# This file pins the version of nixpkgs to a known good version. The nixpkgs is
# imported with an overlay adding Termonad. It is imported from various other
# files.

{ # String representing a GHC version to use.  Normally something like
  # "ghc865".  If null, then use a known-working GHC version.
  compiler ? null
, # A path to nixpkgs.  This will be imported.  If null, use a known-working
  # nixpkgs version.
  nixpkgs ? null
, # Additional overlays to apply when importing nixpkgs.
  additionalOverlays ? []
, # Build all the examples bundled with termonad.  Normally this is only used
  # in CI for testing that the examples all still compile.
  buildExamples ? false
}:

let
  nixpkgsSrc =
    if isNull nixpkgs
      then
        builtins.fetchTarball {
          # Recent version of nixpkgs master as of 2020-03-01.
          url = "https://github.com/NixOS/nixpkgs/archive/4f36e9f9a33da034327188ddebc3aecb3633e4d7.tar.gz";
          sha256 = "sha256:0aa3aldp6m962hx0qzkizkwvamwv2c4yijk6g515dx7h7f5xrary";
        }
      else nixpkgs;

  compilerVersion = if isNull compiler then "ghc882" else compiler;

  # An overlay that adds termonad to all haskell package sets.
  haskellPackagesOverlay = self: super: {
    haskell = super.haskell // {
      packageOverrides = hself: hsuper:
        super.haskell.packageOverrides hself hsuper // {
          termonad =
            let
              filesToIgnore = [
                ".git"
                ".nix-helpers"
                "result"
                ".stack-work"
                ".travis.yml"
              ];

              src =
                builtins.filterSource
                  (path: type: with self.stdenv.lib;
                    ! elem (baseNameOf path) filesToIgnore &&
                    ! any (flip hasPrefix (baseNameOf path)) [ "dist" ".ghc" ]
                  )
                  ./..;

              extraCabal2nixOptions =
                self.lib.optionalString buildExamples "-fbuildexamples";

              termonadDrv =
                hself.callCabal2nixWithOptions
                  "termonad"
                  src
                  extraCabal2nixOptions
                  {
                    inherit (self) gtk3;
                    libpcre2 = self.pcre2;
                    vte_291 = self.vte;
                  };
            in
            termonadDrv;
        };
    };

    # A Haskell package set where we know the GHC version works to compile
    # Termonad.  This is basically just a shortcut so that other Nix files
    # don't need to figure out the correct compiler version to use when it is
    # not given by the user.
    termonadKnownWorkingHaskellPkgSet = self.haskell.packages.${compilerVersion};
  };

in import nixpkgsSrc { overlays = [ haskellPackagesOverlay ] ++ additionalOverlays; }