Health Bars

local Players = game:GetService("Players")
local ServerStorage = game:GetService("ServerStorage")
local Debris = game:GetService("Debris")
local Settings = require(game.ReplicatedStorage.Settings)

local remotes = game.ReplicatedStorage.Remotes
local enemies = workspace.Enemies
local towers = workspace.Towers
local towerPad = {} -- each tower -> the pad it stands on

print("The base can take " .. Settings.BaseHealth .. " hits")

-- The waypoints, in order (they are named 1, 2, 3...)
local waypoints = workspace.Path.Waypoints:GetChildren()
table.sort(waypoints, function(a, b)
	return tonumber(a.Name) < tonumber(b.Name)
end)

-- The base's health, as an attribute of the workspace: every client can read it
workspace:SetAttribute("BaseHealth", Settings.BaseHealth)

-- Every player gets Money on the leaderboard
Players.PlayerAdded:Connect(function(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player

	local money = Instance.new("IntValue")
	money.Name = "Money"
	money.Value = Settings.StartMoney
	money.Parent = leaderstats
end)

-- An enemy reached the base
local function damageBase(amount)
	local health = math.max(0, workspace:GetAttribute("BaseHealth") - amount)
	workspace:SetAttribute("BaseHealth", health)
end

-- Walk an enemy along the path. MoveTo gives up after 8 seconds and says so
-- (MoveToFinished with false), so a slow enemy is sent again until it arrives.
local function walkPath(enemy)
	local humanoid = enemy.Humanoid
	for i = 2, #waypoints do
		repeat
			humanoid:MoveTo(waypoints[i].Position)
		until humanoid.MoveToFinished:Wait() or not enemy.Parent
		if not enemy.Parent then
			return
		end
	end
	-- it reached the base
	damageBase(Settings.Enemies[enemy.Name].Damage)
	enemy:Destroy()
end

-- A new enemy at the gate, walking the path
local function spawnEnemy(kind)
	local enemy = ServerStorage.Enemies[kind]:Clone()
	-- dropped in just above the first waypoint
	enemy:PivotTo(waypoints[1].CFrame + Vector3.new(0, 5, 0))
	local info = Settings.Enemies[kind]
	enemy.Humanoid.MaxHealth = info.Health
	enemy.Humanoid.Health = info.Health
	enemy.Humanoid.WalkSpeed = info.Speed
	enemy.Parent = enemies
	enemy.Humanoid.Died:Connect(function()
		-- every player earns the reward
		for _, player in Players:GetPlayers() do
			player.leaderstats.Money.Value += info.Reward
		end
		enemy:Destroy()
	end)
	task.spawn(walkPath, enemy)
	return enemy
end

-- The nearest living enemy within range of a point, or nil
local function nearestEnemy(position, range)
	local best, bestDistance = nil, range
	for _, enemy in enemies:GetChildren() do
		local root = enemy:FindFirstChild("HumanoidRootPart")
		if root and enemy.Humanoid.Health > 0 then
			local distance = (root.Position - position).Magnitude
			if distance <= bestDistance then
				best, bestDistance = enemy, distance
			end
		end
	end
	return best
end

-- A flash of light from a tower to its target
local function beam(from, to)
	local ray = Instance.new("Part")
	ray.Anchored = true
	ray.CanCollide = false
	ray.CanTouch = false
	ray.Material = Enum.Material.Neon
	ray.Color = Color3.fromRGB(255, 240, 150)
	ray.Size = Vector3.new(0.2, 0.2, (to - from).Magnitude)
	ray.CFrame = CFrame.lookAt((from + to) / 2, to)
	ray.Parent = workspace
	Debris:AddItem(ray, 0.1)
end

