-- a little flame in a functional style

function particle(step, style, t)
    local newStyle = step(style, t)
    return {
        style = newStyle,
        next = function()
            return particle(step, newStyle, t + 1)
        end
    }
end

function flame(particles, t)
    local newParticles = evolve(particles, t)
    return {
        particles = newParticles,
        next = function()
            return flame(newParticles, t + 1)
        end
    }
end

function evolve(particles, t)
    return generate(mutate(prune(particles)), t)
end

function mutate(particles)
    return map(particles, function(p)
        return p.next()
    end)
end

function prune(particles)
    return filter(particles, function(p)
        return p.style.a > 0
    end)
end

function each(things, fn)
    for i, thing in ipairs(things) do
        fn(thing)
    end
end

function map(things, convert)
    local mapped = {}
    each(things, function(thing)
        table.insert(mapped, convert(thing))
    end)
    return mapped
end

function cons(things, ...)
    local all = {}
    each(things, function(t)
        table.insert(all, t)
    end)
    each({...}, function(t)
        table.insert(all, t)
    end)
    return all
end

function filter(things, fn)
    local filtered = {}
    for i, thing in ipairs(things) do
        if fn(thing) then
            table.insert(filtered, thing)
        end
    end
    return filtered
end

function spark(style, t)
    return {
        x = style.x - math.sin(t * 0.436),
        y = style.y + 1,
        r = style.r + (math.sin(t * style.o) * 40),
        g = style.g + (math.sin(t * style.o) * 33),
        b = style.b + (math.sin(t * style.o) * 15),
        a = (style.a - 4 * style.o) * 0.97,
        o = style.o * 0.977,
        radius = 5 - t * 0.03
    }
end

function generate(particles, t)
    return cons(particles,
        particle(spark, {
            x = -3,
            y = 2,
            r = 255,
            g = 40,
            b = 10,
            a = 220,
            o = 0.5
        } , 9),
        particle(spark, {
            x = 2,
            y = 2,
            r = 150,
            g = 73,
            b = 10,
            a = 220,
            o = 0.5
        } , 4),
        particle(spark, {
            x = -1,
            y = 1,
            r = 255,
            g = 128,
            b = 51,
            a = 220,
            o = math.sin(t) * 0.9
        }, t % 10),
        particle(spark, {
            x = -2,
            y = 0,
            r = 111,
            g = 40,
            b = 40,
            a = 191,
            o = 0.714
        } , 9),
        particle(spark, {
            x = 1,
            y = 0,
            r = 170,
            g = 83,
            b = 32,
            a = 220,
            o = 0.4 + (math.sin(t) * 0.362)
        }, t % 3),
        particle(spark, {
            x = 0.7,
            y = 1,
            r = 168,
            g = 83,
            b = 5,
            a = 250,
            o = 0.4
        }, t % 4),
        particle(spark, {
            x = 1,
            y = 0,
            r = 177,
            g = 72,
            b = 17,
            a = 219,
            o = 1.154
        }, 0),
        particle(spark, {
            x = -0.5,
            y = 1,
            r = 189,
            g = 20,
            b = 17,
            a = 219,
            o = 0.6
        }, 3)
    )
end



f = flame({}, 0)

function drawParticle(p)
    love.graphics.setColor(p.style.r, p.style.g, p.style.b, p.style.a)
    love.graphics.circle('fill', p.style.x, p.style.y, p.style.radius)
end

local WIDTH, HEIGHT = love.graphics.getWidth(), love.graphics.getHeight()
function love.draw()
    love.graphics.setBackgroundColor(59, 51, 82, 255)
    love.graphics.translate(WIDTH / 2, HEIGHT / 2)
    each(f.particles, function(p)
        drawParticle(p)
    end)
    f = f.next()
end