# Auto time-of-day theme switch (BACKLOG #79, VISION § D). A user timer
# runs `nomarchy-state-sync auto` at the configured sunrise and sunset,
# which reads settings.autoTheme = { enable, day, night, sunrise, sunset }
# from the state file and applies the day or night preset for the current
# clock — through the SAME one engine as a manual `apply` (no second
# pipeline).
#
# The trigger times are BAKED into OnCalendar at rebuild (originally this
# was a 15-min poll; exact times won on wasted wakeups — Bernardo
# 2026-07-18), so a time edit must rebuild: the menu's Sunrise/Sunset
# writes run `auto --force`, whose apply is that rebuild. Missed
# transitions are covered without polling: Persistent=true catches ones
# that pass while powered off, systemd fires elapsed OnCalendar timers on
# resume from suspend, and OnStartupSec settles the theme just after
# login. The command self-gates (no-op when disabled) and is idempotent
# (it only rebuilds when the active theme actually needs to change), so
# every extra firing is cheap.
#
# Install is gated on the state flag (like nomarchy.updates gates on its
# enable), so a machine not using the feature carries no timer; enabling
# it from the menu (slice 3) writes the flag + rebuilds, which is what
# brings the timer into being.
{ config, lib, pkgs, ... }:

let
  at = config.nomarchy.settings.autoTheme or { };
  # "HH:MM" or the fallback — mirrors _hhmm_to_min in nomarchy-state-sync,
  # so a hand-edited state can't bake an OnCalendar systemd rejects.
  hhmm = v: fallback:
    if builtins.isString v
       && builtins.match "([01][0-9]|2[0-3]):[0-5][0-9]" v != null
    then v else fallback;
in
lib.mkIf (at.enable or false) {
  systemd.user.services.nomarchy-auto-theme = {
    Unit.Description = "Apply the day/night theme for the current time";
    Service = {
      Type = "oneshot";
      # The rebuild (`home-manager switch`) and its tools resolve from the
      # system + per-user profiles — same PATH shape nomarchy-updates uses.
      Environment = "PATH=/run/current-system/sw/bin:/etc/profiles/per-user/${config.home.username}/bin";
      ExecStart = "${pkgs.nomarchy-state-sync}/bin/nomarchy-state-sync auto";
    };
  };

  systemd.user.timers.nomarchy-auto-theme = {
    Unit.Description = "Day/night theme switch at sunrise and sunset";
    Timer = {
      OnStartupSec = "1min";   # settle on the right theme shortly after login
      OnCalendar = [
        "*-*-* ${hhmm (at.sunrise or null) "07:00"}:00"  # sunrise → day
        "*-*-* ${hhmm (at.sunset  or null) "20:00"}:00"  # sunset  → night
      ];
      Persistent = true;       # catch a transition missed while powered off
    };
    Install.WantedBy = [ "timers.target" ];
  };
}