{ }:

let
  splitSystem = builtins.split "-" builtins.currentSystem;
  currentArch = builtins.elemAt splitSystem 0;
  currentOS = builtins.elemAt splitSystem 2;
in with {
  # Look here for information about how pin version of nixpkgs
  #  → https://nixos.wiki/wiki/FAQ/Pinning_Nixpkgs
  pkgs = import (builtins.fetchGit {
    name = "nixpkgs-2021-01-05";
    url = "https://github.com/nixos/nixpkgs/";
    ref = "refs/heads/nixpkgs-unstable";
    rev = "f53c431645da8e6760268092aa10f736b5cfb117";
  }) { };

  isMacOS = currentOS == "darwin";
  isLinux = currentOS == "linux";
  isAarch64 = currentArch == "aarch64";
};

with (pkgs);

let
  darwin-inputs =
    if isMacOS then
      with pkgs.darwin.apple_sdk.frameworks; [
        AppKit
        CoreFoundation
        CoreServices
        CoreVideo
        Foundation
        Metal
        Security
      ]
    else
      [ ];

  linux-inputs =
    if isLinux then
      [
        valgrind
        vulkan-headers
        vulkan-loader
        vulkan-tools
        vulkan-validation-layers
        xorg.libX11
        xorg.libXcursor
        xorg.libXrandr
        xorg.libXi
      ]
    else
      [ ];

  nixos-env =
    if isLinux && builtins.pathExists /etc/nixos/configuration.nix then
      { XDG_DATA_DIRS = "/run/opengl-driver/share:$XDG_DATA_DIRS";
      }
    else
      { };

  llvmPkgs = pkgs.llvmPackages_10;
  zig = import ./nix/zig.nix { inherit pkgs isMacOS isAarch64; };
  inputs = [
    # build libraries
    rustc
    cargo
    clippy
    rustfmt
    cmake
    git
    python3
    llvmPkgs.llvm
    llvmPkgs.clang
    pkg-config
    zig
    # llb deps
    libffi
    libxml2
    zlib
    llvmPkgs.libcxx
    llvmPkgs.libcxxabi
    libunwind
    # faster builds - see https://github.com/rtfeldman/roc/blob/trunk/BUILDING_FROM_SOURCE.md#use-lld-for-the-linker
    llvmPkgs.lld
    # dev tools
    rust-analyzer
    # (import ./nix/zls.nix { inherit pkgs zig; })
    ccls
  ];

in mkShell (nixos-env // {
  buildInputs = inputs ++ darwin-inputs ++ linux-inputs;

  # Additional Env vars
  LLVM_SYS_100_PREFIX = "${llvmPkgs.llvm}";
  APPEND_LIBRARY_PATH = stdenv.lib.makeLibraryPath
    ([ pkg-config llvmPkgs.libcxx llvmPkgs.libcxxabi libunwind ] ++ linux-inputs);
  LD_LIBRARY_PATH = "$LD_LIBRARY_PATH:$APPEND_LIBRARY_PATH";

  # Aliases don't work cross shell, so we do this
  shellHook = ''
    export PATH="$PATH:$PWD/nix/bin"
  '';
})