cache.nix

# usage: cache = import ./cache.nix { pkgs, stackYaml = ./stack.yaml; }
let sources = import ../nix/sources.nix;
in { pkgs ? import sources.nixpkgs { }, stackYaml ? ./stack.yaml }:
let
  s2n = import "${sources.stack-to-nix}/lib.nix" pkgs;
  deps = (s2n.importYAML stackYaml).extra-deps or [ ];
  hashPath = path: pkgs.runCommand "hash-path" {
    preferLocalBuild = true;
  } ''
    echo -n \'\'$(${pkgs.nix}/bin/nix-hash --type sha256 --base32 ${path})\'\' > $out
  '';
in with pkgs.lib;
concatMap (dep:
  if isString dep then
    [ ]
  else
    let
      pkgsrc = builtins.fetchGit {
        url = dep.git;
        ref = "*";
        rev = dep.commit;
      };
    in map (subdir:
      {
        name = s2n.cabalPackageName "${pkgsrc}/${subdir}";
        rev = dep.commit;
        url = dep.git;
        sha256 = import (hashPath pkgsrc);
      } // (optionalAttrs (subdir != "") { inherit subdir; }))
    (dep.subdirs or [ "" ])) deps