module bytes

export byte_vec_to_int, byte_vec_to_string, bit_at, bit_vector

"""
    read_data_size(size::Vector{UInt8})::Real

FIT headers have a data size field, with 4 bytes.
"""
function byte_vec_to_int(byte_vec::Vector{UInt8})::Integer
    result::Integer = 0
    byte_vec = Int64.(byte_vec)

    for i ∈ 0:length(byte_vec) - 1
        result += byte_vec[1 + i] << (8 * i)
    end
    return result
end

"""
    byte_vec_to_string(byte_vec::Vector{UInt8})::AbstractString

Given the byte vec, create a String
"""
function byte_vec_to_string(byte_vec::Vector{UInt8})::AbstractString
    String(Char.(byte_vec))
end

"""
    bit_at(byte::UInt8, idx::Int64; t::Type=Int64)::Int64

Parse the bit at specific index in byte
"""
function bit_at(byte::UInt8, idx::Int64; t::Type=Int64)::Int64
    parse(t, bitstring(byte)[idx])
end

end
# byte_vec_to_string(UInt8.(collect("ABC")))

function bit_vector(byte::UInt8; little_endian=false)::Vector{UInt8}
    range = if little_endian
        8:-1:1
    else
        1:1:8
    end

    s = bitstring(byte)
    [parse(UInt8, s[b]) for b in range]
end


function bit_vector(byte_vector::Vector{UInt8}; little_endian=false)::Vector{UInt8}
    vecs = [bit_vector(byte; little_endian=little_endian) for byte ∈ byte_vector]
    reduce(vcat, vecs)
end