-- dragon curve
-- by retroredge,v0.1,2025

dirs = {{ 1, 0 }, { 0, 1 }, { -1, 0 }, { 0, -1 }}

rec_dep = 10
line_len = 2
sx = 84
sy = 94
curve = {}
count = 1

function flp(tbl)
    new = {}
    for i = 1, #tbl do
        if tbl[i] == "l" then
            add(new, "r")
        else
            add(new, "l")
        end
    end
    return new
end

function rev(tbl)
    new = {}
    for i = #tbl, 1, -1 do
        add(new, tbl[i])
    end
    return new
end

function gen_curve(letters, lvl)
    new = flp(letters)
    add(curve, "l")
    new = rev(new)
    for i = 1, #new do
        add(curve, new[i])
    end

    if lvl < rec_dep then
        gen_curve(curve, lvl + 1)
    end
end

function wrap1to4(i)
 return ((i - 1) % 4) + 1
end

function _init()
    gen_curve(curve, 0)
end

function _draw()
    cls(0)
    dir_ind = 1
    x = sx
    y = sy
    col_max = 1
    col = 4

    for i = 1, count do
        if i > col_max then
            col_max = shl(col_max, 1)
            col += 1
        end
        dir = dirs[dir_ind]
        nx = x + dir[1] * line_len
        ny = y + dir[2] * line_len
        line(x, y, nx, ny, col)
        x = nx
        y = ny
        if curve[i] == "l" then
            dir_ind = wrap1to4(dir_ind - 1)
        else
            dir_ind = wrap1to4(dir_ind + 1)
        end
    end

    if count < #curve then
        count += 1
    end
end

function _update()
    if btn(4) then
        line_len += 1
    elseif btn(5) then
        line_len -= 1
    end

    line_len = min(max(line_len, 2), 16)

    if btn(1) then
        sx += 1
    elseif btn(0) then
        sx -= 1
    end

    if btn(2) then
        sy -= 1
    elseif btn(3) then
        sy += 1
    end
end