#!/usr/bin/python3

from datetime import datetime
from difflib import unified_diff
from typing import List, Union
import random
import string

FAKE_HASH_ALPHABET = string.digits + string.ascii_lowercase[:6]

def diff_strings(old: str, new: str) -> str:
    old += "\n" if old else ""
    new += "\n" if new else ""
    return "".join(list(unified_diff(old.splitlines(keepends=True),
                                     new.splitlines(keepends=True)))[2:])[:-1]

def fake_hash(length: int) -> str:
    return "".join([random.choice(FAKE_HASH_ALPHABET) for i in range(length)])

def styled_date(dt: datetime = None) -> str:
    if not dt:
        dt = datetime.now()

    # res = datetime.strftime(dt, "%a %b %d %H:%M:%S %Y")
    res = dt.ctime()

    offset = dt.astimezone().utcoffset().seconds
    positive = offset >= 0
    hours, minutes = offset // 3600, offset % 3600
    hours, minutes = str(hours).zfill(2), str(minutes).zfill(2)
    sign = "+" if positive else "-"
    res += " " + sign + hours + minutes
    return res

def commit(*, commit_message: Union[List[str], str], branch_name: str = "main",
           old_content: str = None, new_content: str, file: str, name: str,
           email: str, mode: str = "100644", dt: datetime = None) -> str:
    if isinstance(commit_message, str):
        commit_message = [commit_message + "\n"]
    commit_message = [" " * 4 + line if line else "" for line in commit_message]
    if len(commit_message) > 1:
        commit_message.insert(1, "")
    commit_message = "\n".join(commit_message)

    new_file = False
    if old_content is None:
        new_file = True
        old_content = ""

    first_file = "/dev/null" if new_file else file
    second_file = "b/" + file

    first_hash = "0" * 7 if new_file else fake_hash(7)

    index_mode_lines = f"index {first_hash}..{fake_hash(7)}"
    if new_file:
        index_mode_lines = f"""\
new file mode {mode}
{index_mode_lines}"""
    else:
        index_mode_lines += f" {mode}"

    diff = diff_strings(old_content, new_content)

    return f"""\
commit {fake_hash(40)} (HEAD -> {branch_name})
Author: {name} <{email}>
Date:   {styled_date(dt)}

{commit_message}

diff --git {"a/" + file} {second_file}
{index_mode_lines}
--- {first_file}
+++ {second_file}
{diff}"""

example = lambda: commit( \
    commit_message=["Hello, world!", "Greetings :-)", "Lorem ipsum"], \
    # old_content="henlo", \
    new_content="hello", \
    file="message.txt", \
    name="Intel A80486DX2-66", \
    email="larry.holst@disroot.org")

if __name__ == "__main__":
    from sys import argv

    if "--example" in argv:
        print("Example output:")
        print(example())
        raise SystemExit

    print("This script is not interactive. Please run Python 3 interpreter,\n"
          "import this file, and use function git_commit_simulator.commit()")
    print()
    print("""Function prototype:
def commit(*, commit_message: Union[List[str], str], branch_name: str = "main",
           old_content: str = None, new_content: str, file: str, name: str,
           email: str, mode: str = "100644", dt: datetime = None) -> str:""")
    print()
    print("Run with --example to get an example output")