diff --git a/gcmtool.py b/gcmtool.py
new file mode 100644
index 0000000..71aceaa
--- /dev/null
+++ b/gcmtool.py
@@ -0,0 +1,214 @@
+#!/usr/bin/env python3
+from pathlib import Path
+
+
+__version__ = "0.0.1"
+__author__ = "rigodron, algoflash, GGLinnk"
+__license__ = "MIT"
+__status__ = "developpement"
+
+
+DVD_MAGIC = b"\xC2\x33\x9F\x3D"
+FST_TYPE_FILE = 0
+FST_TYPE_DIR = 1
+
+
+######################################################################
+# Todo : add logging ; add extension check ; add --verbose ; add --disable-ignore
+# -> test it on random iso and check that it's the same than dolphin extract
+# -> test it !!!!
+# Add FST rebuild ;
+# add info on unused randoms bytes on initial DVD iso file
+# -> that's why repack iso is different from initial iso
+######################################################################
+class Dol:
+    # Get total length using the sum of the 18 sections length and dol header length (0x100)
+    def getDolLen(self, dolheader_data:bytes):
+        dol_len = 0x100
+        for i in range(18):
+            dol_len += int.from_bytes(dolheader_data[0x90+i*4:0x90+(i+1)*4], "big", signed=False)
+        return dol_len
+
+
+# https://sudonull.com/post/68549-Gamecube-file-system-device
+class GCM:
+    def unpack(self, iso_path:Path):
+        with iso_path.open("rb") as iso_file:
+            bootbin_data = iso_file.read(0x440)
+            if bootbin_data[0x1c:0x20] != DVD_MAGIC:
+                raise Exception("Invalid DVD format - this tool is for ISO/GCM files")
+            bi2bin_data = iso_file.read(0x2000)
+
+            # https://www.gc-forever.com/wiki/index.php?title=Apploader
+            # -> Full apploader size is sum of size and trailerSize, rounded up to 32 bytes.
+            iso_file.seek(0x2454)
+            size = int.from_bytes(iso_file.read(4), "big", signed=False)
+            trailerSize = int.from_bytes(iso_file.read(4), "big", signed=False)
+            
+            # Dolphin Emulator add 32 Null bytes at the end of the extracted apploader.img
+            apploader_size = size + trailerSize + 32
+            
+            iso_file.seek(0x2440)
+            apploaderimg_data = iso_file.read(apploader_size)
+
+            print( 0x2440 + apploader_size )
+            print("fst.bin :", int.from_bytes(bootbin_data[0x424:0x428],"big", signed=False), int.from_bytes(bootbin_data[0x428:0x42c],"big", signed=False))
+            
+            iso_file.seek( int.from_bytes(bootbin_data[0x424:0x428],"big", signed=False) )
+            fstbin_data = iso_file.read( int.from_bytes(bootbin_data[0x428:0x42c],"big", signed=False) )
+
+            dol_offset = int.from_bytes(bootbin_data[0x420:0x424],"big", signed=False)
+            iso_file.seek( dol_offset )
+            dol = Dol()
+            dolheader_data = iso_file.read(0x100)
+            bootdol_data = dolheader_data + iso_file.read( dol.getDolLen( dolheader_data ) - 0x100 )
+            print("dol :", dol_offset, dol.getDolLen( dolheader_data ))
+            base_path = Path(f"{bootbin_data[:4].decode('utf-8')}-{int.from_bytes(bootbin_data[6:7], 'little', signed=False):02}")
+            sys_path = base_path / "sys"
+            sys_path.mkdir(parents=True, exist_ok=True)
+
+            with (sys_path / "boot.bin").open("wb") as bootbin_file, \
+                 (sys_path / "bi2.bin" ).open("wb") as bi2bin_file, \
+                 (sys_path / "fst.bin").open("wb") as fstbin_file, \
+                 (sys_path / "apploader.img").open("wb") as apploaderimg_file,\
+                 (sys_path / "boot.dol").open("wb") as bootdol_file :
+                bootbin_file.write(bootbin_data)
+                bi2bin_file.write(bi2bin_data)
+                fstbin_file.write(fstbin_data)
+                apploaderimg_file.write(apploaderimg_data)
+                bootdol_file.write(bootdol_data)
+            root_path = base_path / "root"
+            root_path.mkdir(exist_ok=True)
+            
+            # And now we parse FST data to unpack all files in the GCM iso file
+            dir_index_path = {0: root_path}
+            currentdir_path = root_path
+
+            # root: index=0 so nextdir is the end
+            nextdir = int.from_bytes(fstbin_data[8:12], "big", signed=False)
+            # offset of filenames block
+            base_names = nextdir * 12
+            # go to parent when index reach next dir
+            nextdir_arr = [ nextdir ]
+
+            for index in range(1, base_names // 12):
+                i = index * 12
+                file_type = int.from_bytes(fstbin_data[i:i+1], "big", signed=False)
+                name = fstbin_data[base_names + int.from_bytes(fstbin_data[i+1:i+4], "big", signed=False):].split(b"\x00")[0].decode("utf-8")
+                
+                while index == nextdir_arr[-1]:
+                    currentdir_path = currentdir_path.parent
+                    nextdir_arr.pop()
+
+                if file_type == FST_TYPE_DIR:
+                    nextdir = int.from_bytes(fstbin_data[i+8:i+12], "big", signed=False)
+                    parentdir = int.from_bytes(fstbin_data[i+4:i+8], "big", signed=False)
+
+                    nextdir_arr.append( nextdir )
+                    currentdir_path = dir_index_path[parentdir] / name
+                    dir_index_path[index] = currentdir_path
