{ config, lib, pkgs, ... }:

let
  cfg = config.gortium.poup16t;
  luksName = cfg.luksName;
in
with lib;

{
  options.gortium.poup16t = {
    enable = mkEnableOption "Poup_16T storage disk (btrfs + LUKS + btrbk snapshots)";

    luksUuid = mkOption {
      type = types.str;
      description = ''
        UUID of the LUKS partition on the 16TB disk (WD Red Pro).

        Find this by running as root when the disk is connected:
          blkid /dev/sdb   # or wherever the disk appears
          lsblk -o NAME,SIZE,FSTYPE,UUID

        Since btrfs is inside LUKS, the FS UUID is hidden — use the
        LUKS partition UUID from blkid (it'll show TYPE=\"crypto_LUKS\").
      '';
      example = "00000000-0000-0000-0000-000000000000";
    };

    luksName = mkOption {
      type = types.str;
      default = "poup_16t";
      description = "Name for the LUKS /dev/mapper/ mapping";
    };

    mountPoint = mkOption {
      type = types.str;
      default = "/mnt/Poup_16T";
      description = "Mount point for the 16TB data disk";
    };

    btrfsOptions = mkOption {
      type = types.listOf types.str;
      default = [ "defaults" "noatime" "compress=zstd:3" "nofail" ];
      description = "Mount options for the btrfs filesystem. 'nofail' ensures boot succeeds when disk is disconnected.";
    };

    btrbk = {
      enable = mkOption {
        type = types.bool;
        default = true;
        description = "Enable btrbk snapshot management on this volume";
      };

      schedule = mkOption {
        type = types.str;
        default = "daily";
        description = "systemd calendar event for btrbk (e.g. 'daily', 'hourly', '*-*-* 00:00:00')";
      };

      preserveMin = mkOption {
        type = types.str;
        default = "2d";
        description = "btrbk snapshot_preserve_min — minimum age before pruning";
      };

      preserve = mkOption {
        type = types.str;
        default = "14d 4w 3m";
        description = "btrbk snapshot_preserve — retention policy (daily, weekly, monthly)";
      };

      snapshotDir = mkOption {
        type = types.str;
        default = ".snapshots";
        description = "Directory name for snapshots relative to volume root";
      };
    };
  };

  config = mkIf cfg.enable {
    # Enable btrfs kernel support (no DKMS needed — it's in-tree)
    boot.supportedFilesystems = [ "btrfs" ];

    # Install btrfs administration tools
    environment.systemPackages = with pkgs; [
      btrfs-progs       # mkfs.btrfs, btrfs, fsck, balance, scrub
      btrbk             # Snapshot management + rotation
    ];

    # LUKS2 unlock at boot (uses keyfile or prompts if unavailable)
    # Since the disk may be disconnected, initrd times out gracefully (~30s)
    boot.initrd.luks.devices.${luksName} = {
      device = "/dev/disk/by-uuid/${cfg.luksUuid}";
      preLVM = false;
      allowDiscards = true;
    };

    # Mount the unlocked mapper device as btrfs
    fileSystems.${cfg.mountPoint} = {
      device = "/dev/mapper/${luksName}";
      fsType = "btrfs";
      options = cfg.btrfsOptions;
    };

    # btrbk — automated snapshot creation and rotation
    services.btrbk = mkIf cfg.btrbk.enable {
      instances.poup16t = {
        onCalendar = cfg.btrbk.schedule;
        settings = {
          snapshot_preserve_min = cfg.btrbk.preserveMin;
          snapshot_preserve = cfg.btrbk.preserve;

          volume.${cfg.mountPoint} = {
            snapshot_create = "always";
            snapshot_dir = cfg.btrbk.snapshotDir;
            subvolume = ".";
          };
        };
      };
    };
  };
}