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

with lib;

let
  cfg = config.services.borgbackup;

  targetOptions = {
    options = {
      repo = mkOption {
        type = types.str;
      };
    
      paths = mkOption {
        type = types.listOf types.str;
        default = [];
      };

      prune = mkOption {
        type = types.attrsOf (types.listOf types.str);
        default = {};
      };

      interval = mkOption {
        type = types.str;
        default = "6h";
      };

      lock = mkOption {
        type = types.nullOr types.str;
        default = "backup";
      };

      network = mkOption {
        type = types.bool;
        default = true;
      };
    };
  };
in {
  options = {
    services.borgbackup = {
      snapshots = mkOption {
        type = types.nullOr (types.enum ["btrfs"]);
        default = null;
      };

      targets = mkOption {
        type = types.attrsOf (types.submodule targetOptions);
        default = {};
      };

      prefix = mkOption {
        type = types.str;
      };
    };
  };

  config = mkIf (any (t: t.paths != []) (attrValues cfg.targets)) {
    services.btrfs-snapshots.enable = mkIf (cfg.snapshots == "btrfs") true;
  
    systemd.timers = (listToAttrs (map ({ target, path, tCfg }: nameValuePair "borgbackup-${target}-${path}" {
      wantedBy = [ "timers.target" ];

      timerConfig = {
        Persistent = false;
        OnBootSec = tCfg.interval;
        OnUnitInactiveSec = tCfg.interval;
      };
    }) (flatten (mapAttrsToList (target: tCfg: map (path: { inherit target path tCfg; }) tCfg.paths) cfg.targets)))) // (mapAttrs (target: tCfg: nameValuePair "borgbackup-prune-${target}" {
      wantedBy = [ "timers.target" ];

      timerConfig = {
        Persistent = false;
        OnBootSec = tCfg.interval;
        OnUnitInactiveSec = tCfg.interval;
      };
    }) cfg.targets);

    systemd.services = (mapAttrs (target: tCfg: nameValuePair "borgbackup-${target}@" (let
      deps = flatten [
        (optional (cfg.snapshots == "btrfs") "btrfs-snapshot@%p.service")
        (optional tCfg.network "network-online.target")
      ];
    in {
      bindsTo = deps;
      after = deps;

      path = with pkgs; [borgbackup] ++ optional (tCfg.lock != null) utillinux;

      script = let
        borgCmd = ''
          borg create \
            --lock-wait 600 \
            --stats \
            --list \
            --filter 'AME' \
            --exclude-caches \
            --keep-exclude-tags \
            --patterns-from .backup \
            --one-file-system \
            --compression auto,lzma \
            ${tCfg.repo}::${cfg.prefix}$1-{utcnow}
        '';
      in if tCfg.lock == null then borgCmd else "flock -xo /var/lock/${tCfg.lock} ${borgCmd}";
      scriptArgs = "%i";

      unitConfig = {
        AssertPathIsDirectory = mkIf (tCfg.lock != null) "/var/lock";
      };

      serviceConfig = {
        Type = "oneshot";
        WorkingDirectory = if (cfg.snapshots == null) then "%p" else "/mnt/snapshot-%i";
        Nice = 15;
        IOSchedulingClass = 2;
        IOSchedulingPriority = 7;
        SuccessExitStatus = [1 2];
      };
    })) cfg.targets) // (mapAttrs (target: tCfg: nameValuePair "borgbackup-prune-${target}" {
      bindsTo = "network-online.target";
      after = "network-online.target";

      script = concatStringsSep "\n" (mapAttrsToList (path: args: ''
        borg prune \
          --prefix "${cfg.prefix}${path}" \
          ${concatStringsSep " " args} \
          ${tCfg.repo}
      '') tCfg.prune);

      serviceConfig = {
        Type = "oneshot";
      };
    }) cfg.targets);
  };
}