local ecs = require 'honey.ecs'
local gl = honey.gl
local glfw = honey.glfw


local module = {}
setmetatable(module, {__index=_G})
setfenv(1, module)


-- helper function for retrieving script functions 
local function getFunction(script)
	local f = require(script.script)
	if script.func then
		return f[script.func]
	else
		return f
	end
end


--===== dispatch messages to handlers =====--

dispatch = function(entities, msg, data)
	local query = entities:queryComponent(msg)
	for id, handler in pairs(query) do
		local f = getFunction(handler)
		f(entities, id, data)
	end
end



--===== transform cascading =====--

transform = function(params)
	return {
		db = params.db,
		update = function(self, dt)
			local entities = self.db:queryComponent("transform")
	
			-- prepare transforms
			for id, transform in pairs(entities) do
				transform._visited = false
			end
	
			-- helper function
			local function recursiveTransform(transform)
				if transform._visited then
					return transform._matrix
				end
	
				if not transform.parent then
					transform._matrix = transform.matrix
				else
					local parentTransform = self.db:getComponent(transform.parent, "transform")
					local parentMatrix = recursiveTransform(parentTransform)
					transform._matrix = parentMatrix * transform.matrix
				end
				transform._visited = true
				return transform._matrix
			end
	
			-- compute transforms
			for id, transform in pairs(entities) do
				recursiveTransform(transform)
			end
		end,
		priority = 0,
	}
end



--===== rendering =====--

function renderCamera(params) 
	return {
		camera = params.camera,
		db = params.db,
		priority = params.priority or 99,
		update = function(self, dt)
			local cameraParams = self.db:getComponent(self.camera, "camera")
			local cameraTransform = self.db:getComponent(self.camera, "transform")
			local view
			if cameraTransform then
				view = cameraTransform._matrix
			else
				view = Mat4():identity()
			end
	
			local entities = self.db:queryComponent("renderMesh")
			for entity, tbl in pairs(entities) do
				-- get shader
				local shader = honey.shader.loadShader(tbl.shader.vertex, tbl.shader.fragment)
				shader:use()
	
				-- bind textures
				local texOffset = 0
				for name, texTbl in pairs(tbl.textures or {}) do
					local texture = honey.image.loadImage(texTbl.filename, texTbl.params)
					gl.BindTexture(gl.TEXTURE_2D + texOffset, texture.texture)
					shader:setInt(name, texOffset)
					texOffset = texOffset + 1
				end
	
				-- configure default uniforms
				local query = self.db:getComponent(entity, "transform")
				local model = (query and query._matrix) or Mat4():identity()
				shader:configure{
					float={
						time=glfw.GetTime(),
					},
					matrix={
						view=view,
						projection=cameraParams.projection,
						model=model,
					},
				}
	
				-- draw mesh
				local mesh = honey.mesh.loadMesh(tbl.mesh.filename, tbl.mesh.index)
				mesh:drawElements()
	
				-- unbind textures
				for i=0,texOffset-1 do
					gl.BindTexture(gl.TEXTURE_2D + i, 0)
				end
			end
		end,
	}
end



--===== script system =====--

script = function(params)
	return {
		db=params.db,
		update=function(self, dt)
			local entities = self.db:queryComponent("script")
			for id, script in pairs(entities) do
				local f = getFunction(script)
				f(self.db, id, dt)
			end
		end
	}
end


--===== physics =====--

physics = function(params)
	local interval = params.interval or 0.01
	local groupSize = params.groupSize or 20
	return {
		db=params.db,
		space=params.space,
		world=params.world,
		contactGroup=ode.JointGroupCreate(groupSize),
		time=interval,
		update=function(self, dt)
			local query = self.db:queryComponent("physics")
			-- TODO: create physics bodies 

			self.time = self.time + dt
			-- only run the update every [interval] seconds
			if self.time > interval then
				self.time = self.time - interval

				-- check for near collisions between geoms
				ode.SpaceCollide(self.space, function(a, b)
					-- check for actual collisions
					local collisions = ode.Collide(a, b, 1)
					if #collisions > 0 then
						-- set up the joint params
						local contact = ode.CreateContact{ surface={
							mode = ode.ContactBounce + ode.ContactSoftCFM,
							mu = ode.Infinity,
							bounce = 0.90,
							bounce_vel = 0.1,
							soft_cfm = 0.001,
						}}
						ode.ContactSetGeom(contact, collisions[1])
						-- create the joint
						local joint = ode.JointCreateContact(
							self.world,
							self.contactgroup,
							contact
						)
						-- attach the two bodies
						local bodyA = ode.GeomGetData(a)
						local bodyB = ode.GeomGetData(b)
						ode.JointAttach(joint, bodyA, bodyB)
					end
				end)
				-- update the world
				ode.WorldQuickStep(self.world, interval)
				-- remove all contact joints
				ode.JointGroupEmpty(self.contactGroup)

				-- update entity transforms
				for id, physics in pairs(query) do
					local x,y,z = ode.BodyGetPosition(physics._body)
					local d,a,b,c = ode.BodyGetQuaternion(physics._body)
					entity.transform
						:identity()
						:translate(Vec3{x,y,z})
						:mul(Quaternion{a,b,c,d}:toMat4())
				end
			end
		end,
	}
end


return module