"""The ``earner-bonus.path`` unit: apply a flat bonus the moment it is earned.

The live bonus pass used to run only on the 15-minute ``workout-sync`` timer,
so a LeetCode solve could wait a quarter of an hour for its shutdown hour
while the gaming hour landed in seconds (2026-10-06). The path unit watches
every flat earner's ledger and starts ``earner-bonus.service``
(``--apply-bonuses``) when a gate writes one.

The watch list is rendered from the ``earned_time`` registry, not kept by
hand. Re-pinning the registry is a pip install that never re-runs the
installer, so :func:`sync_path_unit` -- called from every ``--sync-only``
pass -- rewrites an installed unit that has drifted from the registry. A new
earner is watched within 15 minutes with no step to remember.

``PathChanged=`` and not ``PathModified=``: the gates write a temp file and
rename it into place, which ``PathChanged`` sees, including the first write
into a directory that does not exist yet. ``PathModified`` would also fire
mid-write on a gate that writes in place, and a half-written ledger reads as
"could not check".
"""

from __future__ import annotations

import logging
from pathlib import Path
import subprocess
import sys
from typing import Final

from screen_locker._earned import ledger_file, watched_earners

__all__ = ["PATH_UNIT_NAME", "USER_UNIT_DIR", "render_path_unit", "sync_path_unit"]

_logger = logging.getLogger(__name__)

PATH_UNIT_NAME: Final = "earner-bonus.path"
USER_UNIT_DIR: Final = Path.home() / ".config" / "systemd" / "user"

_HEADER: Final = """\
# Generated by screen_locker._earner_units from the earned_time registry.
# Do not edit: the next --sync-only pass rewrites a unit that has drifted.
[Unit]
Description=Apply a flat earner's shutdown bonus as soon as its ledger changes

[Path]
"""
_FOOTER: Final = """
[Install]
WantedBy=default.target
"""


def render_path_unit() -> str:
    """The unit text: one ``PathChanged=`` per gate earner's ledger.

    Every registry's gates, not just today's (``watched_earners``), so a
    dated cutover (the Automation tutor's ``TUTOR_FROM``) needs no re-render
    on the day. The header keeps saying "flat": changing it would rewrite the
    installed unit for no behavioural change.
    """
    ledgers = dict.fromkeys(ledger_file(e) for e in watched_earners())
    watches = "".join(f"PathChanged={path}\n" for path in ledgers)
    return _HEADER + watches + _FOOTER


def sync_path_unit(unit_dir: Path | None = None) -> bool:
    """Rewrite an installed path unit that no longer matches the registry.

    An absent unit is left absent: it was never installed, or it was removed
    on purpose, and installing units is the installer's job. *unit_dir*
    defaults to :data:`USER_UNIT_DIR`, read at call time.

    Returns True if the unit was rewritten.
    """
    unit = (unit_dir or USER_UNIT_DIR) / PATH_UNIT_NAME
    if not unit.is_file():
        return False
    wanted = render_path_unit()
    try:
        if unit.read_text(encoding="utf-8") == wanted:
            return False
        unit.write_text(wanted, encoding="utf-8")
        subprocess.run(
            ["/usr/bin/systemctl", "--user", "daemon-reload"],
            check=True,
            capture_output=True,
        )
    except (OSError, subprocess.CalledProcessError) as exc:
        _logger.warning(
            "%s differs from the earner registry and could not be refreshed: %s"
            " -- a newly registered earner waits for the 15-minute sync",
            unit,
            exc,
        )
        return False
    _logger.warning(
        "%s was out of date with the earner registry; rewritten and reloaded",
        unit,
    )
    return True


if __name__ == "__main__":
    # install_systemd.sh / arm.sh: write the unit into the given directory.
    target = Path(sys.argv[1]) / PATH_UNIT_NAME
    target.write_text(render_path_unit(), encoding="utf-8")