let
  # sources.nix contains information about which versions of some of our
  # dependencies we should use.  since we use it to pin nixpkgs, all the rest
  # of our dependencies are *also* pinned - indirectly.
  #
  # sources.nix is managed using a tool called `niv`.  as an example, to
  # update to the most recent version of nixpkgs from the 21.11 maintenance
  # release, in the top-level tahoe-lafs checkout directory you run:
  #
  #   niv update nixpkgs-21.11
  #
  # niv also supports chosing a specific revision, following a different
  # branch, etc.  find complete documentation for the tool at
  # https://github.com/nmattia/niv
  sources = import nix/sources.nix;
in
{
  pkgsVersion ? "nixpkgs-22.11" # a string which chooses a nixpkgs from the
                                # niv-managed sources data

, pkgs ? import sources.${pkgsVersion} { } # nixpkgs itself

, pythonVersion ? "python310" # a string choosing the python derivation from
                              # nixpkgs to target

, extrasNames ? [ "tor" "i2p" ] # a list of strings identifying tahoe-lafs extras,
                                # the dependencies of which the resulting
                                # package will also depend on.  Include all of the
                                # runtime extras by default because the incremental
                                # cost of including them is a lot smaller than the
                                # cost of re-building the whole thing to add them.

}:
with (pkgs.${pythonVersion}.override {
  packageOverrides = self: super: {
    # Some dependencies aren't packaged in nixpkgs so supply our own packages.
    pycddl = self.callPackage ./nix/pycddl.nix { };
    txi2p = self.callPackage ./nix/txi2p.nix { };
  };
}).pkgs;
callPackage ./nix/tahoe-lafs.nix {
  # Select whichever package extras were requested.
  inherit extrasNames;

  # Define the location of the Tahoe-LAFS source to be packaged.  Clean up as
  # many of the non-source files (eg the `.git` directory, `~` backup files,
  # nix's own `result` symlink, etc) as possible to avoid needing to re-build
  # when files that make no difference to the package have changed.
  tahoe-lafs-src = pkgs.lib.cleanSource ./.;

  doCheck = false;
}