-- Physics example.
-- This sample demonstrates:
--     - Creating both static and moving physics objects to a scene
--     - Displaying physics debug geometry
--     - Using the Skybox component for setting up an unmoving sky
--     - Saving a scene to a file and loading it to restore a previous state

require "LuaScripts/Utilities/Sample"

local scene_ = nil
local cameraNode = nil
local yaw = 0.0
local pitch = 0.0
local drawDebug = false

function Start()
    -- Execute the common startup for samples
    SampleStart()

    -- 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()
end

function CreateScene()
    scene_ = Scene()

    -- 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
    local zoneNode = scene_:CreateChild("Zone")
    local zone = zoneNode:CreateComponent("Zone")
    zone.boundingBox = BoundingBox(-1000.0, 1000.0)
    zone.ambientColor = Color(0.15, 0.15, 0.15)
    zone.fogColor = Color(1.0, 1.0, 1.0)
    zone.fogStart = 300.0
    zone.fogEnd = 500.0

    -- Create a directional light to the world. Enable cascaded shadows on it
    local lightNode = scene_:CreateChild("DirectionalLight")
    lightNode.direction = Vector3(0.6, -1.0, 0.8)
    local light = lightNode:CreateComponent("Light")
    light.lightType = LIGHT_DIRECTIONAL
    light.castShadows = true
    light.shadowBias = BiasParameters(0.00025, 0.5)
    -- Set cascade splits at 10, 50 and 200 world units, fade shadows out at 80% of maximum shadow distance
    light.shadowCascade = CascadeParameters(10.0, 50.0, 200.0, 0.0, 0.8)
    
    -- 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
    local skyNode = scene_:CreateChild("Sky")
    skyNode:SetScale(500.0) -- The scale actually does not matter
    local skybox = skyNode:CreateComponent("Skybox")
    skybox.model = cache:GetResource("Model", "Models/Box.mdl")
    skybox.material = 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
    local floorNode = scene_:CreateChild("Floor")
    floorNode.position = Vector3(0.0, -0.5, 0.0)
    floorNode.scale = Vector3(1000.0, 1.0, 1000.0)
    local floorObject = floorNode:CreateComponent("StaticModel")
    floorObject.model = cache:GetResource("Model", "Models/Box.mdl")
    floorObject.material = 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
    local body = floorNode:CreateComponent("RigidBody")
    local 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(1.0, 1.0, 1.0))
    
    -- Create a pyramid of movable physics objects
    for y = 0, 7 do
        for x = -y, y do
            local boxNode = scene_:CreateChild("Box")
            boxNode.position = Vector3(x, -y + 8.0, 0.0)
            local boxObject = boxNode:CreateComponent("StaticModel")
            boxObject.model = cache:GetResource("Model", "Models/Box.mdl")
            boxObject.material = cache:GetResource("Material", "Materials/StoneEnvMapSmall.xml")
            boxObject.castShadows = 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
            local body = boxNode:CreateComponent("RigidBody")
            body.mass = 1.0
            body.friction = 0.75
            local shape = boxNode:CreateComponent("CollisionShape")
            shape:SetBox(Vector3(1.0, 1.0, 1.0))
        end
    end

    -- 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 = Node()
    local camera = cameraNode:CreateComponent("Camera")
    camera.farClip = 500.0

    -- Set an initial position for the camera scene node above the floor
    cameraNode.position = Vector3(0.0, 5.0, -20.0)
end

function CreateInstructions()
    -- Construct new Text object, set string to display and font to use
    local instructionText = ui.root:CreateChild("Text")
    instructionText:SetText("Use WASD keys and mouse 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.textAlignment = HA_CENTER

    -- Position the text relative to the screen center
    instructionText.horizontalAlignment = HA_CENTER
    instructionText.verticalAlignment = VA_CENTER
    instructionText:SetPosition(0, ui.root.height / 4)
end

function SetupViewport()
    -- Set up a viewport to the Renderer subsystem so that the 3D scene can be seen
    local viewport = Viewport:new(scene_, cameraNode:GetComponent("Camera"))
    renderer:SetViewport(0, viewport)
end

function SubscribeToEvents()
    -- Subscribe HandleUpdate() function for processing update events
    SubscribeToEvent("Update", "HandleUpdate")

