rope = {}

rope.ActiveRopes = {}

local A = Vector()
local damping = -0.05
local speed = 1
local gravity = {x=0,y=0,z=0}

local temp_vec = Vector() -- temp
local point_contents = util.PointContents
local band = bit.band
local CONTENTS_SOLID = CONTENTS_SOLID

local function add_vel(a, vx, vy, vz, ft)
    a.vel.x = a.vel.x + (vx * ft)
    a.vel.y = a.vel.y + (vy * ft)
    a.vel.z = a.vel.z + (vz * ft)
end

local function check_collision(a, ft)
    temp_vec.x = a.pos.x + (a.vel.x) * ft
    temp_vec.y = a.pos.y + (a.vel.y) * ft
    temp_vec.z = a.pos.z + (a.vel.z) * ft

    local content = point_contents(temp_vec)

    if band(content, CONTENTS_SOLID) == CONTENTS_SOLID then
        a.vel.x = a.vel.x * 0.25
        a.vel.y = a.vel.y * 0.25
        a.vel.z = -a.vel.z * 0.25

        return true
    end
end

local function calc(a, b, ft)
    if not a.first then
        add_vel(a, math.Rand(-1,1)*10, math.Rand(-1,1)*10, math.Rand(-1,1)*10, ft)
        a.first = true
    end

    add_vel(
        a,

        (b.pos.x - a.pos.x) * speed,
        (b.pos.y - a.pos.y) * speed,
        (b.pos.z - a.pos.z) * speed,

        ft
    )

    --add_vel(a, gravity.x,  gravity.y,  gravity.z, ft)

    if not check_collision(a, ft) then
        a.pos.x = a.pos.x + (a.vel.x) * ft
        a.pos.y = a.pos.y + (a.vel.y) * ft
        a.pos.z = a.pos.z + (a.vel.z) * ft
    end

    a.vel.x = a.vel.x + a.vel.x * damping
    a.vel.y = a.vel.y + a.vel.y * damping
    a.vel.z = a.vel.z + a.vel.z * damping
end

function rope.Think()
    A = Entity(483):GetPos()
    local ft = RealFrameTime() * 10

    for key, rope in pairs(rope.ActiveRopes) do
        local points = rope.points

        for i = 2, #points do
            calc(points[i - 1], points[i], ft)
            calc(points[i], points[i - 1], ft)
        end

        for i, var in pairs(rope.attachments) do
            local point = rope.points[i]

            if point then
                if type(var) == "function" then
                    local val = var()
                    point.pos.x = val.x
                    point.pos.y = val.y
                    point.pos.z = val.z
                else
                    local val = var
                    point.pos.x = val.x
                    point.pos.y = val.y
                    point.pos.z = val.z
                end

                point.vel.x = 0
                point.vel.y = 0
                point.vel.z = 0
            end
        end
    end
end

local color_white = color_white
local sprite_mat = Material("particle/particle_sphere")

function rope.Draw()
    for key, rope in pairs(rope.ActiveRopes) do
        local count = #rope.points

        render.SetMaterial(rope.mat)

        render.StartBeam(count)
            for i = 1, count do
                local v = rope.points[i].pos

                temp_vec.x = v.x
                temp_vec.y = v.y
                temp_vec.z = v.z

                render.AddBeam(temp_vec, 20, i/count, color_white)
            end
        render.EndBeam()

        render.SetMaterial(sprite_mat)

        for i = 1, count do
            local v = rope.points[i].pos

            temp_vec.x = v.x
            temp_vec.y = v.y
            temp_vec.z = v.z

            render.DrawSprite(temp_vec, 20, 20, color_white)
        end
    end
end

function rope.Create(points, attachments, mat)
    points = points or 128
    mat = mat or Material("cable/rope")
    attachments = attachments or {[1] = function() return LocalPlayer():EyePos() end, [#points] = function() return Vector(0,0,0) end}

    local data = {}

    data.mat = mat
    data.points = {}
    data.attachments = attachments

    local pos = select(2, next(attachments))
    pos = type(pos) == "function" and pos() or pos or VectorRand()

    for i = 1, points do
        data.points[i] = {
            pos =
            {
                x = pos.x,
                y = pos.y,
                z = pos.z,
            },

            vel = {x=math.Rand(-1,1),y=math.Rand(-1,1),z=math.Rand(-1,1)}
        }
    end

    data.id = table.insert(rope.ActiveRopes, data)
    data.Remove = function()
        table.remove(rope.ActiveRopes, data.id)
    end

    return data
end

hook.Add("Think", "rope", rope.Think)
hook.Add("PostDrawTranslucentRenderables", "rope", rope.Draw)

rope.Create(128, {[1] = function() return Entity(483):GetPos() end, [128] = function() return Entity(485):GetPos() end})