+                    currentdir_path.mkdir(exist_ok=True)
+                else:
+                    fileoffset = int.from_bytes(fstbin_data[i+4:i+8], "big", signed=False)
+                    filesize   = int.from_bytes(fstbin_data[i+8:i+12], "big", signed=False)
+
+                    with (currentdir_path / name).open("wb") as new_file:
+                        iso_file.seek(fileoffset)
+                        new_file.write( iso_file.read(filesize) )
+                        print("file :", fileoffset, filesize)
+    def pack(self, folder_path:Path, iso_path:Path = None):
+        if iso_path == None:
+            iso_path = folder_path.parent / Path(folder_path.name).with_suffix(".iso")
+        with iso_path.open("wb") as iso_file, \
+             (folder_path / "sys" / "boot.bin").open("rb") as bootbin_file, \
+             (folder_path / "sys" / "bi2.bin" ).open("rb") as bi2bin_file, \
+             (folder_path / "sys" / "fst.bin").open("rb") as fstbin_file, \
+             (folder_path / "sys" / "apploader.img").open("rb") as apploaderimg_file,\
+             (folder_path / "sys" / "boot.dol").open("rb") as bootdol_file :
+            bootbin_data = bootbin_file.read()
+            iso_file.write( bootbin_data )
+            iso_file.write(bi2bin_file.read())
+            iso_file.write(apploaderimg_file.read())
+
+            fstbin_offset = int.from_bytes(bootbin_data[0x424:0x428],"big", signed=False)
+            fstbin_len = int.from_bytes(bootbin_data[0x428:0x42c],"big", signed=False)
+            if (folder_path / "sys" / "fst.bin").stat().st_size != fstbin_len:
+                raise Exception("Invalid fst.bin size in boot.bin offset 0x428:0x42c!")
+            iso_file.seek( fstbin_offset )
+            fstbin_data = fstbin_file.read()
+            iso_file.write( fstbin_data )
+            
+            dol_offset = int.from_bytes(bootbin_data[0x420:0x424],"big", signed=False)
+            iso_file.seek( dol_offset )
+            iso_file.write( bootdol_file.read() )
+
+            # Now parse fst.bin for writing files in the iso
+            dir_index_path = {0: folder_path / "root"}
+            currentdir_path = folder_path / "root"
+
+            # root: index=0 so nextdir is the end
+            nextdir = int.from_bytes(fstbin_data[8:12], "big", signed=False)
+            # offset of filenames block
+            base_names = nextdir * 12
+            # go to parent when index reach next dir
+            nextdir_arr = [ nextdir ]
+
+            for index in range(1, base_names // 12):
+                i = index * 12
+                file_type = int.from_bytes(fstbin_data[i:i+1], "big", signed=False)
+                name = fstbin_data[base_names + int.from_bytes(fstbin_data[i+1:i+4], "big", signed=False):].split(b"\x00")[0].decode("utf-8")
+                
+                while index == nextdir_arr[-1]:
+                    currentdir_path = currentdir_path.parent
+                    nextdir_arr.pop()
+
+                if file_type == FST_TYPE_DIR:
+                    nextdir = int.from_bytes(fstbin_data[i+8:i+12], "big", signed=False)
+                    parentdir = int.from_bytes(fstbin_data[i+4:i+8], "big", signed=False)
+
+                    nextdir_arr.append( nextdir )
+                    currentdir_path = dir_index_path[parentdir] / name
+                    dir_index_path[index] = currentdir_path
+                    currentdir_path.mkdir(exist_ok=True)
+                else:
+                    fileoffset = int.from_bytes(fstbin_data[i+4:i+8], "big", signed=False)
+                    filesize   = int.from_bytes(fstbin_data[i+8:i+12], "big", signed=False)
+                    print(fileoffset, filesize)
+
+                    with (currentdir_path / name).open("rb") as new_file:
+                        iso_file.seek(fileoffset)
+                        iso_file.write( new_file.read(filesize) )
+
+
+
+def get_argparser():
+    import argparse
+    parser = argparse.ArgumentParser(description='ISO/GCM packer & unpacker - [GameCube] v' + __version__)
+    parser.add_argument('--version', action='version', version='%(prog)s ' + __version__)
+    parser.add_argument('input_path',  metavar='INPUT', help='')
+    parser.add_argument('output_path', metavar='OUTPUT', help='', nargs='?', default="")
+
+    group = parser.add_mutually_exclusive_group(required=True)
+    group.add_argument('-p', '--pack',   action='store_true', help="-p source_folder (dest_file.iso) : Pack source_folder in new file source_folder.iso or dest_file.iso if specified")
+    group.add_argument('-u', '--unpack', action='store_true', help='-u source_iso.iso (dest_folder) : Unpack the GCM/ISO in new folder source_iso or dest_folder if specified')
+    return parser
+
+
+if __name__ == '__main__':
+    args = get_argparser().parse_args()
+
+    p_input = Path(args.input_path)
+    p_output = Path(args.output_path)
+
+    gcm = GCM()
+
+    if args.pack:
+        logging.info("### Pack")
+        if(p_output == Path(".")):
+            p_output = Path(p_input.with_suffix(".iso"))
+        gcm.pack( p_input, p_output )
+    elif args.unpack:
+        logging.info("### Unpack")
+        if(p_output == Path(".")):
+            p_output = Path(p_input.name)
+        gcm.unpack( p_input, p_output )