{ pkgs, lib }:

let

  testedSystems = lib.filterAttrs (name: value: let
    platform = lib.systems.elaborate value;
  in platform.isLinux || platform.isWindows
  ) lib.systems.examples;

  getExecutable = pkgs: pkgFun: exec:
    "${pkgFun pkgs}${exec}${pkgs.stdenv.hostPlatform.extensions.executable}";

  compareTest = { emulator, pkgFun, hostPkgs, crossPkgs, exec, args ? [] }: let
    pkgName = (pkgFun hostPkgs).name;
    args' = lib.concatStringsSep " " args;
  in crossPkgs.runCommand "test-${pkgName}-${crossPkgs.stdenv.hostPlatform.config}" {
    nativeBuildInputs = [ pkgs.dos2unix ];
  } ''
    # Just in case we are using wine, get rid of that annoying extra
    # stuff.
    export WINEDEBUG=-all

    HOME=$(pwd)
    mkdir -p $out

    # We need to remove whitespace, unfortunately
    # Windows programs use \r but Unix programs use \n

    echo Running native-built program natively

    # find expected value natively
    ${getExecutable hostPkgs pkgFun exec} ${args'} \
      | dos2unix > $out/expected

    echo Running cross-built program in emulator

    # run emulator to get actual value
    ${emulator} ${getExecutable crossPkgs pkgFun exec} ${args'} \
      | dos2unix > $out/actual

    echo Comparing results...

    if [ "$(cat $out/actual)" != "$(cat $out/expected)" ]; then
      echo "${pkgName} did not output expected value:"
      cat $out/expected
      echo "instead it output:"
      cat $out/actual
      exit 1
    else
      echo "${pkgName} test passed"
      echo "both produced output:"
      cat $out/actual
    fi
  '';

  mapMultiPlatformTest = crossSystemFun: test: lib.mapAttrs (name: system: test rec {
    crossPkgs = import pkgs.path {
      localSystem = { inherit (pkgs.stdenv.hostPlatform) config; };
      crossSystem = crossSystemFun system;
    };

    emulator = crossPkgs.stdenv.hostPlatform.emulator pkgs;

    # Apply some transformation on windows to get dlls in the right
    # place. Unfortunately mingw doesn’t seem to be able to do linking
    # properly.
    platformFun = pkg: if crossPkgs.stdenv.hostPlatform.isWindows then
      pkgs.buildEnv {
        name = "${pkg.name}-winlinks";
        paths = [pkg] ++ pkg.buildInputs;
      } else pkg;
  }) testedSystems;

  tests = {

    file = {platformFun, crossPkgs, emulator}: compareTest {
      inherit emulator crossPkgs;
      hostPkgs = pkgs;
      exec = "/bin/file";
      args = [
        "${pkgs.file}/share/man/man1/file.1.gz"
        "${pkgs.dejavu_fonts}/share/fonts/truetype/DejaVuMathTeXGyre.ttf"
      ];
      pkgFun = pkgs: platformFun pkgs.file;
    };

    hello = {platformFun, crossPkgs, emulator}: compareTest {
      inherit emulator crossPkgs;
      hostPkgs = pkgs;
      exec = "/bin/hello";
      pkgFun = pkgs: pkgs.hello;
    };

    pkg-config = {platformFun, crossPkgs, emulator}: crossPkgs.runCommand
      "test-pkg-config-${crossPkgs.stdenv.hostPlatform.config}"
    {
      depsBuildBuild = [ crossPkgs.pkgsBuildBuild.pkg-config ];
      nativeBuildInputs = [ crossPkgs.pkgsBuildHost.pkg-config crossPkgs.buildPackages.zlib ];
      depsBuildTarget = [ crossPkgs.pkgsBuildTarget.pkg-config ];
      buildInputs = [ crossPkgs.zlib ];
      NIX_DEBUG = 7;
    } ''
       mkdir $out
       ${crossPkgs.pkgsBuildBuild.pkg-config.targetPrefix}pkg-config --cflags zlib > "$out/for-build"
       ${crossPkgs.pkgsBuildHost.pkg-config.targetPrefix}pkg-config --cflags zlib > "$out/for-host"
       ! diff "$out/for-build" "$out/for-host"
    '';
  };

  # see https://github.com/NixOS/nixpkgs/issues/213453
  # this is a good test of a lot of tricky glibc/libgcc corner cases
  mbuffer = let
    mbuffer = pkgs.pkgsCross.aarch64-multiplatform.mbuffer;
    emulator = with lib.systems; (elaborate examples.aarch64-multiplatform).emulator pkgs;
  in
    pkgs.runCommand "test-mbuffer" {} ''
      echo hello | ${emulator} ${mbuffer}/bin/mbuffer
      touch $out
    '';

  # This is meant to be a carefully curated list of builds/packages
  # that tend to break when refactoring our cross-compilation
  # infrastructure.
  #
  # It should strike a balance between being small enough to fit in
  # a single eval (i.e. not so large that hydra-eval-jobs is needed)
  # so we can ask @ofborg to check it, yet should have good examples
  # of things that often break.  So, no buckshot `mapTestOnCross`
  # calls here.
  sanity = [
    mbuffer
    #pkgs.pkgsCross.gnu64.bash # https://github.com/NixOS/nixpkgs/issues/243164
    pkgs.gcc_multi.cc
    pkgs.pkgsMusl.stdenv
    pkgs.pkgsLLVM.stdenv
    pkgs.pkgsStatic.bash
    #pkgs.pkgsCross.gnu64_simplekernel.bash   # https://github.com/NixOS/nixpkgs/issues/264989
    pkgs.pkgsCross.arm-embedded.stdenv
    pkgs.pkgsCross.sheevaplug.stdenv  # for armv5tel
    pkgs.pkgsCross.raspberryPi.stdenv  # for armv6l
    pkgs.pkgsCross.armv7l-hf-multiplatform.stdenv
    pkgs.pkgsCross.m68k.stdenv
    pkgs.pkgsCross.aarch64-multiplatform.pkgsBuildTarget.gcc
    pkgs.pkgsCross.powernv.pkgsBuildTarget.gcc
    pkgs.pkgsCross.s390.stdenv
    pkgs.pkgsCross.mips64el-linux-gnuabi64.stdenv
    pkgs.pkgsCross.mips64el-linux-gnuabin32.stdenv
    pkgs.pkgsCross.mingwW64.stdenv

  ] ++ lib.optionals (with pkgs.stdenv.buildPlatform; isx86_64 && isLinux) [
    # Musl-to-glibc cross on the same architecture tends to turn up
    # lots of interesting corner cases.  Only expected to work for
    # x86_64-linux buildPlatform.
    pkgs.pkgsMusl.pkgsCross.gnu64.hello

    # Two web browsers -- exercises almost the entire packageset
    pkgs.pkgsCross.aarch64-multiplatform.qt5.qutebrowser
    pkgs.pkgsCross.aarch64-multiplatform.firefox
  ];

in {
  gcc = (lib.mapAttrs (_: mapMultiPlatformTest (system: system // {useLLVM = false;})) tests);
  llvm = (lib.mapAttrs (_: mapMultiPlatformTest (system: system // {useLLVM = true;})) tests);

  inherit mbuffer sanity;
}