#!/usr/bin/env python3

# Copyright (C) 2023 Matheus Tavares
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

import hashlib, zlib, os, time

def write_obj(objtype, content):
    '''
    Writes the loose object to the git object data base and returns
    its sha1 object. The content must be a byte stream.
    '''
    data = f"{objtype} {len(content)}\0".encode() + content
    sha1 = hashlib.sha1(data)
    hex_sha1 = sha1.hexdigest()
    path = f".git/objects/{hex_sha1[:2]}/{hex_sha1[2:]}"
    os.makedirs(os.path.dirname(path), exist_ok=True)
    with open(path, "wb") as f:
        f.write(zlib.compress(data))
    return sha1

def write_blob(content):
    return write_obj("blob", content.encode())

def write_tree(filenames, hashes):
    mode = 100644
    entries = b""
    for name, hash in zip(filenames, hashes):
        entries += f"{mode} {name}\0".encode() + hash
    return write_obj("tree", entries)

def write_commit(tree_sha1, parents, author, committer, msg):
    content = f"tree {tree_sha1}\n"
    for parent in parents:
        content += f"parent {parent}\n"
    content += f"author {author} {int(time.time())} {time.strftime('%z')}\n"
    content += f"committer {committer} {int(time.time())} {time.strftime('%z')}\n"
    content += "\n"
    content += msg
    return write_obj("commit", content.encode())

def write_branch(name, hash):
    with open(f".git/refs/heads/{name}", "w") as f:
        f.write(hash)

# First commit
author = "John Doe <john@doe>"
blob1_sha1 = write_blob("This is a simple README file\n")
tree1_sha1 = write_tree(["README"], [blob1_sha1.digest()])
commit1_sha1  = write_commit(tree1_sha1.hexdigest(), [], author, author,
                            "Add the README file")

# Second commit
blob2_sha1 = write_blob("This is a simple README file\nWith one extra line\n")
tree2_sha1 = write_tree(["README"], [blob2_sha1.digest()])
commit2_sha1  = write_commit(tree2_sha1.hexdigest(), [commit1_sha1.hexdigest()],
                             author, author, "Add another line to README")

# Create branch
write_branch("my_branch", commit2_sha1.hexdigest())
print("Created 'my_branch'")