Fix levels inside darktable xmp files (migration from version 2.0.7 to 2.2.3)

darktable_xmp_migrate_from_2_0_X_to_2_2_3.py

#!/usr/bin/python3
import struct
import binascii
import sys


if len(sys.argv) != 2:
    print("Usage:")
    print("    darktable_xmp_migrate_from_2_0_X_to_2_2_3.py filename")
    print("")
    print("Please note the file will be rewritten. Be sure you created a backup")
    sys.exit(1)


out = []
stage = 0
stage_lines = [
        "<rdf:li",
        "darktable:operation=\"levels\"",
        "darktable:enabled",
        "darktable:modversion",
        "darktable:params"
    ]


fin = open(sys.argv[1])
while True:
    line = fin.readline()
    if line == "":
        break
    linestrip = line.strip()
    lineseg = linestrip.split("=")

    if stage == 0 and linestrip == stage_lines[0]:
        stage = 1
        out.append(line)
        continue

    if stage == 1 and linestrip == stage_lines[1]:
        stage = 2
        out.append(line)
        continue

    if stage == 2 and lineseg[0] == stage_lines[2]:
        stage = 3
        out.append(line)
        continue

    if stage == 3 and lineseg[0] == stage_lines[3]:
        stage = 4
        out.append(line)
        continue

    if stage == 4 and lineseg[0] == stage_lines[4]:
        stage = 0
        paramhex_pre = lineseg[1][1:33]
        paramhex = lineseg[1][-25:-1]
        infloathex1 = paramhex[0:8]
        infloathex2 = paramhex[8:16]
        infloathex3 = paramhex[16:24]
        infloat1 = struct.unpack('<f', bytes.fromhex(infloathex1))[0]
        infloat2 = struct.unpack('<f', bytes.fromhex(infloathex2))[0]
        infloat3 = struct.unpack('<f', bytes.fromhex(infloathex3))[0]
        outfloat1 = 1.0 - infloat3
        outfloat2 = 1.0 - infloat2
        outfloat3 = 1.0 - infloat1
        outfloathex1 = hex(struct.unpack('>I', struct.pack('<f', outfloat1))[0])[2:].rjust(8, '0')
        outfloathex2 = hex(struct.unpack('>I', struct.pack('<f', outfloat2))[0])[2:].rjust(8, '0')
        outfloathex3 = hex(struct.unpack('>I', struct.pack('<f', outfloat3))[0])[2:].rjust(8, '0')
        out.append("      %s=\"%s%s%s%s\"\n" % (lineseg[0], paramhex_pre, outfloathex1, outfloathex2, outfloathex3,))
        continue

    stage = 0
    out.append(line)
fin.close()


fout = open(sys.argv[1], "w")
for line in out:
    fout.write(line)
fout.close()