// Copyright (c) 2008-2023 the Urho3D project
// License: MIT

#include <Urho3D/Core/CoreEvents.h>
#include <Urho3D/Engine/Engine.h>
#include <Urho3D/Graphics/Camera.h>
#include <Urho3D/Graphics/DebugRenderer.h>
#include <Urho3D/Graphics/Graphics.h>
#include <Urho3D/Graphics/Light.h>
#include <Urho3D/Graphics/Material.h>
#include <Urho3D/Graphics/Model.h>
#include <Urho3D/Graphics/Octree.h>
#include <Urho3D/Graphics/Renderer.h>
#include <Urho3D/Graphics/Skybox.h>
#include <Urho3D/Graphics/Zone.h>
#include <Urho3D/Input/Input.h>
#include <Urho3D/IO/File.h>
#include <Urho3D/IO/FileSystem.h>
#include <Urho3D/Physics/CollisionShape.h>
#include <Urho3D/Physics/PhysicsWorld.h>
#include <Urho3D/Physics/RigidBody.h>
#include <Urho3D/Resource/ResourceCache.h>
#include <Urho3D/Scene/Scene.h>
#include <Urho3D/UI/Font.h>
#include <Urho3D/UI/Text.h>
#include <Urho3D/UI/UI.h>

#include "Physics.h"

#include <Urho3D/DebugNew.h>

URHO3D_DEFINE_APPLICATION_MAIN(Physics)

Physics::Physics(Context* context) :
    Sample(context),
    drawDebug_(false)
{
}

void Physics::Start()
{
    // Execute base class startup
    Sample::Start();

    // Create the scene content
    CreateScene();

    // Create the UI content
    CreateInstructions();

    // Setup the viewport for displaying the scene
    SetupViewport();

    // Hook up to the frame update and render post-update events
    SubscribeToEvents();

    // Set the mouse mode to use in the sample
    Sample::InitMouseMode(MM_RELATIVE);
}

void Physics::CreateScene()
{
    auto* cache = GetSubsystem<ResourceCache>();

    scene_ = new Scene(context_);

    // Create octree, use default volume (-1000, -1000, -1000) to (1000, 1000, 1000)
    // Create a physics simulation world with default parameters, which will update at 60fps. Like the Octree must
    // exist before creating drawable components, the PhysicsWorld must exist before creating physics components.
    // Finally, create a DebugRenderer component so that we can draw physics debug geometry
    scene_->CreateComponent<Octree>();
    scene_->CreateComponent<PhysicsWorld>();
    scene_->CreateComponent<DebugRenderer>();

    // Create a Zone component for ambient lighting & fog control
    Node* zoneNode = scene_->CreateChild("Zone");
    auto* zone = zoneNode->CreateComponent<Zone>();
    zone->SetBoundingBox(BoundingBox(-1000.0f, 1000.0f));
    zone->SetAmbientColor(Color(0.15f, 0.15f, 0.15f));
    zone->SetFogColor(Color(1.0f, 1.0f, 1.0f));
    zone->SetFogStart(300.0f);
    zone->SetFogEnd(500.0f);

    // Create a directional light to the world. Enable cascaded shadows on it
    Node* lightNode = scene_->CreateChild("DirectionalLight");
    lightNode->SetDirection(Vector3(0.6f, -1.0f, 0.8f));
    auto* light = lightNode->CreateComponent<Light>();
    light->SetLightType(LIGHT_DIRECTIONAL);
    light->SetCastShadows(true);
    light->SetShadowBias(BiasParameters(0.00025f, 0.5f));
    // Set cascade splits at 10, 50 and 200 world units, fade shadows out at 80% of maximum shadow distance
    light->SetShadowCascade(CascadeParameters(10.0f, 50.0f, 200.0f, 0.0f, 0.8f));

    // Create skybox. The Skybox component is used like StaticModel, but it will be always located at the camera, giving the
    // illusion of the box planes being far away. Use just the ordinary Box model and a suitable material, whose shader will
    // generate the necessary 3D texture coordinates for cube mapping
    Node* skyNode = scene_->CreateChild("Sky");
    skyNode->SetScale(500.0f); // The scale actually does not matter
    auto* skybox = skyNode->CreateComponent<Skybox>();
    skybox->SetModel(cache->GetResource<Model>("Models/Box.mdl"));
    skybox->SetMaterial(cache->GetResource<Material>("Materials/Skybox.xml"));