-- Frost: an enemy walks at a fraction of its speed for 2 seconds
local function slow(enemy, factor)
	if enemy:GetAttribute("Slowed") then
		return
	end
	enemy:SetAttribute("Slowed", true)
	local speed = Settings.Enemies[enemy.Name].Speed
	enemy.Humanoid.WalkSpeed = speed * factor
	task.delay(2, function()
		if enemy.Parent then
			enemy.Humanoid.WalkSpeed = speed
			enemy:SetAttribute("Slowed", nil)
		end
	end)
end

-- A shot: damage the target (and, from a Cannon, everyone near it)
local function shoot(tower, target, info)
	local damage = info.Damage * tower:GetAttribute("Level")
	local at = target.HumanoidRootPart.Position
	if info.Splash then
		for _, enemy in enemies:GetChildren() do
			local root = enemy:FindFirstChild("HumanoidRootPart")
			if root and (root.Position - at).Magnitude <= info.Splash then
				enemy.Humanoid:TakeDamage(damage)
			end
		end
	else
		target.Humanoid:TakeDamage(damage)
	end
	if info.Slow and target.Parent then
		slow(target, info.Slow)
	end
	beam(tower.Head.Position, at)
end

-- A tower's life: aim at the nearest enemy in range, shoot, wait its cooldown
local function runTower(tower)
	local info = Settings.Towers[tower.Name]
	while tower.Parent do
		local target = nearestEnemy(tower.Head.Position, info.Range)
		if target then
			tower.Head.CFrame = CFrame.lookAt(tower.Head.Position, target.HumanoidRootPart.Position)
			shoot(tower, target, info)
			task.wait(info.Cooldown)
		else
			task.wait(0.1)
		end
	end
end

-- Build a tower on a pad
local function placeTower(pad, kind)
	local tower = ServerStorage.Towers[kind]:Clone()
	tower:PivotTo(pad.CFrame + Vector3.new(0, pad.Size.Y / 2 + 1, 0))
	tower:SetAttribute("Level", 1)
	tower.Parent = towers
	pad:SetAttribute("Used", true)
	towerPad[tower] = pad
	task.spawn(runTower, tower)
end

-- The client asks for a tower on a pad. Check everything: a real, free pad,
-- a real tower, and the money to pay for it.
remotes.Place.OnServerEvent:Connect(function(player, pad, kind)
	if typeof(pad) ~= "Instance" or pad.Parent ~= workspace.Pads or pad:GetAttribute("Used") then
		return
	end
	local info = typeof(kind) == "string" and Settings.Towers[kind]
	if not info then
		return
	end
	local money = player.leaderstats.Money
	if money.Value < info.Price then
		return
	end
	money.Value -= info.Price
	placeTower(pad, kind)
end)

-- An upgrade: the next level costs more each time, and each level adds the
-- tower's damage again
remotes.Upgrade.OnServerEvent:Connect(function(player, tower)
	if typeof(tower) ~= "Instance" or tower.Parent ~= towers then
		return
	end
	local level = tower:GetAttribute("Level")
	local cost = math.floor(Settings.Towers[tower.Name].Price * Settings.UpgradeCost * level)
	local money = player.leaderstats.Money
	if money.Value < cost then
		return
	end
	money.Value -= cost
	tower:SetAttribute("Level", level + 1)
end)

-- Selling: half the price back, and the pad is free again
remotes.Sell.OnServerEvent:Connect(function(player, tower)
	if typeof(tower) ~= "Instance" or tower.Parent ~= towers then
		return
	end
	player.leaderstats.Money.Value += math.floor(Settings.Towers[tower.Name].Price / 2)
	towerPad[tower]:SetAttribute("Used", nil)
	towerPad[tower] = nil
	tower:Destroy()
end)

-- One wave: its enemies one by one, then wait until they are all gone
local function runWave(list)
	for _, kind in list do
		spawnEnemy(kind)
		task.wait(Settings.SpawnGap)
	end
	while #enemies:GetChildren() > 0 do
		task.wait(0.2)
	end
end

-- The waves, each after a break
for i, list in Settings.Waves do
	task.wait(Settings.WaveBreak)
	runWave(list)
end