local fps = {}

do
	cvars.RemoveChangeCallback("fps_graph", "fps_graph")
	cvars.RemoveChangeCallback("fps_graph_width", "fps_graph_width")
	cvars.RemoveChangeCallback("fps_graph_points", "fps_graph_points")

	fps.X, fps.Y = 20, 20
	fps.W, fps.H = 0, 150
	fps.PointDistance = 0

	fps.max = GetConVar("fps_max")
	fps.graph = CreateClientConVar("fps_graph", "0", nil, nil, "Draw the FPS counter and/or graph, = 1 draws counter, = 2 draws bar graph and counter, = 3 draws line graph and counter.")
	fps.graph_points = CreateClientConVar("fps_graph_points", "60", nil, nil, "The number of points/bars the FPS graph will have.")
	fps.graph_width = CreateClientConVar("fps_graph_width", "500", nil, nil, "The FPS graph's target width. Will change to match the points.")

	fps.Gradient = Material("vgui/gradient-d")
	fps.Cache = setmetatable({}, {__index = function() return 0 end})

	fps.NextCount = 0
	fps.SinceLastUpdate = 0
	fps.LastFrameNumber = FrameNumber()
end

local function CountFrames()
	if (SysTime() < fps.NextCount) then return end
	fps.NextCount = SysTime() + 1

	local frames = FrameNumber()
	local diff = frames - fps.LastFrameNumber
	local limit = math.max(fps.max:GetInt(), 60)

	table.insert(fps.Cache, 1, math.Clamp(diff / limit, 0, 1))

	if (#fps.Cache > fps.graph_points:GetInt() + 1) then
		table.remove(fps.Cache)
	end

	fps.SinceLastUpdate = diff
	fps.LastFrameNumber = frames
end

local function DrawCounter()
	local x, y = fps.X, fps.Y
	local w, h = fps.W, fps.H
	local FPS = string.format("%i FPS", fps.SinceLastUpdate)

	if (fps.graph:GetInt() == 1) then
		draw.SimpleText(FPS, "DebugOverlay", x, y)
	else
		local mult = fps.Cache[1]
		local tx = x + w + 2
		local ty = y + (h - (h * mult))

		draw.SimpleText(FPS, "DebugOverlay", tx, ty, _, _, TEXT_ALIGN_CENTER)
	end
end

local function DrawBarGraph()
	local x, y = fps.X, fps.Y
	local w, h = fps.W, fps.H

	local pd = fps.PointDistance
	local points = fps.graph_points:GetInt()

	render.SetScissorRect(x, y, x + w, y + h, true)
		surface.SetDrawColor(0, 0, 0, 200)
		surface.DrawRect(x, y, w, h)

		for i = 1, points do
			local mult = fps.Cache[i]

			local bh = math.floor(h * mult)
			local bx = (x + w) - (i * pd)
			local by = y + (h - bh)

			surface.SetDrawColor(Color(255 - 255 * mult, 255 * mult, 0))
			surface.DrawRect(bx, by, pd, bh)
		end
	render.SetScissorRect(0, 0, 0, 0, false)
end

local function DrawLineGraph()
	local x, y = fps.X, fps.Y
	local w, h = fps.W, fps.H

	local pd = fps.PointDistance
	local points = fps.graph_points:GetInt()

	render.SetScissorRect(x, y, x + w, y + h, true)
		surface.SetDrawColor(0, 0, 0, 200)
		surface.DrawRect(x, y, w, h)

		render.ClearStencil()

		render.SetStencilEnable(true)
			render.SetStencilTestMask(0xFF)
			render.SetStencilWriteMask(0xFF)
			render.SetStencilReferenceValue(0x01)

			render.SetStencilCompareFunction(STENCIL_ALWAYS)
			render.SetStencilPassOperation(STENCIL_REPLACE)

			local first = fps.Cache[1]

			local pph = math.floor(h * first)
			local ppx = (x + w) - 1
			local ppy = y + (h - pph)

			for i = 2, points + 1 do
				local mult = fps.Cache[i]

				local ph = math.floor(h * mult)
				local px = ((x + w) - ((i - 1) * pd)) - 1
				local py = y + (h - ph)

				surface.SetDrawColor(0, 255, 0)
				surface.DrawLine(ppx, ppy, px, py)

				ppx, ppy = px, py
			end

			render.SetStencilCompareFunction(STENCIL_LESSEQUAL)
			render.SetStencilFailOperation(STENCIL_KEEP)

			surface.SetMaterial(fps.Gradient)
			surface.SetDrawColor(255, 0, 0)
			surface.DrawTexturedRect(x, y, w, h)
		render.SetStencilEnable(false)
	render.SetScissorRect(0, 0, 0, 0, false)
end

local function GraphChanged(_, old, new)
	old, new = tonumber(old) or 0, tonumber(new) or 0

	if (new > 0) then
		if (old <= 0) then
			fps.SinceLastUpdate = 0
			fps.LastFrameNumber = FrameNumber()
		end

		hook.Add("PreRender", "FPS Counter", CountFrames)

		if (new >= 1) then
			hook.Add("PostDrawHUD", "FPS Counter", DrawCounter)

			if (new == 2) then
				hook.Add("PostDrawHUD", "FPS Graph", DrawBarGraph)
			elseif (new >= 3) then
				hook.Add("PostDrawHUD", "FPS Graph", DrawLineGraph)
			else
				hook.Remove("PostDrawHUD", "FPS Graph")
			end
		end
	else
		table.Empty(fps.Cache)

		hook.Remove("PreRender", "FPS Counter")
		hook.Remove("PostDrawHUD", "FPS Counter")
		hook.Remove("PostDrawHUD", "FPS Graph")
	end
end
cvars.AddChangeCallback("fps_graph", GraphChanged, "fps_graph")

local function FindClosest(width, points)
	local low = width % points
	local high = (width + low) % points

	return low <= high and width - low or width + high
end

local function WidthChanged(_, _, new)
	local points = fps.graph_points:GetInt()
	fps.W = FindClosest(new, points)
	fps.PointDistance = fps.W / points
end
cvars.AddChangeCallback("fps_graph_width", WidthChanged, "fps_graph_width")

local function PointsChanged(_, old, new)
	old, new = tonumber(old) or 0, tonumber(new) or 60

	local target = fps.graph_width:GetInt()
	fps.W = FindClosest(target, new)
	fps.PointDistance = fps.W / new

	if (old < new) then return end

	local diff = old - new

	if (#fps.Cache - diff > new) then
		for i = 1, diff do
			table.remove(fps.Cache)
		end
	end
end
cvars.AddChangeCallback("fps_graph_points", PointsChanged, "fps_graph_points")

GraphChanged(_, _, fps.graph:GetInt())
WidthChanged(_, _, fps.graph_width:GetInt())