local ecs = require 'honey.ecs'
local glm = require 'honey.glm'
local Vec3 = glm.Vec3
local Quaternion = glm.Quaternion
local gl = honey.gl
local glfw = honey.glfw
local ode = honey.ode


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,
		
		priority = 1,
		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,
	}
end



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

function renderCamera(params) 
	return {
		camera = params.camera,
		db = params.db,
		priority = params.priority or 99,
		update = function(self, dt)
			for id, camera in pairs(self.db:queryComponent("camera")) do
				local cameraTransform = self.db:getComponent(id, "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=camera.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,
	}
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 0.016
	local groupSize = params.groupSize or 20
	return {
		db=params.db,
		space=params.space,
		world=params.world,
		contactGroup=ode.JointGroupCreate(groupSize),
		time=interval,

		priority=0,
		update=function(self, dt)
			local query = self.db:queryComponent("physics")
			for id, physics in pairs(query) do
				if not physics._body then
					physics._body = ode.BodyCreate(self.world)
					physics._gc = honey.util.gc_canary(function() 
						print("releasing physics body for " .. id)
						ode.BodyDestroy(physics._body) 
					end)
					local mass = ode.MassCreate()
					local class = physics.mass.class
					if not class then
						-- configure mass manually
					elseif class == "sphere" then
						ode.MassSetSphere(
							mass, 
							physics.mass.density, 
							physics.mass.radius
						)
					end
					ode.BodySetMass(physics._body, mass)
					local m = self.db:getComponent(id, "transform").matrix
					ode.BodySetPosition(
						physics._body,
						m[1][4], m[2][4], m[3][4]
					)
					ode.BodySetRotation(
						physics._body,
						m[1][1], m[1][2], m[1][3],
						m[2][1], m[2][2], m[2][3],
						m[3][1], m[3][2], m[3][3]
					)
					ode.BodySetLinearVel(
						physics._body,
						physics.velocity[1],
						physics.velocity[2],
						physics.velocity[3]
					)
					ode.BodySetAngularVel(
						physics._body,
						physics.angularVelocity[1],
						physics.angularVelocity[2],
						physics.angularVelocity[3]
					)
				end
			end

			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)
					local transform = self.db:getComponent(id, "transform")
					local q = Quaternion{a,b,c,d}
					transform.matrix
						:identity()
						:translate(Vec3{x,y,z})
						:mul(Quaternion{a,b,c,d}:toMat4())

					local vel = physics.velocity
					vel[1], vel[2], vel[3] = ode.BodyGetLinearVel(physics._body)
					local avel = physics.angularVelocity
					avel[1], avel[2], avel[3] = ode.BodyGetAngularVel(physics._body)
				end
			end
		end,
	}
end


return module