using Random, Test, HDF5

import HDF5.datatype

struct Simple
    a::Float64
    b::Int
end

function datatype(::Type{Simple})
    dtype = HDF5.API.h5t_create(HDF5.API.H5T_COMPOUND, sizeof(Simple))
    HDF5.API.h5t_insert(dtype, "a", fieldoffset(Simple, 1), datatype(Float64))
    HDF5.API.h5t_insert(dtype, "b", fieldoffset(Simple, 2), datatype(Int))
    HDF5.Datatype(dtype)
end

@testset "custom" begin
    N = 5
    v = [Simple(rand(Float64), rand(Int)) for i in 1:N, j in 1:N]

    fn = tempname()
    h5open(fn, "w") do h5f
        dtype = datatype(Simple)
        dspace = dataspace(v)
        dset = create_dataset(h5f, "data", dtype, dspace)
        write_dataset(dset, dtype, v)
    end

    h5open(fn, "r") do h5f
        dset = h5f["data"]
        @test_throws ErrorException read(dset, Float64)
        @test_throws ErrorException read(dset, Union{Float64,Int})

        v_read = read(dset, Simple)
        @test v_read == v

        indices = (1, 1:2:4)
        v_read = read(dset, Simple, indices...)
        @test v_read == v[indices...]

        v_read = read(h5f, "data" => Simple)
        @test v_read == v
    end

    v_read = h5read(fn, "data" => Simple)
    @test v_read == v
end