#!/usr/bin/env python3

"""

Generate matplotlirc for installs.

If packagers want to change the default backend, insert a `#backend: ...` line.

Otherwise, use the default `##backend: Agg` which has no effect even after

decommenting, which allows _auto_backend_sentinel to be filled in at import

time.

"""

import sys

from pathlib import Path

if len(sys.argv) != 4:

raise SystemExit('usage: {sys.argv[0]} <input> <output> <backend>')

input = Path(sys.argv[1])

output = Path(sys.argv[2])

backend = sys.argv[3]

template_lines = input.read_text(encoding="utf-8").splitlines(True)

backend_line_idx, = ( # Also asserts that there is a single such line.

idx for idx, line in enumerate(template_lines)

if "#backend:" in line)

template_lines[backend_line_idx] = (

f"#backend: {backend}\n" if backend not in ['', 'auto'] else "##backend: Agg\n")

output.write_text("".join(template_lines), encoding="utf-8")