# ThinkPad battery charge limiter (native sysfs thresholds).
#
# Unlike the HP module (modules/hardware/hp-battery-limit.nix), ThinkPad
# firmware exposes the battery charge thresholds directly via sysfs:
#
#   /sys/class/power_supply/BAT0/charge_control_start_threshold  (resume point)
#   /sys/class/power_supply/BAT0/charge_control_end_threshold    (stop point)
#
# Writing a value < 100 to the end threshold stops charging at that capacity;
# charging resumes once capacity drops to/below the start threshold. The EC
# persists these across reboots (firmware NVRAM), so unlike the HP /proc magic
# no periodic poller is required — a one-shot `apply` at boot re-asserts the
# persisted choice in case the firmware was reset.
#
# Control from the shell / CLI (same interface as the HP module, so the
# QuickShell cog can drive either host):
#   battery-charge-limit on|off|status|apply
# `on`/`off` persist the choice to /var/lib/battery-charge-limit/state and are
# applied immediately. petere has NOPASSWD sudo so the QuickShell cog can call
# `sudo battery-charge-limit on/off` directly.
{
  config,
  lib,
  pkgs,
  ...
}:

let
  cfg = config.my.hardware.thinkpadBatteryLimit;

  stateDir = "/var/lib/battery-charge-limit";
  stateFile = "${stateDir}/state";

  sysfs = "/sys/class/power_supply/BAT0";

  controlScript = pkgs.writeShellScriptBin "battery-charge-limit" ''
    set -eu

    state_dir=${stateDir}
    state_file=${stateFile}
    start_threshold=${sysfs}/charge_control_start_threshold
    end_threshold=${sysfs}/charge_control_end_threshold
    capacity=${sysfs}/capacity

    stop_at=${toString cfg.stopAt}
    resume_at=${toString cfg.resumeAt}

    read_end_threshold() {
      cat "$end_threshold" 2>/dev/null || echo 100
    }

    ensure_state() {
      mkdir -p "$state_dir"
      if [ ! -f "$state_file" ]; then
        # Infer the current firmware state so the toggle reflects reality on
        # first run (e.g. a limit set from BIOS/Vantage persists in the EC).
        if [ "$(read_end_threshold)" -lt "$stop_at" ]; then
          echo on > "$state_file"
        else
          echo off > "$state_file"
        fi
      fi
    }

    get_state() {
      ensure_state
      cat "$state_file"
    }

    apply_policy() {
      local state
      state=$(get_state)
      case "$state" in
        on)
          # Enable the limit: resume charging below resume_at, stop at stop_at.
          echo "$resume_at" > "$start_threshold"
          echo "$stop_at" > "$end_threshold"
          ;;
        *)
          # off (or unknown) -> full charge range (0..100).
          echo 0 > "$start_threshold"
          echo 100 > "$end_threshold"
          ;;
      esac
    }

    case "$1" in
      on)
        ensure_state
        echo on > "$state_file"
        apply_policy
        echo on
        ;;
      off)
        ensure_state
        echo off > "$state_file"
        apply_policy
        echo off
        ;;
      status)
        get_state
        ;;
      apply)
        apply_policy
        ;;
      *)
        echo "usage: battery-charge-limit {on|off|status|apply}" >&2
        exit 2
        ;;
    esac
  '';
in
{
  options.my.hardware.thinkpadBatteryLimit = {
    enable = lib.mkEnableOption "ThinkPad battery charge limiter (stop charging at stopAt%, re-enable below resumeAt%).";
    stopAt = lib.mkOption {
      type = lib.types.int;
      default = 80;
      description = "Charge capacity % at which charging is inhibited (charge_control_end_threshold).";
    };
    resumeAt = lib.mkOption {
      type = lib.types.int;
      default = 75;
      description = "Charge capacity % below which auto charging is re-enabled (charge_control_start_threshold).";
    };
  };

  config = lib.mkIf cfg.enable {
    environment.systemPackages = [ controlScript ];

    # One-shot re-assert at boot (ThinkPad EC persists thresholds, so no
    # poller is needed; this only recovers from firmware resets).
    systemd.services.battery-charge-limit = {
      description = "ThinkPad battery charge limiter (${toString cfg.stopAt}% cap)";
      wantedBy = [ "multi-user.target" ];
      serviceConfig = {
        Type = "oneshot";
        RemainAfterExit = true;
        ExecStart = "${controlScript}/bin/battery-charge-limit apply";
      };
    };
  };
}