    {
        // Create a floor object, 1000 x 1000 world units. Adjust position so that the ground is at zero Y
        Node* floorNode = scene_->CreateChild("Floor");
        floorNode->SetPosition(Vector3(0.0f, -0.5f, 0.0f));
        floorNode->SetScale(Vector3(1000.0f, 1.0f, 1000.0f));
        auto* floorObject = floorNode->CreateComponent<StaticModel>();
        floorObject->SetModel(cache->GetResource<Model>("Models/Box.mdl"));
        floorObject->SetMaterial(cache->GetResource<Material>("Materials/StoneTiled.xml"));

        // Make the floor physical by adding RigidBody and CollisionShape components. The RigidBody's default
        // parameters make the object static (zero mass.) Note that a CollisionShape by itself will not participate
        // in the physics simulation
        /*RigidBody* body = */floorNode->CreateComponent<RigidBody>();
        auto* shape = floorNode->CreateComponent<CollisionShape>();
        // Set a box shape of size 1 x 1 x 1 for collision. The shape will be scaled with the scene node scale, so the
        // rendering and physics representation sizes should match (the box model is also 1 x 1 x 1.)
        shape->SetBox(Vector3::ONE);
    }

    {
        // Create a pyramid of movable physics objects
        for (int y = 0; y < 8; ++y)
        {
            for (int x = -y; x <= y; ++x)
            {
                Node* boxNode = scene_->CreateChild("Box");
                boxNode->SetPosition(Vector3((float)x, -(float)y + 8.0f, 0.0f));
                auto* boxObject = boxNode->CreateComponent<StaticModel>();
                boxObject->SetModel(cache->GetResource<Model>("Models/Box.mdl"));
                boxObject->SetMaterial(cache->GetResource<Material>("Materials/StoneEnvMapSmall.xml"));
                boxObject->SetCastShadows(true);

                // Create RigidBody and CollisionShape components like above. Give the RigidBody mass to make it movable
                // and also adjust friction. The actual mass is not important; only the mass ratios between colliding
                // objects are significant
                auto* body = boxNode->CreateComponent<RigidBody>();
                body->SetMass(1.0f);
                body->SetFriction(0.75f);
                auto* shape = boxNode->CreateComponent<CollisionShape>();
                shape->SetBox(Vector3::ONE);
            }
        }
    }

    // Create the camera. Set far clip to match the fog. Note: now we actually create the camera node outside the scene, because
    // we want it to be unaffected by scene load / save
    cameraNode_ = new Node(context_);
    auto* camera = cameraNode_->CreateComponent<Camera>();
    camera->SetFarClip(500.0f);

    // Set an initial position for the camera scene node above the floor
    cameraNode_->SetPosition(Vector3(0.0f, 5.0f, -20.0f));
}

void Physics::CreateInstructions()
{
    auto* cache = GetSubsystem<ResourceCache>();
    auto* ui = GetSubsystem<UI>();

    // Construct new Text object, set string to display and font to use
    auto* instructionText = ui->GetRoot()->CreateChild<Text>();
    instructionText->SetText(
        "Use WASD keys and mouse/touch to move\n"
        "LMB to spawn physics objects\n"
        "F5 to save scene, F7 to load\n"
        "Space to toggle physics debug geometry"
    );
    instructionText->SetFont(cache->GetResource<Font>("Fonts/Anonymous Pro.ttf"), 15);
    // The text has multiple rows. Center them in relation to each other
    instructionText->SetTextAlignment(HA_CENTER);

    // Position the text relative to the screen center
    instructionText->SetHorizontalAlignment(HA_CENTER);
    instructionText->SetVerticalAlignment(VA_CENTER);
    instructionText->SetPosition(0, ui->GetRoot()->GetHeight() / 4);
}

void Physics::SetupViewport()
{
    auto* renderer = GetSubsystem<Renderer>();

    // Set up a viewport to the Renderer subsystem so that the 3D scene can be seen
    SharedPtr<Viewport> viewport(new Viewport(context_, scene_, cameraNode_->GetComponent<Camera>()));
    renderer->SetViewport(0, viewport);
}

void Physics::SubscribeToEvents()
{
    // Subscribe HandleUpdate() function for processing update events
    SubscribeToEvent(E_UPDATE, URHO3D_HANDLER(Physics, HandleUpdate));

    // Subscribe HandlePostRenderUpdate() function for processing the post-render update event, during which we request
    // debug geometry
    SubscribeToEvent(E_POSTRENDERUPDATE, URHO3D_HANDLER(Physics, HandlePostRenderUpdate));
}

void Physics::MoveCamera(float timeStep)
{
    // Do not move if the UI has a focused element (the console)
    if (GetSubsystem<UI>()->GetFocusElement())
        return;

    auto* input = GetSubsystem<Input>();

