CC: Simple Planets Program

-- CLASSES --------------------------------------------------------

Particle = {

    new = function(self, x, y, w, h, velMult, icon)
        local starting_values = {
            pos = vector.new(x, y),
            w = w,
            h = h,
            vel = vector.new(cf.randomFloat(-1 * velMult, 1 * velMult), cf.randomFloat(-1 * velMult, 1 * velMult)),
            icon = icon,

            acc = vector.new(),
            mass = 10,
        }
        setmetatable(starting_values, {__index = self})
        return starting_values
    end,

    show = function(self)
        shape.point(self.pos, self.icon) -- draw the particle

        -- -- draw an arrow representing the velocity vector
        -- if (self.vel.x < -0.5) then
        --  local x = self.pos.x - 1
        --  if (x >= 1) then
        --      shape.point({x=x, y=self.pos.y}, "-")
        --  end
        -- elseif (self.vel.x > 0.5) then
        --  local x = self.pos.x + 1
        --  if (x <= self.w-1) then
        --      shape.point({x=x, y=self.pos.y}, "-")
        --  end
        -- end

        -- if (self.vel.y < -0.5) then
        --  local y = self.pos.y - 1
        --  if (y >= 1) then
        --      shape.point({x=self.pos.x, y=y}, "|")
        --  end
        -- elseif (self.vel.y > 0.5) then
        --  local y = self.pos.y + 1
        --  if (y <= self.h-1) then
        --      shape.point({x=self.pos.x, y=y}, "|")
        --  end
        -- end
    end,

    attracted = function(self, target, G, constraint)
        local force = target.pos:sub(self.pos) -- target.pos - self.pos
        local distanceSquared = cf.magSq(force)
        local strength = cf.clamp(G * ((self.mass * target.mass) / distanceSquared), 0, constraint)

        force = force:normalize() -- normalizes the vector, so the hypotenuse is 1
        force = force:mul(strength)

        self.acc = self.acc:add(force:mul(1/self.mass)) -- F = m * a, a = F / m, a = F * (1/m)
    end,

    update = function(self)
        self.vel = self.vel:add(self.acc)
        self.pos = self.pos:add(self.vel)
    end

}

Attractor = {

    new = function(self, x, y)
        local starting_values = {
            pos = vector.new(x, y),
            icon = "#",
            mass = 400,
        }
        setmetatable(starting_values, {__index = self})
        return starting_values
    end,

    show = function(self)
        shape.point(self.pos, self.icon)
    end

}



-- FUNCTIONS --------------------------------------------------------

function createParticles(n, x, y, w, h, velMult)
    local particles = {}
    for id = 1, n do
        local icon = string.char(32 + id) -- All chars except the space char.
        particles[#particles+1] = Particle:new(x, y, w, h, velMult, icon)
        -- particles[#particles+1] = Particle:new(math.random(w-1), math.random(h-1), w, h, velMult, icon)
    end
    return particles
end

function createAttractors(n, w, h)
    local attractors = {}
    attractors[#attractors+1] = Attractor:new(w, h)
    return attractors
end



-- CODE EXECUTION --------------------------------------------------------

local G = 0.1
local constraint = 0.015
local particleCount = 5 -- 94 by default
local velMult = 0.1

local w, h = term.getSize()
local particles = createParticles(particleCount, w/4, h/4, w, h, velMult)
local attractors = createAttractors(5, w/2, h/2)

while true do
    if not rs.getInput(cfg.disableSide) then
        -- cf.clearTerm()

        for i = 1, #particles do
            particle = particles[i]

            for j = 1, #attractors do
                attractor = attractors[j]
                particle:attracted(attractor, G, constraint)
            end

            particle:update()

            local x = particle.pos.x
            local y = particle.pos.y
            local inCanvas = particle.pos.x >= 1 and particle.pos.x <= w and particle.pos.y >= 1 and particle.pos.y <= h

            if inCanvas then
                particle.icon = dithering.getClosestChar(cf.clamp(particle.vel:length() / 2, 0, 1))
                particle:show()
            end

            particle.acc = particle.acc:mul(0) -- reset the acceleration
        end

        attractors[1]:show()

        cf.tryYield()
        -- os.sleep(0.05)
    else
        sleep(1)
    end
end