import tempfile
import subprocess
import os.path
import string

SAFECHARS = string.ascii_letters + string.digits + " _-"

def extract_pages(source, bookmark, start=None, end=None, count=1):

    return extract_and_concat([(source, bookmark, start, end, count)])

def extract_and_concat(items):
    
    # create a temporary directory for our sections
    d = tempfile.TemporaryDirectory(prefix="polyphonic_")
    pdfmarks = os.path.join(d.name, 'pdfmarks.txt')
    marks = open(pdfmarks, 'w')

    sections = []
    current_page = 1

    for i, (source, bookmark, start, end, count) in enumerate(items):

        if count == 0:
            continue

        if not start:
            sections.append(source)

        else:

            if not end:
                end = start

            dest = os.path.join(d.name, f'section_{i}.pdf')

            cmd = ['gs', '-sDEVICE=pdfwrite', '-dBATCH', '-dNOPAUSE', 
                f'-dFirstPage={start}', f'-dLastPage={end}', 
                f'-sOutputFile={dest}',
                source]

            bookmark = "".join(filter(lambda c: c in SAFECHARS, bookmark))

            marks.write(f'[/Title ({bookmark}) /Page {current_page} /OUT pdfmark\n')

            p = subprocess.run(cmd, check=True, capture_output=True)
            pages = len([ x for x in p.stdout.splitlines() if x.decode('utf8').startswith('Page ')])
            for j in range(count):
                sections.append(dest)
                current_page += pages

    marks.close()

    # concat the items
    output = tempfile.NamedTemporaryFile(prefix="polyphonic_", suffix='.pdf')

    cmd = ['gs', '-sDEVICE=pdfwrite', '-q', '-dBATCH', '-dNOPAUSE',
           '-sOutputFile=-']
    cmd.extend(sections)
    cmd.append(pdfmarks)

    subprocess.run(cmd, stdout=output)

    output.seek(0)
    return output