using WaterLily
using StaticArrays

function block(L=2^5;Re=250,U=1,amp=0,ϵ=0.5,thk=2ϵ+√2)
    # Set viscosity
    ν=U*L/Re

    # Create dynamic block geometry
    function sdf(x,t) 
        # SDF defines form a paddle (a rectangle)
        y = x .- SVector(0.,clamp(x[2],-L/2,L))
        # this confuses me! the last line of function is returned.
        # so this the same as `return √sum(abs2,y)-thk/2` 
        √sum(abs2,y)-thk/2 
    end
    function map(x,t)
        α = -t*U/L # rotation of paddle at time 't' in simulation
        R = @SMatrix [cos(α) sin(α); -sin(α) cos(α)] #2D rotation matrix
        val = R * (x.-SVector(3L+L*sin(t*U/L)+0.01,3L+L*cos(t*U/L)+0.01))
        return val
    end

    body = AutoBody(sdf,map)

    Simulation((6L+2,6L+2),zeros(2),L;U,ν,body,ϵ) #  new instance of Simulation
end

include("TwoD_plots.jl")
sim_gif!(block();duration=20π,step=π/32,remeasure=true,μbody=true,cfill=:Blues,legend=false,border=:none)