local Pos = require"common.coords".Pos
local class = require"common.class"
local tau = 2*math.pi

math.randomseed(os.time())

local function random_unit_vec()
	local theta = math.random()*tau
	return Pos:make(math.cos(theta),math.sin(theta))
end
local function lerp(a,b,t) return (1-t)*a + t*b end
local function smoothstep(x)
	if x<0 then return 0 end
	if x>1 then return 1 end
	return x*x*(3 - 2*x)
end
local function slerp(a,b,t) return lerp(a,b,smoothstep(t)) end

local PerlinNoise = class()
function PerlinNoise.make(cls)
	local grid = {}
	setmetatable(grid,{__index=function(t,k) t[k] = {} return t[k] end})
	return setmetatable({grid=grid},cls)
end
function PerlinNoise.vertex(self,ix,iy)
	local v = self.grid[ix][iy]
	if v then return v end
	vv = random_unit_vec()
	self.grid[ix][iy] = vv
	return vv
end

function PerlinNoise.at(self,x,y)
	local x0 = math.floor(x)
	local y0 = math.floor(y)
	local x1 = x0 + 1
	local y1 = y0 + 1

	local v00 = self:vertex(x0,y0)
	local v01 = self:vertex(x0,y1)
	local v10 = self:vertex(x1,y0)
	local v11 = self:vertex(x1,y1)

	local p = function(...) return Pos:make(...) end
	local d00 = v00:dot(p(x-x0,y-y0))
	local d01 = v01:dot(p(x-x0,y-y1))
	local d10 = v10:dot(p(x-x1,y-y0))
	local d11 = v11:dot(p(x-x1,y-y1))

	local q0 = slerp(d00,d01,y-y0)
	local q1 = slerp(d10,d11,y-y0)
	local z  = slerp(q0,q1,x-x0)
	return z
end

local NoiseAgg = class()
function NoiseAgg.make(cls,things)
	return setmetatable({things=things or {}},cls)
end
function NoiseAgg.at(self,x,y)
	local n = 0
	local t = 0
	assert(#self.things>0,"can't generate noise with no noise things")
	for _,thing in ipairs(self.things) do
		local gen,scale,amp = thing.gen,thing.scale,thing.amp
		n = n + amp
		t = t + gen:at(x/scale,y/scale)*amp
	end
	return t/n
end

-- local chars = "$@B%8&WM#*oahkbdpqwmZO0QLCJUYXzcvunxrjft/\\|()1{}[]?-_+~<>i!lI;:,\"^`'. "

-- local scale = 3

-- for x=1,10-10/40,10/40 do
-- 	for y = 1,10-10/60,10/60 do

-- 		local n = at(1+(x-1)/scale,1+(y-1)/scale)
-- 		local nn = (n +1)/2
-- 		local nnn = 1+nn*#chars
-- 		local c = chars:sub(nnn,nnn)
-- 		io.write(c)
-- 	end
-- 	io.write("\n")
-- end

return {PerlinNoise=PerlinNoise,NoiseAgg=NoiseAgg}