How do you efficiently structure an AI?

I've made this enemy AI which just follows the player and attacks when close enough. It uses the path finding service, so it's horribly inefficient at getting to a moving target. Is there any better way to balance out efficiency (with pathfinding) and getting to the target as fast as possible?

Here is my code:

local Stats = {walk = 6, run = 22, health = 250, radius = 20, range = 10, id = 2549507798, damage = 10, attackspeed = 1}

local PathfindingService = game:GetService("PathfindingService")
local NpcTarget = require(game.ServerScriptService.Modules.NpcTarget)

local pointModel = Instance.new("Model")
pointModel.Name = "Points"
pointModel.Parent = workspace

local subject = script.Parent
local humanoid = subject.Humanoid

local lastHealth = humanoid.Health
local active = false

local lastFailedDirection = nil

local origin = subject.HumanoidRootPart.Position

local target = nil
local walkCount = 0
local canAttack = true
local dead = false

local startPos = subject.HumanoidRootPart.Position

local rng = Random.new()

local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID="..Stats.id

local track = humanoid:LoadAnimation(animation)

function outOfRangeRegen()
	for i = 1,5 do
		wait(0.1)
		humanoid.Health = humanoid.Health + 5
	end
end	

function attackCooldown()
	canAttack = false
	coroutine.resume(coroutine.create(function()
		wait(Stats.attackspeed)
		canAttack = true
	end))
end

function findRandomPos()
	local pos = Vector3.new(subject.HumanoidRootPart.Position.X + rng:NextInteger(-25,25), 
								subject.HumanoidRootPart.Position.Y + rng:NextInteger(-5,5), 
								subject.HumanoidRootPart.Position.Z + rng:NextInteger(-25,25))
	
	
	if not testOverLand(pos) then
		pos = findRandomPos()
	end

	return pos
end

function calcPath(pos)
	local start = subject.HumanoidRootPart.Position
	local path = PathfindingService:FindPathAsync(start, pos)
	
    return path
end

function originalPos()
	walk(startPos)
end

function findTarget()
	local testTarget = NpcTarget.findClosest(subject)
	if not testTarget then
		active = false
		originalPos()
	else
		--[[if testTarget ~= target then
			local onDied = target.Humanoid.Died:Connect(function()
				target = findTarget()
			end)
		end]]
	end
	return testTarget
end

function detectTargets()
	coroutine.resume(coroutine.create(function()
		while not active do
			wait(1)
			for i,v in pairs(game.Players:GetChildren()) do
				local char = v.Character
				if char then
					if (char.HumanoidRootPart.Position - subject.HumanoidRootPart.Position).magnitude < Stats.range then
						local target = findTarget()
						active = true
					end
				end
			end
		end
	end))
end

function testOverLand(pos)
	local ray = Ray.new(pos, ((pos - Vector3.new(0,100,0)) - pos).unit * 300)
	local part, position = workspace:FindPartOnRay(ray, subject, false, true)
	
	if part then
		if part.Name == "Baseplate" then
			return false
		end
	else
		return false
	end
	
	return pos
end

function walk(opPos)
	humanoid.WalkSpeed = Stats.walk
	local pos = findRandomPos()
	
	if opPos then
		pos = opPos
	end
		
	local path = calcPath(pos)
	
	if path:CheckOcclusionAsync(1) == -1 then
		humanoid:MoveTo(pos)
		wait(0.01)
	end
		
	local points = path:GetWaypoints()
	local distance = 0
	
	for i = 2,#points do
		local lastWaypoint = points[i - 1]
		local currentWaypoint = points[i]
		
		humanoid:MoveTo(currentWaypoint.Position)
		repeat
			wait(0.01)
			distance = (subject.HumanoidRootPart.Position - currentWaypoint.Position).magnitude
		until distance <= 2.5 or active
		
		if currentWaypoint.Action == Enum.PathWaypointAction.Jump then
			humanoid.Jump = true
		end

	end	

	return true
end

function testRangeDistance()
	if not active then
		if (subject.HumanoidRootPart.Position - origin).magnitude > Stats.radius then
			return true
		end
	end
	
	return false
end

function pause()
	local w = math.random(1,5) 
	local count = 0
	
	while not active and count < w do
		wait(1)
		count = count + 1
		target = findTarget()
	end
end

function testTargetDistance()
	if (target.HumanoidRootPart.Position - subject.HumanoidRootPart.Position).magnitude <= 5 then
		return true
	end
	
	return false
end

function run()
	humanoid.WalkSpeed = 18
	local pos = target.HumanoidRootPart.Position
	local path = calcPath(pos)
	
	if path.Status == Enum.PathStatus.NoPath then
		outOfRangeRegen()
		return
	end
	
	if path:CheckOcclusionAsync(1) == -1 and not testTargetDistance() then
		humanoid:MoveTo(target.HumanoidRootPart.Position)
		wait(0.01)
	end
	
	local points = path:GetWaypoints()
	local distance = 0
	
	local willAttack = false
	
	for i = 2,#points do
		local lastWaypoint = points[i - 1]
		local currentWaypoint = points[i]
		
		humanoid:MoveTo(currentWaypoint.Position)
		
		repeat
			wait(0.05)
			distance = (subject.HumanoidRootPart.Position - currentWaypoint.Position).magnitude
			willAttack = testTargetDistance()
		until distance <= 6 or not active or target.Humanoid.Health <= 0 or willAttack
		
		if willAttack then
			humanoid:MoveTo(subject.HumanoidRootPart.Position)
			attack()
		end
		
		if currentWaypoint.Action == Enum.PathWaypointAction.Jump then
			humanoid.Jump = true
		end

	end	
		
	return true
end

function attack()
	if testTargetDistance() and canAttack and not dead then
		track:Play()
		target.Humanoid:TakeDamage(Stats.damage)
		attackCooldown()
	end
end

function died()
	local function fadePart(part)
		coroutine.resume(coroutine.create(function()
			for i = 1,25 do
				wait(0.01)
				part.Transparency = part.Transparency + 0.04
			end
		end))
	end
	dead = true
	subject.Humanoid.WalkSpeed = 0
	subject.Humanoid.JumpPower = 0
	local animation = Instance.new("Animation")
	animation.AnimationId = "http://www.roblox.com/Asset?ID=2614501451"
	local track = subject.Humanoid:LoadAnimation(animation)
	track:Play()
	
	track.KeyframeReached:Connect(function(keyframe)
		if keyframe == "Dead" then
			for i,v in pairs(subject:GetChildren()) do
				if v:IsA("BasePart") then
					fadePart(v)
				end
			end
		end
		
		game.Debris:AddItem(subject, 1)
	end)
end

function tookDamage()
	active = true
end

humanoid.HealthChanged:Connect(function(health)
	if health <= 1 then
		local ff = Instance.new("ForceField")
		ff.Parent = subject
		ff.Visible = false
		died()
	end
	if health < lastHealth and not active then
		tookDamage()
	end
end)

while not dead do
	wait()
	if not active then
		detectTargets()
		local decision = math.random(1,3)
		
		if decision > 1 and walkCount < 4 then
			local success, msg = pcall(function()
				walk()
			end)
			
			walkCount = walkCount + 1
			wait(1)
		else
			pause()
			walkCount = 0
		end
		
		if testRangeDistance() then
			local success, msg = pcall(function()
				walk(origin)
			end)
		end
	else
		target = findTarget()
		if not target then
			active = false
		end
		local success, msg = pcall(function()
			run()
		end)
	end
end