"""Freeze a font's default variation and give it a unique preview/export family name."""
import sys
from fontTools.ttLib import TTFont, newTable
from fontTools.varLib.instancer import instantiateVariableFont

def prepare(source, destination, family):
    font = TTFont(source, recalcTimestamp=False)
    if 'fvar' in font:
        axes = {axis.axisTag: axis.defaultValue for axis in font['fvar'].axes}
        for axis in font['fvar'].axes:
            if axis.axisTag == 'wght':
                axes['wght'] = max(axis.minValue, min(axis.maxValue, 400))
        font = instantiateVariableFont(font, axes, inplace=True)
    for record in font['name'].names:
        if record.nameID in (1, 2, 3, 4, 6, 16, 17):
            value = 'Regular' if record.nameID in (2, 17) else family
            if record.nameID == 6:
                value = family.replace(' ', '-')[:63]
            record.string = value.encode(record.getEncoding(), errors='replace')
    # Two reference fonts declare OS/2 v5 but only contain the 96-byte v4 table.
    # Correct the version tag without inventing missing metrics or changing outlines.
    metrics = font.reader['OS/2']
    if len(metrics) == 96 and int.from_bytes(metrics[:2], 'big') == 5:
        table = newTable('OS/2')
        table.decompile(b'\x00\x04' + metrics[2:], font)
        font['OS/2'] = table
    # A unique family per selected face prevents fontconfig confusing weight variants.
    font['OS/2'].fsSelection &= ~((1 << 0) | (1 << 5))
    font['OS/2'].fsSelection |= 1 << 6
    font['OS/2'].usWeightClass = 400
    font['head'].macStyle &= ~3
    font.save(destination)

if __name__ == '__main__':
    prepare(*sys.argv[1:4])