"""Keep the optional sections the user chose in dashboard.html, and delete the rest.

Usage:  python sections.py <dashboard.html> [checkpoints] [admin] [login]

Each section sits between marker lines, in HTML, CSS and script:
    <!-- OPTIONAL:admin BEGIN -->  /* OPTIONAL:admin BEGIN */  // OPTIONAL:admin BEGIN
    ...                             ...                         ...
    <!-- OPTIONAL:admin END -->    /* OPTIONAL:admin END */    // OPTIONAL:admin END
Chosen sections lose only their marker lines. Unchosen ones lose everything.
The file is rewritten in place. Name no sections to remove all of them.
"""
import re
import sys
from pathlib import Path

SECTIONS = ("checkpoints", "admin", "login")
BLOCK = re.compile(r"^[ \t]*(?:<!--|/\*|//) OPTIONAL:(\w+) BEGIN.*\n((?:.*\n)*?)[ \t]*(?:<!--|/\*|//) OPTIONAL:\1 END.*\n", re.M)


def keep(html, chosen):
    unknown = set(chosen) - set(SECTIONS)
    if unknown:
        sys.exit(f"unknown section(s) {', '.join(sorted(unknown))}; choose from {', '.join(SECTIONS)}")
    html = BLOCK.sub(lambda m: m[2] if m[1] in chosen else "", html)
    if "OPTIONAL:" in html:
        sys.exit("an OPTIONAL marker has no matching BEGIN/END line; fix the template")
    return html


if __name__ == "__main__":
    if len(sys.argv) < 2:
        sys.exit(__doc__)
    page = Path(sys.argv[1])
    page.write_text(keep(page.read_text(encoding="utf-8"), sys.argv[2:]), encoding="utf-8")
    print(f"{page}: kept {', '.join(sys.argv[2:]) or 'no optional sections'}")