using Test

using stlProcess

using FileIO
using MeshIO

using LinearAlgebra

function _check_volume(triangles; scale=1)
    """
    Slow algorithm just used to test the other algorithms
    Reference:
        https://people.eecs.berkeley.edu/~wkahan/VtetLang.pdf
    """

    volume = 0.0
    for tri in triangles
        a, b, c = tri .* scale

        W = sqrt(sum((a .- b) .^ 2))
        V = sqrt(sum((b .- c) .^ 2))
        U = sqrt(sum((c .- a) .^ 2))

        v = sqrt(sum(a .^ 2))
        u = sqrt(sum(b .^ 2))
        w = sqrt(sum(c .^ 2))

        X = (w - U + v) * (U + v + w)
        Y = (u - V + w) * (V + w + u)
        Z = (v - W + u) * (W + u + v)

        x = (U - v + w) * (v - w + U)
        y = (V - w + u) * (w - u + V)
        z = (W - u + v) * (u - v + W)

        ξ = sqrt(x * Y * Z)
        η = sqrt(y * Z * X)
        ζ = sqrt(z * X * Y)
        λ = sqrt(x * y * z)

        volume += sqrt((ξ + η + ζ - λ) * (λ + ξ + η - ζ) * (η + ζ + λ - ξ) * (ζ + λ + ξ - η)) / (192 * u * v * w)
    end

    return volume
end

@testset "simple cube stl" begin
    """
    inertia math:
        https://hepweb.ucsd.edu/ph110b/110b_notes/node26.html

    Cube is a standard cube with a length of 2 for each side.
    """
    cube_path = raw"test_assets\cubeblender.stl"
    stl = load(cube_path)

    @testset "get_mass_properties function" begin
        props = get_mass_properties(stl)

        @test props.volume == 8.0
        @test all(props.center_of_gravity .== 0.0)
        @test all(eigvals(props.inertia) .≈ (5.0 + 1 / 3))

        @testset "get_volume function" begin
            @test _check_volume(stl; scale=1) ≈ props.volume rtol = 0.01
            @test _check_volume(stl; scale=4) ≈ (4 * 2)^3 rtol = 0.01
        end
    end
    @testset "Compare volumes with scaling" begin
        for scale in 1:5
            props = get_mass_properties(stl; scale=scale)
            volume = _check_volume(stl; scale=scale)

            @test props.volume ≈ volume rtol = 0.01
        end
    end
end