PDF metadata writing script for Julia

insert_pdf_description.jl

# Author: Anshul Singhvi
# Works as of 20220507
# Basically, the function is used to edit the metadata of a PDF using Ghostscript
# This could be made pure-Julian with the right logic (searching for keywords, etc.)
# but that is annoying to do.

using Ghostscript_jll

const AUTHOR = Ref{String}("Anshul Singhvi")

function insert_pdf_description(
    file, desc::String;
    title = splitext(splitdir(path)[2])[1],
    author = AUTHOR[],
    keywords = [],
    additional_gs_flags = String[]
    )

    @assert endswith(file, ".pdf")
    path = abspath(file)

    gs_options = Cmd(vcat(additional_gs_flags, [
        "-dBATCH",                      # run ghostscript in batch mode
        "-dNOPAUSE",                    # run without pause, exit immediately after complete
        "-dQUIET",                      # no output to stdout
        "-dProcessDSCComments=false",   # try to maintain metadata (this fails) see https://bugs.ghostscript.com/show_bug.cgi?id=693400
        "-sDEVICE=pdfwrite",            # use the `pdfwrite` device
        "-sOutputFile=-",               # output to stdout
    ]))

    gs_cmds = ``` $gs_options -f $path -c "[ /Subject ($desc) /Keywords ($(join(keywords, ", "))) /DOCINFO pdfmark"```

    pdf = Ghostscript_jll.gs() do gs_exe
        read(`$gs_exe $gs_cmds`, String)
    end

    write(path, pdf)

    return true

end