#!/usr/bin/env python3

import copy
import re
import subprocess
import sys


def usage(retval: int) -> None:
    """Output a usage message and exit."""
    if retval == 0:
        file_ = sys.stdout
    else:
        file_ = sys.stderr

    print(f"Usage: {sys.argv[0]} --command cmd --minute 0 --hour 0 --day-of-month 1 --month 1 --day-of-week 1", file=file_)

    sys.exit(retval)


class Options:
    """Deal with command line options."""

    def __init__(self) -> None:
        """Init."""
        self.minute = "*"
        self.hour = "*"
        self.day_of_month = "*"
        self.month = "*"
        self.day_of_week = "*"
        self.full_command = ""

        while sys.argv[1:]:
            if sys.argv[1] == "--minute":
                self.minute = sys.argv[2]
                del sys.argv[1]
            elif sys.argv[1] == "--hour":
                self.hour = sys.argv[2]
                del sys.argv[1]
            elif sys.argv[1] == "--day-of-month":
                self.day_of_month = sys.argv[2]
                del sys.argv[1]
            elif sys.argv[1] == "--month":
                self.month = sys.argv[2]
                del sys.argv[1]
            elif sys.argv[1] == "--day-of-week":
                self.day_of_month = sys.argv[2]
                del sys.argv[1]
            elif sys.argv[1] == "--command":
                self.full_command = sys.argv[2]
                del sys.argv[1]
            elif sys.argv[1] in ("-h", "--help"):
                usage(0)
            else:
                print(f"{sys.argv[0]}: unrecognized option: {sys.argv[1]}", file=sys.stderr)
                usage(1)

            del sys.argv[1]

        all_good = True
        if self.full_command == "":
            all_good = False
            print(f"{sys.argv[0]}: --command is a required option", file=sys.stderr)

        if not all_good:
            print(f"{sys.argv[0]}: One or more items in preflight check failed", file=sys.stderr)
            sys.exit(1)


def read_original_crontab() -> list[str]:
    """Inhale the initial crontab -l, and return it as a list of strings."""
    subp = subprocess.run(["crontab", "-l"], capture_output=True, text=True, check=True)

    lines = subp.stdout.rstrip("\n").splitlines()

    w_newlines = [line + "\n" for line in lines]

    return w_newlines


def modify_crontab(
    *,
    original_crontab,
    minute,
    hour,
    day_of_month,
    month,
    day_of_week,
    full_command,
) -> list[str]:
    """Modify the crontab: if the command already exists, replace it. If the command doesn't yet exist, append it."""
    modified_crontab = copy.deepcopy(original_crontab)
    hits = 0

    # This might be better with shlex?
    command_fields = full_command.split()

    base_command = command_fields[0]
    new_crontab_line = f"{minute} {hour} {day_of_month} {month} {day_of_week} {full_command}\n"
    for lineno, line in enumerate(modified_crontab):
        line_wo_comments = re.sub("#.*$", "", line)
        fields = line_wo_comments.split()
        if fields[5:] and fields[5] == base_command:
            hits += 1
            modified_crontab[lineno] = new_crontab_line

    if hits > 1:
        print(f"{sys.argv[0]}: more than one {base_command} found. Terminating", file=sys.stderr)
        sys.exit(1)

    if hits == 0:
        modified_crontab.append(new_crontab_line)

    return modified_crontab


def write_modified_crontab(crontab_content: list[str]) -> None:
    """Write the modified crontab content to the crontab command (usually /usr/bin/crontab)."""
    subp = subprocess.Popen(
        ["crontab"],  # Replace 'cat' with your target command/program
        stdin=subprocess.PIPE,
        # stdout=subprocess.PIPE,  # Optional: if you want to capture output
        # stderr=subprocess.PIPE,  # Optional: if you want to capture errors
        text=True,
        encoding="utf-8",
    )
    for line in crontab_content:
        subp.stdin.write(line)
    subp.stdin.close()


def main() -> None:
    """Start the ball rolling."""
    options = Options()
    original_crontab = read_original_crontab()
    # print(f"original_crontab: {original_crontab}")
    # modify crontab
    modified_crontab = modify_crontab(
        original_crontab=original_crontab,
        minute=options.minute,
        hour=options.hour,
        day_of_month=options.day_of_month,
        month=options.month,
        day_of_week=options.day_of_week,
        full_command=options.full_command,
    )
    # print(f"modified_crontab: {modified_crontab}")
    write_modified_crontab(modified_crontab)


if __name__ == "__main__":
    main()