# compile using
# gfortran -shared -fPIC osbrac.f90 -o osbrac.so
# gfortran -shared -fPIC allosbrac.f90 -o allosbrac.so

using Libdl

function cal_BRAC(Emax, Λ, l1, l2)
    ϵ = (2 * Emax - Λ) % 2
    N = (l1 - l2 + Λ - ϵ) ÷ 2
    M = (l1 + l2 - Λ - ϵ) ÷ 2
    L = Λ
    NQMAX = 2 * Emax
    CO = 1/sqrt(2)
    SI = 1/sqrt(2)
    FIRSTCALL = true
    # dimensions BRAC(0:L,0:(NQMAX-L)/2,0:(NQMAX-L)/2,0:(NQMAX-L)/2,0:(NQMAX-L)/2)
    BRAC = zeros(Float64, 1 + L, 1 + (NQMAX - L) ÷ 2, 1 + (NQMAX - L) ÷ 2, 1 + (NQMAX - L) ÷ 2, 1 + (NQMAX - L) ÷ 2)

    lib = Libdl.dlopen("OSBRACKETS/osbrac.so") # Open the library explicitly.
    sym = Libdl.dlsym(lib, :osbrac_)   # Get a symbol for the function to call.
    # call signature OSBRAC(N,M,L,NQMAX,CO,SI,FIRSTCALL,BRAC)
    @ccall $sym(N::Ref{Int32},M::Ref{Int32},L::Ref{Int32},NQMAX::Ref{Int32},CO::Ref{Float64},SI::Ref{Float64},FIRSTCALL::Ref{UInt8},BRAC::Ptr{Array{Float64}})::Cvoid
    Libd.dlclose(lib)

    return BRAC
end

function get_bracket(BRAC, Emax, Λ, n1′, l1′, n2′, l2′, n1, n2)
    ϵ = (2 * Emax - Λ) % 2
    NP = (l1′ - l2′ + Λ - ϵ) ÷ 2
    N1P = n1′
    MP = (l1′ + l2′ - Λ - ϵ) ÷ 2
    N1 = n1
    N2 = n2
    N2P = n2′
    if MP+N1P+N2P == M+N1+N2
        # BRAC(NP,N1P,MP,N1,N2)
        return BRAC[1 + NP, 1 + N1P, 1 + MP, 1 + N1, 1 + N2]
    else
        return 0
    end
end