{
  description = "A naersk based rust flake";

  inputs = {
    utils.url = "github:numtide/flake-utils";
    naersk = {
      url = "github:nix-community/naersk";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    index = {
      flake = false;
      url = "github:rust-lang/crates.io-index";
    };
  };

  outputs =
    {
      self,
      nixpkgs,
      utils,
      naersk,
      index,
    }:
    let
      crate = self.lib.crate "bat";
      pname = crate.latest.name;
      filterAttrs =
        pred: set:
        builtins.removeAttrs set (builtins.filter (name: !pred name set.${name}) (builtins.attrNames set));
      forPkgs = pkgs: rec {
        # # `nix build`
        # packages.${pname} = crate.latest.package { inherit pkgs; };

        # # `nix run`
        # apps.${pname} = utils.lib.mkApp {
        #   drv = packages.${pname};
        # };
        # defaultApp = apps.${pname};
      };
      forSystem = system: forPkgs nixpkgs.legacyPackages."${system}";
    in
    (utils.lib.eachDefaultSystem forSystem)
    // rec {
      packages.crates_io =
        let
          traverse =
            path: levels:
            let
              entries = (builtins.readDir path);
              filterTy = t: builtins.attrNames (filterAttrs (_: ty: ty == t) entries);
              dirs = filterTy "directory";
              crateDirs = builtins.filter (dir: (builtins.substring 0 1 dir) != ".") dirs;
              files = filterTy "regular";
            in
            if levels == 0 then
              map (name: "${path}/${name}") files
            else
              builtins.concatLists (map (dir: traverse "${path}/${dir}" (levels - 1)) crateDirs);
          cratePaths = traverse "${index}" 2;
          crateVersions =
            path:
            let
              meta = builtins.readFile path;
              metaLines = builtins.split "\n" meta;
              versionsLines = builtins.filter (l: builtins.isString l && builtins.stringLength l > 10) metaLines;
              versionsMeta = map builtins.fromJSON versionsLines;
              versions = map (
                meta:
                let
                  inherit (meta) vers;
                in
                {
                  name = vers;
                  value = meta // {
                    build = lib.buildCrate meta;
                  };
                }
              ) versionsMeta;
            in
            (
              (builtins.listToAttrs versions)
              // {
                "latest" = (builtins.elemAt versions (builtins.length versions - 1)).value;
              }
            );
          crateNames = map baseNameOf cratePaths;
        in
        builtins.listToAttrs (
          map (path: {
            name = baseNameOf (builtins.unsafeDiscardStringContext path);
            value = crateVersions path;
          }) cratePaths
        );
      lib = rec {
        config = builtins.fromJSON (builtins.readFile "${index}/config.json");
        buildCrate =
          meta:
          extra@{ pkgs, ... }:
          let
            naersk-lib = naersk.lib."${pkgs.system}";
          in
          naersk-lib.buildPackage (
            (removeAttrs extra [ "pkgs" ])
            // {
              root = pkgs.runCommandLocal "unpack-${meta.name}" { } ''
                mkdir -p $out
                tar xzvf ${meta.tarball} -C $out --strip-components=1
              '';
            }
          );
        crate =
          name:
          let
            dbg = val: builtins.trace val val;
            strlen = builtins.stringLength;
            substr = builtins.substring;
            path =
              if strlen name < 4 then
                "${toString (strlen name)}/${substr 0 1 name}/${name}"
              else
                "${substr 0 2 name}/${substr 2 2 name}/${name}";
            versions =
              builtins.foldl'
                (
                  p: i:
                  let
                    meta = i // rec {
                      url = "${config.dl}/${name}/${i.vers}/download";
                      package = buildCrate meta;
                      tarball = builtins.fetchurl {
                        inherit url;
                        sha256 = i.cksum;
                      };
                    };
                  in
                  p
                  // {
                    latest = meta;
                    "${i.vers}" = meta;
                  }
                )
                { }
                (
                  map builtins.fromJSON (
                    builtins.filter (s: builtins.isString s && strlen s > 0) (
                      builtins.split "\n" (builtins.readFile "${index}/${path}")
                    )
                  )
                );
          in
          versions;
      };
    };

}