel + (cMass * params.rule1Scale) + (colVel * params.rule2Scale) +
                (cVel * params.rule3Scale);

            // clamp velocity for a more pleasing simulation
            vVel = normalize(vVel) * clamp(length(vVel), 0.0, 0.1);
            // kinematic update
            vPos = vPos + (vVel * params.deltaT);

            // Wrap around boundary
            if (vPos.x < -1.0) {
                vPos.x = 1.0;
            }
            if (vPos.x > 1.0) {
                vPos.x = -1.0;
            }
            if (vPos.y < -1.0) {
                vPos.y = 1.0;
            }
            if (vPos.y > 1.0) {
                vPos.y = -1.0;
            }

            // Write back
            particlesB.particles[index].pos = vPos;
            particlesB.particles[index].vel = vVel;
            return;
        }
    )");

    auto bgl = utils::MakeBindGroupLayout(
        device, {
                    {0, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Uniform},
                    {1, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Storage},
                    {2, wgpu::ShaderStage::Compute, wgpu::BufferBindingType::Storage},
                });

    wgpu::PipelineLayout pl = utils::MakeBasicPipelineLayout(device, &bgl);

    wgpu::ComputePipelineDescriptor csDesc;
    csDesc.layout = pl;
    csDesc.compute.module = module;
    csDesc.compute.entryPoint = "main";
    updatePipeline = device.CreateComputePipeline(&csDesc);

    for (uint32_t i = 0; i < 2; ++i) {
        updateBGs[i] = utils::MakeBindGroup(
            device, bgl,
            {
                {0, updateParams, 0, sizeof(SimParams)},
                {1, particleBuffers[i], 0, kNumParticles * sizeof(Particle)},
                {2, particleBuffers[(i + 1) % 2], 0, kNumParticles * sizeof(Particle)},
            });
    }
}

wgpu::CommandBuffer createCommandBuffer(const wgpu::TextureView backbufferView, size_t i) {
    auto& bufferDst = particleBuffers[(i + 1) % 2];
    wgpu::CommandEncoder encoder = device.CreateCommandEncoder();

    {
        wgpu::ComputePassEncoder pass = encoder.BeginComputePass();
        pass.SetPipeline(updatePipeline);
        pass.SetBindGroup(0, updateBGs[i]);
        pass.DispatchWorkgroups(kNumParticles);
        pass.End();
    }

    {
        utils::ComboRenderPassDescriptor renderPass({backbufferView}, depthStencilView);
        wgpu::RenderPassEncoder pass = encoder.BeginRenderPass(&renderPass);
        pass.SetPipeline(renderPipeline);
        pass.SetVertexBuffer(0, bufferDst);
        pass.SetVertexBuffer(1, modelBuffer);
        pass.Draw(3, kNumParticles);
        pass.End();
    }

    return encoder.Finish();
}

void init() {
    device = CreateCppDawnDevice();

    queue = device.GetQueue();
    swapchain = GetSwapChain();

    initBuffers();
    initRender();
    initSim();
}

void frame() {
    wgpu::TextureView backbufferView = swapchain.GetCurrentTextureView();

    wgpu::CommandBuffer commandBuffer = createCommandBuffer(backbufferView, pingpong);
    queue.Submit(1, &commandBuffer);
    swapchain.Present();
    DoFlush();

    pingpong = (pingpong + 1) % 2;
}

int main(int argc, const char* argv[]) {
    if (!InitSample(argc, argv)) {
        return 1;
    }
    init();

    while (!ShouldQuit()) {
        utils::ScopedAutoreleasePool pool;
        frame();
        utils::USleep(16000);
    }
}