vec3.lua

local ffi = require "ffi"
local sqrt = math.sqrt

ffi.cdef [[
	typedef struct {
		double x, y, z;
	} mlml_vec3;
]]

local vec3 = {}

local mlml_vec3 = ffi.typeof("mlml_vec3")
vec3.new = mlml_vec3

function vec3.clone(a, result)
	result = result or vec3.new()
	ffi.copy(result, a, ffi.sizeof(mlml_vec3))
	return result
end

function vec3.new_array(n)
	return ffi.new("mlml_vec3[?]", n)
end

function vec3.unpack(a)
	return a.x, a.y, a.z
end

function vec3.to_table(a)
	return {x = a.x, y = a.y, z = a.z}
end

function vec3.to_flat_table(a)
	return {a.x, a.y, a.z}
end

function vec3.from_table(t)
	return vec3.new(t.x, t.y, t.z)
end

-- a, left operand
-- b, right operand
-- [result], output vector to store results in
-- returns the component-wise addition of two vectors
function vec3.add(a, b, result)
	result = result or vec3.new()
	result.x = a.x + b.x
	result.y = a.y + b.y
	result.z = a.z + b.z
	return result
end

-- accepts a scalar as the right hand operand
function vec3.add_scalar(a, s, result)
	result = result or vec3.new()
	result.x = a.x + s
	result.y = a.y + s
	result.z = a.z + s
	return result
end

function vec3.sub(a, b, result)
	result = result or vec3.new()
	result.x = a.x - b.x
	result.y = a.y - b.y
	result.z = a.z - b.z
	return result
end

function vec3.sub_scalar(a, s, result)
	result = result or vec3.new()
	result.x = a.x - s
	result.y = a.y - s
	result.z = a.z - s
	return result
end

-- scalar as right hand operand
function vec3.mul(a, s, result)
	result = result or vec3.new()
	result.x = a.x * s
	result.y = a.y * s
	result.z = a.z * s
	return result
end

function vec3.mul_vec3(a, b, result)
	result = result or vec3.new()
	result.x = a.x * b.x
	result.y = a.y * b.y
	result.z = a.z * b.z
	return result
end

-- scalar as right hand operand
function vec3.div(a, s, result)
	result = result or vec3.new()
	result.x = a.x / s
	result.y = a.y / s
	result.z = a.z / s
	return result
end

function vec3.div_vec3(a, b, result)
	result = result or vec3.new()
	result.x = a.x / b.x
	result.y = a.y / b.y
	result.z = a.z / b.z
	return result
end

function vec3.cross(a, b, result)
	result = result or vec3.new()
	result.x = a.y*b.z - a.z*b.y
	result.y = a.z*b.x - a.x*b.z
	result.z = a.x*b.y - a.y*b.x
	return result
end

function vec3.normalize(a, result)
	result = result or vec3.new()
	local l = vec3.len(a)
	if l == 0 then l = 1 end
	result.x, result.y, result.z = a.x / l, a.y / l, a.z / l
	return result
end

function vec3.equality(a, b)
	return a.x == b.x and a.y == b.y and a.z == b.z
end

function vec3.dot(a, b)
	return a.x * b.x + a.y * b.y + a.z * b.z
end

function vec3.len(a)
	return sqrt(a.x * a.x + a.y * a.y + a.z * a.z)
end

function vec3.dist(a, b)
	local dx = a.x - b.x
	local dy = a.y - b.y
	local dz = a.z - b.z
	return sqrt(dx * dx + dy * dy + dz * dz)
end

function vec3.dist2(a, b)
	local dx = a.x - b.x
	local dy = a.y - b.y
	local dz = a.z - b.z
	return (dx * dx + dy * dy + dz * dz)
end

function vec3.lerp(a, b, s)
	return a + s * (b - a)
end

function vec3.tostring(a)
	return string.format("(%+0.3f,%+0.3f,%+0.3f)", a.x, a.y, a.z)
end

local vec3_mt = {}

vec3_mt.__index = vec3
vec3_mt.__call = vec3.new
vec3_mt.__tostring = vec3.tostring

function vec3_mt.__unm(a)
	return vec3.new(-a.x, -a.y, -a.z)
end

function vec3_mt.__eq(a,b)
	return vec3.equality(a, b)
end

function vec3_mt.__add(a, b)
	if type(a) == "number" then
		return vec3.add_scalar(b, a)
	elseif type(b) == "number" then
		return vec3.add_scalar(a, b)
	else
		return vec3.add(a, b)
	end
end

function vec3_mt.__sub(a, b)
	if type(a) == "number" then
		return vec3.sub_scalar(b, a)
	elseif type(b) == "number" then
		return vec3.sub_scalar(a, b)
	else
		return vec3.sub(a, b)
	end
end

function vec3_mt.__mul(a, b)
	if type(a) == "number" then
		return vec3.mul(b, a)
	elseif type(b) == "number" then
		return vec3.mul(a, b)
	else
		return vec3.mul_vec3(a, b)
	end
end

function vec3_mt.__div(a, b)
	if type(a) == "number" then
		return vec3.div(b, a)
	elseif type(b) == "number" then
		return vec3.div(a, b)
	else
		return vec3.div_vec3(a, b)
	end
end

ffi.metatype(mlml_vec3, vec3_mt)
return setmetatable({}, vec3_mt)