#!python
# -*- mode: python; Encoding: utf-8; coding: utf-8 -*-
# Last updated: <2024/11/23 07:02:41 +0900>
"""
Adding gamma correction to mtl file.

Usage: python add_gamma.py INPUT.mtl

Windows10 x64 21H2 + Python 3.10.10 64bit
"""

import argparse
import os
import sys
import re

# DBG = True
DBG = False


def linearrgb_to_srgb(c):
    """Gamma correction."""
    r = 0.0
    if c < 0.0031308:
        r = 0.0 if c < 0.0 else c * 12.92
    else:
        r = 1.055 * pow(c, (1.0 / 2.4)) - 0.055
    return round(r, 6)


def main():
    parser = argparse.ArgumentParser(description="Adding gamma correction to mtl file.")
    parser.add_argument("infile", type=str, help=".mtl filename")
    args = parser.parse_args()
    infile = args.infile

    if not os.path.isfile(infile):
        print("Error : Not found %s" % (infile))
        sys.exit()

    bakfile = "%s.orig.bak" % (infile)

    # read file
    with open(infile) as f:
        lines = [s.rstrip() for s in f.readlines()]

    pattern = r"^Kd (\d+\.\d+) (\d+\.\d+) (\d+\.\d+)$"
    newlines = []
    for s in lines:
        result = re.match(pattern, s)
        if result:
            r = linearrgb_to_srgb(float(result.group(1)))
            g = linearrgb_to_srgb(float(result.group(2)))
            b = linearrgb_to_srgb(float(result.group(3)))
            nline = "Kd %f %f %f" % (r, g, b)
            newlines.append(nline)
            if DBG:
                print("%s  ->  %s" % (s, nline))
        else:
            newlines.append(s)

    # backup file. rename original file
    os.rename(infile, bakfile)

    # write file
    with open(infile, "w", newline="\n") as fo:
        for s in newlines:
            fo.write("%s\n" % (s))


if __name__ == "__main__":
    main()