    // Movement speed as world units per second
    const float MOVE_SPEED = 20.0f;
    // Mouse sensitivity as degrees per pixel
    const float MOUSE_SENSITIVITY = 0.1f;

    // Use this frame's mouse motion to adjust camera node yaw and pitch. Clamp the pitch between -90 and 90 degrees
    IntVector2 mouseMove = input->GetMouseMove();
    yaw_ += MOUSE_SENSITIVITY * mouseMove.x_;
    pitch_ += MOUSE_SENSITIVITY * mouseMove.y_;
    pitch_ = Clamp(pitch_, -90.0f, 90.0f);

    // Construct new orientation for the camera scene node from yaw and pitch. Roll is fixed to zero
    cameraNode_->SetRotation(Quaternion(pitch_, yaw_, 0.0f));

    // Read WASD keys and move the camera scene node to the corresponding direction if they are pressed
    if (input->GetKeyDown(KEY_W))
        cameraNode_->Translate(Vector3::FORWARD * MOVE_SPEED * timeStep);
    if (input->GetKeyDown(KEY_S))
        cameraNode_->Translate(Vector3::BACK * MOVE_SPEED * timeStep);
    if (input->GetKeyDown(KEY_A))
        cameraNode_->Translate(Vector3::LEFT * MOVE_SPEED * timeStep);
    if (input->GetKeyDown(KEY_D))
        cameraNode_->Translate(Vector3::RIGHT * MOVE_SPEED * timeStep);

    // "Shoot" a physics object with left mousebutton
    if (input->GetMouseButtonPress(MOUSEB_LEFT))
        SpawnObject();

    // Check for loading/saving the scene. Save the scene to the file Data/Scenes/Physics.xml relative to the executable
    // directory
    if (input->GetKeyPress(KEY_F5))
    {
        File saveFile(context_, GetSubsystem<FileSystem>()->GetProgramDir() + "Data/Scenes/Physics.xml", FILE_WRITE);
        scene_->SaveXML(saveFile);
    }
    if (input->GetKeyPress(KEY_F7))
    {
        File loadFile(context_, GetSubsystem<FileSystem>()->GetProgramDir() + "Data/Scenes/Physics.xml", FILE_READ);
        scene_->LoadXML(loadFile);
    }

    // Toggle physics debug geometry with space
    if (input->GetKeyPress(KEY_SPACE))
        drawDebug_ = !drawDebug_;
}

void Physics::SpawnObject()
{
    auto* cache = GetSubsystem<ResourceCache>();

    // Create a smaller box at camera position
    Node* boxNode = scene_->CreateChild("SmallBox");
    boxNode->SetPosition(cameraNode_->GetPosition());
    boxNode->SetRotation(cameraNode_->GetRotation());
    boxNode->SetScale(0.25f);
    auto* boxObject = boxNode->CreateComponent<StaticModel>();
    boxObject->SetModel(cache->GetResource<Model>("Models/Box.mdl"));
    boxObject->SetMaterial(cache->GetResource<Material>("Materials/StoneEnvMapSmall.xml"));
    boxObject->SetCastShadows(true);

    // Create physics components, use a smaller mass also
    auto* body = boxNode->CreateComponent<RigidBody>();
    body->SetMass(0.25f);
    body->SetFriction(0.75f);
    auto* shape = boxNode->CreateComponent<CollisionShape>();
    shape->SetBox(Vector3::ONE);

    const float OBJECT_VELOCITY = 10.0f;

    // Set initial velocity for the RigidBody based on camera forward vector. Add also a slight up component
    // to overcome gravity better
    body->SetLinearVelocity(cameraNode_->GetRotation() * Vector3(0.0f, 0.25f, 1.0f) * OBJECT_VELOCITY);
}

void Physics::HandleUpdate(StringHash eventType, VariantMap& eventData)
{
    using namespace Update;

    // Take the frame time step, which is stored as a float
    float timeStep = eventData[P_TIMESTEP].GetFloat();

    // Move the camera, scale movement with time step
    MoveCamera(timeStep);
}

void Physics::HandlePostRenderUpdate(StringHash eventType, VariantMap& eventData)
{
    // If draw debug mode is enabled, draw physics debug geometry. Use depth test to make the result easier to interpret
    if (drawDebug_)
        scene_->GetComponent<PhysicsWorld>()->DrawDebugGeometry(true);
}