#!/bin/bash

COMPILER='ghc822'
HASKVER='_8_2'
NIXPKGS='import <darwin> {}'
HASKPKGS="haskellPackages${HASKVER}"
PKGNAME=$(basename "$PWD")

START="$PWD"
while [[ "$PWD" != "/" && ! -f default.nix ]]; do
    cd ..
done

if [[ "$PWD" = "/" ]]; then
    cd "$START"
    while [[ "$PWD" != "/" && ! -d .git && ! -f .git ]]; do
        cd ..
    done
fi

if [[ "$PWD" = "/" ]]; then
    echo "Error: Could not find default.nix or .git"
    exit 1
fi

read -r -d '' INPUT <<- EOM
let nixpkgs = ${NIXPKGS};
    pkgs = nixpkgs.pkgs;

    haveDefault = builtins.pathExists ./default.nix;

    package =
      if haveDefault
      then import ./default.nix {
             compiler = "${COMPILER}";
             nixpkgs = pkgs.lib.recursiveUpdate nixpkgs
               { pkgs.lib.inNixShell = false; };
           }
      else pkgs.${HASKPKGS}.callCabal2nix "${PKGNAME}" ./. {};

    compiler =
      if haveDefault
      then pkgs.${HASKPKGS}.ghc
      else package.compiler;

    packages =
      if haveDefault
      then package.buildInputs
      else pkgs.haskell.lib.getHaskellBuildInputs package;

    cabalInstallVersion = {
      ghc802 = "1.24.0.2";
      ghc822 = "2.0.0.1";
      ghc842 = "2.2.0.0";
    };

    hoogleExpr = <nixpkgs/pkgs/development/haskell-modules/hoogle.nix>;

    haskell-ide-engine = import (pkgs.fetchFromGitHub {
      owner  = "domenkozar";
      repo   = "hie-nix";
      rev    = "dbb89939da8997cc6d863705387ce7783d8b6958";
      sha256 = "1bcw59zwf788wg686p3qmcq03fr7bvgbcaa83vq8gvg231bgid4m";
      # date = 2018-03-27T10:14:16+01:00;
    }) {};

    hie = {
      ghc802 = haskell-ide-engine.hie80;
      ghc822 = haskell-ide-engine.hie82;
      ghc842 = throw "HIE not supported on GHC 8.4.2 yet";
    };

    ghcEnv = compiler.withPackages
      (p: with p;
         let hoogle = callPackage hoogleExpr { inherit packages; }; in
         [ hpack criterion hdevtools hoogle hie.${COMPILER}
           (callHackage "cabal-install" cabalInstallVersion.${COMPILER} {})
         ] ++ packages);

in ghcEnv
EOM

exec nix-shell -p "$INPUT" "$@"