    -- Subscribe HandlePostRenderUpdate() function for processing the post-render update event, during which we request
    -- debug geometry
    SubscribeToEvent("PostRenderUpdate", "HandlePostRenderUpdate")
end

function MoveCamera(timeStep)
    -- Do not move if the UI has a focused element (the console)
    if ui.focusElement ~= nil then
        return
    end

    -- Movement speed as world units per second
    local MOVE_SPEED = 20.0
    -- Mouse sensitivity as degrees per pixel
    local MOUSE_SENSITIVITY = 0.1

    -- Use this frame's mouse motion to adjust camera node yaw and pitch. Clamp the pitch between -90 and 90 degrees
    local mouseMove = input.mouseMove
    yaw = yaw + MOUSE_SENSITIVITY * mouseMove.x
    pitch = pitch + MOUSE_SENSITIVITY * mouseMove.y
    pitch = Clamp(pitch, -90.0, 90.0)

    -- Construct new orientation for the camera scene node from yaw and pitch. Roll is fixed to zero
    cameraNode.rotation = Quaternion(pitch, yaw, 0.0)

    -- Read WASD keys and move the camera scene node to the corresponding direction if they are pressed
    if input:GetKeyDown(KEY_W) then
        cameraNode:TranslateRelative(Vector3(0.0, 0.0, 1.0) * MOVE_SPEED * timeStep)
    end
    if input:GetKeyDown(KEY_S) then
        cameraNode:TranslateRelative(Vector3(0.0, 0.0, -1.0) * MOVE_SPEED * timeStep)
    end
    if input:GetKeyDown(KEY_A) then
        cameraNode:TranslateRelative(Vector3(-1.0, 0.0, 0.0) * MOVE_SPEED * timeStep)
    end
    if input:GetKeyDown(KEY_D) then
        cameraNode:TranslateRelative(Vector3(1.0, 0.0, 0.0) * MOVE_SPEED * timeStep)
    end
    
    -- "Shoot" a physics object with left mousebutton
    if input:GetMouseButtonPress(MOUSEB_LEFT) then
        SpawnObject()
    end
    
    -- 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) then
        scene_:SaveXML(fileSystem:GetProgramDir().."Data/Scenes/Physics.xml")
    end
    if input:GetKeyPress(KEY_F7) then
        scene_:LoadXML(fileSystem:GetProgramDir().."Data/Scenes/Physics.xml")
    end

    -- Toggle debug geometry with space
    if input:GetKeyPress(KEY_SPACE) then
        drawDebug = not drawDebug
    end
end

function SpawnObject()
    -- Create a smaller box at camera position
    local boxNode = scene_:CreateChild("SmallBox")
    boxNode.position = cameraNode.position
    boxNode.rotation = cameraNode.rotation
    boxNode:SetScale(0.25)
    local boxObject = boxNode:CreateComponent("StaticModel")
    boxObject.model = cache:GetResource("Model", "Models/Box.mdl")
    boxObject.material = cache:GetResource("Material", "Materials/StoneEnvMapSmall.xml")
    boxObject.castShadows = true

    -- Create physics components, use a smaller mass also
    local body = boxNode:CreateComponent("RigidBody")
    body.mass = 0.25
    body.friction = 0.75
    local shape = boxNode:CreateComponent("CollisionShape")
    shape:SetBox(Vector3(1.0, 1.0, 1.0))

    local OBJECT_VELOCITY = 10.0

    -- Set initial velocity for the RigidBody based on camera forward vector. Add also a slight up component
    -- to overcome gravity better
    body.linearVelocity = cameraNode.rotation * Vector3(0.0, 0.25, 1.0) * OBJECT_VELOCITY
end

function HandleUpdate(eventType, eventData)
    -- Take the frame time step, which is stored as a float
    local timeStep = eventData:GetFloat("TimeStep")

    -- Move the camera, scale movement with time step
    MoveCamera(timeStep)
end

function HandlePostRenderUpdate(eventType, eventData)

    -- If draw debug mode is enabled, draw physics debug geometry. Use depth test to make the result easier to interpret
    -- Note the convenience accessor to the physics world component
    if drawDebug then
        scene_:GetComponent("PhysicsWorld"):DrawDebugGeometry(true)
    end
end
